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Diversity of reproduction. Asexual reproduction Parthenogenesis Hermaphrodites Sequential hermaphrodites - protogyny (F  M) or protoandry (M  F) Sexual reproduction. Male/female reproductive strategy.

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Diversity of reproduction

  • Asexual reproduction
  • Parthenogenesis
  • Hermaphrodites
  • Sequential hermaphrodites - protogyny (FM) or protoandry (MF)
  • Sexual reproduction

Male/female reproductive strategy

  • Asymmetrical gamete size (anisogamy) means the sex with smaller gametes should usually compete for access to the sex with larger gametes.
  • This results in greater variation among males than among females for reproductive success.

Males should, therefore, fight over females and females should select for resources

  • Sexual selection - The advantage which certain individuals have over others of the same sex and species, in exclusive relation to reproduction (Darwin, 1871)

A form of natural selection that occurs when individuals vary in their ability to compete with others for mates or in their attractiveness to members of the opposite sex.

  • As with natural selection, sexual selection leads to genetic changes in the population over time

Intrasexual selection

  • Competition for copulation



        • friendship with females
        • male coalition
        • female mimicry
        • satellite males
        • forced copulation

Competition for fertilization

Sperm competition

    • Physical, chemical, mate guarding, etc
  • Competition after fertilization
  • Bruce effect
  • Infanticide

Female choice

  • Unequivocal female preference, not a result of male competition
  • Choice based on "genetic quality“
    • runaway selection — Fisher
    • good genes (survival skill)
    • handicap principle — Zahavi
    • rare male effect

Choice based on 'non-genetic' benefit

    • resource defense
    • parental ability
  • Mating systems: monogamy, polygyny, polyandry, promiscuity

Cooperation or mutualism-- a mutually helpful action

  • Reciprocal altruism (reciprocity)-- a helpful action that will be repaid in the future by the recipient
  • Altruism-- helpful behavior that raises the recipient's direct fitness while lowering the donor's direct fitness

Kin selection

  • A form of selection in which alleles differ in their rate of propagation because they influence the survival of kin who carry the same allele

Indirect fitness-- the genes contributed by an individual indirectly by helping non-descendant kin, in effect creating relatives that would not have existed without the help

  • inclusive fitness-- the sum of an individual's direct and indirect fitness
  • B/C > 1/ r or rB - C > 0

Cooperative breeding

  • a social systems in which some group members defer their own reproduction, even as adults, and help care for the young of a few breeding individuals
  • Helpers are typically (but not always) related to breeders and are often individuals that do not disperse instead aid in the rearing of their siblings

found in only about 3% of birds and mammals (roughly 200-300 bird species and about 120 mammal species)

  • Helper's duties--feeding, carrying, huddling, babysitting, grooming, defense, teaching, incubation, etc.
  • Do helpers really help?

Increase breeding success

    • correlation approach
    • exp. removal of helper
  • Increase number of breeding free females from caring fledgling
  • Increase breeder survivorship

Social behavior

  • Societies--groups of conspecifics organized in a cooperative manner
  • Evolutionary advantages of living in groups
    • Protection from physical factors
    • Protection against predator
    • Assembling for mates
    • Finding resources, beater effect, overwhelm prey

Group defense of resources

    • Division of labors among specialists
    • Richer learning environment for young that develop slowly, social facilitation
  • Cooperative defense against predator
    • Increase vigilance, alarm
    • Dilution effect
    • Selfish herd hypothesis
    • Mobbing, fight back

Evolutionary disadvantages of group living

    • Increase competition
    • Increase chances of spreading diseases and parasites
    • Interference with reproduction
    • Reduce fitness due to inbreeding
    • Attracting predators

Eusocial insect

  • cooperative care of young
  • reproductive castes
  • overlap between generations

Possible explanations for worker sterility

  • Kin selection – haplodiploidy
  • But, they are more closely related to their own male offspring (r = 1/2) and their nephews (r = 3/8) than their brothers (r = 1/4). Therefore, expect workers to lay unfertilized eggs

If mothers are polyandrous (mate multiple times), then workers may be more closely related to their brothers than to half-nephews (r=1/8).

  • Expect workers to kill unfertilized eggs laid by other workers. Example: honeybees and yellowjackets are polyandrous and have low levels of worker reproduction

What about diploid eusocial animals (e.g. termites, naked mole rats)?

  • One proposed hypothesis is that these populations undergo cycles of inbreeding. With high levels of inbreeding-mother-son and sister brother can rapid approach r>3/4 for both males and females.

But high levels of inbreeding can lead to inbreeding depression

  • Thus inbreeding might alternate with some dispersal.
  • A rare disperser morph is found in mole rats: it is fatter, attempts to disperse in captive settings, solicits mating with non-colony members. Once settled reverts to xenophobia and loses fat stores