Sex differences in energy expenditure in non-human primates

Female mammals bear the energetic costs of gestation and lactation. Therefo re, it is often assumed that the overall energetic costs are greater for fe males than they are for males. However, the energetic costs to males of int rasex competition may also be considerable, particularly if males maintain a much larger body size than females. Using data from 19 non-human primates , this paper examines the relationship between male and female energetic co sts both in the short term (daily energy expenditure) and the long term (th e energetic cost of producing a single offspring). It is shown that the maj or determinant of sex differences in energetic costs is body size dimorphis m. In the long term, the energetic costs are often greater for females, but , when male body size exceeds female body size by 60% or more, male energet ic costs are greater than those for females. That is, in highly sexually di morphic species the energetic costs of gestation and lactation for the fema les are matched by the energetic costs to the males of maintaining a large body size.