The effects of group versus intensive housing on the retention of genetic diversity in insurance populations

Background: Retention of genetic diversity and demographic sustainability are the cornerstones of conservation breeding success. In theory, monogamous breeding with equal reproductive output will retain genetic diversity in insurance populations more effectively than group housing which allows mate choice or intrasexual competition. However, the ecological relevance of group housing to a species can outweigh the theoretical benefits of forced monogamy. Here we investigated the influence of different types of captive housing (group (mate choice) versus intensive (forced monogamy)) on reproductive success, litter size and genetic diversity in the endangered Tasmanian devil (Sarcophilus harrisii). Results: For male Tasmanian devils, the proportion of individuals that failed to reproduce was significantly greater in group (maximum 10 individuals) than intensive housing. This suggests greater genetic diversity is retained when devils are bred in intensive housing. For male devils, body weight predicted reproductive success in group housing, suggesting certain individuals are dominant due to a larger body size, leading to unequal genetic contribution. We then used simulation models to predict rates of decline in genetic diversity and inbreeding accumulation over time comparing group and intensive housing. When managed independently, empirically observed reproductive outputs were predicted to result in large accumulations in inbreeding and loss of gene diversity in both housing types, although these effects were greater in group housing. Transferring individuals between the housing facilities decreased inbreeding accumulation and increased gene diversity in both housing types highlighting the importance of managing independent zoo populations collectively. Conclusions: If conservation programs wish to provide mate choice opportunities through group housing, the impact intrasexual competition will have on dominance and sequential reproductive opportunities needs to be understood prior to commencement. Group housing is becoming increasingly topical as it provides potential ecological benefits, may decrease mate incompatibilities and increase offspring fitness, however it can also result in the loss of genetic diversity in already genetically depauperate species.