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Mating Systems

Mating Systems. Recombination Common, Not Universal Sexual Reproduction: Recombinant Genotypes Basic Questions: Sex. Basic Questions: Mating Systems. 1 . Sex Versus Non-Sex Mitotic Replicates, No Recombination Clonal Growth Isogamy, Recombination Equal Gametes

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Mating Systems

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  1. Mating Systems Recombination Common, Not Universal Sexual Reproduction: Recombinant Genotypes Basic Questions: Sex

  2. Basic Questions: Mating Systems 1. Sex Versus Non-Sex Mitotic Replicates, No Recombination Clonal Growth Isogamy, Recombination Equal Gametes Anisogamy, Sexual Reproduction Unequal Gametes Parthenogenesis

  3. Anisogamy

  4. Sex versus Asexuality

  5. Sex versus Asexuality Asexual Lineages Disappear; Sexual Lineages Persist • “Bet Hedging” Against Environmental Unpredictability • Thwart Specialized Pathogens • Group Selection, Possible

  6. Basic Questions: Mating Systems Given Anisogamy, Sex Ratio: Males/Female Zygotic, Birth, Sexual Maturity Operational Sex Ratio: During Mating

  7. Basic Questions: Mating Systems 3. Given Sex Ratio, Mating System Polygyny, Monogamy, Polyandry “Parental Investment,” Correlative/Comparative Approach Sexual Selection, Predictive Approach

  8. Sex Ratio Given Evolved Anisogamy, Female & Male “Strategies” Ratio Males/Female Human Zygotic 1.15 Birth 1.05 15 Yrs 1.0

  9. Sex Ratio Sex Ratio Evolution, R.A. Fisher Economically Rational Grandparent (Male and Female: Autosomal) Assign Sex to Offspring Maximize No. Grandoffspring, Given Competition with Others ESS: Sex Ratio

  10. Sex Ratio Sex Ratio Evolution: Rarer Sex Has Fitness Advantage Assume Population: F females, M males Each Female: 2 Offspring Diploid Genetics

  11. Sex Ratio Individual Fitness: Gene Copies Female Fitness 2 F (1/2)/F = 1 Independent of Sex Ratio M/F 2 Offspring, (1/2) Genome

  12. Sex Ratio Individual Fitness: Gene Copies Male Fitness 2 F (1/2)/M= F/M Inverse of Sex Ratio

  13. Sex Ratio IF F < M (Females Rare) Males Fitness = F/M < 1 = Female Fitness Natural Selection Favor Gene: More Daughters Since Females More Fit than Males

  14. Sex Ratio IF F > M (Males Rare) Males Fitness = F/M > 1 = Female Fitness Natural Selection Favor Gene: More Sons Since Males More Fit than Females

  15. Sex Ratio IF F = M (Sexes Equally Frequent) Males Fitness = F/M = 1 = Female Fitness Sex Ratio Selection at Equilibrium Each Sex Has Same Fitness Rational Grandparents Produce Females & Males Equally

  16. Sex Ratio General Sex Ratio Theory Stable Equilibrium: Invest Parental Resources Equally in Daughters & Sons IF Sexes Have Different Cost: Produce Fewer of Costly Sex

  17. Sex Ratio Sex Ratio Theory Gene with Sex-Linked Transmission XX, XY: Heterogametic Sex Y Chromosome: Appears in Sons Only Bias Sex Ratio Extinction, “Marriage Squeeze”

  18. Parental Investment “PI” and Mating Systems PI: Investment in Current Offspring Reduces Capacity to Produce Future Offspring Investment Costly: Time, Energy, Limited Nutrient(s), Exposure to Predation

  19. Parental Investment “PI” and Mating Systems Given Anisogamy, Two Sexes Often Differ in Pattern of Parental Investment Define Pattern in Mating Systems, Sexual Selection

  20. Parental Investment Many Animals: Males Lower PI Males Compete for Chance to Mate with Females, Greater PI Females Exercise Mate Choice, Generate (Incite) Competition Among Males for Access to Females

  21. Parental Investment Many Animals: Males Lower PI Variance in Reproductive Success Greater Among Males Males Larger, More Aggressive Polygynous Mating Systems

  22. Polygyny

  23. Polygyny

  24. Parental Investment Some Animals: Sexes (app.) Equal PI Each Sex, Low Variance in Reproductive Success Body-Size Differences Reduced Monogamy

  25. Parental Investment Few Animals: Females Lower PI Females Compete for Chance to Mate with Males, Greater PI Variance in Reproductive Success Greater Among Females Females More Aggressive Polyandry

  26. Polygyny Common Mating System Access to Females (female gametes) Limits Male Reproductive Success Rep. Success: More Variable in Males Male PI < Female PI

  27. Polygyny Three Polygyny Models Resource Defense Female Defense Male Dominance (lek)

  28. Polygyny Resource Defense Females Unpredictable in Both Space and Time Resource Required by (Mating) Females Highly Predictable [Food, Water,…] Males Compete to Defend Resource & So Acquire Chance to Mate

  29. Polygyny Female Defense Females Predictable in Both Space and Time Males Compete to Defend Harems, Gain Mating Opportunities

  30. Polygyny Male Dominance Neither Females nor Required Resources Sufficiently Predicable Males Form “Lek,” Compete for Locations Where Females Arrive to Mate

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