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Sexual Selection

Sexual Selection. Darwin & Evolution. Evolution by natural selection Struggle for existence Adaptations increase individual survival. Darwin. The sight of a feather in a peacock’s feather, whenever I gaze at it, makes me sick. Hmm what’s that about…. Darwin on Sex… .

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Sexual Selection

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  1. Sexual Selection

  2. Darwin & Evolution • Evolution by natural selection • Struggle for existence • Adaptations increase individual survival

  3. Darwin The sight of a feather in a peacock’s feather, whenever I gaze at it, makes me sick

  4. Hmm what’s that about…

  5. Darwin on Sex… • Why do males & females of the same species differ from one another, with males exhibiting morphological and behavioral phenotypes more exaggerated than those of females?

  6. Darwin on Sex… • Why do males of closely related species exhibit much greater differences in morphology and behavior than the females of closely related species?

  7. Exaggerated characteristics were more prevalent in males Why are they adaptive for male & not female Characteristics like, color, behavior, morphology are correlated to but not essential for reproduction He also noticed that ….

  8. And that… • May or may not involve physical competition • Adaptation not always beneficial to an individuals survival

  9. Sexual Characteristics • Primary sexual characteristics • Structures needed for reproduction • Ex Genitalia • Secondary sexual characteristics • Structures not necessarily needed for reproduction • Large peacock tail, beard • Aids in attracting mate • Often energetically costly

  10. Darwin’s Theory of Sexual Selection • "struggle between the individuals of one sex, generally the males, for the possession of the other sex“ • The Origin of Species • Reduced survivorship of males with elaborate characteristics is more than compensated for by increased advantage in mating • Mechanisms • Male-male competition • Sexual characteristics are driven by male competition for less common females • Female choice • Females passively stand by and mate with winning males • Victorian perspective

  11. Wallace • Co-discovered natural selection & sexual selection • Agreed with Darwin about importance of male-male competition • Elaborate structures adaptive to attain mates • Recognized the importance of female choice • Crypsis is adaptive

  12. Sexual Selection vs Natural Selection • Sexual selection is different than natural selection • Evolutionary selection forces specific to sexual reproduction • Characteristics not always adaptive • Ex. Peacock tail • Individuals are favored by their fitness relative to other members of the same sex • Natural selection works on the fitness of a genotype relative to the whole population

  13. Sexual Selection Works 2 Ways • Selection on mating behavior, either through competition among members of one sex (usually males) for access to members of the other sex Or • Though choice by members of one sex (usually female)

  14. Sexual Selection Mechanisms • Intrasexual selection • Male competition • Males compete for access to females • Phenotype with competitive advantage selected for • Physical, behavioral, physiological • Intersexual selection • Female choice • Females prefer males with elaborate traits • Preferred males mate more often

  15. Intrasexual Selection Direct competition among individuals of one sex.

  16. Intrasexual Selection Indirect competition among individuals of one sex.

  17. Intrasexual Selection

  18. Intrasexual Selection

  19. Intrasexual Selection http://www.youtube.com/watch?v=989uJug7zrg

  20. Intrasexual Selection

  21. Intrasexual Selection

  22. Intrasexual Selection

  23. Intrasexual Selection

  24. Intrasexual Selection • http://www.spike.com/video/flatworms-penis/2458366

  25. Intersexual Selection • aka Female choice • Individuals of one sex are choosy in selecting their mates from individuals of the opposite sex • Results in secondary sexual characteristics that are not used for competition

  26. Female Choice Figure 23.16x2 Male peacock

  27. Marion Petrie & the Blasted Peacock • Male peacock have an average of 150 eyes • Males with fewer than 130 eyes rarely mate • Illustrated female choice

  28. www.birdsandbushtours.com.au/ gallery.htm

  29. Female Choice www.naturalhistorymag.com/ 0302/0302_feature.html

  30. http://www.youtube.com/watch?v=mNXgh333ihQ http://www.youtube.com/watch?v=7l79rgG9bDk&feature=related

  31. Cryptic Female Choice

  32. Cryptic Female Choice

  33. Female gametes Few Large Costly Limiting factor is resource availability Male gametes Many Small Cheap Limiting factor is female availability Why Male Competition & Female Choice?

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