NATAL DISPERSAL AND PHILOPATRY IN THE CARNIVOROUS MARSUPIAL PHASCOGALE-TAPOATAFA (DASYURIDAE)

The proximate and ultimate causes of dispersal in semelparous carnivor ous marsupials (Phascogalinae) have previously been hypothesized to be maternal aggression and inbreeding avoidance, respectively. This stud y tests these hypotheses by exposing 26 litters of Phascogale tapoataf a to a diverse range of social and environmental conditions that: pote ntially affect dispersal(e. g. supplemental feeding, post-weaning dese rtion by the mother, orphaning, and release of subadults into unoccupi ed habitat). The mean dispersal age was 162 +/- 5.6 d, which is about 3 wk after weaning is complete. Juvenile dispersal was strongly male b iased under all conditions, suggesting that extrinsic proximate causes do not adequately account for male emigration. Home range establishme nt by males was contingent on the presence of females. Half of the mon itored daughters were philopatric, and others typically settled adjace nt to the natal site, thus possibly enhancing their reproductive poten tial by occupying an area of known resource quality. Because philopatr y increases the risk of incest, females may be selected to preferentia lly mate with unrelated males (immigrants), when they are available, t o avoid inbreeding. If so, the presence of immigrant males would reduc e the probability of locally born, related males reproducing at their natal site. Thus inbreeding avoidance by females may create local mate competition among males and select for male dispersal. Emigration als o ensured that males avoided inbreeding, but, if they dispersed into u noccupied habitat, male P. tapoatafa often returned to the natal area. This 'boomerang strategy' of returning to mate with related females s uggests that, in the absence of conspecifics along the dispersal path of a male, mate competition will be weak at the natal site and female mate choice will not preclude related males. Thus while inbreeding avo idance by either or both sexes is perhaps the most parsimonious explan ation of male-biased emigration, dispersal patterns were apparently st rongly influenced by additional factors, so that the ultimate causatio n of the dispersal regime may be more complex.