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

Next week’s lab: Stream Ecology

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

TA help with writing paper/data analysis Where: 164 Burrill Computer Rooms Use WEST door closest to Bio Library + NHB When: LABDATE/DAYTIME M27S WED4-6 T27S WED6-8 or … R28S THURS4-6 W28S THURS6-8 F28S THURS8-10 Read: Guidelines: Scientific Writing (pg 33-39) Guidelines: A Sample Manuscript (pg 41-51)

Chapter 11: Sex and Evolution

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

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.

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

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

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

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

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

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?

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

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.

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? Sex ratio when sexes are separate

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

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

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

***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?

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

Repertoire size Date of pair formation

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.

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

***Explain how female choice can lead to runaway sexual selection? Do such traits represent a handicap (and thus demonstrate a superior genotype?)(the handicap principle)

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

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.

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

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

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.

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

Vocabulary