This document discusses Trichoplax adhaerens, the sole member of the phylum Placozoa. It describes Trichoplax as the simplest living metazoan, with an irregular shape and only four cell types. The author became interested in Trichoplax after learning about it from their teacher in 1979 and discussing its potential role as the earliest branching metazoan lineage. The document provides background on Trichoplax's simple anatomy, life cycle, and distribution, while also exploring open questions about its biology and relationships to hypotheses about the earliest evolution of animals.
1) Carl Woese and Ralph Wolfe discovered that methanogenic bacteria were not related to other known bacteria based on differences in their 16S ribosomal RNA sequences. This led to the realization that archaea are a distinct third domain of life in addition to bacteria and eukaryotes.
2) 16S rRNA sequences can reveal evolutionary relationships because they contain thousands of "building blocks" that can be aligned and compared between organisms. Archaeal 16S rRNA sequences contained large "gaps" compared to bacterial sequences.
3) The Last Universal Common Ancestor (LUCA) was an early organism from which the domains of archaea and bacteria diverged based on current phylogenetic trees, and it likely lived in an oxygen
Arthropods emerged near the base of the Cambrian period based on early trace fossils and body fossils from the Cambrian. Molecular evidence indicates arthropods are monophyletic and part of the Ecdysozoa clade. Key insights include hexapods being crustaceans rather than allies of myriapods, and lobopodians representing stem lineages rather than relatives of onychophorans. The diversity of Cambrian lobopodians and anomalocaridids sheds light on the stem group leading to crown-group euarthropods.
Paleobotany is the study of fossil plants and their relationship to modern plants. Early angiosperms first appeared in the fossil record during the Lower Cretaceous period, around 130 million years ago. However, they diversified and dominated plant communities only later in the Cretaceous. Transitional fossils like Archaefructus provide evidence of early flowering plants, but their exact position is unclear. During the Lower and Mid-Cretaceous, there was an increase in the diversity of angiosperm leaves, pollen, and plant families, indicating the rapid radiation and rise of flowering plants.
The ascomycetes are a large phylum of fungi that includes yeasts and molds. They reproduce sexually through the formation of an ascus, a saclike structure where karyogamy and meiosis occurs to produce ascospores. Asexually, they produce conidia for rapid reproduction. Yeasts are unicellular ascomycetes that evolved from multicellular ancestors and reproduce mainly asexually through budding. They have long been used in baking, brewing, and winemaking due to their ability to ferment carbohydrates. Yeasts also serve as important model organisms in genetics and molecular biology research.
This science project explores angiosperms through their fossil record, evolution, diversity, and life cycle. Key points include:
- The earliest angiosperm fossils date back 125 million years and display both primitive and derived traits.
- Angiosperms originated over 140 million years ago and diversified into major branches during the late Mesozoic.
- There are two main groups of flowering plants - monocots and dicots - as well as more basal lineages like magnoliids.
- Flowers and fruits are key adaptations that enabled the evolution and success of angiosperms through sexual reproduction.
1. The document discusses various aspects of fungal genetics including the life cycles, modes of reproduction, and nuclear states of fungi.
2. It notes that fungi typically have haploid vegetative states and undergo plasmogamy and karyogamy during sexual reproduction, followed immediately by meiosis.
3. The document also discusses asexual reproduction in fungi through spores, as well as parasexual reproduction which involves nuclear fusion without meiosis.
1. Heterothallism is the production of two types of fungal structures (thalli or hyphae) designated as + and - strains. These structures undergo nuclear fusion to form zygotes.
2. Blakeslee demonstrated that in heterothallic fungi species, zygospores are only produced when hyphae of opposite strains (+ and -) fuse together. No zygospores are formed when hyphae of the same strain fuse.
3. Fungi produce sex hormones that facilitate the recognition and fusion of opposite strain hyphae, allowing for reproduction. Examples include trisporic acid in Mucor mucedo and alpha factor in yeast.
The document discusses several theories about the origin and evolution of angiosperms. It describes theories that proposed various plant groups as possible ancestors of angiosperms including isoetes, conifers, gnetales, bennettitales, caytoniales, and pentoxylales. However, many of these theories were later contradicted or disagreed with based on evidence from vascular anatomy, seed structure, and other characteristics. The document also outlines primitive and advanced characteristics seen in different angiosperm groups, showing their diverse evolutionary lines.
1) Carl Woese and Ralph Wolfe discovered that methanogenic bacteria were not related to other known bacteria based on differences in their 16S ribosomal RNA sequences. This led to the realization that archaea are a distinct third domain of life in addition to bacteria and eukaryotes.
2) 16S rRNA sequences can reveal evolutionary relationships because they contain thousands of "building blocks" that can be aligned and compared between organisms. Archaeal 16S rRNA sequences contained large "gaps" compared to bacterial sequences.
3) The Last Universal Common Ancestor (LUCA) was an early organism from which the domains of archaea and bacteria diverged based on current phylogenetic trees, and it likely lived in an oxygen
Arthropods emerged near the base of the Cambrian period based on early trace fossils and body fossils from the Cambrian. Molecular evidence indicates arthropods are monophyletic and part of the Ecdysozoa clade. Key insights include hexapods being crustaceans rather than allies of myriapods, and lobopodians representing stem lineages rather than relatives of onychophorans. The diversity of Cambrian lobopodians and anomalocaridids sheds light on the stem group leading to crown-group euarthropods.
Paleobotany is the study of fossil plants and their relationship to modern plants. Early angiosperms first appeared in the fossil record during the Lower Cretaceous period, around 130 million years ago. However, they diversified and dominated plant communities only later in the Cretaceous. Transitional fossils like Archaefructus provide evidence of early flowering plants, but their exact position is unclear. During the Lower and Mid-Cretaceous, there was an increase in the diversity of angiosperm leaves, pollen, and plant families, indicating the rapid radiation and rise of flowering plants.
The ascomycetes are a large phylum of fungi that includes yeasts and molds. They reproduce sexually through the formation of an ascus, a saclike structure where karyogamy and meiosis occurs to produce ascospores. Asexually, they produce conidia for rapid reproduction. Yeasts are unicellular ascomycetes that evolved from multicellular ancestors and reproduce mainly asexually through budding. They have long been used in baking, brewing, and winemaking due to their ability to ferment carbohydrates. Yeasts also serve as important model organisms in genetics and molecular biology research.
This science project explores angiosperms through their fossil record, evolution, diversity, and life cycle. Key points include:
- The earliest angiosperm fossils date back 125 million years and display both primitive and derived traits.
- Angiosperms originated over 140 million years ago and diversified into major branches during the late Mesozoic.
- There are two main groups of flowering plants - monocots and dicots - as well as more basal lineages like magnoliids.
- Flowers and fruits are key adaptations that enabled the evolution and success of angiosperms through sexual reproduction.
1. The document discusses various aspects of fungal genetics including the life cycles, modes of reproduction, and nuclear states of fungi.
2. It notes that fungi typically have haploid vegetative states and undergo plasmogamy and karyogamy during sexual reproduction, followed immediately by meiosis.
3. The document also discusses asexual reproduction in fungi through spores, as well as parasexual reproduction which involves nuclear fusion without meiosis.
1. Heterothallism is the production of two types of fungal structures (thalli or hyphae) designated as + and - strains. These structures undergo nuclear fusion to form zygotes.
2. Blakeslee demonstrated that in heterothallic fungi species, zygospores are only produced when hyphae of opposite strains (+ and -) fuse together. No zygospores are formed when hyphae of the same strain fuse.
3. Fungi produce sex hormones that facilitate the recognition and fusion of opposite strain hyphae, allowing for reproduction. Examples include trisporic acid in Mucor mucedo and alpha factor in yeast.
The document discusses several theories about the origin and evolution of angiosperms. It describes theories that proposed various plant groups as possible ancestors of angiosperms including isoetes, conifers, gnetales, bennettitales, caytoniales, and pentoxylales. However, many of these theories were later contradicted or disagreed with based on evidence from vascular anatomy, seed structure, and other characteristics. The document also outlines primitive and advanced characteristics seen in different angiosperm groups, showing their diverse evolutionary lines.
Cell culture refers to growing cells outside of their natural environment in an artificial setting. Some key developments in cell culture include Wilhelm Roux demonstrating maintenance of living cells outside the body in saline buffer in 1885, and Ross Granville Harrison developing the first techniques of cell culture in vitro using frog embryonic tissue in 1907. In the 1920s, composition of salt solutions was formulated for cell cultures. The first cell line, called the "L cell line", was established by Earle in 1948 using cells from mouse tissue. Hayflick and Moorhead defined the finite lifespan of normal human cells in 1961. Cell culture remains an important tool in biomedical research today.
This document discusses botanical nomenclature and the rules for naming plants. It begins by explaining that botanical nomenclature is the process of naming plants according to international rules proposed by botanists. It then discusses the history of plant naming including the development of the binomial system by Linnaeus and establishment of Latin as the language for plant names. The document concludes by outlining some of the key principles and rules of the International Code of Botanical Nomenclature including requirements for valid publication of new plant names.
Heterothallic species have sexes that reside in different individuals. . The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable of sexual reproduction from a single organism.
Jennifer Griffith conducted a study using Drosophila melanogaster to determine the inheritance patterns of two mutations: white-eyes and apterous wings. She performed controlled crosses between wildtype and mutant flies and analyzed the phenotypes of offspring. Her results showed that white-eyes is an X-linked recessive trait as the ratio of offspring phenotypes matched expectations. Apterous wings was found to be an autosomal recessive trait. Testcrosses of offspring supported these findings as the ratios also matched expected Mendelian ratios. Griffith concluded that the two mutations are located on different chromosomes and are not linked.
Protists are a diverse group of eukaryotic organisms that are either photosynthetic like plants, heterotrophic like animals, or decomposers like fungi. They include algae, protozoa, and other microscopic organisms. Protists can be autotrophic using photosynthesis or heterotrophic ingesting other organisms. They play important roles in ecosystems as producers, consumers, and decomposers and are foundational to many food webs. However, some protists are also pathogens that can cause diseases.
