Abstract

For bottlenecked populations of threatened species, supplementation often leads to improved population metrics (genetic rescue), provided that guidelines can be followed to avoid negative outcomes. In cases where no “ideal” source populations exist, or there are other complicating factors such as prevailing disease, the benefit of supplementation becomes uncertain. Bringing multiple data and analysis types together to plan genetic management activities can help. Here, we consider three populations of Tasmanian devil, Sarcophilus harrisii, as candidates for genetic rescue. Since 1996, devil populations have been severely impacted by devil facial tumour disease (DFTD), causing significant population decline and fragmentation. Like many threatened species, the key threatening process for devils cannot currently be fully mitigated, so species management requires a multifaceted approach. We examined diversity of 31 putatively neutral and 11 MHC‐linked microsatellite loci of three remnant wild devil populations (one sampled at two time‐points), alongside computational diversity projections, parameterized by field data from DFTD‐present and DFTD‐absent sites. Results showed that populations had low diversity, connectivity was poor, and diversity has likely decreased over the last decade. Stochastic simulations projected further diversity losses. For a given population size, the effects of DFTD on population demography (including earlier age at death and increased female productivity) did not impact diversity retention, which was largely driven by final population size. Population sizes ≥500 (depending on the number of founders) were necessary for maintaining diversity in otherwise unmanaged populations, even if DFTD is present. Models indicated that smaller populations could maintain diversity with ongoing immigration. Taken together, our results illustrate how multiple analysis types can be combined to address complex population genetic challenges.

Highlights

  • A recent review of genetic rescue data indicated that 92.9% of recipient populations showed a fitness benefit, such as increased fecundity and reduced inbreeding coefficients (Frankham, 2015)

  • Genetic rescue is still rarely applied in conservation due to concerns over outbreeding depression, potential demographic disruption (Frankham, 2015) and a greater focus on threat abatement (Pierson et al, 2016), but there have been several iconic success stories such as the wolf Canis lupus (Vilà et al, 2003) and Florida panther Puma concolor (Hostetler, Onorato, Jansen, & Oli, 2013)

  • This study was developed in response to a series of management questions from the Save the Tasmanian Devil Program given the persistence of wild devil populations with devil facial tumour disease (DFTD) (Lazenby et al, 2018), but these types of questions are not unique to devils

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Summary

| INTRODUCTION

High rates of species extinction and large declines in biodiversity are critical issues facing conservationists today (Fa, Funk, & O’Connell, 2011). An increase in genetic diversity among hybrid offspring, relative to inbred offspring, was seen at low‐diversity immune genes (Toll‐like receptors) but not at high‐diversity immune regions (major histocompatibility complex) (Grueber, Sutton, et al, 2017) Another useful resource to inform genetic rescue planning is stochastic population modelling (e.g., Vortex [Lacy & Pollak, 2014], AlleleRetain [Weiser, Grueber, & Jamieson, 2012]). We generate genetic rescue recommendations for three wild devil populations, in the face of a prevailing threat, by combining four major analysis types: 1. 3. Quantitative data on the demographic effects of DFTD in wild devil populations, based on previous analysis of 20 years of field data from DFTD‐present and DFTD‐absent populations across Tasmania (Grueber, Fox, Belov, Pemberton, & Hogg, 2018; Lazenby et al, 2018). Our analysis serves as a model for combining multiple data and analysis types to assess genetic rescue options in an applied conservation context

| MATERIALS AND METHODS
Findings
| DISCUSSION
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