Genetic mixing for population management: From genetic rescue to provenancing

Abstract

Animal and plant species around the world are being challenged by the deleterious effects of inbreeding, loss of genetic diversity, and maladaptation due to widespread habitat destruction and rapid climate change. In many cases, interventions will likely be needed to safeguard populations and species and to maintain functioning ecosystems. Strategies aimed at initiating, reinstating, or enhancing patterns of gene flow via the deliberate movement of genotypes around the environment are generating growing interest with broad applications in conservation and environmental management. These diverse strategies go by various names ranging from genetic or evolutionary rescue to provenancing and genetic resurrection. Our aim here is to provide some clarification around terminology and to how these strategies are connected and linked to underlying genetic processes. We draw on case studies from the literature and outline mechanisms that underlie how the various strategies aim to increase species fitness and impact the wider community. We argue that understanding mechanisms leading to species decline and community impact is a key to successful implementation of these strategies. We emphasize the need to consider the nature of source and recipient populations, as well as associated risks and trade-offs for the various strategies. This overview highlights where strategies are likely to have potential at population, species, and ecosystem scales, but also where they should probably not be attempted depending on the overall aims of the intervention. We advocate an approach where short- and long-term strategies are integrated into a decision framework that also considers nongenetic aspects of management.

Keywords: adaptation; conservation; genetic variation; population size; revegetation.

Figure 1

Burramys parvus adult population size at Mount Buller over time. Solid line is the population size estimate based on capture–recapture data with standard error (mean) bars. Dashed line represents the number of unique observed individuals. Arrows indicate the 2011 and 2014 introduction of six males from a central alpine region source population. Modified from Weeks et al. (2017)

Figure 2

Fitness metrics (a) longevity and (b) lifetime reproductive success varied significantly with hybrid index (0, pure recipient genotype; 1, pure immigrant genotype). Blue and red lines indicate relative fitness between females and males, respectively. Shading around solid lines represents 95% confidence bands around regressions. Modified from Fitzpatrick et al. (2020)

Figure 3

Relative growth rates of high, average, and low growth genotypes (HGG, AGG, LGG, respectively) at temperatures increasing from current day climates. Shading around solid lines reflects variation in growth around the mean growth profile. Modified from Browne et al. (2019)

Figure 4

Population size versus environmental change in genetic mixing strategies. As recipient population size decreases, the potential impact of deleterious alleles reaching fixation increases, and the focus shifts to genetic rescue. However, as rates of environmental change experienced by the recipient population increase, the focus shifts to adaptive genetic diversity

Figure 5

A framework for making management decisions around the implementation of genetic mixing. All components of the framework need to be considered in determining investment even if data are imperfect