Effects of admixture in native and invasive populations of Lythrum salicaria

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

doi:10.1007/s10530-018-1707-2

Abstract

Intraspecific hybridization between diverged populations can enhance fitness via various genetic mechanisms. The benefits of such admixture have been proposed to be particularly relevant in biological invasions, when invasive populations originating from different source populations are found sympatrically. However, it remains poorly understood if admixture is an important contributor to plant invasive success and how admixture effects compare between invasive and native ranges. Here, we used experimental crosses in Lythrum salicaria, a species with well-established history of multiple introductions to Eastern North America, to quantify and compare admixture effects in native European and invasive North American populations. We observed heterosis in between-population crosses both in native and invasive ranges. However, invasive-range heterosis was restricted to crosses between two different Eastern and Western invasion fronts, whereas heterosis was absent in geographically distant crosses within a single large invasion front. Our results suggest that multiple introductions have led to already-admixed invasion fronts, such that experimental crosses do not further increase performance, but that contact between different invasion fronts further enhances fitness after admixture. Thus, intra-continental movement of invasive plants in their introduced range has the potential to boost invasiveness even in well-established and successfully spreading invasive species.

Highlights

Biological invasions are a global problem and we still do not know why some introduced plants become invasive whereas others do not (Kolar and Lodge2001)
Admixture between diverged populations can alleviate the negative effects of inbreeding depression by masking the effects of deleterious mutations that were fixed in individual populations, contributing to heterosis (Xiao et al 1995)
These analyses confirmed stronger responses to the experimental soil treatments in invasive populations: plants from both ranges showed similar total plant biomass under drought conditions, but invasive plants benefitted much more than native plants did from optimal growing conditions (Fig. 2)

Summary

Introduction

Biological invasions are a global problem and we still do not know why some introduced plants become invasive whereas others do not (Kolar and Lodge2001). Admixture has potential enhancing effects for population success, for instance by increasing genetic variation, creating novel genotypes and masking effects of fixed deleterious recessive mutations leading to heterosis (Rieseberg et al 2003; Seehausen 2004; Verhoeven et al 2011; Rius and Darling 2014). Inbreeding depression is in part caused by accumulation and expression of deleterious recessive mutations and leads to plant fitness decrease (Charlesworth and Willis 2009). Admixture between diverged populations can alleviate the negative effects of inbreeding depression by masking the effects of deleterious mutations that were fixed in individual populations, contributing to heterosis (Xiao et al 1995). An alternative effect of admixture, observed in crosses between very distant populations, can be outbreeding depression, due to dilution of local adaptation and disruption of co-adapted gene complexes that have diverged over evolutionary time (Waser and Price 1989; Verhoeven et al 2011)

Methods

Results

Conclusion