Chapter 9

1. Chapter 9

2. Natural selection can change allele frequencies in the next generation, but it does not drive genotype frequencies away from predicted values under H-W. • Balancing selection, overdominance and heterozygote superiority are synonymous? • Heterozygote inferiority or disruptive selection reduces genetic diversity within populations, but helps maintain genetic diversity among populations. • Explain why random genetic drift is the antithesis of natural selection. • What is an extinction vortex?

3. While working on your tan at an island in the Caribbean you determine that 22 iguanas migrated onto this island from a neighboring island. You ask the local witch doctor how many iguanas lived on the island prior to the migration event and he tells you 478. Please calculate the migration coefficient (m).

4. 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

5. 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

6. 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

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

10. 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

11. 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

12. 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

13. 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

15. 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

17. 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

18. 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

22. 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

23. 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

24. 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

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

27. 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

29. Significant positive correlation • Sperm competition and testes size

30. Complex Adaptations in Current Research • Will now examine how researchers use the methods mentioned above to investigate hypotheses about complex topics • Experiments • Observational studies • Comparative Method

31. Phenotypic Plasticity • We have assumed that phenotypes are fixed • In reality, many phenotypes are plastic, i.e., individuals with identical genotypes may have different phenotypes if they live in different environments • Phenotypic plasticity is a trait that can evolve • It may or may not be adaptive

32. Phenotypic Plasticity • Water flea, Daphnia magna, lives in lakes • Usually reproduces asexually • Good for studies of phenotypic plasticity because genotype is known • Luc de Meester studied plasticity in phototactic behavior • Selected 10 genotypes and used clones of each to test • In graduated cylinder, illuminated from above and recorded which direction they swam

33. Phenotypic Plasticity • Each lake population has genetic variation • Tested Daphnia by using water from lakes where fish occurred and where they were absent • Hypothesized that when fish are present negative phototaxis is more adaptive • Phototactic behavior was phenotypically plastic

34. Phenotypic Plasticity • Genetic variation in plasticity • Some populations were more plastic than others • Genotype-by-environment interaction

35. Evolution of Adaptive Traits • Every adaptive trait evolves from something else • How did the mammalian ear evolve? • Mammalian ear has three bones (ossicles) • Malleus, incus, and stapes • Other vertebrates do not have all three • Ear bones transmit energy from tympanic membrane to oval window in inner ear

37. Evolution of Adaptive Traits • Why do we have three bones instead of one? • Increases sensitivity of hearing • To figure out where the bones came from we must: • Establish the ancestral condition • Understand the transformational sequence • How and why they changed over time

38. Trade-Offs and Constraints • Organisms cannot optimize all features at once • Many factors limit adaptive evolution • Trade-offs • Functional constraints • Lack of genetic variation

39. Trade-Offs and Constraints • Begonia involucrata is a monoecious plant pollinated by bees • Male flowers offer pollen to bees • Female flowers offer nothing • Female flowers resemble male flowers to trick bees into visiting them • What mode of selection do bees impose on flower size?

41. Trade-Offs and Constraints • Schemske and Agren’s two hypotheses • The more closely female flowers resemble males, the more often they are visited by bees • Stabilizing selection toward mean male phenotype • The more closely female flowers resemble the most rewarding males, the more often they are visited by bees • If large male flowers offer bigger rewards, directional selection for larger flowers

42. Trade-Offs and Constraints • Schemske and Agren made artificial flowers put equal numbers of three sizes in a forest • The larger the flower, the more often bees visited it • Why aren’t female flowers always large? • Maladaptive • Maybe not enough genetic variation

43. Trade-Offs and Constraints • Expanded study to inflorescences • Trade-off: the larger female flowers are, the fewer they can have per inflorescence • Begonia involucrata female flower size determined by directional selection for larger flowers and trade-off between flower size and number

45. Trade-Offs and Constraints • Flower color change in Fuchsia excoricata • Bird-pollinated tree in New Zealand • Bell-shaped hypanthium (floral tube) and sepals • Hypanthium is green 5.5 days after opening • Then it turns red • Transition is 1.5 days • Red flowers remain for 5 days • Then red flowers drop off of tree

47. Trade-Offs and Constraints • Pollination occurs during green and intermediate phases • Nectar is produced days 1–7 • Birds prefer green flowers and ignore red ones • Color change is cue to pollinator • Why doesn’t Fuchsia drop its flowers after 7 days instead of changing color?

48. Trade-Offs and Constraints • Two hypotheses of Delph and Lively • Red attracts pollinator to tree because of bright color • Green flowers surrounded by red flowers should be pollinated most • Removed red flowers from some trees and found no evidence for pollinator-attraction hypothesis

49. Trade-Offs and Constraints • Two hypotheses of Delph and Lively • Physiological constraint keeps Fuchsia from dropping flowers sooner • Growth of pollen tube takes time • Flower should not drop before pollen fertilizes egg • Hand pollinated flowers and examined how long pollen took to reach ovary • Takes three days to reach ovary

50. Trade-Offs and Constraints • Fuchsia cannot drop flowers until after pollen reaches ovary (3 days) and abcission zone forms to drop flower (1.5 days) • Flower must wait 4.5 days