Abstract
We investigated the effects of maternal weight and age and density of breeding females on sex ratio (percentage of males) in litters of wild bushy-tailed woodrats ( Neotoma cinerea ), a sexually dimorphic rodent. Sex ratios in full-sized litters (i.e., those that had not likely experienced mortality during gestation or lactation) were unaffected by experimentally reduced densities of females, nor did they differ between litters born to yearling and adult (≥2 years) mothers. However, sex ratios in litters were strongly correlated ( R = 0.71, P = 0.0001) with prebreeding body weight in adult mothers, suggesting that adult woodrats adjust sex ratios in litters at conception or early gestation in relation to maternal condition. Although yearling mothers did not appear to adjust prebirth sex ratios, postbirth loss was more strongly male-biased in litters born to yearling mothers than in those born to adults, and we suggest that yearlings may adjust sex ratios during the investment period from birth to weaning.
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