Short & Sweet Male Intrasexual Competition

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

7. 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

8. The males

11. Traumatic Insemination

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

13. 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

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

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

17. Red Backed Salamander

18. 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

20. Tooth rake marks

21. 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

23. 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

24. 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)

26. Dastardly Fellow

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

29. Female Resistance

30. Female Counteradaptation

31. Forced Copulation • Snow Geese • Monogamous pairs

32. Nest in Colonies

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

34. 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

35. Eastern Mosquitofish

36. Small Males

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

38. 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

39. 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

40. Hanuman langurs

41. 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

42. Lion Pride

43. 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

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

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

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

47. 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

48. 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

49. 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

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