Temporal changes in Tasmanian devil genetic diversity at sites with and without supplementation

Management interventions for threatened species are well documented with
genetic data now playing a pivotal role in informing their outcomes.
However, in situ actions, such as supplementations (the release of
individuals into an existing population of conspecifics) are often
restricted to a single site to advise species-level management decisions.
A considerable amount of research and management effort has been dedicated
to conserving the endangered Tasmanian devil (Sarcophilus harrisii),
offering a unique opportunity to investigate the temporal genetic
consequences of supplementation at multiple sites, in comparison to
outcomes observed in the absence management interventions. Using 1,778
genome-wide SNPs across 1,546 individuals, we compared four wild
supplemented sites to four monitoring-only sites (not supplemented;
control sites) over nine years (2014-2022). By the end of the study,
genetic differentiation among supplemented sites had significantly
decreased compared to among not-supplemented sites. We found statistically
significant variation in patterns of genetic change over time between
sites using linear mixed-effects modelling with random slopes.
Investigating this among-site variation showed that three of the
supplemented sites conformed to predictions that supplementations would
have a positive impact on the genetic diversity of devils. We predicted
there would be no change over time at our fourth site due to relatively
high gene flow previously observed there, however, that site did not align
with predictions, instead showing a decrease in genetic diversity and
increase in relatedness. Amongst not supplemented sites, there was no
consistent pattern of temporal genetic change, suggesting that devil sites
across Tasmania are highly heterogeneous, likely reflecting variation in
connectivity among sites, genetic drift, and non-genetic factors. Our
study demonstrates that long term concurrent monitoring of multiple sites,
including controls, is necessary to contextualize the influence of
management interventions against natural fluctuations within a species
system.