ON THE EVOLUTIONARY STABILITY OF FEMALE INFANTICIDE

Territoriality among female rodents may have evolved as an adaptation to intraspecific competition for resources or, alternatively, to defen d pups against infanticide. In order to evaluate the latter, we analys e the conditions that allow an infanticidal strategy to invade a popul ation of non-infanticidal females, and the circumstances under which i nfanticide may become an evolutionarily stable strategy (ESS). Our gam e theoretical analyses indicate that infanticide has to be associated with some direct (cannibalism) or indirect (reduced competition) resou rce benefits in order to invade a non-infanticidal population We also expect that females will primarily kill litters of nearby neighbors, t hereby removing the closest competitors while keeping costs at a low l evel. However, once established in a population, infanticide may be an ESS, if even females do not gain any resource benefits. This is theor etically possible if a female through infanticide can reduce the possi bility that other, potentially infanticidal, females establish and/or stay close to her nest. While behavioral data indicate that these spec ial circumstances sometimes occur, they may be too specific to apply g enerally to small rodents. Therefore, we expect that the evolutionary stability of infanticide often requires resource benefits, and that fe male infanticide in small rodents may, in fact, be a consequence rathe r than a cause of territoriality.