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Macro evolution-natural-selection-speciation
Populations, rather than individuals, are the units of evolution. A population is a group of interbreeding individuals of the same species living in the same area. Five agents can drive microevolution within a population: mutation, genetic drift, gene flow, non-random mating, and natural selection. Natural selection leads to differential reproductive success and is the only agent that can result in adaptation to the environment.
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Macro evolution-natural-selection-speciation
- 1. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings Populations are the units of evolution Figure 13.6
- 2. 1. What isevolving? gene pool, microevolution 2. Five agents of evolution 3. Types of natural selection Why do organisms change?
- 3. • Evolution happenswhen populations of organisms with inherited variations are exposed to environmental factors that favor the reproductive success of some individuals over others Figure 1.6C
- 4. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings Populations are the units of evolution • A population is a group of interbreeding individuals • A species is a group of populations whose individuals can interbreed and produce fertile offspring Figure 13.6
- 5. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • gene pool = total collection of genes in a population at any one time • Microevolution is a change in the relative frequencies of alleles in a gene pool What is evolving?
- 6. Five agents ofmicroevolution 1. Mutation changes alleles 2. Genetic drift = random changes in allele frequency Bottleneck Founder effect
- 7. LARGE POPULATION =10,000 SMALL POPULATION = 10 allele frequency = 1,000 10,000 = 10% allele frequency = 1 10 = 10% 50% of population survives, including 450 allele carriers 50% of population survives, with no allele carrier among them allele frequency = 450 5,000 = 9% allele frequency = 0 5 = 0% little change in allele frequency (no alleles lost) dramatic change in allele frequency (potential to lose one allele) Genetic drift - effects of population size:
- 8. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings Founder effect Figure 13.11B, C Bottleneck effect Population size is critical in preserving species.
- 9. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings 3. Gene flow can change a gene pool due to the movement of genes into or out of a population ex. Migration 4. Nonrandom mating within a population 5. Natural selection leads to differential reproductive success
- 10. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Male and female lions Figure 13.20x
- 11. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Natural selection - results in the accumulation of traits that adapt a population to its environment - the only agent of evolution that results in adaptation.
- 12. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings What are sources of genetic variation? • Mutation can create new alleles, new genes. • Sex - Recombination of genes in sexual reproduction
- 13. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Natural selection tends to reduce variability in populations. Mechanisms which counteract: – The diploid condition preserves variation by “hiding” recessive alleles (Bb) – Balanced polymorphism (2+ phenotypes stable in population) may result from: 1. heterozygote advantage Aa > aa and AA 2. frequency-dependent selection 3. variation of environment for a population Why doesn’t natural selection eliminate all genetic variation in populations?
- 14. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Many populations exhibit polymorphism and geographic variation Figure 13.13
- 15. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Neutral; no apparent advantage or disadvantage – Example: human fingerprints Not all genetic variation may be subject to natural selection Figure 13.16
- 16. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Low genetic variability may reduce their capacity to survive as humans continue to alter the environment – cheetah populations Endangered species often have reduced variation Figure 13.17
- 17. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals • Production of fertile offspring is the only score that counts in natural selection What is an organism’s evolutionary fitness?
- 18. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings There are three general outcomes of natural selection Figure 13.19 Frequencyof individuals Original population Phenotypes (fur color) Original population Evolved population Stabilizing selection Directional selection Diversifying selection
- 19. beak depth 1976 1978 Average beak depth, 1978 Average beakdepth, 1976 Beak depth (mm) Shift of average beak depth during drought 5 6 7 8 9 10 11 12 13 14 0 20 40 60 80Numberofindividuals
- 20. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria – Example: Mycobacterium tuberculosis Figure 13.22
- 21. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • This is due to: – historical constraints – adaptive compromises – chance events – availability of variations Natural selection cannot fashion perfect organisms
- 22. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • appearance alone does not always define a species Figure 14.1A – Example: eastern and western meadowlarks What is a species?
- 23. What is aspecies? • Naturally interbreeding populations - potentially interbreeding - reproductively isolated from other species What about asexually reproducing organisms? Extinct species? Shy species?
