ONTOGENY OF SEXUAL DIMORPHISM IN SIZE AMONG POLYTOCOUS MAMMALS - TESTS OF 2 CARNIVOROUS MARSUPIALS

In many species of carnivorous marsupials (Dasyuridae), adult males ar e far heavier than females (less than or equal to 100%). The theory of maternal investment predicts that juvenile males should receive great er lactational investment than female littermates, especially if mater nal condition is good, because rapid growth disproportionately benefit s reproductive fitness of males. I examine the development of size dim orphism between male and female siblings of Phascogale tapoatafa and D asyurus geoffroii and compare litters of captive mothers with food giv en ad lib. to litters in the wild. In captivity, sons are significantl y heavier and larger than daughters prior to weaning. Wild juveniles a re not sexually dimorphic in size until after they begin to forage for themselves. The ontogeny of sexual dimorphism in size among wild P. t apoatafa and D. geoffroii occurs gradually after weaning and is primar ily a somatic as opposed to skeletal divergence in size. The somatic e nergy stores of males are catabolized during the short breeding season and allow a reduction in foraging effort during this critical period of high activity.