Population density and movement data for predicting mating systems of arboreal marsupials

A model, based on the number of encounters between male and female arboreal marsupials, was used to predict the rate of polygyny (the proportion of males fathering offspring with more than one female). The model predicted that the rate of polygyny would increase to an asymptote as population density increased. This result formalises previous suggestions that mating systems of arboreal marsupials may change with population density. Data on movements derived from radio telemetry and trap-recapture methods were used to predict the rate of polygyny in a population of the mountain brushtail possum (Trichosurus caninus) at Cambarville, Victoria, southeastern Australia. The model predicted that 26% of males that successfully raised offspring in 1995 would be polygynous. In 1995, blood samples were taken from 13 offspring to determine paternity by DNA profiling. The model predicted that it is unlikely (P = 0.006) that the 13 offspring would be fathered by 13 different males if T. caninus mated polygynously. Thus, the model may be used to construct hypotheses about the mating system of arboreal marsupials that may be tested with subsequent genetic analysis.