- 24. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • When geographically isolated, species evolution may occur – gene pool then changes to cause reproductive isolation = allopatric speciation When does speciation occur? MECHANISMS OF SPECIATION Figure 14.3
- 25. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • A ring species may illustrate the process of speciation Figure 14.1C OREGON POPULATION 1 2 COASTAL POPULATIONS Yellow- eyed Monterey 3 Sierra Nevada Yellow- blotched Gap in ring Large- blotched INLAND POPULATIONS
- 26. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings Reproductive barriers between species • Habitat - different locations • Timing - mating, flowering • Behavioral - mating rituals, no attraction • Mechanical - structural differences • Gametic - fail to unite • Hybrid weak or infertile
- 27. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Courtship ritual in blue-footed boobies is an example of behavioral isolation • Many plant species have flower structures that are adapted to specific pollinators – mechanical isolation Figure 14.2A, B
- 28. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Hybrid sterility is one type of postzygotic barrier – A horse and a donkey may produce a hybrid offspring, a mule – Mules are sterile Figure 14.2C
- 29. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings Sympatric speciation • No geographical isolation • Mutation creates reproductive isolation • Polyploidization • Hybridization
- 30. Medium ground finch Cactus ground finch Small treefinch Large ground finch Small ground finch Large cactus ground finch Sharp-beaked ground finch Vegetarian finch Seed eaters Ground finches Cactus flower eaters Bud eaters Tree finches Insect eaters Medium tree finch Large tree finch Mangrove finch Woodpecker finch Green warbler finch Gray warbler finch Warbler finches Common ancestor from South America mainland When does speciation occur?
- 31. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Specialists - Galapagos finches • Generalists - horseshoe crabs, cockroaches • New environments - ecological niche When does speciation occur?
- 32. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Adaptive radiation on an island chain - specialization for different niches Figure 14.4B Species A from mainland 1 A 2 B B 3B C 4 C C 5 B C D C D
- 33. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • Continental drift is the slow, steady movement of Earth’s crustal plates on the hot mantle Continental drift has played a major role in macroevolution Figure 15.3A Pacific Plate North American Plate Nazca Plate South American Plate African Plate Eurasian Plate Split developing Indo-Australian Plate Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events) Antarctic Plate
- 34. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • influenced the distribution of organisms – Continental mergers triggered extinctions – Separation of continents caused the isolation and diversification of organisms Figure 15.3B Millionsofyearsago Eurasia CENOZOICMESOZOICPALEOZOIC North America Africa IndiaSouth America Antarctica Australia Laurasia Gondwana Pangaea
- 35. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings Speciation - how much change is needed? • Gradual vs. jerky • Evidence: – Fossil record – Genetic differences between species – Homeotic genes
- 36. Copyright © 2003Pearson Education, Inc. publishing as Benjamin Cummings • homeotic genes control body development • Single mutation can result in major differences in body structure Figure 11.14 Mouse chromosomes Mouse embryo (12 days) Adult mouse Fly chromosomes Fruit fly embryo (10 hours) Adult fruit fly
Editor's Notes
- #8 Figure: FG17-05 Title: Genetic drift. Caption: a. In a hypothetical population of 10,000 individuals, 1 in 10 carries a given allele. The population loses half its members to a disease, including 550 individuals who carried the allele. The frequency of the allele in the population thus drops from 10 percent to 9 percent. b. A population of 10 with the same allele frequency likewise loses half its members to a disease. Because the one member of the population who carried the allele is not a survivor, the frequency of the allele in the population drops from 10 percent to zero.
- #20 Figure: FG17-09 Title: Who survives in a drought? Caption: sharp focus in 1977, when a tiny Galapagos is-land, Daphne Major, suffered a severe drought. Rain that normally begins in January and lasts through July scarcely came at all that year. This was a disaster for the island's two species of finches; in January 1977 there were 1,300 of them, but by December the number had plunged to fewer than 300. Daphne's medium-sized ground finch, Geospiza fortis, lost 85 percent of its population in this calamity. The staple of this bird's diet is plant A large percentage of the population of Geospiza fortis died on a Galapagos Island, Daphne Major, during a drought in 1977. Peter Grant observed in 1978 that individuals who survived the drought had a greater average beak depth than average individuals surveyed before the drought, in 1976.Individuals with larger beaks were better able to crack open the large, tough seeds that were available during the drought. The offspring of the survivors likewise had larger average beak size than did the population before the drought. Thus, evolution through natural selection was observed in just a few years on the island.