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Short & Sweet Male Intrasexual Competition

Short & Sweet Male Intrasexual Competition. Male-Male Competition. Andersson, 1994 “Sexual Selection” 5 fundamental areas of male-male competition Scrambles Endurance Rivalry Contests Sperm competition Mate choice (Female choice). Alternative Contests. When it pays to be a wimp

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Short & Sweet Male Intrasexual Competition

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  1. Short & SweetMale Intrasexual Competition

  2. Male-Male Competition • Andersson, 1994 “Sexual Selection” • 5 fundamental areas of male-male competition • Scrambles • Endurance Rivalry • Contests • Sperm competition • Mate choice (Female choice)

  3. Alternative Contests • When it pays to be a wimp • Poor competitors avoid direct contests by using alternative behaviors • Adaptations that promote • Sneaky behaviors • Hermaphrodites • Dwarfism • Coersion & forced copulations • Infanticide

  4. Coercion • Male coerces or forces copulations • Traumatic insemination • Coercion • Forced copulations • Adaptations • Large size • Strength • Coercive behaviors

  5. Traumatic Insemination • External genitalia penetrates the female abdominal wall • Extragenital insemination • Internal insemination without the involvement of female genitalia • Common in insects, snails, flatworms • Adaptation to reduce sperm competition with other males • Circumvents sperm plugs & scooping

  6. The males

  7. Traumatic Insemination

  8. Bed Bugs http://www.youtube.com/watch?v=WfKCcSPCOQo

  9. Bed Bugs • Traumatic insemination • Male penetrates female abdomen with intromittent organ • Injected sperm migrate over to female ovary to fertilize eggs • Female genital only used for egg laying • Added cost to reproduction • Injury repair • Pathogen exposure • Male adaptation to avoid female mating resistance • Sexual conflict, antagonistic coevolution

  10. Female Response • Females have evolved paragenitalia to mitigate costs • Organ of Berlese • Fat pad that assists in repairing wound

  11. Sexual Coercion • Smuts & Smuts, 1993 • Males use of force or subversion in mating tactics • Causes female to mate with suboptimal male

  12. Red Backed Salamander

  13. Red Backed Salamander • Males exhibit coercive behavior • Behavior more prevalent with promiscuous females • Threat posture • Biting • Less time touching • Other species females exhibit coercive behavior with males

  14. Tooth rake marks

  15. Sexual Coercion • Tooth rake marks used to measure aggression • Female rake marks examined • Compared reproductive & non-reproductive females • Indian ocean bottleneck dolphin • Mate with multiple males

  16. Sexual Coercion • Male Chimpanzees exhibit high levels of aggression with reproductive females • Aggression includes • Beating with branches, clubs • Aggressive males mated more with females that they beat

  17. Forced Copulation • Scorpionfly • Male provides female with saliva • Female eats the gift and uses the resources to make eggs • The larger the gift, the longer copulation event the male gains • Some males force female • Forcibly grabs with genital forceps & clamping device (notal organ)

  18. Dastardly Fellow

  19. Forced Copulation • Common in ducks & geese • Most species monogamous • Unmated males force copulations on paired female • Some action is better than no action

  20. Female Resistance

  21. Female Counteradaptation

  22. Forced Copulation • Snow Geese • Monogamous pairs

  23. Nest in Colonies

  24. Male Mate Guards Female & Nest Until Eggs are laid Force copulations on neighboring females

  25. Forced Copulation • Males do not court • Females do not choose • Coercive mating is the only reproductive strategy • Small males forcibly mate with females by sneaking up on them • Very low success rate… • try, try, try again

  26. Eastern Mosquitofish

  27. Small Males

  28. Coercive mating in waterstriders Westlake Rowe & Currie (2000)

  29. Infanticide • Killing of young offspring by a mature animal of its own species • Male or female can kill offspring • Infanticide caused by sexual conflict • New male or female using infanticide to increase reproductive fitness

  30. Infanticide • Males kill dependent offspring so females become sexually receptive sooner • Can also be used to reduce competition for limited resources. Ex food • Common in many species • Mice, ground squirrels, bears, deer, prarie dogs, fishes, dwarf mongoose, dung beetle, jacana • Adaptations • Infanticidal behavior

  31. Hanuman langurs

  32. Infanticide • Hanuman langurs • Live in 2 social groups • Male bands • Female, infant, 1 male • Resident male challenged by incumbent male • Infants killed by new male • Non-nursing female return into reproductive receptivity • Reduces intraspecific competition between offspring of old male & new male

  33. Lion Pride

  34. Infanticide • Lion • Male lions live in small troops • Male troops take control of existing prides • New males will attempt to kill all cubs 9 months & younger • ¼ of yearling cubs die from infanticide • Conditions for sexual conflict • Males reproductive cylce spans ave 2 yrs • Females give birth once every 2 years http://video.aol.com/video-detail/lion-infanticide-1/754336908 http://www.youtube.com/watch?v=4XyQEo9X4gM

  35. Infanticide • Jacana • Reversed roles • Females practice infanticide

  36. Costs of Infanticide • Reduced reproductive effort by female • Risk & cost of injury

  37. Counter adaptations of Infanticide • Aid female in circumventing male infanticide • Salvages her reproductive fitness

  38. Hanuman langurs • Females may leave the group with young and ousted male • Females who remain may develop false estrous • Mate with new male so that he believes her offspring are his

  39. Promiscuity • Females mate with many males • Conceals the parentage of offspring • Males are less likely to practice infanticide if they are unsure of their paternity • Ex. Langurs

  40. Concealed Ovulation • No signal to male when female is ovulating • Ex. Human females • Evidence supports female awareness of ovulation • Females initiate sex more often when ovulating • Are males aware? • Studies suggest fertile females appear more attractive • Males find fertile female voice more attractive • Ex Strippers

  41. Concealed Ovulation • 2 Hypotheses • Parental investment hypothesis • Reduced infanticide hypothesis • Bipedalism & move to Savannah

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