Social dominance and breeding success in captive brushtail possums, Trichosurus vulpecula

The brushtail possum (Trichosurus vulpecula) is New Zealand's most importan t mammal pest. Options for the biological control of possums are being eval uated, particularly fertility control. The functions of social dominance hi erarchies in possums have not been determined, but in many species dominant males breed more successfully than subordinates. This paper describes the effect on breeding success in captive groups of possums of vasectomising th e dominant male. Dominance was measured by recording the outcome of social interactions during monthly observations. In groups of two male and two fem ale brushtail possums, the dominant male was vasectomised (n = 7) or left u ntreated (n = 5). Five other groups with one male and two females were used as additional controls. In the groups where the dominant male was vasectom ised, its dominance status remained unchanged after treatment but there wer e no further births, whereas young continued to be born in pens where males were untreated. At least in captivity, dominant males are therefore capabl e of behaviourally or physiologically inhibiting reproduction by subordinat e males. This is the first evidence for such an effect in possums.