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Sexual Selection
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I.Motivation Sexual Dimorphism is Frequent
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Figure 11-1
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Figure 11-3
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The sexual dimorphism in long-tailed widowbirds Scarlet Tanagers, male, female Wesern Tanagers, male female
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Human males and females differ in height
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Why this sexual dimorphism Selection on survivorship and reproduction Ability to obtain mates: Sexual Selection: Different reproductive success due to variation among individuals in success at getting mates If there is heritable variation in a trait that affects to ability to obtain mates, then variants with higher success at obtaining mates will become more common over time
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II. Limits to reproduction differ between the sexes
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Guess What? With few exceptions, females invest much more time and energy in the production of young
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Figure 11-6
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Asymmetries in sexual reproduction in rough-skinned newts
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females males
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Exception to the Rule?” Asymmetries in sexual reproduction in broad-nosed pipefish Male with Kids (in pouch)
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Males Females
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Consequences of Asymmetric Limits on Fitness Members of the sex subject to strong sexual selection will be competitive (Male-male competition) Members of the sex subject to weak sexual selection will be choosy (Female Choice) Bateman’s rule, males limited by access to mates, females limited by resources
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III. Natural Selection Limits Sexual Selection e.g., marine iguanas
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Larger iguanas expend more energy on metabolism
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Male marine iguanas in combat
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Large territorial males
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Alternative mating strategies in coho salmon
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IV. Male Access to Females Sperm Competition
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Sperm competition in damselflies
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Sperm morphology in rodents All for one and one for All! Sperm Swimming Speeds
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Infanticide
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V. Evidence for Sexual Selection on Trait: Female Choice
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Long tail feathers are a ball-and-chain for male red-collared widowbirds
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Female red-collared widowbirds prefer long-tailed males
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VI. Fisher’s Run Away Sexual Selection An example from UMD
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How runaway selection works in theory
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VII. Good genes model of sexual selection
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Are male gray tree frogs that give long calls genetically superior to males that give short calls??
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Courtship and mating in hangingflies
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VIII. Origin of Trait Selection Water mite waiting in ambush for a copepod, male has found her
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A phylogeny of the water mite Neumania papillator and several related species. The boxes above the tips of the branches indicate which species have net-stance and which species have male courtship trembling. A colored box indicates the trait is present; an open box indicates the trait is absent. The two versions of the phylogeny show the two most likely scenarios for the evolution of these two traits. Redrawn from Proctor (1992).
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Lilies from from SW Aust.
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IX. Sexual Selection in Plants
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X. SEXUAL SELECTION IN HUMANS Kipsigis men and women
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A. Preindustrial Finnish Population B. Pimbwe, a horitcultural society in Tanzania
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unokais (killers) versus non-unokais among Yanomamö men
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Figure 11-50
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Human Stature
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Taller Polish Men Have More Children:
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Importance of physical attractiveness in mate choice versus parasite prevalence in 29 human cultures
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GENETIC DIVERSITY REVEALED IN HUMAN FACES Hanne C. Lie, Gillian Rhodes, and Leigh W. Simmons: Evolution 2008
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XI. Conclusion Sexual Dimorphism Sexual Selection Males limited by access to mates Females limited by resources Exceptions Universal, aspects found in plants and animals YOU too may be a target for sexual selection Very Kewl
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