This document provides an overview of mating systems in basidiomycetes fungi. It discusses two main types of mating systems - homothallism, where a single organism can sexually reproduce on its own, and heterothallism, which requires two compatible partners. Heterothallism can be further broken down into bipolar systems controlled by one gene and tetrapolar systems controlled by two unlinked genes (A and B loci). The structure and large number of alleles at these loci allows for high outbreeding success and thousands of possible mating types in some species.
This document summarizes morphology and reproduction in protozoa. It begins with an introduction to protozoa, describing them as unicellular eukaryotic microorganisms. It then discusses their morphology, including that they resemble animal cells with organelles like nuclei and mitochondria. Their cytoplasm is divided into outer ectoplasm and inner endoplasm. Reproduction methods include asexual budding, binary fission, and sexual conjugation or gametogony, where genetic material is exchanged between two protozoa or gametes are formed.
This document provides evidence for organic evolution from several sources:
1) Fossil records from sedimentary rocks show connecting links between different species over time.
2) Homologous and analogous organs between different species indicate common ancestry.
3) Embryological studies show that animals of the same class have common early embryonic structures.
4) Connecting links are organisms that exhibit characteristics of two adjacent groups, providing transitional forms.
5) Geographic distribution patterns show that isolated populations of the same ancestral species vary over generations in different climates.
The document discusses the six kingdoms of life: Archaea, Bacteria, Protista, Fungi, Plantae, and Animalia. It provides details on the distinguishing characteristics of each kingdom, such as Archaea thriving in extreme environments, Bacteria having cell walls made of peptidoglycans or amino sugars, Protista being generally unicellular and eukaryotic, Fungi having cell walls made of chitin and decomposing organic matter, Plantae having cell walls made of cellulose and performing photosynthesis, and Animalia being multicellular and lacking cell walls. The document also compares prokaryotic and eukaryotic cells as well as plant and animal cells
This document discusses cladistics, which is a method of classifying organisms into clades based on their evolutionary relationships and shared characteristics with a common ancestor. It provides examples of how cladograms are used to show evolutionary relationships between different groups like birds, dinosaurs, and crocodiles. The document also discusses how genetic evidence from DNA and protein sequencing provides more accurate evidence of evolutionary relationships than morphology alone. It explains how cladistics has resulted in some groups being reclassified based on their true evolutionary origins.
The document discusses taxonomy and systematics. It defines taxonomy as the original description and naming of species, while systematics is the arrangement of species into evolutionary groups. It describes the historical development of classification systems from Linnaeus' focus on morphology to the modern three domain system based on molecular evidence. The key approaches of evolutionary systematics, numerical taxonomy, and phylogenetic systematics are also summarized.
- Cell biology began with ancient Greek philosophers observing common structures in plants and animals in the 4th century BC.
- Advances in microscope technology in the 16th-18th centuries allowed scientists like Hooke, van Leeuwenhoek, and Malpighi to observe cells directly for the first time.
- In 1838, Schleiden proposed that plants are composed of cells, and in 1839, Schwann extended this to animals, establishing the foundations of the cell theory.
The document discusses the classification of life into domains, kingdoms, and other taxonomic groups. It describes the three domains as bacteria, archaea, and eukarya. It then discusses the six kingdoms of life - archaebacteria, eubacteria, fungi, protists, plantae, and animalia - providing one or two examples and key characteristics of each, such as whether they are unicellular or multicellular, autotrophic or heterotrophic, and how they reproduce. It concludes with sample test questions about plant classification and the classification system overall.
This document summarizes key characteristics of four phyla - Porifera, Cnidaria, Platyhelminthes, and Mollusca. It describes their defining features, classes, and examples of each class. Porifera includes sponges and has classes of Calcarea, Hexactinellida, Demospongiae, and Sclerospongiae. Cnidaria includes jellyfish, corals, and sea anemones, with classes of Hydrozoa, Scyphozoa, and Anthozoa. Platyhelminthes includes flatworms divided into Turbellaria, Trematoda, and Cestoda. Mollusca covers snails, mussels, oct
This document provides information on protists, including their characteristics, models of eukaryotic origins, evidence for the endosymbiotic hypothesis, candidate kingdoms of protists, life cycles of various protist groups, and the evolution of multicellularity. It addresses topics such as amoeboid movement, the life cycle of Plasmodium, conjugation in Paramecium, classification of algae, and differences between plasmodial and cellular slime molds.
5.3 classification and biodiversity.docBob Smullen
The document discusses the binomial system of scientific naming of species and the taxonomic classification of organisms. It provides guidance on classifying organisms into the three domains of life - Archaea, Bacteria, and Eukarya. Eukaryotes are further classified into kingdoms, phyla, classes, orders, families, genera, and species. Characteristics of common plant and animal phyla are outlined to allow identification. The construction of dichotomous keys is also discussed as a method for identifying organisms. Natural classifications help in identification of species and allow prediction of characteristics shared within taxonomic groups.
Caenorhabditis elegans is a tiny, free-living nematode found worldwide. Newly hatched larvae are 0.25 millimeters long and adults are 1 millimeter long. Their small size means that the animals are usually observed with either dissecting microscopes, which generally allow up to 100X magnification, or compound microscopes, which allow up to 1000X magnification. Because C. elegans is transparent, individual cells and subcellular details are easily visualized using Nomarski (differential interference contrast, DIC) optics.
C. elegans has a rapid life cycle and exists primarily as a self-fertilizing hermaphrodite, although males arise at a frequency of <0.2%. These features have helped to make C. elegans a powerful model of choice for eukaryotic genetic studies. In addition, because the animal has an invariant numbers of somatic cells, researchers have been able to track the fate of every cell between fertilization and adulthood in live animals and to generate a complete cell lineage. Researchers have also reconstructed the shape of all C. elegans cells from electron micrographs, including each of the 302 neurons of the adult hermaphrodite. Moreover, because of the invariant wild-type cell lineage and neuroanatomy of C. elegans, mutations that give rise to developmental and behavioral defects are readily identified in genetic screens. Finally, because C. elegans was the first multicellular organism with a complete genome sequence, forward and reverse genetics have led to the molecular identification of many key genes in developmental and cell biological processes.
The experimental strengths and the similarities between the cellular and molecular processes present in C. elegans and other animals across evolutionary time (metabolism, organelle structure and function, gene regulation, protein biology, etc.) have made C. elegans an excellent organism with which to study general metazoan biology. At least 38% of the C. elegans protein-coding genes have predicted orthologs in the human genome, 60-80% of human genes have an ortholog in the C. elegans genome, and 40% of genes known to be associated with human diseases have clear orthologs in the C. elegans genome. Thus, many discoveries in C. elegans have relevance to the study of human health and disease.
My daughter's beloved pet dog Heart, a miniature Pinscher, became ill and had to be put down after four years as a member of their family. Heart brought great joy to both my daughter and myself with her playful antics and the sound of her jingling collar. After noticing Heart's declining health and suffering from a serious adrenal condition, I made the difficult decision to euthanize her. I deeply mourned the loss of Heart for weeks until I had a comforting experience where I felt and heard her, knowing she was now healthy and at peace.
Este documento presenta una lista de términos taxonómicos de peces con su terminología correcta y pronunciación en español. Incluye nombres de filos, órdenes, subórdenes, superfamilias, familias, subfamilias, tribus y géneros como Carangidae, Thunnini, Serranidae, Chaetodontidae y Chloroscombridae.
The narrator is a 17-year-old southern boy who has yet to find a girlfriend. One night, his mother sends him to deliver a package to the MacArthur's home. There, he sees the shadow of a mysterious, beautiful girl moving through the house. For the next few nights, he dreams of her shadow. Determined to find out who she is, he visits the MacArthur's under the pretense of delivering jam. He falls into a pit on the way but is rescued by Nora, a visiting northern girl staying with the MacArthur's. They become close friends over the summer.
Cell culture refers to growing cells outside of their natural environment in an artificial setting. Some key developments in cell culture include Wilhelm Roux demonstrating maintenance of living cells outside the body in saline buffer in 1885, and Ross Granville Harrison developing the first techniques of cell culture in vitro using frog embryonic tissue in 1907. In the 1920s, composition of salt solutions was formulated for cell cultures. The first cell line, called the "L cell line", was established by Earle in 1948 using cells from mouse tissue. Hayflick and Moorhead defined the finite lifespan of normal human cells in 1961. Cell culture remains an important tool in biomedical research today.
This document discusses botanical nomenclature and the rules for naming plants. It begins by explaining that botanical nomenclature is the process of naming plants according to international rules proposed by botanists. It then discusses the history of plant naming including the development of the binomial system by Linnaeus and establishment of Latin as the language for plant names. The document concludes by outlining some of the key principles and rules of the International Code of Botanical Nomenclature including requirements for valid publication of new plant names.
Heterothallic species have sexes that reside in different individuals. . The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable of sexual reproduction from a single organism.
Jennifer Griffith conducted a study using Drosophila melanogaster to determine the inheritance patterns of two mutations: white-eyes and apterous wings. She performed controlled crosses between wildtype and mutant flies and analyzed the phenotypes of offspring. Her results showed that white-eyes is an X-linked recessive trait as the ratio of offspring phenotypes matched expectations. Apterous wings was found to be an autosomal recessive trait. Testcrosses of offspring supported these findings as the ratios also matched expected Mendelian ratios. Griffith concluded that the two mutations are located on different chromosomes and are not linked.
Protists are a diverse group of eukaryotic organisms that are either photosynthetic like plants, heterotrophic like animals, or decomposers like fungi. They include algae, protozoa, and other microscopic organisms. Protists can be autotrophic using photosynthesis or heterotrophic ingesting other organisms. They play important roles in ecosystems as producers, consumers, and decomposers and are foundational to many food webs. However, some protists are also pathogens that can cause diseases.
This document provides an overview of mating systems in basidiomycetes fungi. It discusses two main types of mating systems - homothallism, where a single organism can sexually reproduce on its own, and heterothallism, which requires two compatible partners. Heterothallism can be further broken down into bipolar systems controlled by one gene and tetrapolar systems controlled by two unlinked genes (A and B loci). The structure and large number of alleles at these loci allows for high outbreeding success and thousands of possible mating types in some species.
