To mix or not to mix gene pools for threatened species management? Few studies use genetic data to examine the risks of both actions, but failing to do so leads disproportionately to recommendations for separate management

Abstract Many small, isolated populations lose genetic variation and suffer inbreeding, increasing their extinction risk. Augmenting gene flow may alleviate these issues if populations are compatible to mix. Accordingly, recommendations for genetic management should weigh the risk of allowing populations to remain small and separate (e.g. inbreeding depression) against augmenting gene flow through gene-pool mixing (e.g. outbreeding depression). To understand how studies examine the risks of alternative management actions, we reviewed the genetic analyses conducted and evidence used to inform their recommendations. Our review analysed 626 studies that discussed the management of small, isolated populations, and for a subset of 198 studies, we extracted details of the risk-assessment, genetic analyses, and recommendations made. Approximately 56% of studies did not refer to any genetic risks when making management recommendations. While separate management was the most common recommendation overall, studies that considered both inbreeding depression and outbreeding depression were more likely to recommend gene-pool mixing than separate management. The genetic data collected generally offer the potential for evidence-based decisions about the risks posed by different management options, yet our analyses suggest that recommendations were often based on limited use of evidence, creating risks to the effective management of threatened species.