Lecture 2 The Evolution of Sexual Differences

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11 Feb 2012
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Lecture 2 bio220 the evolution of sexual differences (dimorphisms) Sexually selected traits function solely to enhance mating success. It is a subset of natural selection but it can be useful to consider them separately. Fitness depends on: survival (both males and females, reproductive rate (mostly females, number of mates/mating success (mostly males) The origin of sexual differences: anisogamy (unequal sized gametes) Parental investment theory (trivers, 1972: sexes differ in reproductive investment, members o the sex that invest little in offspring compete to mate with members that invest more in offspring, large gametes are limiting. Males: linear correlation between number of mates and number of offspring. Increased number of mates produces increased offspring but plateaus due to the limited gametes, resources. Males: higher number of maximum number of offspring produced in lifetime. Reproductive potential: high for males, low for females. Intrasexual selection: male-male competition (precopulatory; # of copulations, post- Manifestations of male-male competition: fighting behavior, territoriality, social status, sperm competition.

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