The effects of maternal presence on natal dispersal are seasonally flexible in an asocial rodent

Abstract

In mammals, social tolerance among females, the philopatric sex, is formed through continued physical proximity between kin after offspring are weaned. However, the benefits of continued close association may be outweighed by costs such as local resource competition and risk of inbreeding. We hypothesized that for ‘philopatric females’, a flexible tendency towards either natal dispersal or philopatry is an important behavioral response to changes in social conditions. We examined this using an asocial rodent, Apodemus speciosus, which exhibits two discrete breeding seasons, one in spring and the second in autumn. Daughters and mothers were shown to recognize each other as kin at the time of weaning in both seasons. In spring, some mothers reproduced twice, and some first-litter daughters matured and reproduced in the same season. In autumn, however, only mothers reproduced, and there were no second litters. In spring, the proportion of natal dispersers was higher among weaned offspring whose mother remained present than those whose mother was absent, while in autumn, natal dispersal was more frequent when the mother was absent than when she remained. Sons dispersed earlier than their female littermates. Population density alone is insufficient to explain these patterns. We suggest that variable levels of reproductive competition between female kin result in seasonal differences in female natal dispersal. Breeding condition can be modulated by environmental factors, and the promotion of reproductive activity of females in spring may cause natal dispersal of daughters, while the inhibition of reproductive activity in autumn may permit philopatry.