Chapter 26: Taxonomy and Systematics


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Chapter 26: Taxonomy and Systematics

  1. 1. CHAPTER 26 LECTURE SLIDES Prepared by Brenda Leady University of ToledoTo run the animations you must be inSlideshow View. Use the buttons on theanimation to play, pause, and turn audio/texton or off. Please note: once you have usedany of the animation functions (such as Play orPause), you must first click in the whitebackground before you advance the next slide. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. Taxonomy and systematics Taxonomy  Science of describing, naming, and classifying living and extinct organisms and viruses Systematics  Study of biological diversity and the evolutionary relationships among organisms, both extinct and modern Taxonomic groups are now based on hypotheses regarding evolutionary relationships derived from systematics 2
  3. 3. Taxonomy Hierarchical system involving successive levels Each group at any level is called a taxon Domain  Highest level  All of life belongs to one of 3 domains  Bacteria, Archaea, and Eukarya 3
  4. 4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Domains: Bacteria Archaea Eukarya Eukaryotic Excavata Land plants and algal relatives Alveolata Stramenopila Rhizaria Amoebozoa Opisthokonta supergroups:Large eukaryotic Plantae Fungi Animalia kingdoms: 4
  5. 5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Taxonomic Gray wolf Number of group found in speciesDomain Eukarya ~ 4– 10 millionSupergroup Opisthokonta >1 millionKingdom Animalia >1 millionPhylum Chordata ~50,000Class Mammalia ~5,000Order Carnivora ~270Family Canidae 34Genus Canis 7Species lupus 1 5
  6. 6. Binomial nomenclature Genus name and species epithet Genus name always capitalized Species epithet never capitalized Both names either italicized or underlined Rules for naming established and regulated by international associations 6
  7. 7. Phylogenetic trees Phylogeny – evolutionary history of a species or group of species To propose a phylogeny, biologists use the tools of systematics Trees are usually based on morphological or genetic data 7
  8. 8. Phylogenetic tree Diagram that describes phylogeny A hypothesis of evolutionary relationships among various species Based on available information New species can be formed by  Anagenesis – single species evolves into a different species  Cladogenesis – a species diverges into 2 or more species 8
  9. 9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Present F I G J H K B E Millions of years ago (mya) 5 CTime D B 10 A 9
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  11. 11.  Monophyletic group or clade  Group of species, taxon, consisting of the most recent common ancestor and all of its ancestors Smaller and more recent clades are nested within larger clades that have older common ancestors Paraphyletic group  Contains a common ancestor and some, but not all, of its descendents 11
  12. 12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.H I J K L M N O H I J K L M N O H I J K L M N O D E F G D E F G D E F G B C B C B C A A A(a) Monophyletic (b) Paraphyletic (c) Polyphyletic 12
  13. 13.  Over time, taxonomic groups will be Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. KEY reorganized so only Orders Classes monophyletic groups and snakes and snakes Crocodiles Crocodiles are recognized Lizards Lizards Turtles Turtles Birds Birds Reptiles were a paraphyletic groups because birds were excluded Reptiles (a) Reptiles as a (b) Reptiles as a Reptiles paraphyletic taxon monophyletic taxon 13
  14. 14. Homology Similarities among various species that occur because they are derived from a common ancestor Bat wing, human arm and cat front leg Genes can also be homologous if they are derived from the same ancestral gene 14
  15. 15. Morphological analysis First systematic studies focused on morphological features of extinct and modern species Convergent evolution (traits arise independently due to adaptations to similar environments) can cause problems 15
  16. 16. 16
  17. 17. Molecular systematics Analysis of genetic data, such as DNA and amino acid sequences, to identify and study genetic homologies and propose phylogenetic trees DNA and amino acid sequences from closely related species are more similar to each other than to sequences from more distantly related species 17
  18. 18. Cladistics Study and classification of species based on evolutionary relationships Cladistic approach discriminates among possible phylogenetic trees by considering the various possible pathways of evolutionary changes and then choosing the tree that requires the least complex explanation for all of the available data Phylogenetic trees or cladograms 18
  19. 19.  Cladistic approach compares homologous traits, also called characters, which may exist in two or more character states Shared primitive character or symplesiomorphy  Shared by two or more different taxa and inherited from ancestors older than their last common ancestor Shared derived character or synapomorphy  Shared by two or more species or taxa and has originated in their most recent common ancestor 19
  20. 20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.D E F G B C A 20
