short sweet male intrasexual competition
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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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male male 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
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
  • Male coerces or forces copulations
  • Traumatic insemination
  • Coercion
  • Forced copulations
  • Adaptations
    • Large size
    • Strength
    • Coercive behaviors
traumatic insemination
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
bed bugs
Bed Bugs

bed bugs13
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
female response
Female Response
  • Females have evolved paragenitalia to mitigate costs
  • Organ of Berlese
    • Fat pad that assists in repairing wound
sexual coercion
Sexual Coercion
  • Smuts & Smuts, 1993
  • Males use of force or subversion in mating tactics
  • Causes female to mate with suboptimal male
red backed salamander18
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
sexual coercion21
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
sexual coercion23
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
forced copulation
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)
forced copulation28
Forced Copulation
  • Common in ducks & geese
  • Most species monogamous
  • Unmated males force copulations on paired female
    • Some action is better than no action
forced copulation31
Forced Copulation
  • Snow Geese
  • Monogamous pairs
male mate guards female nest until eggs are laid
Male Mate Guards Female & Nest Until Eggs are laid

Force copulations on neighboring females

forced copulation34
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

Coercive mating in waterstriders

Westlake Rowe & Currie (2000)

  • 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
  • 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
  • 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
  • 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

  • Jacana
  • Reversed roles
  • Females practice infanticide
costs of infanticide
Costs of Infanticide
  • Reduced reproductive effort by female
  • Risk & cost of injury
counter adaptations of infanticide
Counter adaptations of Infanticide
  • Aid female in circumventing male infanticide
  • Salvages her reproductive fitness
hanuman langurs47
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
  • 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
concealed ovulation
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
concealed ovulation50
Concealed Ovulation
  • 2 Hypotheses
  • Parental investment hypothesis
  • Reduced infanticide hypothesis
  • Bipedalism & move to Savannah
parental investment hypothesis
Parental Investment Hypothesis
  • Human evolution led to increased supplemental parental investment
    • Altricial young need more care
  • Hidden ovulation aided in acquiring male parental investment
    • Since males did not know when females were ovulating they stayed with 1 female & repeatedly mated with her to ensure fitness
  • Male assistance with parental care increased offspring success and increased fitness for both sexes
reduced infanticide hypothesis
Reduced Infanticide Hypothesis
  • Hidden ovulation reduced the possibility of infanticide by males
  • Males unable to detect female fertile periods so unable to assess whether offspring were theirs or not
  • Males unable to selectively kill rival offspring
  • Strategy also exhibited by other primates
    • Langurs
induced abortion
Induced Abortion
  • Bruce effect
    • Female aborts and resorbs young in development
    • Occurs after a new male takes over
  • Prevents young from being killed after birth
    • Saves female investment
  • How does she know?
    • Mice induce abortion with olfactory cues from novel male
  • See daly 108
spotted hyena
Spotted Hyena
  • Matriarchal community (clan)
  • Females larger than males
  • Enlarged clitoris
  • Labia fused to form “scrotum”