Infanticide

Ultimate Explanations for Infanticide Langurs Killing pups leaves the mother no choice but to mate with the new male Elimination of the nursing youngster enables the female to resume cycling more quickly If this is the adaptive reason, then the behavior should be seen in other species with a similar social system Lions, mice, 50 other mammalian species Females can be infanticidal too, particularly when the male provides the parental care (water bug, jacana waterbird)

Determining Paternity In langurs and lions, infanticide occurs when a male invades a new group In mixed population, colony breeding animals like mice, paternity must be determined in some other way Circadian monitoring of # days since last ejaculation/mating experience

Mechanisms of Infanticide vs Parental Care Hormones Testosterone Progesterone Estrogen

Progesterone Receptor KO mice do not kill their pups Mated males, these were their pups, genetically Schneider et al 2003

Virgin PR KO mice are more parental Schneider et al 2003

PR activation correlates with parenting Blocks PR Less PR activation, better parenting behavior in fathers Activates PR Schneider et al 2003

Hormone levels in California mouse

And in the experimental PR KO mice Not a significant difference Schneider et al 2003

Extra P doesn’t change parental urge fathers

But those non-parental males were more violent on P Not fathers No change in testosterone levels Light grey= attacked pups Dark gray=ignored pups Schneider 2009

Human ‘Infanticide’ and the cost of motherhood Deaths occurred in the year following the birth of the child

Abortion is a form of infanticide Embryos unlikely to survive are spontaneously aborted Miscarriages Sometimes completely undetected by the mother Willingness to terminate a pregnancy that may produce healthy offspring Ability to provide and ensure that child reaches adulthood healthy and viable

Other factors affect the decision Age, marital status, health of mother, likelihood of future opportunity to marry