Chapter 9

1. Chapter 9 Studying Adaptation: Evolutionary Analysis of Form and Function

2. Adaptation • This next unit looks more deeply into adaptation and how natural selection increases adaptation • Research that demonstrates that traits of organisms are adaptations is known as the adaptationist program • There are many obvious explanations for why we have particular traits • We must test each explanation to see if it really arose because of adaptation

3. Adaptation • Will examine a variety of methods used by evolutionary biologists to test hypotheses about adaptations • Experiments • Observational studies • Comparative Method

4. All Hypotheses Must be Tested: the Giraffe’s Neck • Everyone knows that the giraffe evolved a long neck to be able to eat the tallest leaves, thereby escaping from competition with other herbivores • Simmons and Scheepers challenged this notion and offered an alternative explanation for the giraffe’s long neck

5. All Hypotheses Must be Tested: the Giraffe’s Neck • They found that giraffe’s most often ate leaves at shoulder height, not from the tops of trees

6. All Hypotheses Must be Tested: the Giraffe’s Neck • They also found that males with the longest necks have the largest, hardest skulls • Maybe long necks evolved for competition for females • Female necks became longer because of selection for longer male necks • Neck-as-a-weapon hypothesis

8. All Hypotheses Must be Tested: the Giraffe’s Neck • Pratt and Anderson classified social status of males • Class C were young adults • Class A were large adults • Class B were small adults • Class A males had wider, stronger heads • Studied displacement by classes and receptivity of females of classes

10. All Hypotheses Must be Tested: the Giraffe’s Neck • There is evidence for selection on longer necks for reaching high and male-male competition • When studying adaptation remember that: • Differences among populations or species are not always adaptive • Not every trait is an adaptation • Not every adaptation is perfect

12. Function of Wing Markings and Wavings of Zonosemata • Tephritid fly that has distinct dark bands on wings • Holds wings up and waves them • Display seems to mimic threat display of jumping spiders • Perhaps flies mimic jumping spiders to avoid predation • Avoid predation by other predators • Or mimic jumping spiders to avoid predation by jumping spiders

13. Function of Wing Markings and Wavings of Zonosemata • Phrase a precise question • Do wing markings and waving behavior of Zonosemata mimic threat displays of jumping spiders and deter predation? • List three alternative hypotheses • Flies do not mimic jumping spiders • Display may be used in courtship • Flies mimic jumping spiders to deter non-spider predators • Flies mimic jumping spiders to deter jumping spiders

14. Function of Wing Markings and Wavings of Zonosemata • Experimental procedure • Clipped wings of Zonosemata and house flies, exchanged wings, and glued them on opposite fly • Clipping and gluing did not affect flying or displaying • Created five experimental groups to test hypotheses

17. Function of Wing Markings and Wavings of Zonosemata • Jumping spiders retreated from flies displaying with marked wings • Other predators killed and ate test flies

18. Function of Wing Markings and Wavings of Zonosemata • Results consistent with hypothesis 3 but not 1 or 2 • Support for hypothesis that Zonosemata deters its predators by acting like one • Important experimental design • Testing control groups • All treatments handled identically • Randomization of order of treatments • Replication of treatments

19. Function of Wing Markings and Wavings of Zonosemata • Why was replication important? • Reduced distortion of results by unusual individuals or conditions (variance) • Can estimate precision of results • Study successful because many variables were tested, but each was tested independently

20. Observational Studies • Experimental studies are preferred but it is often not feasible to experiment • e.g., cannot exchange giraffe’s necks with other animal • Behavior is hard to experiment with because the experiment often alters the natural behavior • Must use observational studies sometimes • Often they are nearly as powerful as experimental studies

21. Behavioral Thermoregulation • Desert iguanas (Dipsosaurus dorsalis) are ectothermic • Must regulate body temperature behaviorally • Can only function between 15° and 45°C • Examine thermal performance curve to see adaptation to particular temperature • Body temperature affects physiological performance • Keep body temperature close to 38°C

23. Night Retreats of Garter Snakes • Do snakes make adaptive choices of where to sleep at night? • Ray Huey implanted garter snakes with radio transmitters with thermometers • Preferred body temperature is 28– 32°C • Keep body temperature near preferred during day • Exposed or under rocks

25. Night Retreats of Garter Snakes • How do they choose good retreats at night? • Thickness of rock determines microhabitat temperature • Thin rocks heat alot during day and cool alot during night • Thick rocks heat and cool slowly • Medium rocks heat and cool just enough • Garter snakes should choose medium rocks

26. Night Retreats of Garter Snakes • Huey placed snake models under different rocks, in burrows, and on surface • Tested temperature fluctuations • Found that snakes choose medium rocks to heat and cool near preferred temperature range

30. The Comparative Method • Purpose of the comparative method is to remove the effects of evolutionary history from an analysis (phylogenetic independence) • The reasons why you need to remove effects of phylogeny from ecological or behavioral analyses are best demonstrated through examples

