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Mating Systems

Reproductive side. Mating Systems. Parental care side. Mating Systems. Dimensions of Mating Systems 1. Bonding : Do male and female have an arrangement that goes beyond copulation?

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Mating Systems

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  1. Reproductive side Mating Systems

  2. Parental care side Mating Systems

  3. Dimensions of Mating Systems 1. Bonding: Do male and female have an arrangement that goes beyond copulation? 2. Multiple mating: No? If yes: By male only? By female only? By both? If both, which mates with more individuals? 3. Parental care: Both? Female only? Male only? Neither? 4. Other stuff (Alcock chapt 11)

  4. mating systems terminology derived from anthropology

  5. Mating systems are best defined in terms of Reproductive Variance (RV) = variance in reproductive success polygyny: male RV > female RV monogamy: male RV  female RV polyandry: female RV> male RV polygamy: polygyny or polyandry promiscuity: no bonds, males and females mate multiple times

  6. Mating systems are best defined in terms of Reproductive Variance (RV) = variance in reproductive success Important point: The degree of asymmetry in RV is an indicator of the intensity of sexual selection.

  7. Mating systems are best defined in terms of Reproductive Variance (RV) = variance in reproductive success Other component of the mating system is the form of parental care. Usually: polygyny – female parental care monogamy – biparental care polyandry – male parental care

  8. Some mating systems we will consider in detail: • elephant seal • primates • gorillas & chimps • gibbons & siamangs • tamarins • fish (stickleback type) • rhea (a bird) • seahorses & pipefish • kiwi

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

  10. An extreme case: elephant seals • Polygyny • Female parental care • Male RV >> Female RV

  11. Gorillas, Chimpanzees – Polygynous

  12. Siamangs, Owl Monkeys – Monogamous

  13. Gibbons & Siamangs: Monogamy & shared parental care • Territorial • Young dependent on parents until age 3. Parental care primarily by mother in the 1st year, but switches to father in the 2nd year.

  14. Cotton-top Tamarins • monogamy occurs in groups where a sufficient number of older offspring remain to help. • polyandry occurs in groups lacking old offspring. In these situations, pairs recruit the help of additional male.

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

  16. Trivers’s assumptions: • PI sex difference is prior (cause, not effect) • PI and Mating Effort (ME) are mutually exclusive (trade off)

  17. Reproductive Effort = Mating Effort + Parental Effort or

  18. Reproductive Effort = Mating Effort + Parental Effort Polygynous In this view ME and PE are mutually exclusive

  19. Reproductive Effort = Mating Effort + Parental Effort Polygynous In this view ME and PE are mutually exclusive

  20. 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 sexual selection. 3. A program for the optimal allocation of reproductive effort.

  21. Reproductive Effort = Mating Effort + Parental Effort Polygynous What if ME and PE are not mutually exclusive?

  22. Does High Male PI always → Sex Role Reversal? Most parental care in fish is by males! But Role Reversal is rare, and male RV generally > female RV

  23. In most fish male PI > female PI but no Sex Role Reversal Stickleback

  24. In most fish male PI > female PI but no Sex Role Reversal In sticklebacks, though male has to care for eggs in the nest, he can still courtfemalesandthepresenceofeggs attracts additional mates! ME & PI often not mutually exclusive in fish!

  25. A bird with male-only parental care but no sex role reversal Rhea (South America) • harem polygyny • male incubation & parental care • + sequential polyandry!

  26. A bird with male-only parental care but no sex role reversal What factors might favor male parental care in Rheas? • Which sex loses more by desertion? • Which sex is better equipped for parental care? • Which sex will take longer to get ready for next round of mating? concept of the operational sex ratio

  27. Operational Sex Ratio = # Sexually Receptive Males # Sexually Receptive Females OSR = 10:1 Primary Sex Ratio = # Males : # Females PSR = 1:1 In this example, potential reproductive rate of males is higher than that of females.

