When does gene flow facilitate evolutionary rescue?

Abstract

9Experimental and theoretical studies have highlighted the impact of gene flow on the prob-10 ability of evolutionary rescue in structured habitats. Mathematical modelling and simulations 11 of evolutionary rescue in spatially or otherwise structured populations showed that interme-12 diate migration rates can often maximize the probability of rescue in gradually or abruptly 13 deteriorating habitats. These theoretical results corroborate the positive effect of gene flow 14 on evolutionary rescue that has been identified in experimental yeast populations. The ob-15 servations that gene flow can facilitate adaptation are in seeming conflict with traditional 16 population genetics results that show that gene flow usually hampers (local) adaptation. The 17 conditions for when gene flow facilitates survival chances of populations rather than reducing 18 them remains a key unresolved theoretical question. We here present a simple analytically 19 tractable model for evolutionary rescue in a two-deme model with gene flow. Our main re-20 sult is a simple condition for when migration facilitates evolutionary rescue, as opposed as 21 no migration. We further investigate the roles of asymmetries in gene flow and / or carrying 22 capacities, and the effects of density regulation and local growth rates on evolutionary rescue.23

A test of island biogeographic theory applied to estimates of gene flow in a Fijian bird is largely consistent with neutral expectations

“…Indeed, there are several cases in Fiji in which small islands have distinct species from the large islands (honeyeaters, Andersen et al., 2014; monarch‐flycatchers, Andersen et al., 2015; fruit‐doves, Cibois et al., 2014). Despite the potential for genetic swamping, this asymmetric gene flow could also facilitate genetic rescue of small island populations in deteriorating conditions (Brown & Kodric‐Brown, 1977; Tomasini & Peischl, 2020).…”

“…Indeed, a recent study of insular avian gene flow found more migrants from a larger to a smaller island (Cooper & Uy, 2017). This higher rate of gene flow suggests increased genetic homogenization between insular populations and could facilitate genetic rescue of smaller populations (Bell, 2017; Brown & Kodric‐Brown, 1977; Tomasini & Peischl, 2020).…”

Demography, genetic diversity and expansion load in the colonizing species Leontodon longirostris (Asteraceae) throughout its native range

“…In general, expansion load increases under conditions that favour genetic surfing, such as small population size, high growth and low migration rate from neighbour populations (Klopfstein et al, 2006; Peischl et al, 2013). Conversely, mechanisms favouring increased migration to range‐front populations throughout the course of range expansion, such as the evolution of higher dispersal rates at the leading edge (“spatial sorting”; Shine et al, 2011), could reduce genetic drift and “rescue” populations from incurring expansion load (Peischl & Gilbert, 2020; Tomasini & Peischl, 2020). In the same way, when range expansions occur along environmental gradients, the expansion is slowed by the need for colonizing populations to adapt to the novel local environment.…”

Evolution of the genetic architecture of local adaptations under genetic rescue is determined by mutational load and polygenicity

“…the adaptive response and recovery from reduced absolute fitness due to environmental change. Also, Tomasini & Peischl (2019) investigated the effect of local adaptations on evolutionary rescue. But whether GR would lead to the loss of unique local adaptations, or whether local adaptations could affect the process of fitness restoration by GR, remain largely unexplored.…”