This document summarizes morphology and reproduction in protozoa. It begins with an introduction to protozoa, describing them as unicellular eukaryotic microorganisms. It then discusses their morphology, including that they resemble animal cells with organelles like nuclei and mitochondria. Their cytoplasm is divided into outer ectoplasm and inner endoplasm. Reproduction methods include asexual budding, binary fission, and sexual conjugation or gametogony, where genetic material is exchanged between two protozoa or gametes are formed.
This document provides evidence for organic evolution from several sources:
1) Fossil records from sedimentary rocks show connecting links between different species over time.
2) Homologous and analogous organs between different species indicate common ancestry.
3) Embryological studies show that animals of the same class have common early embryonic structures.
4) Connecting links are organisms that exhibit characteristics of two adjacent groups, providing transitional forms.
5) Geographic distribution patterns show that isolated populations of the same ancestral species vary over generations in different climates.
The document discusses the six kingdoms of life: Archaea, Bacteria, Protista, Fungi, Plantae, and Animalia. It provides details on the distinguishing characteristics of each kingdom, such as Archaea thriving in extreme environments, Bacteria having cell walls made of peptidoglycans or amino sugars, Protista being generally unicellular and eukaryotic, Fungi having cell walls made of chitin and decomposing organic matter, Plantae having cell walls made of cellulose and performing photosynthesis, and Animalia being multicellular and lacking cell walls. The document also compares prokaryotic and eukaryotic cells as well as plant and animal cells
This document discusses cladistics, which is a method of classifying organisms into clades based on their evolutionary relationships and shared characteristics with a common ancestor. It provides examples of how cladograms are used to show evolutionary relationships between different groups like birds, dinosaurs, and crocodiles. The document also discusses how genetic evidence from DNA and protein sequencing provides more accurate evidence of evolutionary relationships than morphology alone. It explains how cladistics has resulted in some groups being reclassified based on their true evolutionary origins.
The document discusses taxonomy and systematics. It defines taxonomy as the original description and naming of species, while systematics is the arrangement of species into evolutionary groups. It describes the historical development of classification systems from Linnaeus' focus on morphology to the modern three domain system based on molecular evidence. The key approaches of evolutionary systematics, numerical taxonomy, and phylogenetic systematics are also summarized.
- Cell biology began with ancient Greek philosophers observing common structures in plants and animals in the 4th century BC.
- Advances in microscope technology in the 16th-18th centuries allowed scientists like Hooke, van Leeuwenhoek, and Malpighi to observe cells directly for the first time.
- In 1838, Schleiden proposed that plants are composed of cells, and in 1839, Schwann extended this to animals, establishing the foundations of the cell theory.
The document discusses the classification of life into domains, kingdoms, and other taxonomic groups. It describes the three domains as bacteria, archaea, and eukarya. It then discusses the six kingdoms of life - archaebacteria, eubacteria, fungi, protists, plantae, and animalia - providing one or two examples and key characteristics of each, such as whether they are unicellular or multicellular, autotrophic or heterotrophic, and how they reproduce. It concludes with sample test questions about plant classification and the classification system overall.
This document summarizes key characteristics of four phyla - Porifera, Cnidaria, Platyhelminthes, and Mollusca. It describes their defining features, classes, and examples of each class. Porifera includes sponges and has classes of Calcarea, Hexactinellida, Demospongiae, and Sclerospongiae. Cnidaria includes jellyfish, corals, and sea anemones, with classes of Hydrozoa, Scyphozoa, and Anthozoa. Platyhelminthes includes flatworms divided into Turbellaria, Trematoda, and Cestoda. Mollusca covers snails, mussels, oct
This document provides information on protists, including their characteristics, models of eukaryotic origins, evidence for the endosymbiotic hypothesis, candidate kingdoms of protists, life cycles of various protist groups, and the evolution of multicellularity. It addresses topics such as amoeboid movement, the life cycle of Plasmodium, conjugation in Paramecium, classification of algae, and differences between plasmodial and cellular slime molds.
5.3 classification and biodiversity.docBob Smullen
The document discusses the binomial system of scientific naming of species and the taxonomic classification of organisms. It provides guidance on classifying organisms into the three domains of life - Archaea, Bacteria, and Eukarya. Eukaryotes are further classified into kingdoms, phyla, classes, orders, families, genera, and species. Characteristics of common plant and animal phyla are outlined to allow identification. The construction of dichotomous keys is also discussed as a method for identifying organisms. Natural classifications help in identification of species and allow prediction of characteristics shared within taxonomic groups.
Caenorhabditis elegans is a tiny, free-living nematode found worldwide. Newly hatched larvae are 0.25 millimeters long and adults are 1 millimeter long. Their small size means that the animals are usually observed with either dissecting microscopes, which generally allow up to 100X magnification, or compound microscopes, which allow up to 1000X magnification. Because C. elegans is transparent, individual cells and subcellular details are easily visualized using Nomarski (differential interference contrast, DIC) optics.
C. elegans has a rapid life cycle and exists primarily as a self-fertilizing hermaphrodite, although males arise at a frequency of <0.2%. These features have helped to make C. elegans a powerful model of choice for eukaryotic genetic studies. In addition, because the animal has an invariant numbers of somatic cells, researchers have been able to track the fate of every cell between fertilization and adulthood in live animals and to generate a complete cell lineage. Researchers have also reconstructed the shape of all C. elegans cells from electron micrographs, including each of the 302 neurons of the adult hermaphrodite. Moreover, because of the invariant wild-type cell lineage and neuroanatomy of C. elegans, mutations that give rise to developmental and behavioral defects are readily identified in genetic screens. Finally, because C. elegans was the first multicellular organism with a complete genome sequence, forward and reverse genetics have led to the molecular identification of many key genes in developmental and cell biological processes.
The experimental strengths and the similarities between the cellular and molecular processes present in C. elegans and other animals across evolutionary time (metabolism, organelle structure and function, gene regulation, protein biology, etc.) have made C. elegans an excellent organism with which to study general metazoan biology. At least 38% of the C. elegans protein-coding genes have predicted orthologs in the human genome, 60-80% of human genes have an ortholog in the C. elegans genome, and 40% of genes known to be associated with human diseases have clear orthologs in the C. elegans genome. Thus, many discoveries in C. elegans have relevance to the study of human health and disease.
My daughter's beloved pet dog Heart, a miniature Pinscher, became ill and had to be put down after four years as a member of their family. Heart brought great joy to both my daughter and myself with her playful antics and the sound of her jingling collar. After noticing Heart's declining health and suffering from a serious adrenal condition, I made the difficult decision to euthanize her. I deeply mourned the loss of Heart for weeks until I had a comforting experience where I felt and heard her, knowing she was now healthy and at peace.
Este documento presenta una lista de términos taxonómicos de peces con su terminología correcta y pronunciación en español. Incluye nombres de filos, órdenes, subórdenes, superfamilias, familias, subfamilias, tribus y géneros como Carangidae, Thunnini, Serranidae, Chaetodontidae y Chloroscombridae.
The narrator is a 17-year-old southern boy who has yet to find a girlfriend. One night, his mother sends him to deliver a package to the MacArthur's home. There, he sees the shadow of a mysterious, beautiful girl moving through the house. For the next few nights, he dreams of her shadow. Determined to find out who she is, he visits the MacArthur's under the pretense of delivering jam. He falls into a pit on the way but is rescued by Nora, a visiting northern girl staying with the MacArthur's. They become close friends over the summer.
Eddie and Donna play their weekly chess game at the Shady Grove Home for the Elderly. Donna feels lonely since her husband Earl passed away. During their game, Eddie notices Josephine, his pet cat, is missing and calls out for her in concern. Josephine eventually comes running to Eddie, revealing a ring around her collar. Eddie tells Donna that he and Josephine would like her to join their family, bringing Donna to tears as she realizes she will no longer feel lonely.
Carlee was a young girl who fell in love with a puppy named Henry. When she met a boy named David who had lost his family, she sensed his sadness and bonded with him over Henry. Though Henry was her beloved dog, she selflessly gave him to David to help heal the boy's grief. David and Carlee formed a lifelong friendship, with Henry playing an important role in bringing them together and supporting each other through difficult times. Carlee never replaced Henry but found joy in seeing how he helped David recover from his tragedy.
Vera met Peter in school but married someone else. Years later, after divorcing due to falling for a coworker, she reached out to Peter for help. When they met again, Peter had matured and consoled Vera. After a few coffee dates, Vera fell in love with Peter, who treated her well. They married in Las Vegas in 2009 and remain happily married.
INTRODUCTION TO CELLS
INTRODUCTION TO CELL THEORY
HISTORY
FORMULATION OF CELL THEORY
CLASSICAL CELL THEORY
DRAWBACKS OF CLASSICAL THEORY
MORDEN CELL THEORY
EXCEPTION OF CELL THEORY
SIGNIFICANCE OF CELL THEORY
HOW HAS THE CELL THEORY BEEN USED
CONCLUSION
The document discusses the cell theory and the history of cell discovery. It outlines three key points:
1. The cell theory states that cells are the basic unit of life, all living things are made up of cells, and cells only come from preexisting cells.
2. Early microscope observations in the 1600s by Hooke and improved microscopes in the 1800s led to the discovery of cell structures like the nucleus and cytoplasm.
3. In the 1830s, Schleiden and Schwann combined evidence to propose the first comprehensive cell theory, establishing cells as the fundamental unit of life.
I: Evolution
If I have seen further it is by standing on the shoulders of Giants.
-- Sir Isaac Newton
1
Theories in Science
In the context of scientific inquiry, a theory is:
A conceptual framework supported by a large body of evidence
Broader in scope than a hypothesis. A theory ties information together and leads to specific testable hypotheses
In other words, a theory is a big deal in science, NOT a synonym for guessing
2
2
3
(This used to be a joke, but I’m not laughing anymore.)
3
Historical Overview
What can explain both the unity and diversity of life on Earth?
Organic evolution: genetically based change over time. It acts on individuals in the present, but only manifests in the population over generations.
Natural Selection: mechanism causing the match between organisms and their environment (adaptive evolution = adaptation)
4
4
Traditional views involved unchanging and perfect species inhabiting a young Earth (Old Testament, Linnaeus, etc.)
The emergence of paleontology and geology helped lay the groundwork for Darwin’s contributions
Other areas of research also influenced his thinking, including studies on human population growth
6
6
Fig. 22-2
American Revolution
French Revolution
U.S. Civil War
1900
1850
1800
1750
1795
1809
1798
1830
1831–1836
1837
1859
1837
1844
1858
The Origin of Species is published.
