Social status and physical condition of mother and sex ratio of offspring in cervids

Abstract

In cervids, the degree of polygyny and litter size vary between species, and both these variables can potentially influence the relationship between maternal condition and offspring sex ratio. Good foraging conditions have usually been found to favour a trend toward female-biased population birth sex ratios. This appears to apply to even the most polygynous species, red deer ( Cervus elaphus) and reindeer ( Rangifer tarandus). However, analysis of offspring sex ratio within populations of these species indicates that high-ranking females produce more males than low-ranking ones. Owing to monoparity and a high degree of polygyny, these species probably offer the clearest starting points for evaluating Trivers and Willard's hypothesis that, in the case of polygynous mammals, females in good condition produce more males than females in poorer condition. In the genera Odocoileus and Alces litter size is not fixed to one, and parental investment per litter may therefore be affected by both offspring sex and litter size. Available evidence of offspring sex ratio variation within these genera is less conclusive than in Cervus and Rangifer.