Next week’s lab: Stream Ecology

1. EXAM 1 next Tuesday 12:30 here Lectures/Chapters thru ThursdayPractice exam with answers: On course website on Exam dateFormat: Choice of ?s to answer Longer: 4 of 5 (interpret figures)Shorter: 4 of 6Questions? 6

2. Next week’s lab: Stream Ecology

3. Next lecture: Ch 12 Family, Society, and EvolutionNext lab: Group Proposal Worksheet due 3 days BEFORE lab

4. TA help with writing paper/data analysisWhere: 164 Burrill Computer RoomsUse WEST door closest to Bio Library + NHBWhen: Read: Guidelines: Scientific Writing (pg 33-39) Guidelines: A Sample Manuscript (pg 41-51)

5. Chapter 11:Sex and Evolution

6. Objectives • Why sex? • Costs of sexual vs. asexual reproduction • Sex ratio • Mating systems • Plants • Animals • Sexual selection • Size important for offspring success • Male-male competition • Female choice

7. Sample Exam Question: • The mean number of offspring is the same for males and females in elephant seals, a polygynous species. Individual male and female seals differ greatly in their mating success during any one breeding season. • 1. Graph the results found in the first sentence. Label axes. • 2. In this species, which gender has the more variable mating success? Write the answer; then add this result to the graph. • 3. What basic asymmetry of reproduction is responsible for this difference? Explain.

8. Sexual reproduction • mixes genetic material of individuals---> variable offspring • Meiosis --> variable gametes • Fertilization ----> variable offspring

9. Asexual reproduction produces offspring usually identical to parent and to one another.

10. Sexual reproduction is costly. • Need a partner (takes time, energy, resources) • Lose good combinations of genes via recombination • Cost of meiosis: contribute only 1/2 of genes

11. ***The ‘cost of meiosis’: How many genes does a female contribute via sexual vs. asexual reproduction? Which mode of reproduction does this cost favor?

12. ***Explain how ‘cost of meiosis’ is avoided by: • hermaphrodites (both male and female in one individual) • male parental care

13. Asexual reproduction…. • If advantageous, it should be common and widely distributed among many lineages. • Most asexual species are in genera with sexual species. • So no long evolutionary history • Asexual lines die out over time…because of reduced genetic variability?

14. Asexual--> Identical offspring; OK in unchanging environment Sexual---> offspring differ from parents---> adaptive in changing environment? What is the advantage of sexual reproduction?

15. Sex: any short-term advantage? • Models on environmental variability fail to find enough advantage to overcome cost of meiosis. • An alternative hypothesis: • Genetic variability is necessary to respond to biological changes in the environment, especially pathogens/parasites that can evolve virulence rapidly and drive host species to extinction. • The Red Queen Hypothesis: • continual selective pressure from pathogen requires continual evolution of populations ---> • need variable offspring and sex to stay ahead.

16. Sex ratio when sexes are separate • modified by evolution to maximize individual fitness. It balances the contribution of genes to progeny through male and female function. • Usually 1:1 ratio of male : female offspring at evolutionary equilibrium • What happens if deviate from 1:1 ratio that returns it to 1:1?

17. Frequency-dependent selection: • genes are selected for when at low frequency and against when at high frequency

18. ***Explain how the rare-sex advantage leads to a 1:1 sex ratio via frequency-dependent selection.

19. Why do sex ratios deviate from 1:1?When there is inbreedingand local mate competition(e.g. competition among brothers)---> favors production of daughters. 16 sets of genes in grandkids 49 sets of genes in grandkids

20. ***Mother’s condition and skewed sex ratio • Males must be large to be successful. • Females mate regardless of size. • Should stressed mother switch nourishment to daughters or sons? • Should well-fed mother switch nourishment to daughters or sons?

21. MATING SYSTEMS:Individuals may have female function, male function, or both. • Hermaphrodites: both functions • simultaneousorsequential • Monoecious: separate male and female flowers • Dioecious: separate male and female individuals • ***How do plants and animals differ?

22. Perfect flowers: both male and female parts • Can be outcrossing or selfing depending on compatibility genes

23. ***What is the pattern of pollen:ovule ratios? Explain the pattern.

24. ***Separate sexes versus hermaphroditism: Is it advantageous to add a second sexual function in A or B? B A • Hermaphroditism when male or female function can be added with little depressing effect on opposite sexual function.

25. ***Sequential hermaphroditism: How does sex change with body size? How is fitness increased by changing sex? Why? Protandry Protogyny

26. Mating systems: patterns of pairing of males and females within a population. • Asymmetry in sexually reproducing organisms: • Female: • success depends on ability to make eggs • eggs require large amount of resource • ability to gather resources determines • her fecundity • Male: • success depends on number of eggs he can fertilize • small gametes require few resources • ability to mate with many females determines his fecundity

27. Mating systems Promiscuity:mating at large in population; no bonds arises when males contribute little, other than genes, to number or survival of offspring (all outcrossing plants and most animals) Polygamy: • Polyandry: female mates with more than 1 male • Polygyny: male mates with more than 1 female • arises when males can monopolize either resources or mates through male- male competition

28. Male-male aggression in polygyny; male guards his harem.

29. Monogamy: male and female mate only with each other; strong pair bond • Males can increase fitness more by caring for offspring than by seeking additional matings. Rare in mammals; common in birds • BUT can be extra-pair copulations which leads to mate guarding by male

30. If females gain greater fitness by joining already mated male that holds a superior territory--> switch from monogamy to polygyny.

31. Sexual selection: selection by one sex for specific characteristics in the other sex. It leads to: sexual dimorphism secondary sexual characteristics

32. Sexual dimorphism Arises from: 1) dissimilar sexual functions of male and female (e.g. larger body of female-->more offspring) 2) male-male competition for female access 3) female choice among potential mates females choose and males compete as a consequence of asymmetry of parental investment.

33. Male-male competition can result in male-male conflict and elaborate male ornamentation (secondary sex traits).

34. Female choice based on male vocal display No. displays by female Male song repertoire size

35. Date of pair formation Repertoire size

36. Female choice when males compete for mates and females choose among them ---> leads to elaborate structures and courtship displays in males that indicate their fitness.

37. ***Is male-male competition or female choice driving development of this secondary sexual characteristic?

38. ***Explain how female choice can lead to runaway sexual selection?Do such traits representa handicap (and thus demonstrate a superiorgenotype?)(the handicapprinciple)

39. Parasite-mediated sexual selection • Parasites reduce host fitness. • Parasites alter male showiness. • Parasite resistance is inherited. • Females choose less parasitized males.

40. Parasite-mediated sexual selection: • Lice produce feather damage. • Doves with lice have reduced insulation and are lighter in body mass. • Females prefer clean to lousy males.

41. Sexual selection in plants Male-male competition: • extremes in floral display to attract pollinators and get pollen moved to other plants Female choice among pollen: • some males get selected during germination of pollen tubes Female choice among offspring: selective abortion of developing seeds and fruits on basis of paternity

42. ***How is pollen germination a period of female choice?

43. Sample Exam Question: • The mean number of offspring is the same for males and females in elephant seals, a polygynous species. Individual male and female seals differ greatly in their mating success during any one breeding season. • 1. Graph the results found in the first sentence. Label axes. • 2. In this species, which gender has the more variable mating success? Write the answer; then add this result to the graph. • 3. What basic asymmetry of reproduction is responsible for this difference? Explain.

44. Objectives • Why sex? • Costs of sexual vs. asexual reproduction • Sex ratio • Mating systems • Plants • Animals • Sexual selection • Size important for offspring success • Male-male competition • Female choice

45. Vocabulary