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BIOE 109 Summer 2009 Lecture 10- part I Mating systems

BIOE 109 Summer 2009 Lecture 10- part I Mating systems. Types of Mating Systems. Mating Systems In Nature. Mating Systems In Nature. Monogamy. Monogamy. Monogamy. Polygyny. Polyandry. Polygyny. Mating Systems In Nature. ?. Mating Systems In Nature. Promiscuous.

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BIOE 109 Summer 2009 Lecture 10- part I Mating systems

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  1. BIOE 109 Summer 2009 Lecture 10- part I Mating systems

  2. Types of Mating Systems

  3. Mating Systems In Nature

  4. Mating Systems In Nature Monogamy Monogamy Monogamy Polygyny Polyandry Polygyny

  5. Mating Systems In Nature ?

  6. Mating Systems In Nature Promiscuous

  7. Mating Systems In Nature Promiscuous

  8. Hypothesis for the evolution of mating systems • Based on parental care and ecological constraints

  9. Hypothesis for the evolution of mating systems • Based on parental care and ecological constraints Who can ditch first?

  10. Hypothesis for the evolution of mating systems • Based on parental care and ecological constraints Who can ditch first? Is ditching worth it?

  11. Sex allocation

  12. Sex allocation • the allocation of resources to male versus female production in sexual species (Charnov 1982). • Sex Ratio?

  13. What is sex ratio? • sex ratio is defined as the proportion of males to females.

  14. What is sex ratio? • sex ratio is defined as the proportion of males to females. • two distinct sex ratios exist:

  15. What is sex ratio? • sex ratio is defined as the proportion of males to females. • two distinct sex ratios exist: 1. the population sex ratio i.e., the proportion of males to females in the population

  16. What is sex ratio? • sex ratio is defined as the proportion of males to females. • two distinct sex ratios exist: 1. the population sex ratio i.e., the proportion of males to females in the population 2. the individual sex ratio

  17. What is sex ratio? • sex ratio is defined as the proportion of males to females. • two distinct sex ratios exist: 1. the population sex ratio i.e., the proportion of males to females in the population 2. the individual sex ratio i.e., the sex ratio of progeny from a female

  18. The evolution of sex ratio -In many species sex chromosomes cause 1:1 sex ratio

  19. The evolution of sex ratio Mammals: females are homogametic (XX) males are heterogametic (XY) Birds: males are homogametic (ZZ) females are heterogametic (WZ)

  20. Mammals: females are homogametic (XX) males are heterogametic (XY) Birds: males are homogametic (ZZ) females are heterogametic (WZ) Sex chromosomes do not guarantee a 1:1 sex ratio!

  21. Why equal numbers of males and females? • R.A. Fisher (1930) provided a genetic explanation for the evolution of a stable sex ratio of 1:1.

  22. Why equal numbers of males and females? • R.A. Fisher (1930) provided a genetic explanation for the evolution of a stable sex ratio of 1:1. • since every individual has one mother and one father, each sex contributes equally, on average, to subsequent generations.

  23. Why equal numbers of males and females? • R.A. Fisher (1930) provided a genetic explanation for the evolution of a stable sex ratio of 1:1. • since every individual has one mother and one father, each sex contributes equally, on average, to subsequent generations. • therefore, males and females must have the same average fitness.

  24. Suppose: • 25% male males will have high fitness • 75% female because they mate with multiple females • Suppose: • 75% male females will have high fitness • 25% female because they mate with multiple males • Members of the rarer sex will experience increased reproductive success relative to common sex • frequency-dependent selection results in stable equilibrium sex ratio of 1:1.

  25. Exceptions to Fisher’s theory NOT ALWAYS 1:1

  26. Exceptions to Fisher’s theory • Local mate competition (Hamilton 1967) • 2. Condition-dependent sex allocation (Trivers and Willard 1973)

  27. Exceptions to Fisher’s theory 1. Local mate competition (Hamilton 1967) • proposed to account for female-biased sex ratios (e.g., parasitoid wasps).

  28. Exceptions to Fisher’s theory 1. Local mate competition (Hamilton 1967) • proposed to account for female-biased sex ratios (e.g. parasitoid wasps). • here, a single foundress produces a small group of closely related individuals that mate among themselves. 

