The Origin of Species

1. The Origin of Species Chapter 8

3. Types of Natural Selection • Natural Selection  the way in which nature favors the reproductive success of some individuals in a population or species over others • Directional Selection • Stabilizing Selection • Disruptive Selection • Sexual Selection Malaria or No Malaria? Malaria .

4. Directional Selection • Occurs when selection favours individuals with a more extreme variation of a trait • Ex. Giraffes  directional selection favours individuals with a longer neck • The end result of directional selection is a shift away from the original average • Very common in artificial selection • Ex. strawberries

5. Stabilizing Selection • Occurs when the average phenotype within a population is favoured by the environment • Ex. Human birth weight • Environmental pressures will reduce the reproductive success of individuals with extreme versions of a trait

6. Disruptive Selection • Occurs when environmental pressures selected against the mean and for the extreme for a trait in a population • Ex. Darwin’s Finches

7. Sexual Selection • The favouring of any trait that specifically enhances the mating success of an individual • Often leads to the males and females of a species evolving an appearance and behaviour that are quite different from each other • Ex. Birds http://www.youtube.com/watch?v=W7QZnwKqopo • Two main types of sexual selection: • Female mate choice • Male vs. male competition http://www.youtube.com/watch?v=huxDnZs2_OQ

9. Evolutionary Change without Selection • Not all evolutionary changes are the result of natural selection. • Changes in the genetic make up of a population can occur by: • Genetic Drift • Bottlenecks • Founder Effect

10. Genetic Drift • The changes in allele frequency in a population as a result of chance • Small populations vs. large populations? • When alleles are lost due to genetic drift it results in a reduction in the genetic diversity of that population

11. Bottleneck • Results in a loss in genetic diversity following an extreme reduction in the size of a population. • Ex: Cheetahs  all thought to have descended from about 7 cheetahs that remained after experiencing a severe bottleneck about 10,000 years ago • When a bottleneck occurs, many alleles, and rare alleles in particular, are likely to be eliminated from the population.

12. Founder Effect • Occurs when a small number of individuals establish a new population • Ex: Amish • Populations effected by bottleneck or founder effect also experience genetic drift, which makes the population more likely to differ from the original population

13. Speciation • A biological species includes all the members of a population that can interbreed under natural conditions • Individuals of a different species cannot interbreed under natural conditions • Multiple Modes of Speciation: • Reproductive Isolation • Allopatric Speciation • Sympatric Speciation • Human Influence on Speciation

14. Reproductive Isolation • Prezygotic Mechanism – reproductive isolation that prevents interspecies mating and fertilization • Behavioural Isolation • Different courtship and mating routines • Temporal Isolation • Different breeding times in the year • Ecological Isolation • Similar species might live in different habitats of a region • Mechanical Isolation • Morphological features makes them incompatible • Gametic Isolation • Male gamete may not be able to recognize or fertilize the female’s egg

15. Reproductive Isolation Cont’d. • Postzygotic Mechanism - reproductive isolation that prevents maturation or reproduction in interspecies offspring • Zygotic Mortality • Zygote is unable to develop properly • Hybrid Inviability • A hybrid individual forms but either dies before birth or cannot survive past maturity • Hybrid Infertility • Hybrid offspring is viable but cannot reproduce

16. Allopatric Speciation • The formation of a new species as a result of evolutionary changes caused by a period of geographic isolation • Separation = no genetic material exchange, so they will evolve independent from the other • After enough time, usually the two populations will evolve a sort of reproductive isolating mechanism • Ex: Isthmus of Panama • 7 original species have now evolved into 14 distinct species • Ex: The Rocky Mountains

17. Sympatric Speciation • A new species evolves from within a larger population by becoming genetically isolated, which may occur suddenly or gradually • Ex: Hawthorn fly • This is thought to have occurred many times in the evolution of plants • Sexual vs. Asexual Reproduction • Polyploidy and hybrids can also arise from sympatric speciation • Ex: Ontario’s Eastern Gray Treefrog

18. Human Influence on Speciation • Many human activities are causing once large areas to be separated into smaller, isolated populations: • Agricultural Expansion • Road Construction • Housing Development • If humans ensure that connectivity between habitats is maintained, then gene flow can continue • Ex: Wildlife corridors

19. Adaptive Radiation • The relatively fast evolution of a single species into many new species, each adapted to a new niche • Ex: Darwin’s Finches • 13 finch species evolved from one original species

20. Divergent Evolution • The large scale evolution of a group into many different forms • Rodents • Ontario has over 20 species of rodents that are closely related due to divergent evolution • Divergent Evolution leads to two outcomes: • Competition between species is minimized • Given enough time, new species continue to evolve until most available resources are used and most niches are filled. • The end result is increased biodiversity

21. Convergent Evolution • The evolution of similar traits in distantly related species • Ex: Shark and Dolphins • They have a similar streamline body shape, however they are from completely different evolutionary paths (Fish vs. Mammal) • Convergent evolution leads to two outcomes: • Natural selection will favour the evolution of similar traits in similar environments • While some traits will converge in form / function, each species will retain traits that show their distinct evolutionary past

22. Coevolution • Process in which species evolve in response to the evolution of another species • Very common between plants and animals or plants and insects • Coevolution can lead to one or both species becoming increasingly dependant on the other • Often seen in symbiotic relationships

23. Evolutionary Pace • Gradualism vs. Punctuated Equilibrium • Theory of Gradualism • Theory that attributes large evolutionary changes in species to the accumulation of many small and ongoing changes and processes • Theory of Punctuated Equilibrium • Theory that attributes most evolutionary changes to relatively rapid spurts of change, followed by long periods of little or no change

24. Macroevolution • Large scale evolutionary changes including the formation of new species and taxa • Abiogenesis – the study of life originating from non-living mater

25. Cladistics and Phylogeny • Cladograms are used to illustrate the evolutionary relationships, or phylogeny of different groups of species of organisms • Cladistics is a method of determining evolutionary relationships based on the presence or absence of recently evolved or derived traits • Cladistics also looks at synapomorphies, which are derived traits shared by two or more species / groups

26. Cladograms • The key to cladistic analysis is to make inferences based on synapomophies • Sample Problem:

27. Cladograms Continued • Create a synapomorphies table from the characteristics table, and figure out which feature is most shared and start from there.