Multiple paternity in a field population of a small carnivorous marsupial, the agile antechinus, Antechinus agilis

Multiple paternity within broods or litters occurs in many species across a variety of social mating systems. Here we present data on paternity patterns in the agile antechinus, Antechinus agilis, a small carnivorous marsupial. In this species, all males die after a highly synchronised breeding season and females store sperm in oviducal crypts for about 2 weeks. Previous work suggests that the species has a lekking promiscuous mating system; however, in the absence of field data on paternity, this is not confirmed. In our study, microsatellite data from two field-seasons show that of the 47 litters sampled, 46 litters were fathered by more than 1 male, with many litters sired by a minimum of 3 males (n=22). Kinship analysis showed that litters were most likely sired by between 1 and 7 males, with an average for 1st-year breeding females of 4.1 in 1999 (n=16) and 3.3 in 2000 (n=23). For 2nd-year females, the estimated number of sires was 4.0 in 1999 (n=3) and 2.6 in 2000 (n=5). The number of sires per litter correlated positively with the number of pouch young in the litter. Our data clearly show multiple matings by females during a single oestrus period, indicating the potential for sperm competition. Females may mate with multiple males to ensure fertility (direct benefit), since male ejaculates contain low numbers of spermatozoa and all males may die before females ovulate. Furthermore, females may gain indirect benefits from mating with multiple males, such as genetic compatibility.