Gene flow from an adaptively divergent source causes rescue through genetic and demographic factors in two wild populations of Trinidadian guppies

Abstract

Genetic rescue, an increase in population growth owing to the infusion of new alleles, can aid the persistence of small populations. Its use as a management tool is limited by a lack of empirical data geared toward predicting effects of gene flow on local adaptation and demography. Experimental translocations provide an ideal opportunity to monitor the demographic consequences of gene flow. In this study we take advantage of two experimental introductions of Trinidadian guppies to test the effects of gene flow on downstream native populations. We individually marked guppies from the native populations to monitor population dynamics for 3 months before and 26 months after gene flow. We genotyped all individuals caught during the first 17 months at microsatellite loci to classify individuals by their genetic ancestry: native, immigrant, F1 hybrid, F2 hybrid, or backcross. Our study documents a combination of demographic and genetic rescue over multiple generations under fully natural conditions. Within both recipient populations, we found substantial and long‐term increases in population size that could be attributed to high survival and recruitment caused by immigration and gene flow from the introduction sites. Our results suggest that low levels of gene flow, even from a divergent ecotype, can provide a substantial demographic boost to small populations, which may allow them to withstand environmental stochasticity.

The power of evolutionary rescue is constrained by genetic load

“…This study demonstrates clearly that evolution can rapidly alter ecological dynamics, but also highlights that evolution is a double‐edged sword—with both beneficial and deleterious processes powerfully shaping population size and performance. To manage the deleterious side, ongoing migration between otherwise isolated populations may be crucial for long term population health (Frankham, ), and the pros and cons of facilitating such migration should be considered carefully, especially if migrants are not adapted to the habitat (Fitzpatrick et al., ).…”

An experimental test of alternative population augmentation scenarios

“…Similarly, Fitzpatrick et al. () found evidence for both demographic and genetic rescue from adaptively divergent immigrants in a field experiment but lacked controls to fully separate the 2 types. We expanded on these studies in a long‐term mesocosm experiment that simulated a broad range of augmentation scenarios.…”

Experimental test of genetic rescue in isolated populations of brook trout

“…Frameworks for predicting outbreeding depression following GR‐motivated translocations have been proposed and are based on the outcomes of previous GR studies (Frankham, ; Frankham et al., ; Weeks et al., ). However, applications of GR to date have lacked controls for environmental conditions in wild populations and have otherwise not been performed in an experimental manner (but see Fitzpatrick et al., ). Additional studies with replicates and controls that monitor the multigenerational consequences of GR would help practitioners understand the utility of GR (Edmands, ; Tallmon et al., ; Whiteley et al., ).…”