Wallace sends his hypothesis to Darwin.
Darwin begins his notebooks.
Darwin writes essay on descent with modification.
Darwin travels around the world on HMS Beagle.
Malthus publishes “Essay on the Principle of Population.”
Lyell publishes Principles of Geology.
Lamarck publishes his hypothesis of evolution.
Hutton proposes his theory of gradualism.
Linnaeus (classification)
Cuvier (fossils, extinction)
Malthus (population limits)
Lamarck (species can change)
Hutton (gradual geologic change)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
7
7
Younger stratum
with more recent
fossils
Layers of deposited
sediment
Older stratum
with older fossils
8
8
Several 18th century naturalists (including Erasmus Darwin) suggested life evolves as environments change
Jean-Baptiste Lamarck hypothesized that species evolve through use and disuse of body parts and subsequent inheritance of acquired characteristics
This mechanism is unsupported by evidence (e.g., even if you and your mate lost the same finger, your children would still be born with all ten), but it did refocus subsequent research
Lamarck’s Hypothesis
9
9
10
The miniature phenotype of Bonsai trees is caused by manipulations of a bonsai master, not genetics. Would the next generation still be stunted if we planted their seeds and allowed them to grow naturally?
11
12
After first studying medicine, then theology at Cambridge, Darwin took an unpaid position as naturalist for a 5-year voyage around the world
During his travels on HMS Beagle, he collected thousa ...
This document discusses the classification of metazoan animals based on their anatomy and embryonic development. It describes how animals can be divided into three main groups: acoelomates without a body cavity, pseudocoelomates with only remnants of a blastocoel cavity, and coelomates with a true body cavity called a coelom. Within coelomates, animals are further divided into protostomes and deuterostomes based on differences in their early embryonic development. The classification systems discussed provide insights into evolutionary relationships among metazoan phyla.
Dolly the sheep was the first mammal successfully cloned from an adult cell. She was cloned at the Roslin Institute in the UK in 1996 from a cell taken from a six-year-old ewe. Dolly gave birth to six lambs over her lifetime and helped demonstrate that cloning is possible in mammals.
This is a slideshow (with notes) of the Creation-Evolution Controversy presented to Calvary Coastal Fellowship in Auckland.
DISCLAIMER: Appropriate acknowledgement of copyright material has been made. However, information to rectify any oversight is welcomed.
The Burgess Shale was discovered in 1909 in Canada and contains fossils over 500 million years old. It is one of the most important fossil formations because it preserves not just hard body parts but also soft tissues and organs, providing evidence that soft-bodied creatures lived at that time. Similar formations have been found around the world.
Drosophila melanogaster is a popular model organism for teaching biology. It has a short lifespan of 2 weeks, allowing many generations to be studied quickly. It is easy and inexpensive to culture in large numbers. Students can observe Drosophila's morphology, life cycle, sexual dimorphism, and mutants. Activities include extracting and staining polytene chromosomes from salivary glands to observe banding patterns. Drosophila is a useful tool for teaching genetics and demonstrates principles like dominance, inheritance of sex-linked traits, and similarities to human diseases.
Exam 2 Study Guide. All questions will be over these concepts, voc.docxSANSKAR20
Exam 2 Study Guide. All questions will be over these concepts, vocabulary, and facts
Chp 10:
Cell Cycle
Genome
Mitosis
Chp11:
Meiosis
Gamete
Haploid & Diploid cell
Sexual reproduction
Chp12:
Gregor Mendel
Traits
Genotype & Phenotype
Allele
Dominant Trait & Recessive trait
Homozygous & Heterozygous
Punnet Square (concept. You will not do one on the exam)
Predictable Genetic frequencies (pedigree, farming genetic disorders)
Wild Type
Law of Segregation
Law of Independent assortment
Chp14:
DNA
Backbone
Nucleic Acid
Nucleotides
Base
Base Pair
Codon
Gene
Chromosome
DNA Polymerase (concept, vocab word)
Helicase (concept, vocab word)
Okazaki Fragment (concept, vocab word)
Proof Reading
Telomeres
DNA bases (4) and which bind
RNA: Uracil
Steps of DNA Replication (just listing the steps: min 5 max 10, depending on word choice)
Chp 15:
The Central Dogma of Biology
Transcription (steps, concepts)
Translation (steps, concepts)
tRNA
Mutation
Biotechnology
Chp 18:
Evolution
Natural Selection
Charles Darwin & Alfred R. Wallace
“Survival of the fittest” is incorrect.
Adaptation
Species
Hybrid (species): Postzygotic & Prezygotic
Speciation
Allopatric Speciation
Sympatric Speciation
Adaptive Radiation
Gradual Speciation & Punctuated Equilibrium
Chp 19:
Evolution
Evolution cumulative functions of: (know each)
Mutation, Genetic Drift, Migration, Natural Selection
Chance (involved with Evolution): Fixation, Founder Effect, Population Bottleneck
Natural Selection: 3 conditions for occurrence; what it looks like; what it does/does not do
Convergent Evolution
Evolution’s influence over, but not its “purpose”
Species are the basic unit of Biodiversity
Chp 20:
Phylogeny
Phylogenetic Trees/models
Concept of “shared ancestry”
Taxonomy: concept, define, & list 8 hierarchical categories
Convergent Evolution
Molecular Systematics & DNA Homology
Compare Phylogeny verse the “species concept”
Chp 21-29:
Biodiversity
Flora, Fauna, Biota
Virus (concept, importance to Evolution by Natural Selection)
Importance of “Domain”
Prokaryotes: Define, importance/role in Nature
Stromatolites as evidence
Biofilms
Protists: define, importance/role in Nature
Fungi: Define, importance/role in Nature
3 descriptors of Fungi
Fungal DNA
Hyphae & Mycelium
Decomposer
Mycorrhizae
Plants:
Ancestry (phylogeny)
Plants: Define, importance/role in nature
3 defining descriptors of Plants
Specific adaptations for evolution to land
3 problems all plants (as a phylogenetic group) face
Non-vascular Plant
Vascular Plant
Vascular Seed Plant
Vascular Tissue: Xylem & Phloem
Roots, True leaves
Waxy Cuticle
Important role of Ecological Succession of Plants to Life
Seed Plants:
Seed: define, role/importance of to a plant, water & reproduction
Spermatophytes
Gymnosperm
Angiosperm,
Flower & Fruit
Flower: Stamen, Carpel, Petal, Ovary)
Herbivory
Pollination & Pollinators: Trickery, Bribery, coevolution of
Importance of Plants to Humans
Humans and Plants coevolution
The life of a bee is very different f ...
This document provides an overview of the diversity of living organisms and key concepts in biology. It discusses how life first emerged on Earth over 3.5 billion years ago. It then outlines the fundamental properties shared by all living things, such as cellular organization, metabolism, reproduction, and evolution. Major topics in biology like taxonomy, morphology, physiology, and ecology are introduced. The document also examines levels of biological organization from cells to tissues to organ systems. Finally, it describes systems of biological classification and important related concepts like symmetry, coelom, and the three domains of life.
Cell biology is the study of cells, including their structure, function, growth, reproduction, and genetics. A cell is the basic unit of life, composed of protoplasm enclosed within a membrane and containing a nucleus. The development of the cell theory began with early philosophers and microscopists observing plant and animal tissues as being made up of smaller units. In the 19th century, scientists such as Schleiden and Schwann formulated the cell theory stating that cells are the fundamental unit of structure and function in living things. The modern cell theory recognizes that all living things are made of cells, cells carry out metabolic functions, cells only arise from preexisting cells, and cells contain hereditary information.
Kumar bentley: computational embryology_ past, present and futureArchiLab 7
This document summarizes the history of embryology and computational embryology. It discusses key contributions from Aristotle to modern developmental biology. It also describes different types of computational embryogenies, including explicit and implicit embryogenies. The document then presents experiments that evolved predefined shapes using explicit and implicit embryogenies. The results showed that both embryogenies could define morphologies, but the implicit embryogeny did not increase in size as the problem was scaled.
The document discusses the concepts of ontogeny and phylogeny. Ontogeny refers to the development of an individual organism from fertilized egg to adult form, while phylogeny refers to the evolutionary history and relationships between groups of organisms. It describes Ernst Haeckel's inaccurate biogenetic law which stated that ontogeny recapitulates phylogeny, or that development replays evolutionary history. While some connections exist, ontogeny does not generally recapitulate phylogeny as was once believed.
HYPOTHESISThe evolution and conservation of left-right pat.docxadampcarr67227
HYPOTHESIS
The evolution and conservation of left-right patterning
mechanisms
Martin Blum‡, Kerstin Feistel, Thomas Thumberger* and Axel Schweickert
ABSTRACT
Morphological asymmetry is a common feature of animal body plans,
from shell coiling in snails to organ placement in humans. The
signaling protein Nodal is key for determining this laterality. Many
vertebrates, including humans, use cilia for breaking symmetry during
embryonic development: rotating cilia produce a leftward flow of
extracellular fluids that induces the asymmetric expression of Nodal.
By contrast, Nodal asymmetry can be induced flow-independently in
invertebrates. Here, we ask when and why flow evolved. We propose
that flow was present at the base of the deuterostomes and that it is
required to maintain organ asymmetry in otherwise perfectly
bilaterally symmetrical vertebrates.
KEY WORDS: Cilia, Evolution, Left-right asymmetry, Left-right
organizer, Leftward flow
Introduction
Symmetry is a guiding principle for the construction of animal body
plans. Apart from sponges, which are considered the most basal
branch of the animal phylogenetic tree (see Box 1), all other phyla
are characterized by one or several planes of symmetry along their
longitudinal axis. In radially symmetrical cnidarians, such as the
freshwater polyp Hydra, multiple planes of symmetry can be drawn.
All other major animal phyla belong to the bilateria, which are
marked by one plane of symmetry along the head to tail axis,
perpendicular to the dorsal-ventral axis. It has been suggested that
symmetry is used as a measurement of genetic fitness of a potential
mate in sexual selection (Brown et al., 2005). Asymmetry, in that
respect, is widely considered a defect. However, asymmetry is also
ubiquitously encountered in nature. This ranges from the chirality of
biomolecules, to functional asymmetries in symmetrical structures,
to the overt morphological asymmetries of organs.
