ENHANCEMENT OF REPRODUCTIVE SUCCESS THROUGH MATE CHOICE IN A SOCIAL ROCK-WALLABY, PETROGALE-ASSIMILIS (MACROPODIDAE) AS REVEALED BY MICROSATELLITE MARKERS

The reason why a female who is socially paired to one particular male seeks extra-pair copulations (EPCs) with others has important implicat ions in life history models and to the study of behaviour. The Allied rock-wallaby, Petrogale assimilis, lives in spatially isolated colonie s in tropical north Queensland, Australia. Extensive observations of a colony at Black Rock showed that intense behavioural bonding occurs b etween pairs of adult males and females; about two-thirds 1 of males p aired with one female, the remainder paired with two females simultane ously. Single-locus microsatellite profiling determined the paternity of 63 offspring from 21 females for which long-term behavioural data w ere available. One-third of the young were fathered by males which wer e not paired socially with the mother. The mating system was heterogen eous: (1) all offspring of 11 females were fathered by the mother's pa rtner, (2) all young of 5 females were fathered by extra-pair males, a nd (3) only some of the young of 5 females were Fathered by their regu lar consort. Analysis of individual longitudinal demographic records s howed that females whose young were always fathered by their consort h ad higher reproductive success than those whose young were always fath ered as a result of(EPCs). However, females with some offspring father ed by their regular consort and others via EPCs had the highest probab ility of raising young to independence. These females were significant ly more likely to have an offspring fathered as a result of an EPC if their previous young had failed to survive to pouch emergence. These r esults are consistent with the hypothesis that females choose mates fo r their genetic quality. Comparison of the males with which these fema les sought EPCs and the regular consorts suggested that arm length rat her than body weight or testes size was used as the index of genetic q uality. Results from a second colony of rock-wallabies in which the re productive rate was accelerated were also consistent with the genetic- quality hypothesis. These results imply that by choosing better-qualit y fathers irrespective of social pairing, females are able to maximise their overall lifetime reproductive success, and presumably, those of their offspring.