Ab11_10notes - Sexual behavior and mating systems Why...

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1 Sexual behavior and mating systems Why sexual reproduction? Benefits of sexual reproduction: offspring are more varied mutations are reduced Costs of sexual reproduction: loss of 50% of genes energetic cost of producing gametes time and energy invested in courtship and mating
2 Why two sexes? Gamete size Proto-male Proto-female Disruptive selection Sexual reproduction does not require it: isogamy in microorganisms; anisogamy in most plants & animals Parker, G. A. et al. (1972) The origin and evolution of gamete dimorphism and the male–female phenomenon. J. Theor. Biol. 36 , 181–198. Sex Ratio Sex ratio is usually 1:1 …. why? R. A. Fisher (1930) proposed that the common 1:1 sex ratio can be explained in terms of selection acting on the individual A. B.
3 1:1 sex ratio R. A. Fisher (1930) Lots of females in population: advantage to produce males Lots of males in population: advantage to produce females Bonellia viridis Ferguson & Joanen (1982): alligator sex determined by the temperature of the egg during the 2nd and 3rd weeks of incubation. 30°C or below produces females; 34°C or above produce males. At 32°C, 87% of the hatchlings were female.
4 Red deer (Clutton-Brock, 1984) Red deer (Clutton-Brock, 1984)
5 1:1 sex ratio .. exceptions Acarophenax tribolii: viviparous mite Female produces a brood of 1 son and about 20 daughters. The son mates with his sisters inside the mother and dies before he is born! Hamilton, W.D. (1967) Science 156: 477-488. Mating systems Evolutionary view Energetics & Economics Egg vs. Sperm Greater cost of reproduction for the female Female is the more “selective” sex (sexual selection) “Ideal” mating systems Male acquires as many mates as possible and invests little in parental care Female selects “fit” male and leaves parental duties to him, while acquiring resources required to produce more offspring
6 Bateman effect: Bateman (1948) 0 30 60 90 120 0 1 2 3 4 0 30 60 90 120 0 1 2 3 4 150 150 # mates mean # offspring Bateman effect: Mean # offspring
7 Sex differences in the maximum number of offspring produced – from Krebs & Davies (1993) ** from 27 pregnancies * Moulay Ismail the Bloodthirsty, Emperor of Morocco source: Guinness Book of World Records 69** 888* Man 14 24 Red deer 8 100 Elephant seal Female Male Species Maximum number of offspring produced during lifetime Moulay Ismail, Emperor of Morocco from 1672-1727: 888 offspring? Moulay Ismail 548 sons and 340 daughters through a harem of 500 women during his life. 1.2 copulations/day for 62 years

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