In vertebrates, visceral and abdominal organs are asymmetrically
positioned with respect to the two main body axes (Fig. 1). This
arrangement, termed situs solitus (see Glossary, Box 2), is rarely
altered. Only ∼1/10,000 humans shows a mirror image of the
normal organ display (situs inversus; see Glossary, Box 2). Other
vertebrate asymmetries, such as left and right handedness, vary with
much higher frequencies in human populations and are not covered
here. Asymmetric organ morphogenesis and placement is initiated
during embryogenesis. In the early vertebrate neurula embryo, three
genes – those encoding Nodal, its feedback inhibitor Lefty and the
homeobox transcription factor Pitx2 – become asymmetrically
expressed in the left lateral plate mesoderm (LPM). This so-called
Nodal cascade (see Box 3) is a conserved feature of vertebrate left-
right (LR) axis formation. The functional importance of this
asymmetric expression has been demonstrated in all classes of
vertebrates (Yoshiba and Hamada, 2014). However, the mechanism
of symmetry .
The document summarizes key concepts in the evolution of life. It discusses early theories of spontaneous generation and the Miller-Urey experiment demonstrating organic molecules can form from inorganic precursors. Modern evolutionary theory developed from Darwin's principles of variation within populations, a struggle for existence, and survival of the fittest. Evidence for evolution includes homologous and vestigial structures, transitional fossils, embryological similarities, and molecular comparisons. Present-day evolution theories have expanded on Darwin's work through ideas like punctuated equilibrium, selfish genes, and the endosymbiotic origin of eukaryotic cells. New species arise through genetic isolation of populations and their gradual differentiation over time. The appearance of human beings is traced from early homin
Modern biology is a broad field composed of many interconnected subdisciplines that study life at different scales. While diverse, biology is unified by some key concepts like evolution, cells as the basic unit of life, and genes as the basic unit of heredity. Subdisciplines include biochemistry, molecular biology, botany, cellular biology, physiology, ecology, and evolutionary biology. Biology has developed significantly since ancient times, with major advances in microscopy revealing cells and advances in genetics revealing DNA as the carrier of heredity. The modern synthesis of Darwin's theory of evolution by natural selection with genetics and population genetics formed the foundation of modern biology.
The document provides an introduction to zoology, discussing several key topics:
- Theories of evolution from scientists like Lamarck and Cuvier are summarized, with Darwin's theory of natural selection identified as the most accurate.
- The complex life cycle of the monarch butterfly is used as an example to illustrate different life cycle stages like egg, larva, pupa, and adult.
- Adaptation strategies animals use to survive harsh environments like the desert and polar regions are outlined.
- The process of mitosis and key differences in replication between prokaryotes and eukaryotes are summarized.
- Homeostatic mechanisms that allow animals to maintain stable body conditions are briefly
A cell is the fundamental unit of life that can carry out all functions necessary to sustain life, such as nutrition, respiration, transport, response to stimuli, growth, and reproduction. All living organisms are composed of cells, which come in various shapes and sizes. A typical cell is enclosed by a membrane and contains a nucleus and organelles that carry out specific functions necessary for the cell's activities and survival. Key organelles include the mitochondria, which generates energy for the cell, and the endoplasmic reticulum and Golgi apparatus, which package and transport cellular products. The cell theory states that all living things are made of one or more cells and that the cell is the basic unit of structure and function in living organisms.
This document provides a historical overview of the development of cell theory from the early microscopic observations of cells in the 17th century to the formal establishment of cell theory in 1838-1839. It describes key early observations and advances that contributed to the theory, such as Hooke's discovery and naming of cells in 1665, the identification of the nucleus in the early 19th century, and technological improvements to microscopy. It then summarizes how in 1838 Schleiden applied the cell concept to plants and in 1839 Schwann extended it to animals, formally establishing that cells are the fundamental unit of structure and function in living things.
This document contains a series of photomicrographs and diagrams related to the internal anatomy and life cycles of various parasitic flatworms and roundworms. The images show structural features like the pharynx, intestine, reproductive organs, and larvae of tapeworms, flukes, and schistosomes. Labels on the images identify anatomical structures and developmental stages depicted.
This document provides preservation methods for various invertebrate species. It recommends fixing sponges in alcohol to preserve their spicules, relaxing flatworms in Bouin's fluid before storing in alcohol, and fixing nematodes in hot alcohol or formalin with added glycerin. Crustaceans should be killed in dilute formalin and stored in alcohol or glycerin-alcohol solution. Insects and spiders are stored in glycerin-alcohol solution after collection in alcohol. Earthworms can be killed with chloroform or anesthetized before storage in formalin or alcohol. Most mollusks, echinoderms, annelids, and cnidarians are relaxed before storage
This document discusses the ecology of protozoa that inhabit bryophytes. Protozoa are found on nearly all bryophytes and play important roles in nutrient cycling as they consume bacteria, fungi, and other microorganisms. They exhibit vertical zonation within bryophyte tissues based on factors like temperature, moisture, and food availability. Testate amoebae communities vary between bryophyte species and habitats like bogs versus forests. Bryophytes provide protozoa refuge during dry periods by trapping moisture and allowing encystment. The protozoan communities associated with bryophytes are still not fully described.
This document provides various methods for narcotizing or relaxing small invertebrates and other small organisms for examination or dissection. The methods include placing organisms in solutions of chemicals like chloroform, ether, magnesium sulfate, or menthol to relax them. Specific organisms can be relaxed using targeted methods, such as earthworms in ethanol, echinoderms in magnesium chloride, and rotifers in phenylephrine. The document also recommends carbon dioxide exposure, chloral hydrate, clove oil, or tricaine methanesulfonate for additional types of organisms. Methods are aimed to relax organisms without harming them so they can be revived after examination.
1) The document provides instructions for setting up freshwater aquariums, marine aquariums, and terrariums. It recommends cleaning and preparing the tank, adding gravel or sand, plants to oxygenate the water, and waiting several days before adding animals.
2) For marine aquariums, it recommends using saltwater, an under-gravel filter, and waiting two weeks before adding invertebrates. Up to 18-20 medium invertebrates can be kept in a 20-gallon tank.
3) Small marine aquariums can be created in jars using plastic filters. Terrariums can be made for woodlands, deserts, or semiaquatic environments
Los nematodos o gusanos redondos son un filo con más de 25,000 especies descritas que incluyen formas tanto de vida libre como parásitas. Poseen un cuerpo cilíndrico cubierto por una cutícula y sistemas de alimentación, circulatorio, nervioso y reproductivo adaptados a sus diversos hábitats acuáticos y terrestres.
Valentine et al 1999 (fossils, molecules and embryos new perspectives on the ...dreicash
The Cambrian explosion refers to the geologically rapid appearance of numerous metazoan body plans between 530-520 million years ago, representing about 1.7% of the duration of the animal fossil record. Earlier evidence of animal activity is found as far back as 600 million years ago in the form of trace fossils. The timing and significance of the Cambrian explosion remains debated, as some argue it was not a major evolutionary event while others view it as the establishment of the Phanerozoic biosphere. New fossil and molecular evidence provides a more complex picture, with increasing metazoan diversity and activity in the lead-up to the explosion, though it remains a prominent diversification event when most animal phyla first appear in
This document discusses Trichoplax adhaerens, the sole member of the phylum Placozoa. It describes Trichoplax as the simplest living metazoan, with an irregular shape and only four cell types. The author became interested in Trichoplax after learning about it from their teacher in 1979 and discussing its potential role as the earliest branching metazoan lineage. The document provides background on Trichoplax's simple anatomy, life cycle, and uncertainties about its sexual reproduction. It discusses historical debates about Trichoplax's phylogenetic position and its relevance to hypotheses about the earliest evolution of multicellularity.
Los rotíferos son pequeños animales acuáticos de entre 50-2000 micrómetros que presentan una gran diversidad de formas y estilos de vida. Poseen un órgano ciliado llamado corona que les permite alimentarse y moverse. Se reproducen de forma sexual o asexual dependiendo de la clase, y algunas especies forman quistes resistentes. Juegan un papel importante en las redes tróficas acuáticas.
Los micrognatozoos son un filo recientemente descubierto de invertebrados microscópicos que contiene una sola especie, Limnognathia maerski. L. maerski fue descubierto en Groenlandia en 2000 y mide solo 130 micras de largo, lo que lo convierte en uno de los animales más pequeños conocidos. Posee mandíbulas altamente complejas formadas por 15 piezas móviles que usa para comer, así como otros rasgos distintivos que justifican su clasificación en un filo separado.
Los onicóforos son un filo de animales invertebrados terrestres con cuerpos aterciopelados similares a orugas. Tienen numerosos pares de apéndices lobulares no articulados que usan para caminar. Están estrechamente relacionados con los artrópodos pero carecen de segmentación corporal. Incluyen aproximadamente 200 especies distribuidas a lo largo de los continentes que conformaron Gondwana, divididas en dos familias.
This document examines various life history traits of dicyemids to understand their reproductive strategies and adaptations to living as endoparasites in cephalopod renal organs. It finds that dicyemids have a hermaphroditic gonad that produces roughly equal numbers of eggs and sperm. Fecundity increases with adult body size. Embryo size correlates with host size, suggesting host factors influence dispersal and infection of new hosts. While individual fecundity is low, total reproductive capacity per community is high due to asexual multiplication within the host. Adult size appears constrained by the volume and features of the renal habitat within different host species.
El filo Gnathostomulida está formado por alrededor de 80 especies pequeñas que habitan en espacios intersticiales de arena y lodo de aguas costeras. Se caracterizan por tener mandíbulas, ser hermafroditas, triblásticas, bilaterales y no segmentadas, y alimentarse raspando bacterias y hongos con sus mandíbulas. Los gnathostomulidos se dividen en dos órdenes, Filospermoidea y Bursovaginoidea.
Resumen braquiopoda zoologia. sintana r. carlos t.dreicash
Los braquiópodos son animales marinos bentónicos protegidos por dos valvas. Presentan un cuerpo con lofóforo y masa visceral. Se reproducen sexualmente y poseen un estado larvario libre y natatorio llamado larva lobulada. Su registro fósil data de hace 600 millones de años, aunque actualmente solo existen unas 335 especies.
