Male-biased predation and its effect on paternity skew and life history in a population of common brushtail possums (Trichosurus vulpecula).

Jane L Degabriel,William J Foley,Ben D Moore,Christopher N Johnson

doi:10.1371/journal.pone.0111746

Abstract

Differences in predation risk may exert strong selective pressures on life history strategies of populations. We investigated the potential for predation to shape male mating strategies in an arboreal folivore, the common brushtail possum (Trichosurus vulpecula Kerr). We predicted that possums in a tropical population exposed to high natural levels of predation would grow faster and reproduce earlier compared to those in temperate populations with lower predation. We trapped a population of possums in eucalypt woodland in northern Australia each month to measure life history traits and used microsatellites to genotype all individuals and assign paternity to all offspring. We observed very high levels of male-biased predation, with almost 60% of marked male possums being eaten by pythons, presumably as a result of their greater mobility due to mate-searching. Male reproductive success was also highly skewed, with younger, larger males fathering significantly more offspring. This result contrasts with previous studies of temperate populations experiencing low levels of predation, where older males were larger and the most reproductively successful. Our results suggest that in populations exposed to high levels of predation, male possums invest in increased growth earlier in life, in order to maximise their mating potential. This strategy is feasible because predation limits competition from older males and means that delaying reproduction carries a risk of failing to reproduce at all. Our results show that life histories are variable traits that can match regional predation environments in mammal species with widespread distributions.

Highlights

The life history strategies of mammals show remarkable interand intra-specific diversity, which may be shaped by several factors, such as resource availability, predation risk and population density [1,2,3]
We used a t-test to determine whether breeding males were heavier than non-breeding males, and a logistic regression model to determine the relationship between male body mass and reproductive success, which we calculated as the number of paternities as a percentage of the total number of offspring produced by females with home ranges overlapping those of the target male
Quantification of predation We observed a high rate of predation by pythons, strongly biased towards male possums

Summary

Introduction

The life history strategies of mammals show remarkable interand intra-specific diversity, which may be shaped by several factors, such as resource availability, predation risk and population density [1,2,3]. In polygynous populations with low death rates of males, younger and smaller individuals are likely to have limited probability of mating success, and the most efficient strategy for a male would be to avoid risk-taking and invest in growth, in order to maximize mating opportunities later in life when a large size has been reached.

Results

Conclusion