Proximate determinants of sexual differences in adult body size

Alternative hypotheses about the causation of sexual size dimorphism (SSD) make different assumptions and predictions about the stage in ontogeny at which sexual dimorphism in mean adult body size is determined. There are two main possibilities for ontogenetic determination of sexual differences in mean adult body size. 1) This dimorphism is determined mainly by the direction and degree of SSD present at the attainment of sexual maturity. Sexual differences in mean adult size are determined by processes operating on juveniles: sex differences either in growth rate or in the age at maturation, 2) Mean adult SSD is determined mainly by sex differences in growth or survival rates during adult life. Differences in adult size between the sexes result because adults of one sex grow faster or survive better than adults of the other sex. Overall, the patterns documented here suggest that differences in pre-maturational growth, age at maturity, or both are the primary determinants of sexual dimorphism in adult body size. Post-maturational differences in growth or survival rates between the sexes are not totally irrelevant but probably influence the direction (as opposed to the degree) of adult SSD only rarely. -from Author