Los gastrotrícos son microorganismos acuáticos que habitan en sedimentos y plantas. Poseen cuerpo dividido en tres regiones y se alimentan mediante bombeo de partículas. Carecen de sistema excretor complejo y su sistema nervioso consiste en dos cordones medulados. La mayoría son hermafroditas o partenogenéticos, con órganos reproductivos simples. Se clasifican en dos órdenes y cuatro subórdenes según características morfológicas y de hábitat.
Este documento presenta las instrucciones para tres prácticas de laboratorio sobre Platyhelminthes, Rotifera y Nemertea. Los estudiantes describirán y compararán dos especies de Platyhelminthes del orden Polycladida, examinarán muestras de Rotifera del lago universitario para identificar sus partes, y observarán especímenes vivos y fijados de Nemertea para describir sus características y reacciones.
Los tardígrados son microscópicos animales acuáticos o terrestres que pueden sobrevivir en condiciones extremas como temperaturas de -272°C a 149°C y niveles altos de radiación. Carecen de sistemas circulatorio y respiratorio pero tienen la capacidad de entrar en un estado de criptobiosis o animación suspendida cuando las condiciones son desfavorables. Los tardígrados tienen un cuerpo cilíndrico segmentado con cuatro pares de patas y pueden moverse y adherirse a superficies. Se reproducen sexualmente
Este documento presenta las instrucciones para una práctica de laboratorio sobre los cnidarios. Los estudiantes examinarán y describirán varias especies de medusas, cubozoos, hidrozoos, anémonas y corales. Reconocerán las estructuras anatómicas clave de cada grupo y observarán muestras tanto vivas como esqueletos bajo el microscopio.
Los gastrotricos son pequeños animales marinos y de agua dulce que viven en ambientes intersticiales. Se alimentan de materia orgánica, bacterias, hongos y protozoos. Son hermafroditas o dioicos, y se reproducen sexualmente. Juegan un papel ecológico importante como parte de las cadenas alimenticias en las comunidades donde habitan.
El filo Cycliophora incluye organismos exclusivamente marinos que viven como parásitos en las piezas bucales de langostas. Son pequeños, entre 85-350 micrómetros, con simetría bilateral y una cutícula diferenciada. Se reproducen sexualmente o asexualmente y presentan un sistema nervioso y digestivo bien desarrollados, aunque carecen de sistema circulatorio. Actualmente solo se conoce una especie, Symbion pandora, y aunque inicialmente se pensó que estaban relacionados con los endoproctos y ectoproctos, estudios gen
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
BREEDING METHODS FOR DISEASE RESISTANCE.pptxRASHMI M G
Plant breeding for disease resistance is a strategy to reduce crop losses caused by disease. Plants have an innate immune system that allows them to recognize pathogens and provide resistance. However, breeding for long-lasting resistance often involves combining multiple resistance genes
ESPP presentation to EU Waste Water Network, 4th June 2024 “EU policies driving nutrient removal and recycling
and the revised UWWTD (Urban Waste Water Treatment Directive)”
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS.pptxRASHMI M G
Abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
Nucleophilic Addition of carbonyl compounds.pptxSSR02
Nucleophilic addition is the most important reaction of carbonyls. Not just aldehydes and ketones, but also carboxylic acid derivatives in general.
Carbonyls undergo addition reactions with a large range of nucleophiles.
Comparing the relative basicity of the nucleophile and the product is extremely helpful in determining how reversible the addition reaction is. Reactions with Grignards and hydrides are irreversible. Reactions with weak bases like halides and carboxylates generally don’t happen.
Electronic effects (inductive effects, electron donation) have a large impact on reactivity.
Large groups adjacent to the carbonyl will slow the rate of reaction.
Neutral nucleophiles can also add to carbonyls, although their additions are generally slower and more reversible. Acid catalysis is sometimes employed to increase the rate of addition.
Remote Sensing and Computational, Evolutionary, Supercomputing, and Intellige...University of Maribor
Slides from talk:
Aleš Zamuda: Remote Sensing and Computational, Evolutionary, Supercomputing, and Intelligent Systems.
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Inter-Society Networking Panel GRSS/MTT-S/CIS Panel Session: Promoting Connection and Cooperation
https://www.etran.rs/2024/en/home-english/
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
What is greenhouse gasses and how many gasses are there to affect the Earth.
Schierwater.bies.2005
1. My favorite animal,
Trichoplax adhaerens
Bernd Schierwater1,2
*
Summary
Trichoplax adhaerens is more simply organized than any
other living metazoan. This tiny marine animal looks like a
irregular ‘‘hairy plate’’ (‘‘tricho plax’’) with a simple upper
and lower epithelium and some loose cells in between.
After its original description by F.E. Schulze 1883, it
attracted particular attention as a potential candidate
representing the basic and ancestral state of metazoan
organization. The lack of any kind of symmetry, organs,
nerve cells, muscle cells, basal lamina and extracellular
matrix originally left little doubt about the basal position
of T. adhaerens. Nevertheless, the interest of zoologists
and evolutionary biologists suddenly vanished for more
than half a century when Trichoplax was claimed to be an
aberrant hydrozoan planula larva. Recently, Trichoplax
has been rediscovered as a key species for unraveling
early metazoan evolution. For example, research on
regulatory genes and whole genome sequencing promise
insights into the genetics underlying the origin and
development of basal metazoan phyla. Trichoplax offers
unique potential for understanding the minimal require-
ments of metazoan animal organization. BioEssays
27:1294–1302, 2005. ß 2005 Wiley Periodicals, Inc.
How I became interested in Placozoa
On Tuesday night, around 6 p.m. on 11 December 1979, my
most respected teacher, Carl Hauenschild, lists several
reasons for Placozoa possibly being a basal metazoan
phylum. Arguments range from smallest metazoan genome,
to the lackof a basal lamina, to overall morphological simplicity.
The black and white pictures thrown from the solid 30 year old
Leitz slide projector onto the well-aged screen are not very
impressive and yet they are somehow fascinating and breath-
taking. This animal looks more like an amoeba than a
metazoan (Fig. 1A). If it wasn’t for the fact that Trichoplax
possesses four different somatic cell types, it could be
classified as a multicellular or colonial protist and nobody
would argue. As a rather inexperienced undergraduate
student, I see only one interpretation: the screen shows the
mother of metazoan life. Trichoplax adhaerens, the only
species of the phylum Placozoa, looks like living proof of (or
possibly just the inspiring model for) Bu¨tschli’s placula
hypothesis and his hypothetical ‘‘urmetazoan’’. According to
Bu¨tschli the latter was a uniform two-cell layered disk adapted
to a benthic life style (similar to living Trichoplax).
When Carl Hauenschild discussed alternative interpreta-
tions regarding the phylogeneticposition of Placozoa, he could
not convince me of a derived position of Placozoa. In the latter
case, Trichoplax would represent a secondarily reduced,
simplified bauplan. If, for example, Placozoa werederived from
Cnidaria, the following question would be hard to answer. How
could a cnidarian give up its cnidae, I-cells, gastric cavity,
entoderm, nerve cells, epitheliomuscular cells, basal lamina,
extracellular matrix and other favorable inventions without
dropping into an ecological and evolutionary no-man’s-land?
In other Hauenschild lectures, I have seen examples of
dramatic secondary reduction of bauplans, the most extreme
ones a result of adopting a parasitic life style or reducing the
life-cycle to neoteny. No example, however, would be as
dramatic as a secondarily reduced Trichoplax scenario.
Placozoans possess neither a basal lamina nor an extra-
cellular matrix (ECM), and losing both these features would
have substantial cytological, physiological and morphological
consequences. Even for a very creative zoologist, it would be
hard to come up with a scenario in which the loss of these
features becomes advantageous to selection.(1)
It is still Tuesday, 11 December 1979, and almost 7 p.m.
now, and the cross-section of Trichoplax (Fig. 2A) shown on
the screen is the last slide for today’s lecture. Already I know,
when I become a researcher I want to study Trichoplax
adhaerens and test Bu¨tschli’s placula hypothesis.
My first contact with Trichoplax
In 1989, the Department of Biology at Yale University, and in
particular the laboratory of my postdoctoral adviser, Leo Buss,
was a very exciting place for me as a postdoc to explore new
things. Alongside my research on cnidarians, I started a
Trichoplax culture with three animals that I had collected from
an aquarium in Philadelphia. It was exciting just to watch
this small, flat and unstructured disc of cells that forms an
irregular body change its shape all the time (Fig. 1C). While
1
ITZ, Ecology and Evolution, Tiera¨rztliche Hochschule Hannover,
Germany.
2
Department of Invertebrates, American Museum of Natural History,
New York, USA.
Funding agency: our work has been supported by the DFG (Schi 277/
10-2) and the HFSP (RGP0221/2001-M).
*Correspondence to: Bernd Schierwater, ITZ, Ecology & Evolution,
TiHo Hannover, Bu¨nteweg 17d, D-30559 Hannover, Germany.
E-mail: bernd.schierwater@ecolevol.de
DOI 10.1002/bies.20320
Published online in Wiley InterScience (www.interscience.wiley.com).
1294 BioEssays 27.12 BioEssays 27:1294–1302, ß 2005 Wiley Periodicals, Inc.
My favorite animal
2. moving—and movement is noticeable only when the animal is
watched closely for several seconds—it leaves behind a
grazing trackof digested and phagocytised algae at the bottom
of the Boveri dish (see Schierwater & Kuhn(2)
) for feeding
conditions). I enjoyed watching individuals grow bigger and
divide into two. This vegetative mode of reproduction is quite
effective: soon I had a few hundred individuals growing in my
Boveri dishes andI had tomovethem intolarger dessert bowls.
I had enough animals to perform phototaxis experiments and
get ready for extracting DNA and RNA for isolating Hox genes,
just before I had to travel to Stanford (California) for a week.
When I came back, all Trichoplax cultures had died. This
happened a second and a third time, and I had to wait until
1993 to establish a new culture in Frankfurt. Two recognized
Figure 1. Photographs of Trichoplax adhaerens. A,B:These specimens belong to the so-called ‘‘Grell clone’’ and are about 2 mm
in diameter. B: Eggs are growing in the interspace between the lower and upper epithelium (photograph by Sven Sagasser, Hannover).
