Lecture17 - 1 Sexual Selection II Monday Feb 24th Wednesday...

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Sexual Selection II Monday, Feb. 24th 1 Wednesday: Guest Lecture by Raime Fronstin The Sexual Selection of Eggshell Color
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Learning Objectives 1. Define intrasexual selection and explain the examples of Premating, Postmating and Postzygotic intrasexual selection 2. Define intersexual selection and differentiate between the three categories of explanation presented for female choice. Explain an example of each. 3. Explain the sexy sons hypothesis and Fisher’s runaway model for the reinforcement of even arbitrary female preference. 2
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Asymmetric Limits on Reproductive Success If females are limited by resources, and males are limited by access to females… We expect males & females to use different strategies to maximize their reproductive success 2 modes of sexual selection: Intrasexual competition (male-male) Males compete amongst themselves for access to females Intersexual competition (female choice) Females can afford to be choosy (quality not quantity) 3
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Intrasexual Selection (male-male competition) 1. Premating Competition: Combat (contests, leks) Alternative strategies 2. Postmating – Prezygotic Competition: Sperm competition Guarding tactics 3. Postzygotic Competition: Infanticide 4
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Intraspecific Sperm Competition If female has multiple mates, sperm must compete for access to egg Large testes large ejaculates → more sperm Gage (1991) looked for evidence of sperm competition in Mediterranean Fruit fly: Experiment - 20 males mated in private 20 raised and mated with rival present Dissected females and counted sperm Result - males in private released > 1400 sperm males with rival released > 3500 sperm 5
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Sperm Competition Sperm scoopers to remove other males’ sperm Damselflies: 6
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Other Postmating Competition Tactics In order to minimize sperm competition,
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  • Spring '11
  • DAVIDSON
  • females, males, Sexual Selection

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