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

Sarah W Fitzpatrick,Cameron K Ghalambor,Corey A Handelsman,Lisa M Angeloni,Emily D Broder,David N Reznick,W Chris Funk,Jill C Gerberich,Julian Torres‐Dowdall,Larissa L Bailey,Andrés López‐Sepulcre

doi:10.1111/eva.12356

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.

Highlights

The fate of wild populations exposed to environmental variation is determined by an interplay between genetic variation and demography (Lande 1988)
Gene flow caused by assisted migration would result in genetic rescue, defined as an increase in population growth owing to the infusion of new alleles by more than the amount attributed to the demographic input alone
Taylor started with slightly lower levels of heterozygosity and subsequently experienced the most dramatic increase in genetic diversity over time, consistent with the larger number of confirmed marked immigrants detected in this stream

Summary

Introduction

The fate of wild populations exposed to environmental variation is determined by an interplay between genetic variation and demography (Lande 1988). Small populations are vulnerable to the loss of genetic variation due to drift and inbreeding, which in turn may cause population decline and an inability to adapt to changing environments (Keller and Waller 2002; Spielman et al 2004). Given that de novo mutations may arise too slowly to benefit genetically imperiled populations (Lande 1980), one way to reconnect recently fragmented small populations, or infuse genetic variation into inbred populations, is through managed movement of individuals or gametes (Weeks et al 2011; Aitken and Whitlock 2013; Carlson et al 2014). Gene flow caused by assisted migration would result in genetic rescue, defined as an increase in population growth owing to the infusion of new alleles by more than the amount attributed to the demographic input alone.

Methods

Results

Discussion

Conclusion