C: Changes of body form. Fig. 1A from Ender A, Schierwater B. 2003 Mol Biol Evol 20:130–134 with permission from Springer. Fig. 1C from
Syed T, Schierwater B. 2002 Senckenbergiana lethaea 82:315–324 with permission from Springer.
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BioEssays 27.12 1295
3. Trichoplax researchers, Drs. Ruthmann and Wenderoth, who
had been culturing the original Grell clone(3–6)
in Bochum for
more than two decades,provided uswith animals. In 1999 both
colleagues, Heinz Wenderoth and August Ruthmann, retired
from university work and handed over the Trichoplax cultures
to our lab. The ‘‘Grell’’ clone was found by the German
protozoologist K.G. Grell, University of Tu¨bingen, in an
algal sample from the Red Sea in 1969 and is now the DNA
source that we provided for the Trichoplax Genome Project
(Trichoplax Genome Consortium 2005; www.jgi.doe.gov/
sequencing/why/CSP2005/trichoplax.html).
The poorly known biology of
Trichoplax adhaerens
If whole genome sequencing had been possible at the start of
the 20th
century, Trichoplax would probably have been one of
Figure 2. Placozoan morphology. A: Cross section of Trichoplax adhaerens; modified after Grell & Ruthmann;(54)
see also Syed and
Schierwater.(23)
UE, upper epithelium; LE, lower epithelium; FC, contractile fiber cell; GC, gland cell; SS, shiny sphere; Mc, mitochondrial
complex; B, (endosymbiotic?) bacterium in endoplasmic reticulum. Note that the interspace between fiber cells and epithelia is free of ECM
and that a basal lamina is missing. B–D: Low-magnification scanning electron micrographs of diverse placozoans; the differences seen
are not necessarily characteristic of the various lineages (electron micrographs by Christiane Pech, Hannover). B: Indo-Pac lineage.
C: Panama #2 lineage. D: Grell clone individual with a ‘‘swarmer’’ being budded off from the upper epithelium. (See also Thiemann &
Ruthmann.(55)
)
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1296 BioEssays 27.12
4. the very first animals to have its genome sequenced because
of its unique, highly primitive morphology. The unique bauplan
is based on a simple, irregular sandwich organization. An
upper and a lower epithelium surround a loose network (not an
epithelium) of so-called fiber cells (Fig. 3a). Traditionally only
four cell types have been described in Trichoplax, upper and
lower epithelial cells, gland cells within the lower, feeding
epithelium, and fiber cells sandwiched between the epithe-
lia.(7–11)
No organs or specialized nerve or muscular cells are
present. A basal lamina and extracellular matrix are likewise
lacking. All these simple bauplan characteristics make
placozoans more similar to protozoans than to any other
existing metazoans. Body shape is irregular and changes
constantly (Fig. 1C). No symmetry of any kind is seen, and
nothing like an oral–aboral or even a dorsoventral polarity
exists. The only polarity present results from the fact that the
lower (¼feeding) epithelium faces the substrate while
the upper epithelium faces the open water (in laboratory
cultures Trichoplax sometimes also floats upside-down at the
water surface).
In the laboratory, we commonly see Trichoplax undergoing
binary fission. Animals grow and then pull apart into two
daughter individuals of similar size.(12)
Another mode of
vegetative reproduction has also been seen, the budding off
of small spherical swarmers (Fig. 2D) which are planktonic.
The latter most likely are dispersal stages, which may float in
the open water for up to a week.(13)
Sexual reproduction
remains enigmatic. Most likely Trichoplax can reproduce
bisexually, i.e. by producing female and male gametes. The
latter have not been observed, the former are comparatively
huge (some 100 mm in diameter) and appear in small numbers
in individual placozoans in the laboratory (Fig. 1B). Beyond
aberrant early cleavage stages, no embryonic development
has been observed.(6,12)
We know nothing about sexual
reproduction in the field. So far, field specimens of Trichoplax
have shown no signs of sexual reproduction (Vicki Pearse and
Allen Collins, personal communications).
Trichoplax occurs in the littoral of all warm oceans and is
distributed globally in tropical and subtropical waters.(14,15)
Finding Trichoplax in the field, however, can be tough. In three
locations of the Great Barrier Reef, I could not find a single
animal within 4 weeks, while in another location I found
10 animals on a single microscope slide, our standard traps for
collecting Trichoplax in the field. Vicki Pearse has been
collecting Trichoplax for almost 2 decades at tropical and
subtropical latitudes throughout the Pacific as well as in the
Caribbean and has observed clear seasonal changes in
abundance (cf also Maruyama(16)
). It has been extracted from
algae, pieces of coral and smooth stones. This is about all we
know of the life of placozoans in the field. From laboratory
cultures, we know that, in addition to the normal mode of
feeding (pinocytosis in the lower epithelium), Trichoplax can
also feed by means of the upper epithelium, a unique mode
called ‘‘transepithelial cytophagy’’.(17)
Nothing is known about
the relative importance of these feeding modes or about the
role of potentially symbiotic bacteria, regularly found in the
endoplasmic reticulum of the fiber cells.(18)
Is Trichoplax adhaerens the mother of
all metazoans?
When the German zoologist Franz Eilhard Schulze published
the description of a new marine animal that looked like a ‘‘sticky
hairy plate’’, he called it Trichoplax adhaerens (Greek
trich ¼ hair, plax ¼ plate, Latin adhaerere ¼ to stick). Schulze’s
histological analysis of Trichoplax, based on microtome
sections and various staining procedures, revealed the
three-layered sandwich organization(19)
outlined above.
Schulze(20–22)
noted features peculiar to Trichoplax: the slow
gliding movement and fluid body shape, the presence of only
four somatic cell types, the lack of typical metazoan histology
(no basal lamina or extracellular matrix); and the lack of any
kind of symmetry. These features indicated to him that
Trichoplax did not fit the patterns of sponges, cnidarians,
ctenophores, or any of the vermiform phyla. Consequently, he
suggested that Trichoplax represents a primitive bauplan
close to the root of the metazoan phylogenetic tree. Schulze’s
observations soon sparked debate on the evolutionary origin
of Metazoa and the hypothetical ‘‘urmetazoan’’ (‘‘archimeta-
zoa’’) between Haeckel, Lankester, Metschnikoff and other
zoologists (for overview and refs. see Syed & Schierwater(23)
).
The idea that Placozoa is basal within Metazoa is reflected
in at least one of the different hypotheses. Otto Bu¨tschli
Figure 3. Placula hypothesis of metazoanevolution. Flagellated protozoans unite to form a benthic-vagile, plate-like metazoanorganism.
The one-layered protist form (a) evolves to the two-layered ‘‘placula’’ (b,c). Cells of the upper layer form the ectoderm, while cells of the
lower layer (orange) adopt a nutritive function and later invaginate to form the entoderm (d–g); modified from O. Bu¨tschli,(24)
and Syed &
Schierwater.(23)
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BioEssays 27.12 1297
5. (University of Heidelberg) modified Haeckel’s ‘‘gastraea
hypothesis’’ intothe‘‘placula hypothesis’’, inwhich the gastraea
derived from a flat, benthic-vagile ancestor, the hypothetical
‘‘placula’’(Fig. 3).(24,25)
Later, Trichoplax adhaerens wasplaced
in the new phylum ‘‘Placozoa’’,(3)
named after Bu¨tschli’s
placula. According to Bu¨tschli, the first metazoans evolved
from colonial flagellates (Protozoa), which formed a benthic,
single-layered organism with ciliary locomotion. Subsequently
a two-layered ‘‘placula’’ developed with an upper ‘‘ectoderm’’
and a lower ‘‘entoderm’’, and invagination of the ‘‘entodermal’’
layer led to a benthic gastraea-like animal (Fig. 3). The
evolutionary scenario of a Trichoplax-like, benthic animal,
which gradually had its lower, nutritive epithelium displaced
into the interior of the body, is also seen in the so-called
benthoblastea–bilaterogastraeahypothesis of Ja¨gersten,(26,27)
yet another modified version of Haeckel’s blastaea–gastraea
hypothesis.(28)
It was expected that elucidating the ontogeny
and the life cycle of Trichoplax adhaerens would be the next
crucialstepinresolvingthephylogeneticpositionofPlacozoa—
a step that remains to be achieved. Instead modern develop-
mental genetics is contributing to the ‘‘urmetazoon’’ discussion
and a first attempt to incorporate regulatory gene data into the
placula hypothesis has been made.(29)
A number of researchers have tried to resolve the
phylogenetic position of Placozoa through molecular studies,
so far without complete success. Analyses of ribosomal
RNA sequences have created several conflicting hypotheses
(e.g. Collins,(30)
Ender & Schierwater(31)
for references). So
far, the only comparatively safe conclusion seems to be based
on mtDNA genome structure, which indicates that Placozoa
are not derived cnidarians but leaves open the question of a
basal position relative to Porifera.(31)
Recent cladistic analyses
of all mitochondrial genes and mtDNA composition suggest
that Placozoa possess the largest and most ancestral mtDNA
of Metazoa.(32)
Taken together, analysis of morphology,
several nuclear genes and 16S rRNA structure also point
towards a basal position of Placozoa.(29)
Current and future research on
Trichoplax adhaerens
The description of Placozoa in an evolutionary context
represented the first wave of research on Trichoplax. It lasted
for about three decades around the turn of the 20th
century.
Schulze’s article of 1914,(22)
in which he rejected the weird and
unsupported hypothesis that Trichoplax was a cnidarian larva,
wasthe last publication on Trichoplax in a zoological journal for
more than half a century. In the 1970s and 1980s a second
waveof organismal data wasinitiated when the cell biologist W.
Kuhl (University of Frankfurt) found Trichoplax in a seawater
aquarium containing organisms from the Mediterranean
Sea(33)
(note that most people say Trichoplax adhaerens
was rediscovered by K.G. Grell in 1969). The third wave of
placozoan research has just recently started and includes
studies at all levels of biological organization.
