Long-term pair-bonds without mating fidelity in a mammal

Abstract

AbstractMost mammals are polygynous and are characterised by male-biased sexual size dimorphism. One hallmark of mammalian monogamy is the lack of such dimorphism. Bobucks, or mountain brushtail possums, Trichosurus cunninghami, lack sexual size dimorphism; however, few behavioural data exist for this species. We studied the mating system of a bobuck population in south-eastern Australia. Adult bobucks were strongly paired: pair-members had exclusive access to a suite of den-trees and overlapped in home range on average by 70%. Pair-members rested together in the same tree-hollow on approximately 70% of days during the breeding season and 47% of days during the non-breeding season. While active, pair-members remained within approximately 8 m of one another during the breeding season and within 31 m of one another during the non-breeding season. Females established pair-bonds at 2-5 years of age; pair-bonds ended only as a result of the death of one pair member. However, molecular paternity analysis established that 35% of young were the result of extra-pair copulations (EPCs). This is the first study to provide strong evidence of long-term pair-bonds in a marsupial and raises questions about the relative benefits of pairing to males and females in this population.