Genetic diversity predicts population fitness and persistence: The value of genetic rescue in conservation

Background/Question/Methods

Biodiversity loss has reached critical levels due in part to anthropogenic forces such as habitat degradation, fragmentation, and climate change. Habitat fragmentation is particularly damaging as naturally contiguous populations become separated, resulting in limited gene flow. Such populations may become less genetically diverse, leading to population declines and reduced adaptive potential. Genetic rescue is a conservation technique involving the translocation of individuals from one population into the genetically deficient population of the same species for the purpose of reintroducing gene flow. This conservation practice has been shown to produce promising results but remains relatively under-used due to a lack of long-term data and monitoring of genetic rescue attempts. To promote a better understanding of genetic rescue and its potential risks and benefits, we reviewed and analyzed all genetic rescue attempts to date to identify whether genetic diversity increases following rescue, and if this change is associated with increased fitness. We used a Bayesian meta-analytical approach to examine the relationship between fitness and genetic diversity. Using this information, we conducted genetic rescue simulations using Vortex software, varying the number of individuals used in genetic rescue (N = 5%, 10% and 15% of initial population size), and simulating single versus multiple introductions.

Results/Conclusions

We examined 27 cases of genetic rescue and found that genetic diversity, represented by heterozygosity, increased following genetic rescue, peaking in the second generation. Further, we found that fitness, as represented by a combination of population level fitness traits, increased to a maximum of 4-fold, peaking in the third generation. Using Bayesian modelling, we found that increased heterozygosity was directly related to increased population fitness. Given our findings, we included genetic variables in our Vortex simulations to determine the optimal genetic rescue approach to ensure increased diversity and fitness over the long term. Our results suggest that a single supplementation resulted in a similar likelihood of extinction over 100 years as doing nothing. However, repeated supplementations over a regular interval notably increased genetic diversity and reduced extinction risk by half. Overall, these results show that genetic rescue appears to have significant beneficial effects on population fitness lasting until at least the third generation, and that genetic rescue can lead to long term benefits if repeated at regular intervals. Further, our findings highlight that contrary to recent debate, neutral genetic variation is an important indicator of population fitness and persistence and merits continued use in conservation genetics.