Counter-strategies to infanticide in mammals: costs and consequences

Infanticide, the killing of conspecific young, has been documented in numer ous species of mammals and is considered an adaptive behavioral strategy to enhance the reproductive success of the perpetrator. The potential benefit s of committing infanticide for males are obtaining nutritional gain and ma ting partners, and for females are acquiring access to resources such as fo od and nest sites. Some costs are associated with committing infanticide su ch as additional energy expenditure, risk of injury, and exposure to predat ion. However, the major costs associated with infanticide are borne by the victim Female and the sire male in loss of fitness. In response to this sel ection, males and females use a variety of counter-strategies to protect th eir young from infanticide. We summarize the published accounts and theory associated with infanticide and the occurrence of counter-strategies in a variety of mammalian groups i n order to explain how infanticide may influence individual behavior as wel l as the social systems of mammals. We focus on the behavioral strategies u sed, primarily by females, to deter major losses in reproductive success. T hese strategies include aggression, female choice of dominant males, and pr omiscuity to confuse paternity as defense against males, and territoriality , association with kin, reproductive suppression, and reproductive synchron y as defenses against females. Male counter-strategies are less well known, but intrasexual territoriality may in part function as defense against inf anticide. The costs associated with the different male and female counter-s trategies are likely to vary, but may include increased energy expenditure, exposure to predators and injury for both sexes, as well as increased comp etition for resources, limited mate choice, and postponed reproduction for females. We propose that the occurrence of infanticide does not only have t he potential to affect the behavior of individuals (e.g. aggression. spacin g and mate choice), but may also have consequences for the shaping of mamma lian mating systems.