16 Evolution of Populations and Speciation

1. 16 Evolution of Populations and Speciation

2. Genetic Equilibrium • Combining Mendel’s work on genetics with Darwins ideas of evolution • Population Genetics: studying evolution from a genetic point of view

3. Variation of Traits in a pop. • Evolution is the change in the genetics of a group of organisms. • A population is the smallest grouping that can evolve. • What would be a larger grouping?

4. Bell Curve • If you measure an observable trait, there is often a large average group, with a few with more, and a few with less.

5. Standard Deviation, • (Greek letter lower case sigma σ ) • Shows the spread around the mean • How far are you from average

6. Causes of Variation • Envi. Factors: food variability • Genetics: Even two brothers will look dif. • Mutations cause some of this • Recombination: when genes get mixed around during meiosis • The random pairing of sperm and eggs (gametes) Coen Brothers

7. Allele Frequencies and the Gene Pool • Gene Pool: Total genetic information available. • If there’s no gene for feathers, then nobody has feathers. • If you know what’s there, you can predict what will be there in the next generation • Like Punnet squares for groups instead of just a mom and dad

8. Allele frequency: divide the number of a certain allele by the total number of alleles of all types in the population. • Expressed as a percent • If it’s 20%, then 1 in 5 chromosomes has it • Shows the amount of diversity in a group • Bloodtypes, eye colors

9. Phenotype Frequency • Number of individuals with a particular phenotype divided by the total number of individuals in the population. • Remember lots of phenotypes are inner (proteins, enzymes) • Is behavior a phenotype? Is it inheritable? Variability in mollusc species, (bean clams)

10. Hardy-Weinberg Equilibrium • A population that doesn’t change its frequencies… • Has no mutation • Has no immigration or emigration • Is very large • Mates are chose randomly • There is no natural selection • This population doesn’t evolve or change • It is hypothetical

11. Disruption of Genetic Equilibrium • How does evolution happen when the Hardy-Weinberg equilibrium is broken?

12. Mutation • Doesn’t happen too often • Mutagens: mutation causing things • Latin: Origin of change • Gamma rays, UV light, • Mostly mutations are harmful, gimp you up. • Often carcinogens: Cancer causing • Teratogen: Birth defect causing • But a good mutation influences evolution

13. Migration • Immigration/emigration • Behavior affects this • Gene Flow: Process of genes moving from one population to another. • Baboons: Since only a few alpha males reproduce in a group young males often leave and find their own group. If humans have humanity do baboons have baboonity?

14. Genetic Drift • Phenomenon by which allele freq. in a population change as a result of random events or chance • how important it is for everyone to reproduce depends on the size of your group disasters change the genetics of a population

15. Non-random mating • Who’s close by? • Assortive mating: Mate with someone who looks like you. • Tall girls & tall guys

16. Natural selection • The most important factor that disrupts a genetic stability • Stabilizing selection: The average individual is best suited for the environment and has the most kids • Everyone becomes more average

18. Directional Selection • One of the extremes of a trait is more successful and has more kids.

19. Disruptive selection • Opposite extremes are more fit than the average • Could lead to two species

20. Sexual Selection • If you are healthy enough to have some weird plumage you’ll make a good dad, and your kids will have even weirder plumage. Tommy Lee, peacocking

22. Formation of Species • New species show up, old species go extinct • Speciation: Forming new species • Well how do you know if you have a new species?

23. Morphological concept • What shape is it? • If it’s shaped like a grizzly bear, then it’s a grizzly bear. • Except sometimes one species will have different shapes. • They look dif, but they’ll breed together.

24. Pheidole barbata Ants look dif, but that’s because they have dif roles in the colony

25. Biological species concept • If a group can breed together, but not with other groups, then it’s a species • Can’t see this for extinct animals The Western meadowlark (left) and the Eastern meadowlark (right) appear to be identical, and their ranges overlap, but their distinct songs prevent interbreeding.

26. Problems • What about asexual organism? • What about potential breeding, like they can’t breed now, but they could if things were dif?

27. Ring species:species with a geographic distribution that forms a ring and overlaps at the ends. • subspecies of Ensatina salamanders • subtle morphological and genetic differences • They all interbreed with their neighbors, but not subspecies across the ring • So where do we mark the point of speciation? • Really matters for endangered species laws and where you can build on habitat

28. Isolating • Sit alone in your room • Two parts of a formerly interbreeding popl stop interbreeding somehow. • Geographicly • Canyons, rivers, deserts show up over the years and seperage groups. • Can be shown experimentally with flies

29. Reproductive isolation • Same area, but suddenly there are barriers to breeding • Prezygotic barriers: Happen before fertilization • Mating dance isn’t right • Mating season isn’t right • These damselfly penises illustrate just how complex insect genitalia may be.  • Postzygotic barrier: happens after fertilization • Weak offspring

30. How long does this take? • Depends, • Bananas reached the Hawaiian islands about a thousand years ago. • Now the moths that eat bananas have several distinct species • Punctuated equilibrium: sometimes change comes fast • The fossil record doesn’t show gradual change • The one hopeful monster that starts a whole new branch.

31. Review • What does a bell curve look like? • What is meant by the term gene pool? • What is genetic equilibrium? • What is genetic drift? • How does mutation disrupt genetic equilibrium? How does immigration? • What is sexual selection? • What are shortcomings of biological species concept? • How can isolation lead to speciation? • What is punctuated equilibrium?