Trichoplax attractsthe attention of modernmultidisciplinary
research for at least three good reasons: (1) it is the most
simply organized metazoan animal, (2) it possesses the
smallest genome of all known metazoans;(35–37)
and (3) it is
currently undergoing whole-genome sequencing (see also
Ref. 34). Thus, understanding the genetic control of its
development will clarify basic principles of metazoan organi-
zation. The success of this research will also depend on
progress at the organismal level, particularly with respect to
documenting the life cycle.
Biodiversity
Placozoan specimens collected from diverse tropical and
subtropical waters around the world appear to be highly similar
morphologically and all fit the description of Trichoplax
adhaerens. Molecular analyses of ITS1-2 and three rRNA
Figure 4. Unexpected diversity has been found in the phylum Placozoa, formerly assumed to be monotypic. Shown is a MP phylogram of
placozoans based on combined SSU and LSU data. The sampling has been very limited so far and in order to unravel biodiversity of this
unique phylum, more and extended studies are urgently needed. See Voigt et al.,(38)
and Tomasetti et al.(56)
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1298 BioEssays 27.12
6. genes, however, reveal substantial genetic variation and deep
phylogenetic separation between strains (Fig. 4).(38–40)
According to these data, the phylum Placozoa is not monotypic
(note that the existence of a formerly described second
species, Treptoplax reptans,(41)
has never been confirmed). It
hasbecomeclear that Placozoa is a group harboring a larger—
although yet unknown—number of species that likely will fall
into different taxonomic units at the genus, family, or even
higher taxonomic level. Unfortunately, the absence of docu-
mented morphological and ecological differences and the lack
of life-cycle information hinder the assignment of new species
and higher taxonomic units. Aleshin et al.(42)
found no
substantial differences between the ‘‘Grell’’ clone and a clone
possibly originating from the Sea of Japan. It seems that a
placozoan species can have world-wide distribution and that
different lineages may occur sympatrically.(38,39)
Yet sampling
has been rather limited and more intensive world-wide collect-
ing is required in order to unravel the biodiversity of Placozoa.
Currently, the paucity of morphological characters and ecolo-
gical data hamper the description of new species and the
creation of a taxonomic system for Placozoa. As a first step, we
have recently begun an endeavor to barcode(43)
all the different
placozoan lineages. Placozoa would be the first metazoan
phylum barcoded as a whole. Barcoding aims to identify DNA
sequences as unique taxon barcodes for each single animal
species. Ideally only a few genes, e.g. the mitochondrial COI
and some ribosomal genes, will harbor sufficient information to
identify all animal species by individual DNA barcodes. For the
phylum Placozoa, we expect barcode markers to also be
informative for resolving placozoan systematics, i.e. assigning
taxonomic levels to genealogical branching patterns.
In collaboration with Maria Balsano (Urbino, Italy), we have
begun electron microscopical studies on the morphology of
different phylogenetic lineages in order to identify morpholo-
gical differences between deeply separated clades and thus
facilitate the description of new species. In collaboration with
John and Vicki Pearse (University of California, Santa Cruz),
Allen Collins (National Marine Fisheries Service, Washington
DC), Stephen Dellaporta (Yale University, New Haven), Paolo
Tomasetti (Central Institute for Marine Research, Rome, Italy)
and Rob DeSalle (American Museum of Natural History, New
York City), we also seek to gain more information from the
biology of Placozoa in the field. Efforts from more research
groups are urgently needed in order to resolve the biodiversity
of Placozoa.
General Biology
Understanding the complete life-cycle of placozoans is an
urgent priority. Although sexual reproduction was suspected in
the early 1970s, (Grell and Benwitz(4,6,44)
reported oogenesis
and cleavage processes), observations on embryonic devel-
opment have never gone beyond the 64-cell stage.(12,37)
Since
no researcher has yet been able to follow development beyond
early stages of embryogenesis, we do not even know if
Trichoplax develops directly or possesses a larval stage. At
present it appears difficult to sustain either full sexual or
embryonic development under laboratory conditions. Whether
these stageswill be found in the field also seems uncertain. It is
conceivable that placozoans in the field reproduce vegeta-
tively only or that sexual reproduction is a rare event occurring
only under certain environmental conditions. Molecular data
Table 1. Developmental regulatory genes reported from Placozoa
Developmental
gene Expression Effect of Inhibition Reference
Trox-2 Body margin between ecto- and entoderm. Cease of vegetative growth
and reproduction.
Jakob et al., 2004
Not Body folds of intact animals. — Martinelli & Spring, 2004
PaxB ‘‘Distinct cell patches along a ring region close to the outer
edge of the animal body.’’
— Hadrys et al., 2005
T-box
1. Brachyury ‘‘In a few cells or groups of (unknown) cells, marginal to the
edge of potential outgrowth zones of larger animals.’’
— Martinelli & Spring, 2003
2. Tbx2/3 ‘‘Body margin in the upper and lower epithelium.’’
Hmx (NK5) Very low to not detectable in adult Trichoplax. — Monteiro et al., 2005,
Unpublished data
Dlx (distal-less) Spatially restricted expression around the periphery. — Monteiro et al., 2005,
Unpublished data
Mnx (NK5) Spatially restricted expression around the periphery. — Monteiro et al., 2005,
Unpublished data
All genes somehow show spatial expression patterns near the outer margin of the animal. This observation might be related to the suggestion that, in this—in
addition to expression studies—gene inhibition studies have been successfully performed; it seems to be involved in polarity determination.(47)
, I would like to
note that the listed Not expression could not be reproduced in our lab. Instead, we regularly see high background signal in ‘‘body folds of intact animals’’ of
Trichoplax.
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BioEssays 27.12 1299
7. on allelic variation of single-locus genes support neither the
regular occurrence of sex nor the complete lack of sex in the
life cycle.(38)
Probably the best means towards progress in
unraveling the life cycle is to culture diverse phylogenetic
lineages in the laboratory under different and changing
conditions. Trichoplax has been cultured in several labora-
tories (in Germany, Italy, Russia, and the US) but no progress
beyond observation of cleavage stages has been reported. In
our laboratory, so far wehave found sexual specimens only in a
Panama clone (Fig. 2C).
Likewise, very little is known about the ecology of
Placozoa.(34,45)
Perhaps the Trichoplax Genome Project
Figure 5. The study of regulatory genes reveals insights into basic and basal mechanisms of metazoan development and evolution. Most
regulatory genes studied so far are expressed within or close to a small region of potentially undifferentiated cells embedded between the
lower and the upper epithelium. A,B: Trichoplax whole mount in situ hybridization for the putative ProtoHox/ParaHox gene, Trox-2; note the
strong and homogenous expression close to the body margin; arrows in B point to small undifferentiated—yet undescribed—cells between
the lower and upper epithelium; from Jakob W, Sagasser S, Dellaporta S, Holland P, Kuhn K, Schierwater B. 2004 Dev Genes Evol 214:170–
175 with permission from Springer. C,D: Trichoplax whole mount in situ hybridization for the putative ProtoPax gene, TriPaxB; note the
more spotted expression along the body margin; the arrow in D points to a small TriPaxB-expressing cell that is similar to cells expressing
the Trox-2 gene (B); from Hadrys T, DeSalle R, Sagasser S, Fischer N, Schierwater B. 2005 Mol Biol Evol 22:1–10 with permission of
Springer.
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8. (see below) will highlight the importance of Placozoa and also
fuel more ecological research and field work. The success of
the latter will obviouslyalso depend on progresswith respect to
biodiversity and systematic issues of Placozoa (see above).
EvoDevo research
In 2001 the Human Frontier Science Program awarded a
Research Grant to the Antp Superclass Gene Consortium in
order to clarify the early evolution of Antp-type genes in basal
metazoans and to develop Trichoplax adhaerens as a model
system for research in development and evolution. Together
with Peter Holland (Oxford) and Stephen Dellaporta (Yale), we
explored Trichoplax adhaerens from different perspectives.
Several new Antp-type genes were isolated, the existence of a
single Hox/ParaHox gene was verified, comparative functional
characters for several Antp superclass genes were analyzed,
and the mitochondrial genome was sequenced. This research
has yielded some surprising results. For example, the putative
Proto-Hox gene Trox-2(2,46)
and the Pax B gene are expressed
in a region where the upper and lower epithelia meet, and
where yet undescribed pluripotent cells are suspected.(47–49)
The Not and T-box gene also seem to be expressed in the
same area (Table 1).(50,51)
Ongoing research promises
insights into the evolutionary origin of a nervous system, a
head (or oral pole) and a body axis (e.g. oral–aboral) from an
animal that lacks any kind of nerve cells, symmetry or main
body axis.(47,48,52,53)
Current efforts also aim to produce cell cultures of dif-
ferent cell lineages, including the yet-undescribed potentially
‘‘pluri-potent’’ cells connecting the lower and the upper epithelia
(Fig. 5).(47)
It has been known that isolated fiber cells live
for hours in seawater,(54)
and our own experiments indicate
proliferation, in cell culture, of small cells that do not belong to
any of the four standard cell types. Unraveling the function of
these cells will likely add to our understanding of placozoan
development.
Whole genome sequencing
As a logical consequence of the work of the Antp Superclass
Gene Consortium, a Trichoplax Genome Consortium was
founded aiming to sequence and describe the complete
genome. The DOE Joint Genome Institute (Walnut Creek,
California) is completing this projectin 2005. Once the genome
sequence is released, I expect the number of research groups
working on Trichoplax adhaerens to substantially increase.
Together with anticipated genome sequences from other
diploblasts (those of the anthozoan Nematostella, the hydro-
zoan Hydra, and the sponge Reniera are imminent), these
data will be of crucial importance for reconstructing the
evolution of metazoan genomes, bauplans and development.
I expect the Trichoplax genome to become the standard basal
genome for the comparative analysis of animal genomes,
genes and biological processes ((http://www.jgi.doe.gov/se-
quencing/why/CSP2005/trichoplax.html).
At present, it is easier to sequence the whole genome than
to describe the basic life cycle of Trichoplax. Maybe this is
another reason why Trichoplax is my favorite animal and
challenge.
Acknowledgments
Special thanks to Max. Vicki Pearse, August Ruthmann and
AdamWilkinscontributedsubstantiallytothemanuscript,andI
am very grateful for their ideas and comments. I acknowledge
support from the Deutsche Forshungsgemeinschaft (Schi
277/10-2) and the Human Frontier Research Program (RGP
0221/2001-M).
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