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Infanticide

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Infanticide as a sexually selected male reproductive strategy.

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Infanticide

  1. 1. Infanticide: A Sexually Selected Male Strategy<br />
  2. 2. One-male groups: Competition to gain access to females is intensified<br />Males compete for access to groups of females<br />Outsiders exert constant pressure on resident males<br />Tenure of resident males often short<br />
  3. 3. Infanticide is a sexually-selected male reproductive strategy<br />Females nurse infants for many months <br />If unweaned infant dies, female resumes cycling immediately<br />Death of infant makes females available for mating sooner<br />Infanticidal males gain immediate mating opportunities<br />If male tenure is short, infanticide enhances male mating opportunities<br />
  4. 4. If infanticide is a sexually-selected male reproductive strategy, we predict: <br />Infanticide will be linked to changes in male residence or status<br />Males will kill unweaned infants<br />Males won’t kill their own infants<br />Infanticidal males will gain reproductive benefits<br />Evidence supports all four predictions<br />
  5. 5. 1. Infanticide is associated with changes in male status:Males don’t kill unless they GAIN reproductive access they did not have before<br />
  6. 6. 1. Males begin to kill infants soon after they join group<br />Hanuman langurs, Borries & Koenig 2000<br />
  7. 7. 2. Males kill unweaned infants<br />Probability of surviving presence of<br /> infanticidal male<br />
  8. 8. 3. Males don’t kill own infants<br />
  9. 9. 4. Infanticidal males gain reproductive benefits<br />Infanticide brings females back into estrus<br />Infanticidal males often mate with mother of dead infant<br />
  10. 10. Infanticide is a major cause of mortality<br />
  11. 11. Counterstrategies to thwart infanticide<br />Defend victims of attack<br />Mothers<br />Female kin<br />Males present at conception<br />Fathers<br />Confuse paternity<br />Estrus swellings<br />Mate with many males<br />Mate with newcomers<br />
  12. 12. In baboons, male-female ties may be response to infanticide<br />In some populations, infanticide is common when new males join group or males rise in status<br />New mothers form associations with particular males <br />possible father of current infant<br />Males protect females’ infants<br />Males provide care and attention preferentially to infants who are actually theirs (they can tell somehow!) <br />
  13. 13. Sexually-selected infanticide has now been documented in a number of taxa<br />All the major groups of primates<br />Prosimians<br />New World monkeys<br />Old World monkeys<br />Apes<br />Lions<br />Rodents<br />Birds<br />Many still think (incorrectly) that it is pathological and not adaptive<br />
  14. 14. Controversy about whether infanticide is a sexually selected strategy persists because people confuse “is” and “ought”<br />This is called the “naturalistic fallacy”<br />assume that natural phenomena are right, just, unchangeable, good<br />Worry that if infanticide is adaptive for langurs or lions, it would be justified in humans<br />But this reasoning is wrong<br />we can’t extract moral meaning from behavior of other animals or what is natural <br />

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