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Sexual Selection

Explore the fascinating phenomenon of sexual selection and sexual dimorphism in different species, including Scarlet and Western Tanagers, long-tailed widowbirds, and humans. Learn about the factors influencing reproductive success, the role of female choice, limits to reproduction, and evidence for sexual selection on traits. Discover the origin of these traits and their impact on fitness.

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Sexual Selection

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  1. Sexual Selection

  2. Motivation • Sexual Dimorphism is • Frequent

  3. Figure 11-1

  4. Figure 11-3

  5. The sexual dimorphism in Scarlet Tanagers, male, female Wesern Tanagers, male female long-tailed widowbirds

  6. Human males and females differ in height

  7. 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

  8. II. Limits to reproduction differ between the sexes

  9. Guess What? With few exceptions, females invest much more time and energy in the production of young

  10. Figure 11-6

  11. Asymmetries in sexual reproduction in rough-skinned newts

  12. Asymmetries in sexual reproduction in rough-skinned newts females males

  13. Exception to the Rule?” Asymmetries in sexual reproduction in broad-nosed pipefish Male with Kids (in pouch)

  14. Males Females

  15. 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

  16. III. Natural Selection Limits Sexual Selection e.g., marine iguanas

  17. Larger iguanas expend more energy on metabolism

  18. Male marine iguanas in combat

  19. Large territorial males

  20. Alternative mating strategies in coho salmon

  21. IV. Male Access to Females Sperm Competition

  22. Sperm competition in damselflies

  23. Sperm Swimming Speeds Sperm morphology in rodents All for one and one for All!

  24. Infanticide

  25. V. Evidence for Sexual Selection on Trait: Female Choice

  26. Long tail feathers are a ball-and-chain for male red-collared widowbirds

  27. Female red-collared widowbirds prefer long-tailed males

  28. VI. Fisher’s Run Away Sexual Selection An example from UMD

  29. How runaway selection works in theory

  30. VII. Good genes model of sexual selection

  31. Are male gray tree frogs that give long calls genetically superior to males that give short calls??

  32. Courtship and mating in hangingflies

  33. VIII. Origin of Trait Selection Water mite waiting in ambush for a copepod, male has found her

  34. 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).

  35. Lilies from from SW Aust.

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