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Reproductive Strategies

Reproductive Strategies. vs. Three types of comparisons: across species within species/ within a sex (alternative mating strategies). Reproductive Strategies.

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Reproductive Strategies

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  1. Reproductive Strategies

  2. vs. • Three types of comparisons: • across species • within species/ • within a sex • (alternative mating strategies) Reproductive Strategies A set of behavioral and physical adaptations designed specifically to maximize an individual’s mating and reproductive success. (more definitions later) specifically • Topics: • Why sex? • Male vs. female • Sexual selection

  3. Why sex? vs. asexual reproduction (cloning) (sexual reproduction) Whiptail lizards some examples Aphids Portuguese man-o-war

  4. Why Not Sex? Because Sex is Costly ! • Gonads are expensive organs to produce and maintain • Mating is risky, costly, time-consuming, often involving elaborate structures and behaviors • Cost of meiosis – this is the most significant cost

  5. Why Not Sex? Sexual Reproduction:Cost of meiosis Asexual cloning Since each sexually-produced offspring only contains half the genetic material of each parent, there is a 50% reduction in fitness compared to asexual reproduction

  6. Why sex? Benefits of Sexual Reproduction Natural selection is limited by fact that even as a species adapts to its biotic environment – its competitors, predators, parasites – that environment is also evolving. → “Arms Race” Genetic variability among offspring permits response to changing biotic environment Red Queen Hypothesis: whereas asexual reproduction is a ‘sitting duck’ target for competitors, pathogens, predators, sex and geneticrecombinationpresentamoving target “It takes all the running you can do to keep in the same place!”

  7. Male and Female • ♂♀ • How define “male” and “female”? • Sex chromosomes not generally useful criterion: •  Mammals: M - XY, F - XX •  Birds: M – XX, F – XZ •  Hymenopterans: M – N, F – 2N •  Hermaphroditic species •  Turtles, alligators: Facultative • (incubation temp dependent)

  8. Male and Female Temperature-dependent Sex Determination

  9. Male and Female • ♂♀ • How define “male” and “female”? • Male and female defined by relative size of their gametes (sex cells): • Females produce relatively few but expensive (provisioned) sex cells. • Males produce many more but cheap sex cells.

  10. Anisogamy = “Unequal gametes” Eggs: few, large, energetically expensive Sperm: many, small, cheap Eggs and Sperm Fig 10.6 Alcock

  11. Sexual Selection

  12. Natural Selection Survival Parental Care

  13. Natural Selection Survival Mating Success Parental Care

  14. Natural Selection Survival Mating Success Parental Care Intrasexual Mate Choice Competition (Epigamic) Sexual Selection

  15. Intrasexual Selection Epigamic Selection

  16. SEXUAL SELECTION Occurs when (1) males compete among themselves for access to females (intrasexual selection) . . .

  17. SEXUAL SELECTION Occurs when (1) males compete among themselves for access to females (intrasexual selection) and/or (2) try to attract females by flashy colors, behaviors etc (epigamic selection). Greater Sage Grouse 1 23

  18. Sharp-tail Grouse

  19. Prairie Chicken

  20. Black Grouse Norway Black Grouse Lek in Norway

  21. What exactly do females see in these guys (besides a pretty face)? Epigamic Selection

  22. Intrasexual selection → weapons

  23. Intrasexual selection → sexual dimorphism

  24. Intrasexual selection → weapons, fighting

  25. Intrasexual selection → weapons, fighting National Geographic Wild America

  26. Alternative Strategies come back to later Bluegill Sunfish

  27. Epigamic Selection Flip side of epigamic selection: Female choice

  28. Reproductive Strategies 1. A set of behavioral and physical adaptations designed specifically to maximize an individual’s mating and reproductive success. 2. A set of behavioral and physical adaptations shaped by sexualselection.

  29. Male-male competition (Intrasexual selection) Female Choice (Epigamic selection) Summing Up: • Sexual Selection tends to produce weapons and elaborate ornaments and displays • Sexual selection has two components: What drives sexual selection? Trivers: Key to sexual selection is parental investment (PI) = effort put into helping your offspring reach reproductive age.

  30. Trivers: Differential Parental Investment drives Sexual Selection Female PI Sexual Selection ♂ - ♂

  31. PARENTAL INVESTMENT (PI) • Initial PI • female's provisioning of egg cell • Specialized PI (mammary glands, incubation patches, etc) – usually supplied by one sex only, and that • is almost always the female • female’s nourishing of the embryo • female’s producing yolk-filled egg (reptiles and birds) • incubation (reptiles and birds) • female lactation • Generalized PI – usually behavioral and can be supplied by either sex • guarding the offspring • feeding the offspring • defending a territory/nest used for feeding and protecting young

  32. female's provisioning of egg cell (initial PI)

  33. female’s nourishing embryo within body

  34. Male-female difference in PI (mammals) Erick Greene

  35. mammals: female lactation

  36. female’s producing yolk-filled egg (reptiles and birds)

  37. Kiwi

  38. Generalized PI

  39. Generalized PI

  40. Generalized PI

  41. Male Randall’s Jawfish Mouth-Broods Eggs

  42. Generalized PI

  43. Generalized PI

  44. Generalized PI

  45. Generalized PI

  46. Generalized PI

  47. PARENTAL INVESTMENT (PI) 1. initial PI: females produce large egg cells, males produce small sperm 2. specialized adaptations directly related to reproduction (e.g., gestation, nursing): usually the female 3. behavioral adaptations (and costs): egg-guarding, protecting and feeding young: females or males (more commonly the female) Generally, female PI is much greater than male PI

  48. SEXUAL SELECTION • Trivers: Key to sexual selection is parental investment (PI). • Trivers: Sexual selection = • Sex investing less will compete for sex investing more (intrasexual selection) • 2. Sex investing more will be discriminating in choosing mates (epigamic selection) • Typically: Female PI > Male PI • so usually its males competing among themselves for females and females choosing among males. • First: consider some consequences…

  49. General Sex Differences in Behavior ♀ Male: ardent, indiscriminant Female: reluctant, discriminating ♀ • FEMALES – “Don’t you Dare.” • MALES – “Laissez Faire.”

  50. Females as the discriminating sex

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