When does gene flow facilitate evolutionary rescue?

Abstract

Experimental and theoretical studies have highlighted the impact of gene flow on the probability of evolutionary rescue in structured habitats. Mathematical modeling and simulations of evolutionary rescue in spatially or otherwise structured populations showed that intermediate migration rates can often maximize the probability of rescue in gradually or abruptly deteriorating habitats. These theoretical results corroborate the positive effect of gene flow on evolutionary rescue that has been identified in experimental yeast populations. The observations that gene flow can facilitate adaptation are in seeming conflict with traditional population genetics results that show that gene flow usually hampers (local) adaptation. Identifying conditions for when gene flow facilitates survival chances of populations rather than reducing them remains a key unresolved theoretical question. We here present a simple analytically tractable model for evolutionary rescue in a two‐deme model with gene flow. Our main result is a simple condition for when migration facilitates evolutionary rescue, as opposed as no migration. We further investigate the roles of asymmetries in gene flow and/or carrying capacities, and the effects of density regulation and local growth rates on evolutionary rescue.

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).…”

The first steps toward a global pandemic: Reconstructing the demographic history of parasite host switches in its native range

“…Post host-switch speciation can occur in the presence of gene flow, if specialization is adaptively favored and selection acts on many genomic regions (26,27). By promoting genomic heterogeneity and introducing beneficial mutations (28), gene flow can ameliorate lost diversity due to selection or inbreeding (29,30), both of which would impact host-switched Varroa populations. Alternatively, de novo mutation rates could contribute to population genetic variation, but our direct estimation of mutation rate did not show exceptionally high mutation rates (>8 × 10-10 per bp per generation), compared to other arthropods (31).…”

The effect of habitat choice on evolutionary rescue in subdivided populations

“…It equals 1 before the first environmental change takes place ( t < 0), and decreases by 1/ M after each environmental deterioration event, until it eventually hits 0, when all patches have undergone the environmental change. This setting corresponds to the one analyzed by Uecker et al (2014), and more recently by Tomasini and Peischl (2020) in the special case of just two patches. The maximum numbers of individuals that can live in a patch of a given habitat type, i.e.…”

“…In fragmented environments, habitat deterioration is not necessarily synchronized across patches: there can be a transient spatially heterogeneous environment consisting of a mosaic of old- and of degraded-habitat patches, until eventually the whole environment has deteriorated. If individuals that populate different patches are able to move between those, the effect of dispersal on evolutionary rescue needs to be taken into account (Uecker et al, 2014; Tomasini and Peischl, 2020). The intensity of dispersal among patches tunes how abruptly environmental change is experienced.…”