Evolution Lecture 12: Adaptation

1. Evolution Lecture 12: Adaptation

2. What is adaptation? • A trait or suite of traits that increases fitness of its possessor is called an adaptation • A trait may be considered adaptive • Individuals in past generations had variable traits, those traits that increased fitness were passed on in the highest number, thus adaptations evolve • Demonstrating that certain traits are adaptive have dominated much of evolutionary literature over the past 140 years-MAJOR FOCUS OF STUDY

3. The adaptationist program • Determining the function of a trait and then determining individuals that posses the trait contribute more genes to future generations is the crux of the research for the adaptationist • However, is it easy to determine that a trait is adaptive? • No explanation for the adaptive value for a trait should be accepted just b/c it is plausible and charming (Gould and Lewontin, 1979)

4. Function of the neck in the Giraffe?

5. Adaptive value of neck in giraffes? • They tend not to feed at their maximum height, but rather in shrubs and bushes at the height of their shoulders • Simmons and Scheepers suggest that males use their necks and heads as clubs during fights…sometimes killing one another • Their necks are 30-40cm longer 1.7x heavier than females, additionally the heads are more heavily armored • Three classes of male giraffe sizes from large to small: A, B and C • Wins competitions: A>B>C • Number of successful mating attempts: A>B>C

6. Need to keep the following in mind when studying adaptation • Differences among populations or species may not be adaptive. Differences may be due to drift and have no function • Not every trait or every use of a trait is an adaptation • Not every adaptation is perfect. Long necks may confer an advantage in terms of mating success, but also make it difficult to get a drink!!

7. Three methods for studying adaptation • Experimental • Observational • Comparative

8. Experimental • Most powerful tool for testing hypotheses • A good experiment restricts differences between study groups to one variable • The tephritid fly has an unusual banding pattern on its wings. When threatened, they hold the wings perpendicular to their body • This looks very similar to a fierce predator…the jumping spider • It was thought that they use this display to deter all types of predators • However, they could be deterring only the jumping spider (one of their main predators) with this look-alike threat! • https://www.youtube.com/watch?v=S4KQEKBdyVI&t=23s –flies • https://www.youtube.com/watch?v=knu5mthQjOM –jumping spiders

9. Three hypotheses to test • Hyp 1: The wings and display do not mimic spiders, perhaps they are only used as courtship displays? • Hyp 2: They deter all types of predators that would fear the bite of a jumping spider…all types of insects, small lizards etc. • Hyp 3. They specifically deter jumping spiders by mimicking their threat!

10. How to test?

11. Predicted results

12. *See considerations for quality experiments p. 338-339 of your text Results Deters spiders, (but not other predators)!

13. Observational studies • Used when experimentation cannot be done: cannot surgically alter the necks of giraffes • May not be valid to bring species in an unnatural experimental setting when you want to determine how they behave in nature • Behavioral regulation in ectothermic vertebrates: snakes • Garter snakes prefer a temperature between 28-32C in the lab • How do they maintain this temperature in the wild, when the temperature constantly change? • Do they behaviorally thermoregulate? If so, how?

14. Iguana thermoregulatory activity

15. Garter snakes Both snakes stay within preferred range determined in lab (28-32 C)

16. Hypotheses • They can stay under rocks, however thick rocks never get warm, and thin rocks get too warm and could kill the snake • They could remain on the surface and shuttle between temperatures, but would get dangerously cold at night • They could remain in burrows, but may also get too cold as well

18. Most snakes found here The snakes may thermoregulate on the surface during the day, but choose medium thick rocks to stay under at night (not random rocks based on availability).

19. Comparative method • Compare among characters and predictions • Why do some bats have larger testes than others? • Sperm competition • Usually occurs in large social groups

20. Variation in testes among bat species-this graph plots the relative testes size of bat species as a function against the roost group size (17 species total)

21. Problem with previous graph, it does not account for phylogenetic effect Imagine only 6 species, however, and what if many are related, would that mean that they simply inherited testes size and didn’t evolve it independently (as a function of the roost size or vice versa).

22. Not a valuable graph! Can correct for this but two data points isn’t great!

23. Must correct for this phylogenetic effect using independent contrasts Can instead look at the change between the sister species pairs as group size changes and plot that instead Each contrast shows the divergence that occurs as sister pairs evolve away from common ancestor

24. Independent contrasts for bats Can still conclude that when bats evolve larger group sizes, males evolve larger testes

25. Trade-offs & Constraints Organisms cannot possibly evolve optimal solutions for all challenges at once Example-bats evolve large testes in group for sperm competition…but it turns out that large testes in bats are correlated with smaller brains (trade-off)

26. Some more examples https://www.youtube.com/watch?v=c7suzKoZWpE https://www.youtube.com/watch?v=zJeu8PAtNj0 https://www.youtube.com/watch?v=SUPtPIm9PCc

27. Trade-offs & Constraints Example-flower color in fuchsias---bird pollinated flower Pollination only occurs during green color phase of flower After pollination, flower turns red, birds do not visit it Why hang on to flower and not drop it after pollinations? Physiological constraint---takes 3 days for pollen to reach ovary, need flower to remain that long for pollination

28. Trade-offs & Constraints Example-host shift in beetles Each species of Ophraella beetle feeds on specific plants Each host plant makes a specific group of toxic compounds Beetle is adapted to know to lay eggs on correct plant, and to defend itself from the plant’s chemicals

29. Trade-offs & Constraints Example-host shift in beetles There have been 4 major host switches in the beetle’s history Why have some host switches happened but not others? Most beetle species do not have enough genetic variation in their feeding and detox mechanisms to feed on other hosts