  28. Pipefish & Seahorses Males receive the gametes, are pregnant, and give birth.

  29. Q1: Does the extent to which ♂ PI >♀ PI predict degree of sex role reversal? Q2: Why male parental care? Male pipefish giving birth

  30. Reversed = ♀-♀ competition ♂♂ choosy Monogamy sex role reversal not consistently correlated with greater ♂PI

  31. Fig 11.2 Alcock Male PI and sex role reversal in the seahorses and pipefish (Syngnathidae) Trivers right that sex role reversal is found in species with high male parental investment – for example some of the Syngnathidae. But sex role reversal is found in only some of these species and there is a poor correlation between sex role reversal and degree of brood pouch development (~ PI) If in the time the male broods the clutch the female can produce at least 1 more clutch of eggs, so that she is ready to mate again before he is, then she will seek out additional males (polyandry) or alternatively she will stay with male and guard him from other females (monogamy).

  32. Operational Sex Ratio = # Sexually Receptive Males # Sexually Receptive Females Primary Sex Ratio = # Males : # Females PSR = 1:1 OSR = 3:8 In this example, potential reproductive rate of females is higher than that of males.

  33. Using history (phylogeny) to make sense of these theories Stickleback-like fish Why is specialized parental care performed by the male in this group?

  34. Importance of Evolutionary History: Steps to male parental care (and sometimes polyandry) in Seahorses & Pipefish placenta pouch brooding male care after Sinervo

  35. Importance of Evolutionary History: Steps to male parental care (and sometimes polyandry) in Seahorses & Pipefish male parental care of eggs male specialization for P.C. & female ability to lay more eggs than male can care for female competition to obtain several males (or mate guarding)

  36. ♀ ♂ selection equally on both ♂ ♀ ♀ ♂ conventional sex role reversed ♂ ♀ ~ no selection on either Intensity of Sexual Selection

  37. Intensity of Sexual Selection ♂ polygynous ♀ Red-winged Blackbird

  38. Intensity of Sexual Selection Sexual selection can occur even in monogamous species with biparental care – its just less intense ♂ ♀ Northern Cardinal monogamous – dimorphic – ♀ somewhat colorful

  39. Intensity of Sexual Selection Sexual selection can occur even in monogamous species with biparental care – its just less intense ♂ ♀ House Finchmonogamous-dimorphic – both sexes less colorful than Cardinal

  40. Intensity of Sexual Selection ♂ ♀ M. Beecher BankSwallow monogamous–monomorphic – differences are behavioral only

  41. Intensity of Sexual Selection strong epigamic selection on both sexes?

  42. Intensity of Sexual Selection ♂ ♀ Eclectus Parrots guess which one is the male?

  43. Intensity of Sexual Selection Kiwi, a New Zealand flightless bird no sexual selection on male or female? • monogamous • split parental care (male incubates egg and guards chick after hatching)

  44. Kiwi

  45. Kiwi parental investment • Female takes 30 days to form egg. • Egg 15–20% of her body mass • Yolk = 65% of egg (bird ave 35–40%)  • Newly hatched chick feeds off yolk 1st 1-2 weeks • Just before its laid, no room for food in her stomach – she must fast for 2-3 days before laying • Male incubates the egg (Brown Kiwi) • He develops incubation patch • Incubation time 70 - 80 days ~ the same as gestation period of a mammal of similar size → “Honorary Mammal”

  46. Human Mating Systems • Monogamy most common • but sequential, also extra-pair mating • Polygyny (mild) also fairly common • Polyandry (milder) also found (rare) • Bi-parental care, division of labor • Take a course in anthropology!

  47. http://www.redorbit.com/news/science/1684408/study_shows_seahorse_ancestors_stood_upright/http://www.redorbit.com/news/science/1684408/study_shows_seahorse_ancestors_stood_upright/

  48. Importance of Evolutionary History: Steps to male parental care (and sometimes polyandry) in Seahorses & Pipefish The male seahorse has a placenta on its pouch. The inside of the pouch changes before he starts the courtship. The walls become full of blood and spongy before the female put her eggs and the male fertilizes them. It is thought that oxygen and carbon dioxide diffuses through the blood vessel network on the walls of the pouch. Food is probably passed to the eggs in the same manner that the mammalian placenta, through blood. http://www.angelfire.com/fl/franciscobeltran/seahorse.html placenta pouch brooding male care after Sinervo

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