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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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Short sweet male intrasexual competition l.jpg

Short & SweetMale Intrasexual Competition

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Male-Male Competition

  • Andersson, 1994 “Sexual Selection”

  • 5 fundamental areas of male-male competition

    • Scrambles

    • Endurance Rivalry

    • Contests

    • Sperm competition

    • Mate choice (Female choice)

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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

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  • Male coerces or forces copulations

  • Traumatic insemination

  • Coercion

  • Forced copulations

  • Adaptations

    • Large size

    • Strength

    • Coercive behaviors

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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

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Bed Bugs

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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

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Female Response

  • Females have evolved paragenitalia to mitigate costs

  • Organ of Berlese

    • Fat pad that assists in repairing wound

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Sexual Coercion

  • Smuts & Smuts, 1993

  • Males use of force or subversion in mating tactics

  • Causes female to mate with suboptimal male

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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

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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

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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

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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)

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Forced Copulation

  • Common in ducks & geese

  • Most species monogamous

  • Unmated males force copulations on paired female

    • Some action is better than no action

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Forced Copulation

  • Snow Geese

  • Monogamous pairs

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Male Mate Guards Female & Nest Until Eggs are laid

Force copulations on neighboring females

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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

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Coercive mating in waterstriders

Westlake Rowe & Currie (2000)

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  • 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

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  • 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

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  • 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

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  • 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

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  • Jacana

  • Reversed roles

  • Females practice infanticide

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Costs of Infanticide

  • Reduced reproductive effort by female

  • Risk & cost of injury

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Counter adaptations of Infanticide

  • Aid female in circumventing male infanticide

  • Salvages her reproductive fitness

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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

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  • 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

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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

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Concealed Ovulation

  • 2 Hypotheses

  • Parental investment hypothesis

  • Reduced infanticide hypothesis

  • Bipedalism & move to Savannah

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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

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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

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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

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Spotted Hyena

  • Matriarchal community (clan)

  • Females larger than males

  • Enlarged clitoris

  • Labia fused to form “scrotum”

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