31. The Comparative Method • Why do some bat species have bigger testes? • Some bats have larger testes for their body size than others • Hosken hypothesized that bigger testes evolved for sperm competition • Female bats may mate with more than one male so the more sperm deposited by a male, the better chance he has of fertilizing the eggs • Bigger testes mean more sperm

32. The Comparative Method • Hosken reasoned that bat species that live in larger groups would have greater sperm competition • Therefore, they should evolve larger testes • Hosken collected data on roost group size and testes size and found a significant correlation

34. The Comparative Method • Hosken realized that this correlation may be misleading

35. The Comparative Method • Joe Felsenstein developed a way to evaluate cross-species correlation among traits • Start with a phylogeny • Look at where sister species diverge • Does the species that evolves larger group sizes also evolve larger testes? • Plot pairs of sister species connected • Drag closest point to origin • Erase origin points and examine independent contrasts

37. Significant positive correlation • Sperm competition and testes size

38. Strategies for Asking Interesting Questions • Study natural history • Wing markings of Zonosemata • Question conventional wisdom • Neck of giraffe • Question assumptions of research technique • Felsenstein’s independent contrasts • Draw analogies among fields • Testes size in other mammals

39. The human CCR5 gene has three genotypes +/+, +/∆32 and ∆32/∆32. If a large number of ∆32 alleles were introduced into either African or East Asian human populations (q=.2), what would you expect to happen to this allele over time? (a) be quickly lost due to purifying selection, (b) invade the population due to directional selection, (c) be lost due to drift, (d) invade the population due to disruptive selection, (e) be lost due to disruptive selection. • Selection will lead to evolutionary change (a) when phenotypes differ, (b) when phenotypes differ in fitness (c) when phenotypes differ in reproductive success and are heritable (d) when population sizes are very small. • If a population is Hardy-Weinberg equilibrium, no evolution is occurring. (a) True or (b) False? • Which of the following factors typically result in linkage disequilibrium? (Choose all correct answers to get credit). (a) mutation (b) selection (c) recombination (d) random genetic drift (e) population admixture. • The locus (gene) Z determines flower color and has two alleles, Z and z. Genotypes and phenotypes are the following: ZZ = red flowers, Zz = white flowers, zz = white flowers. Which allele is recessive? (a) Z (b) z (c) you cannot tell with the information given.

40. A population has a gene “B” with two alleles, B1 (allele freq. = p) and B2 (allele freq. = q). The frequency of adult heterozygotes formed after random mating would be (a) 2pq, (b) q, (c) q2 , (d) p. • Gene duplication is probably the most important source for new genes; what are the potential fates of the “new” gene copy? (a) becomes a psuedogene, (b) becomes a transposable element, (c) gains a new function, (d) both a and c, (e) both a and b. • Point mutations generally result from errors made by DNA polymerase during DNA synthesis (a) True, (b) False. • The Hardy-Weinberg equilibrium principle yields which of the following conclusions? (a) The allele frequencies in a population will not change over time, (b) If the allele frequencies in a population are given by p2, 2pq and q2, the genotype frequencies are given by p and q, (c) If the allele frequencies in a population are given by p and q, the genotype frequencies are given by p2, 2pq and q2, (d) a and b are correct, (e) a and c are correct. • In evolutionary biology, migration is synonymous with (a) evolution, (b) selection, (c) mutation, (d) gene flow.

41. The HIV epidemic is unlikely to lead to an increase in the frequency of the CCR5 delta-32 allele over the short term because (a) in populations with a high frequency of the allele, selection pressure is relatively low, (b) in populations with high selection pressure, the allele frequency is high, (c) the allele is recessive and deleterious, (d) because the human genes encoding HIV resistance are linked. • If migration proceeds unopposed by any other evolutionary process, the result will be (a) an increase in the frequency of homozygotes in all populations, (b) an increase in rare allele frequency among populations, (c) homogenization of allele frequencies among populations, (d) the loss of one or more alleles in one or more populations. • In a species with three main populations you determine that gene flow is occurring among the populations, but you also know that selection is occurring (selection is different in each population). Which statement is FALSE (a) all three populations will be homogenized if the rate of migration is stronger than selection, (b) all three populations will evolve in the same direction (allele frequencies will change similarly across populations) if migration is weaker than selection, (c) if selection is stronger than migration, selection determines allele frequency change, (d) high migration will counteract local selection on allele frequencies.

42. Imagine a population with the dominant allele having a frequency of 0.05. In this population we would expect allele frequency change via selection (either for or against the dominant allele) to be (a) very slow because of recessive alleles being masked in heterozygotes (b) rapid compared to a recessive allele, (c) countered by genetic drift (d) slow because the dominant genotypes are most common. • Analyses of loss-of-function mutations underestimate actual mutation rates. One reason this is the case is (a) all non-synonymous mutations have effects too subtle for researchers to detect, (b) synonymous mutations produce no change in amino acid sequences, and so are uncounted by these analyses, (c) phenotypic changes can't be caused by point mutations, (d) all are correct. • In a species with 5 populations, you determine that Nm (# migrants per generation) is zero among the populations, thus (a) each population may evolve independently due to genetic drift, (b) different alleles may be fixed in each population, (c) natural selection can work differently in each population, (d) both a and b are true (e) all of the above are true.

