Genetic rescue remains underused for aiding recovery of federally listed vertebrates in the United States

Abstract

Restoring gene flow among fragmented populations is discussed as a potentially powerful management strategy that could reduce inbreeding depression and cause genetic rescue. Yet, examples of assisted migration for genetic rescue remain sparse in conservation, prompting several outspoken calls for its increased use in genetic management of fragmented populations. We set out to evaluate the extent to which this strategy is underused and to determine how many imperiled species would realistically stand to benefit from genetic rescue, focusing on federally threatened or endangered vertebrate species in the United States. We developed a “genetic rescue suitability index (GR index)” based on concerns about small population problems relative to risks associated with outbreeding depression and surveyed the literature for 222 species. We found that two-thirds of these species were good candidates for consideration of assisted migration for the purpose of genetic rescue according to our suitability index. Good candidate species spanned all taxonomic groups and geographic regions, though species with more missing data tended to score lower on the suitability index. While we do not recommend a prescriptive interpretation of our GR index, we used it here to establish that assisted migration for genetic rescue is an underused strategy. For example, we found in total, “genetic rescue” was only mentioned in 11 recovery plans and has only been implemented in 3 of the species we surveyed. A potential way forward for implementation of this strategy is incorporating genetic rescue as a priority in USFWS recovery documentation. In general, our results suggest that although not appropriate for all imperiled species, many more species stand to benefit from a conservation strategy of assisted migration for genetic rescue than those for which it has previously been considered or implemented.

Planning and implementing genetic rescue of an endangered freshwater fish population in a regulated river, where low flow reduces breeding opportunities and may trigger inbreeding depression

“…genetic rescue) without negative fitness effects (outbreeding depression; Frankham et al., 2014). Despite the urgency of conservation interventions and the alluring simplicity and cost‐effectiveness of augmented gene flow, this approach is not yet a mainstream management tool and test cases on how best to perform it remain in demand (Bell et al., 2019; Fitzpatrick et al., 2023).…”

Pitfalls and windfalls of detecting demographic declines using population genetics in long-lived species

“…Modern-day wild populations are experiencing declines and bottleneck events from an unprecedented array of threats, including climate change, habitat fragmentation, and disease (Haddad et al, 2015; McCarty, 2001; Pimm et al, 2014). Population responses to these threats are often species-specific and context-dependent (Debinski & Holt, 2000; Fitzpatrick et al, 2023); for example, populations of species with specialized habitat requirements are more likely to experience sharp demographic declines when their habitat is disturbed than populations of generalist species. Populations that have undergone dramatic declines are at risk of extirpation due to environmental and demographic stochasticity and have a higher risk of experiencing inbreeding depression compared to populations that have been historically small (D. Charlesworth & Willis, 2009; Lande, 1988).…”

Developing demo-genetic models to simulate genetic rescue

“…Many threatened species only persist as small and isolated populations where the combined effects of inbreeding and genetic drift can accumulate deleterious mutations and reduce genetic diversity, together increasing the risk of extinction (Frankham, 2005;Kardos et al, 2021). In addition to the protection and restoration of habitats, the successful conservation of many threatened species will require the deliberate movement of genetically differentiated individuals from one population to another to increase the genetic diversity and tness of target populations -a process known as genetic rescue (Bell et al, 2019;Fitzpatrick et al, 2023;Ralls et al, 2020;Whiteley et al, 2015). However, genetic rescue is often applied to small or declining populations that might be already vulnerable to random uctuations in growth rates (Bell et al, 2019;Fitzpatrick et al, 2023;Melbourne & Hastings, 2008;Ralls et al, 2020;Whiteley et al, 2015).…”