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Diversity of reproduction. Asexual reproduction Parthenogenesis Hermaphrodites Sequential hermaphrodites - protogyny (F  M) or protoandry (M  F) Sexual reproduction. Why sex?. Cost & benefit of sex Sex ratio Local mate competition Local resource competition

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diversity of reproduction
Diversity of reproduction
  • Asexual reproduction
  • Parthenogenesis
  • Hermaphrodites
  • Sequential hermaphrodites - protogyny (FM) or protoandry (MF)
  • Sexual reproduction
why sex
Why sex?
  • Cost & benefit of sex
  • Sex ratio
    • Local mate competition
    • Local resource competition
    • Maternal condition (Trivers/Willard effect)
male female reproductive strategy
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
  • Parental investment - whatever a parent does to↑the probability that existing offspring will survive to reproduce at the cost of the parent's ability to generate additional offspring
sexual selection
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
Intrasexual selection
  • Competition for copulation



        • friendship with females
        • male coalition
        • female mimicry
        • satellite males
        • forced copulation
Game theory and Evolutionary Stable Strategy (ESS)
  • Strategy = the behavioral response of an individual
  • ESS = a strategy which if adopted by all members of a population can not be invaded by other strategy
  • Game theory is needed when fitness consequences of a behavior depend on what others are doing
hawks and doves
Hawks and Doves
  • Possible behaviors
    • Display
    • Fight but risk injury
    • retreat
  • Possible strategies
    • Hawks: fight until injured of opponent retreats
    • Doves: display initially but retreats if opponent fights
payoff matrix
Payoff matrix


hawks doves

Actor hawks (V-C)/2 V

doves 0 V/2

  • Payoff of actors after confronting opponents
  • V = values of resources being contested
  • C = cost of fighting due to injury
pure ess
Pure ESS


hawks doves

Actor hawks 1/2 2

doves 0 1

  • Resource = 2 > cost = 1
  • ½ > 0, hawks resist dove invasion; 2 > 1, doves are invaded by hawks  pure ESS = all hawks
mixed ess
Mixed ESS


hawks doves

Actor hawks -1/2 1

doves 0 1/2

  • Resource = 1 < cost = 2
  • -½ < 0, doves can invade hawks ; 1 > ½ , hawks can invade dove  mixed ESS = mix of hawks and doves
If frequency of hawks is p, and frequency of doves is 1-p, and at the ESS the fitness of hawks = the fitness of doves, then
  • (-1/2)p + (1-p) = (0)p + (1/2)(1-p)
  • 1 – 3p/2 = 1/2 – p/2  1/2 = p
  • Either an individual can perform strategy one or another w/ probability p or 1-p ; or polymorphic state in which a fraction, p, of the population adopts one strategy
polymorphism in ruff grouse
Polymorphism in Ruff Grouse
  • 16% light, 84% dark. Dark dominates over light and is territorial. Only a few dark mate. Light follows the female. Reproductive success is the same.
alternative sponge isopod
Alternative sponge isopod
  • α♂ defend cavities and discard γ♂. β♂behaves like♀. Morphs are due to 3 alleles at 1 genetic locus. Mating success is 1.51, 1.35, 1.37 for α, β and γ
blue gill sunfish
Blue-gill Sunfish
  • 3 male morphs: sneaker, female mimic, territorial
  • Non-ESS alternative strategies
    • ESS predicts all strategies obtain equal fitness
    • Alternatively, strategies may be condition dependent
    • Males in lower condition may adopt alternative strategies to obtain some mating
Competition for fertilization

Sperm competition

    • physical: e.g. scrub out sperm, peck at the cloaca
    • chemical: e.g. contraceptive douche, copulatory plug, homosexual mating, anti-aphrodisiac substance, eupyrene vs. apyrene,
Mate guarding: cost and benefit
    • first-male vs. last-male
    • colonial vs. solitary
    • early vs. later season
  • Competition after fertilization

Bruce effect


female choice
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
Hypotheses on male monogamy
    • mate-guarding monogamy
    • mate-assistance monogamy
    • female-enforced monogamy
  • Extra-paired copulation (EPC)
    • fertility insurance hypothesis
    • better sperm hypothesis
    • material benefit hypothesis
    • more parental care hypothesis
Polyandry – polygynandry vs. sex role reverse polyandry
  • Dunnocks - mating system changes with access to resources
  • Polygyny occurs in small territories, polyandry in large territories
  • Provisioning caused a reduction in female territory size and a change from polyandry (or polygynandry) to monogamy (or polygyny)
Consequently, females have higher reproductive success in poor environments while successful males have higher reproductive success in rich environments
  • Females solicit copulations from males to keep them around
  • Male feeding rates are proportional to their paternity
  • Emlen-Oring theory
    • Female defense polygyny
    • Resources defense polygyny
      • polygyny threshold model
      • deception hypothesis
prediction of ptm
Prediction of PTM
  • Polygyny should be most common in patchy habitats
  • Male territory quality influences number of females attracted
  • Females who mate with already mated males should have at least as high reproductive success as females choosing unmated males
blackbird experiments
Blackbird experiments
  • Higher fledging success in larger harems
  • Harem size correlates with habitat quality
  • Female removals do not lower fledging success; therefore, females do not pay any cost to being secondarily polygynous
Scramble competition polygyny
    • scarce females
    • explosive breeding assemblage
  • Lek polygyny
    • central position hypothesis
    • hotshot satellite hypothesis
factors favoring leks
Factors favoring leks
  • No paternal care
  • Males cluster on traditional display sites
  • Mating aggregations occur away from any resource required by females
  • Females are free to choose between displaying males
    • In antelope & grouse, female home range↑ as male territory↓ and mating system switches from resource defense to lekking.
observed pattern
Observed pattern