43. In the Lake Erie water snake example, the color polymorphism was controlled at a single locus with two alleles. We know selection occurred on the island populations and that banded is dominant, thus which of these are true for the island population. (a) w = 1,1,1-s and m is zero, (b) w = 1, 1-s, 1 and m is low (c) w = 1-s, 1-s, 1 and m > s (d) w =1,1-s, 1 and m< s (e) w =1-s,1, 1, and m = s. • Let A1 frequency = p and A2 frequency = q. In a population with genotypes A1A1, A1A2, A2A2 you determine p=0.6 and q=0.4. There are 100 individuals in this population. Twenty years you return and find that p has drifted to 0.2 in this population. Based on this new information on the allele frequencies, what is the probability of the neutral allele A1 ever becoming fixed at 100% in the population? (a) 0.8, (b) 0.2, (c) 0.12, (d) 0.36, (e) none of the above. • There is a species that lives on the coast of Ecuador that has genotype frequencies for gene A as follows: AA=25%, Aa=50%, and aa=15%. This year we found a population of the mainland species that must have colonized the island (by swimming) within the last few years. The population now only has 10 individuals and there is no evidence that the population was ever large on the island. The island population has genotype frequencies that are very different than the mainland but are in H-W equilibrium. What is the best explanation for the island population having different genotype frequencies compared to the mainland? (a) linkage disequilibrium, (b) genetic drift (c) selection (d) founders effects (e) mutation-selection balance. • Even if a particular allele is negatively selected for, it may take a long time to be completely eliminated from a population. If the negatively selected allele is a, and the more fit allele is A,a would be completely eliminated faster if the a allele was: (a) dominant, (b) recessive.

44. The Hardy-Weinberg equilibrium model assumes that there is no selection; this is a must because (a) selection is dangerous, (b) selection can affect genotype frequencies in the parent population, (c) selection can affect allele frequencies in the parent population (d) selection can affect allele frequencies in the next generation, (e) b, c and d. • True or false: John Maynard Smith developed two null hypotheses for the evolution of sex: first, females reproductive mode does not effect number of offspring and second, males reproductive mode does not affect the probability of offspring survivorship. (a) True, (b) False. • Generally, in an unstable environment, which reproductive mode has a selection advantage? (a) sexual, (b) asexual, (c) both are equally fit, (d) neither b and c. • Overdominance is generally associated with unstable equilibriums while underdominance is associated with stable equilibrium. (a) True, (b) False. • When heterozygotes have a superior fitness, natural selection (a) removes both homozygotes from the population, (b) causes allele frequencies to eventually reach an unstable equilibrium, (c) reduces homozygosity and increases heterozygosity, (d) both a and c, (e) both b and c. • The Elderflower orchids constantly change genotype frequencies to fool bees, which is an example of (a) frequency-dependent selection, (b) positive selection, (c) disruptive selection, (d) balancing selection, (e) directional selection.

45. When you have a synergistic deleterious interaction among mutation, population size and random genetic drift this is called? (a) population dynamics, (b) evolution by drift, (c) mutational meltdown, (d) Robertsonian effects. • Genetic polymorphism can be maintained by? (a) recombination, (b) random genetic drift, (c) natural selection, (d) none of the above (e) both b and c. • In the collard lizard example, populations were isolated overtime due to the lack of (a) hurricanes, (b) thunderstorms, (c) logging, (d) fire, (e) b, c and d are correct. • Having a dN/dS ratio greater than 1 suggests (a) balancing selection, (b) directional selection, (c) positive selection, (d) all of the above, (e) both b and c. • When an evolutionary biologist talks about sex they generally mean (Choose all correct answers to get credit). (a) meiosis with crossing-over, (b) mating between unrelated individuals, (c) recombination, (d) mitosis, (e) gene duplication

46. Figure _____ most likely represents the simulations performed on the smallest population. (a) A, (b) B, (c) C. • Figure _____ most likely represents the simulations performed on the largest population. (a) A, (b) B, (c) C. • The figures above only show the effects of allele change once alleles are already in the population. If we introduced mutations (at a steady rate per individual) into each of the populations above, which figure shows the population that you expect to have the highest evolutionary rate. (a) A, (b) B, (c) C, (d) all would have the same evolutionary rate. • Now... forget the explanation of the graphs I have given above... If I told you that figure A was the result of selection against heterozygotes, what type of selection would this represent? (a) underdominance, (b) overdominance, (c) heterozygote superiority, (d) stable selection.