11-14-11 Sex and Sexual Selection Continued

11-14-11 Sex and Sexual Selection Continued - ZOL 445...

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ZOL 445 Evolution November 14, 2011 Sex and Sexual Selection: Continued Intrasexual competition: Male-male competition Example of the marine iguanas o The y-axis on b is related to fitness, so what form of selection is acting on size? Which island has stronger selection? Why do larger males contradict what we would have expected by natural selection alone (ignoring sexual selection)? Directional selection Genovesa has stronger selection Harder to get away from predators? More likely to be seen by predators? Standardized selection differential : Number of standard deviations between the population mean and the mean of selected individuals (who mate) o The appearance of maladaptations when sexual selection is not considered o Beetle horn length Increases as body size increases Defensive sperm competition: o Mate guarding o Copulatory plugs (mucus deposited by male after sperm to prevent other sperm deposition) o Accessory gland proteins (Acps) Acps from male elevate egg production and egg laying, reducing ability of females to generate eggs that are fertilized by other males later in life.
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Acps also reduces female receptivity during mating Offensive sperm competition o Accessory gland proteins Acps also displace and neutralize previously stored sperm. Sperm competition:
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11-14-11 Sex and Sexual Selection Continued - ZOL 445...

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