  • > 90% of birds, females disperse farther presumably to pick best resource
  • < 10% of mammals (e.g. canids, beaver, carnivorous bats)
    • Males help provision young - canids, carnivorous bats, marmosets
    • Females solitary and males can only defend 1 female - dik-dik, some rodents
  • very rare in insects (carrion beetles), fishes and herps
  • > 90% of mammals, males defend females when they can, males disperse farther presumably to find a female group
    • Females solitary, range of 2 or more defensible by male - prosimian primates
    • Females solitary, range not defensible - moose, orangutan
    • Females social, range defensible by male
seasonal harems - elephant seals, red deer
      • permanent harems - hamadryas baboons, spear-nosed bats, zebra
  • Females social, range not defensible
    • Female movements predictable, males wait for females on territories, e.g. topi, waterbuck, Uganda kob - analogous to bird leks
    • Female movements unpredictable, males follow estrous females, e.g. elephant, mountain sheep
In polygynous birds, males defend food or nesting sites (blackbirds, grouse)


  • Rare in birds, very rare in mammals, but fairly common in fishes
  • This occurs in birds where resources are very patchy and available for only a short period.
    • Sequential - sanderling, Temminck's stint, spotted sandpiper
    • Simultaneous - phalarope, jacana
    • Cooperative - pukeko
Promiscuity - both sexes mate multiple times
  • Common in insects
  • Hibernating bats ??
parental care
Parental care

Types of care

  • Care before birth of offspring -- Ex. preparation of nests, burrows, or territories
  • Investment in gamete production -- Ex. female katydids consume spermatophores provided by males have larger eggs which survive overwintering better
Care of eggs -- Ex. incubation by birds, egg guarding by fish, carrying brood by waterbugs and seahorses
  • Provisioning or protecting young -- Ex. provisioning by birds, brooding fry in mouth in some fish, lactation in mammals
  • Care following nutritional independence -- Ex. support in conflicts in social primates
who provides pc
Who provides PC?
  • Terrestrial Arthropods
    • PC is uncommon - found in only 85 orders
    • Care by females much more common than care by males
  • Bony Fish - male care more common than female care
Amphibians - care-giving by males and females fairly similar
  • Reptiles - care by females more common
  • Birds - 90% of over 9000 species show biparental care
  • E. Mammals - 100% of species show care by females (gestation, lactation) but less than 5% show direct male care
why is female care more common
Why is female care more common?
  • paternity certainty
  • the order of game release
  • the association with young


internal external


male care 2 61

female care 14 24

no care 5 100


parent offspring conflict
Parent-offspring conflict
  • Costs to parent and benefits to offspring change over the period of offspring dependency such that the B/C ratio shows continual decrease
  • From a parent's point of view -- want to terminate parental investment in offspring as soon as it becomes more advantageous to invest in future offspring (i.e. when B/C ratio drops to 1.0)
From offspring's point of view -- want parental investment to continue until costs exceed 2X benefits (i.e. when B/C ratio drops to 0.5)
  • This is because parents are related to both current and future offspring by same degree of relatedness (0.5) but offspring are related by twice as much to themselves as to future siblings (1.0 vs. 0.5)
This generates a conflict of interest between parents and offspring over when parent investment should be terminated
  • When future offspring are expected to be half siblings rather than full siblings, period of conflict should extend longer
other predictions
Other predictions
  • Level of investment should be greater and period of investment should be longer as parental age↑ because of ↓ residual reproductive value of the parent
  • Offspring should be selected to be manipulators of parents and parents to detect and resist manipulation by offspring
  • Prevalence of weaning conflict and tantrums in many birds and mammals

(Am. Sci. 78:438-449, 1990)

  • Juvenile mortality resulted from the overt aggression of sibling
    • Black eagle, osprey, blue-footed booby. great egret, cattle egret
5 common characters
5 common characters
  • resource competition
  • provision of food in small units
  • weaponry
  • spatial confinement
  • competitive disparity between sibling
Younger ones are marginal individual or replacement if elder sibling died
  • Time to siblicide
    • own viability met
    • resource inadequate