  21. 21.  Branch point – 2 species differ in shared derived characters Ingroup – group we are interested in Outgroup – species or group of species that is assumed to have diverged before the species in the ingroup An outgroup will lack one or more shared derived characters that are found in the ingroup 21
  22. 22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lancelet Lamprey Salmon Lizard Rabbit Notochord Yes Yes Yes Yes Yes Vertebrae No Yes Yes Yes Yes Hinged jaw No No Yes Yes Yes Tetrapod No No No Yes Yes Mammary No No No No Yes glands(a) Characteristics among species Lancelet Lamprey Salmon Lizard Rabbit Mammary glands Tetrapod Hinged jaw Vertebrae Notochord 22(b) Cladogram based on morphological traits
  23. 23.  Cladogram can also be constructed with gene sequences 7 species called A-G A mutation that changes the DNA sequence is analogous to a modification of a characteristic 23
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  25. 25. Constructing a cladogram1. Choose species2. Choose characters3. Determine polarity of character states  Primitive or derived? 25
  26. 26. 4. Analyze cladogram based on  All species (or higher taxa) are placed on tips in the phylogenetic tree, not at branch points  Each cladogram branch point should have a list of one or more shared derived characters that are common to all species above the branch point unless the character is later modified  All shared derived characters appear together only once in a cladogram unless they arose independently during evolution more than once4. Choose the most likely cladogram among possible options5. Choose a noncontroversial outgroup as root 26
  27. 27. Principle of parsimony Preferred hypothesis is the one that is the simplest for all the characters and their states Challenge in a cladistic approach is to determine the correct polarity of events  Itmay not always be obvious which traits are primitive and came earlier and which are derived and came later in evolution  Fossils may be analyzed 27
  28. 28. Example 4 taxa (A-D) A is the outgroup  Has all the primitive states 3 potential trees  Tree 3 requires fewest number of mutations so is the most parsimonous 28
  29. 29. According to the principle of parsimony, tree number 3 is the more likely choicebecause it requires only five mutations. 29
  30. 30. Molecular clocks Favorable mutations rare and detrimental mutations eliminated Most mutations are neutral If neutral mutations occur at a constant rate they can be used to measure evolutionary time Longer periods of time since divergence allows for a greater accumulation of mutations Not perfectly linear over long periods of time  Not all organisms evolve at the same rate  Differences in generations times 30
  31. 31. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Nucleotidedifferences ina homologousgene betweendifferent pairsof species 0 Evolutionary time since divergence of pairs of species 31 (millions of years)
  32. 32. Primate evolution example Evolutionary relationships derived by comparing DNA sequences for cytochrome oxidase subunit II  Tends to change fairly rapidly on an evolutionary timescale 3 branch points to examine (A, D, E) Ancestor A  Thisancestor diverged into two species that ultimately gave rise to siamangs and the other five species  23 million years for siamang genome to accumulate changes different from other 5 species 32
  33. 33.  Ancestor D  This ancestor diverged into two species that eventually gave rise to humans and chimpanzees  Differences in gene sequences between humans and chimpanzees are relatively moderate Ancestor E  This ancestor diverged into two species of chimpanzees  Two modern species of chimpanzees have fewer differences in their gene sequences 33
  34. 34. 34
  35. 35. Cooper and Colleagues Extracted DNA from ExtinctFlightless Birds and Modern Species to Propose a NewPhylogenetic Tree Ancient DNA analysis or molecular paleontology Under certain conditions DNA samples may be stable as long as 50,000 – 100,000 years Discovery based sciences- gather data to propose a hypothesis Sequences are very similar New Zealand colonized twice by the ancestors of flightless birds  First by moa ancestor, then by kiwi ancestor
  36. 36. Horizontal gene transfer Any process in which an organism incorporates genetic material from another organism without being the offspring of that organism Vertical evolution  Changes in groups due to descent from a common ancestor 38
  37. 37. Due to Horizontal Gene Transfer, theTree of Life Is Really a “Web of Life” Vertical evolution involves changes in species due to descent from a common ancestor Horizontal gene transfer is the transfer of genes between different species Significant role in phylogeny of all living species Still prevalent among prokaryotes but less common in eukaryotes Horizontal gene transfer may have been so prevalent that the universal ancestor may have been a community of cell lineages
  38. 38. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Bacteria Archaea Eukarya Fungi Animals Plants KEY Vertical evolution Horizontal gene transfer Common ancestral community of primitive cells
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