The role of relatedness in mate choice by an arboreal marsupial in the presence of fine-scale genetic structure

Where dispersal distances are restricted or generations overlap, kin may remain spatially clustered, leading to positive spatial genetic structure and the potential for inbreeding. In such circumstances, post-dispersal behavioral mechanisms may be required if individuals are to avoid mating with kin. Here, we conducted an empirical investigation of mate choice in the presence of fine-scale genetic structure. We assessed the potential for mating among relatives using genetic spatial autocorrelation analysis among adult mountain brushtail possums (Trichosurus cunninghami). There was significant positive spatial genetic structure among opposite-sexed adults (on a scale of 200 m), suggesting that kin remained spatially clustered after dispersal. Despite this, no genetic evidence of inbreeding was found. We assessed whether females may potentially avoid inbreeding: (1) by seeking distant mates and/or (2) by the active avoidance of kin in mate choice. Individuals did not choose distant mates, as 97 % of pairs that mated were separated by < 200 m. We identified two distinct patterns of mate choice within the one population. Approximately half of the females sampled were socially monogamous (pair-bonded), and there was no evidence that these individuals chose mates on the basis of genetic dissimilarity. By contrast, the remaining (non-pair-bonded) females were more likely to select genetically dissimilar mates. This dual mate choice pattern demonstrates that the role of genetic relatedness in mate choice can be dependent on social context and dispersal patterns.