Sex-specific effects of size and condition on timing of natal dispersal in kangaroo rats

Abstract

The effects of proximal cues in eliciting natal dispersal are predicted to vary between sexes because of differences in reproductive strategies. I examined how body mass and condition affected timing of natal dispersal in male and female banner-tailed kangaroo rats (Dipodomys spectabilis), a species that lacks sex-biased dispersal. I experimentally manipulated cues by providing additional food to a subset of offspring prior to dispersal. All supplemented offspring, regardless of sex, grew faster, were in better condition, and had higher survivorship than unsupplemented offspring. Sons who received food supplements dispersed earlier than unsupplemented sons, indicating that timing of dispersal was related to size and condition. Timing of dispersal in daughters was unaffected by resource supplementation, suggesting that size and condition are less important proximal cues. These sex-specific responses match the intersexual differences in mammalian reproductive strategies and parental investment patterns. My results support the hypothesis that sons remain at the natal territory until a certain threshold of size and condition is reached. Male reproductive success is typically dependent on body size, which affects their ability to find and defend mates. By allowing sons to remain at the natal territory until this threshold is attained, mothers likely increase the fitness of their sons. Female reproductive success is influenced more by securing resources than by body size. Thus, dispersing as early as developmentally feasible would allow daughters to secure an existing burrow system and maximize the time available for caching food prior to their first breeding attempt. © 2011 The Author.