The Benefit of Maternal Care and Infanticide by Males as Reproductive Strategies in a Caprellid Amphipod

The survival of juveniles is essential for the continuation of parental genes. Consequently, the presence or potential presence of juveniles can influence the behavior of parents as well as other conspecifics. Maternal care is a key behavioral adaptation that enhances offspring survival through various mechanisms, including protection against potential threats such as infanticide. This study investigated the ability of adults to recognize juveniles and the behavioral changes induced by their presence in the marine crustacean Caprella kominatoensis, a species in which females are well known to provide maternal care. The role of body size in both sexes was examined to evaluate whether maternal care functions as an effective defense against male-inflicted infanticide. It was found that females continued maternal care even after offspring were exchanged with other females, suggesting that maternal care is provided to any conspecific juveniles. When female parents were deprived of any juveniles, the period until female molting was shortened. Infanticide by males was observed only when juveniles were accompanied by the female parent; males did not harm juveniles in the absence of the female parent. Juvenile survival was higher when the female parent associated with the juveniles was larger than the male. These findings suggest that, in this caprellid amphipod, where female parents reproduce only during a brief period after molting, and molting is suppressed during maternal care, males may adopt a reproductive strategy in which infanticide facilitates the termination of maternal care, thereby accelerating female molting and increasing mating opportunities. It is concluded that maternal care is a mechanism of defense against conspecific infanticide, with female parental body size being a key factor in its effectiveness.