Costs and benefits of admixture between foreign genotypes and local populations in the field.

Jun Shi,Katja Tielbörger,Koen J F Verhoeven,Mirka Macel,Jasmin Joshi

doi:10.1002/ece3.3946

Abstract

Admixture is the hybridization between populations within one species. It can increase plant fitness and population viability by alleviating inbreeding depression and increasing genetic diversity. However, populations are often adapted to their local environments and admixture with distant populations could break down local adaptation by diluting the locally adapted genomes. Thus, admixed genotypes might be selected against and be outcompeted by locally adapted genotypes in the local environments. To investigate the costs and benefits of admixture, we compared the performance of admixed and within‐population F1 and F2 generations of the European plant Lythrum salicaria in a reciprocal transplant experiment at three European field sites over a 2‐year period. Despite strong differences between site and plant populations for most of the measured traits, including herbivory, we found limited evidence for local adaptation. The effects of admixture depended on experimental site and plant population, and were positive for some traits. Plant growth and fruit production of some populations increased in admixed offspring and this was strongest with larger parental distances. These effects were only detected in two of our three sites. Our results show that, in the absence of local adaptation, admixture may boost plant performance, and that this is particularly apparent in stressful environments. We suggest that admixture between foreign and local genotypes can potentially be considered in nature conservation to restore populations and/or increase population viability, especially in small inbred or maladapted populations.

Highlights

Population admixture is a genetic process of hybridization between previously isolated populations of one species (Ellstrand & Schierenbeck, 2000)
In the absence of local adaptation, admixture may boost plant performance, and that this is apparent in stressful environments
Small populations can have lower evolutionary potential to adapt to their environments relative to larger populations if genetic variation is low (Hill, 1982; Weber & Diggins, 1990)

Summary

| INTRODUCTION

Population admixture (hereafter: admixture) is a genetic process of hybridization between previously isolated populations of one species (Ellstrand & Schierenbeck, 2000). Selection would put constraints on the dilution of locally adapted gene pools through substantial fitness loss of the admixed offspring relative to either parent (Angert, Bradshaw, & Schemske, 2008) This local adaptation might contribute to isolation of populations by selection against nonlocal genotypes in a population reducing admixture and may enhance inbreeding (Nosil, Vines, & Funk, 2005; Verhoeven et al, 2011). The intrinsic genetic benefits of admixture through heterosis and/or from increased adaptive potential in admixed progenies are intertwined with the environmentally dependent costs of admixture from the dilution of locally adapted genomes in the local habitat and hybrid breakdown in later generations (Keller & Taylor, 2010; van Kleunen, Rockle, & Stift, 2015; Lavergne & Molofsky, 2007; Rius & Darling, 2014). We measured plant growth and reproduction, and herbivory in order to answer the following questions: (1) Is there local adaptation in native L. salicaria? If L. salicaria shows local adaptation, (2) does admixture negatively affect plant performance of locally adapted populations in their local environments (dilution of local adaptation) but not in other environments? And if there is no local adaptation, (3a) does admixture enhance plant performance (heterosis)? Or (3b) does admixture decrease plant performance (hybrid breakdown)?

| METHODS

Findings

| DISCUSSION