No abstract

Litter size is an important component of life history contributing to reproductive success in many animals. Among muroid rodents, spiny mice of the genus Acomys are exceptional because they produce large precocial offspring after a long gestation. We analyzed data on 1,809 litters from laboratory colonies of spiny mice from the cahirinus-dimidiatus group: Acomys cahirinus, Acomys cilicicus, Acomys sp. (Iran), and Acomys dimidiatus.Generalized mixed-effect models revealed that litter size increased with maternal body weight and/or number of immature females present in the family group. Thus, both maternal body reserves and presence of immature descendants demonstrating previous reproductive success enhance further reproduction in this social rodent.

Recruitment of unrelated individuals into a group plays an important role in the social life of the group living animals. The main goal of our study was to analyze the reactions of established, breeding families of the Sinai spiny mouse, Acomys dimidiatus (Muridae, Rodentia), a social species with precocial pups, to male newcomers in the presence and the absence of a breeding resident male. We compared the behaviour of family members of different sex or age to the presence of a new male. The number of non-aggressive and aggressive interactions with the focal male (resident/newcomer male) was recorded during three periods: before, during and one month after the addition of the newcomer. Only a few aggressive and/or non-aggressive types of contacts occurred before and one month after the addition of the new male. During the experiment, both types of contacts arose, but the results were highly variable. Increased aggressive behaviour of the family toward the intruder was explained mainly by the presence of pregnant or lactating females, which suggests that aggression towards a male newcomer is associated with the reproductive status of females. This phenomenon is most likely connected with the counter-infanticide strategy.