  29. Exceptions to Fisher’s theory 1. Local mate competition (Hamilton 1967) • proposed to account for female-biased sex ratios (e.g. parasitoid wasps). • here, a single foundress produces a small group of closely related individuals that mate among themselves.   • females invest heavily in daughters and don’t “waste” effort in producing sons.

  30. Exceptions to Fisher’s theory 1. Local mate competition (Hamilton 1967) Mother Male 1 son to 20 daughters Females Dust mites (Acarophenox)

  31. Exceptions to Fisher’s theory 2. Condition-dependent sex allocation (Trivers and Willard 1973) Red deer, Cervus elaphus

  32. Exceptions to Fisher’s theory 2. Condition-dependent sex allocation (Trivers and Willard 1973) • occurs in polygynous species when females invest heavily in producing and caring for their young.

  33. Exceptions to Fisher’s theory 2. Condition-dependent sex allocation (Trivers and Willard 1973) • occurs in polygynous species when females invest heavily in producing and caring for their young. • a good mother can produce larger, or healthier, individuals when they mature.

  34. Exceptions to Fisher’s theory 2. Condition-dependent sex allocation (Trivers and Willard 1973) • occurs in polygynous species when females invest heavily in producing and caring for their young. • a good mother can produce larger, or healthier, individuals when they mature. • theory predicts that females in extremely good condition should produce males.

  35. Exceptions to Fisher’s theory 2. Condition-dependent sex allocation (Trivers and Willard 1973) • occurs in polygynous species when females invest heavily in producing and caring for their young. • a good mother can produce larger, or healthier, individuals when they mature. • theory predicts that females in extremely good condition should produce males. • Why?

  36. Exceptions to Fisher’s theory 2. Condition-dependent sex allocation (Trivers and Willard 1973) • occurs in polygynous species when females invest heavily in producing and caring for their young. • a good mother can produce larger, or healthier, individuals when they mature. • theory predicts that females in extremely good condition should produce males. • Why? Because sexual selection (usually) occurs more strongly in males and condition matters!

  37. How is sex ratio adjusted by mother? • Not known

  38. Sex Allocation Recap • Sex ratio • Why we see an unbiased sex ratio • Sex chromosomes • Frequency dependent selection • Exceptions to sex ratio: • Local mate competition • Condition-dependent sex allocation

  39. Sex in Plants

  40. Sex in Plants ♂ ♀

  41. Sex in Plants • Why and how do they outbreed? • Why do they inbreed?

  42. The evolution of inbreeding and outbreeding • many plant species have evolved traits to avoid inbreeding.

  43. The evolution of inbreeding and outbreeding • many plant species have evolved traits to avoid inbreeding. 1. Asynchronous male and female functions • pollen shed after or before plant’s stigmas are receptive.

  44. The evolution of inbreeding and outbreeding • many plant species have evolved traits to avoid inbreeding. 1. Asynchronous male and female functions • pollen shed after or before plant’s stigmas are receptive.

  45. The evolution of inbreeding and outbreeding • many plant species have evolved traits to avoid inbreeding. 1. Asynchronous male and female functions • pollen shed after or before plant’s stigmas are receptive. 2. Monoecy • male and female flowers separated on same plant.

  46. The evolution of inbreeding and outbreeding  2. Monoecy • male and female flowers separated on same plant.

  47. The evolution of inbreeding and outbreeding • many plant species have evolved traits to avoid inbreeding. 1. Asynchronous male and female functions • pollen shed after or before plant’s stigmas are receptive. 2. Monoecious • male and female flowers separated on same plant. 3. Dieocy • sexes are separated in different individuals.

  48. The evolution of inbreeding and outbreeding 3. Dieocy • sexes are separated in different individuals.

  49. The evolution of inbreeding and outbreeding 4. Self-incompatibility loci • prevent selfing or breeding with close relatives.

  50. The evolution of inbreeding and outbreeding 4. Self-incompatibility loci • prevent selfing or breeding with close relatives. 5. Heterostyly • two (distyly) or three (tristyly) forms of flowers exist in a species (on different plants).

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