Low genetic diversity contrasts with high phenotypic variability in heptaploid Spartina densiflora populations invading the Pacific coast of North America.

Jesús M Castillo,Stéphane Dréano,Hélène Rousseau,Jean Keller,Dominique Vallet,Brenda J Grewell,Armel Salmon,Oscar Lima,Enrique Figueroa,Malika Aïnouche,Blanca Gallego‐Tévar

doi:10.1002/ece3.4063

Abstract

Species can respond to environmental pressures through genetic and epigenetic changes and through phenotypic plasticity, but few studies have evaluated the relationships between genetic differentiation and phenotypic plasticity of plant species along changing environmental conditions throughout wide latitudinal ranges. We studied inter‐ and intrapopulation genetic diversity (using simple sequence repeats and chloroplast DNA sequencing) and inter‐ and intrapopulation phenotypic variability of 33 plant traits (using field and common‐garden measurements) for five populations of the invasive cordgrass Spartina densiflora Brongn. along the Pacific coast of North America from San Francisco Bay to Vancouver Island. Studied populations showed very low genetic diversity, high levels of phenotypic variability when growing in contrasted environments and high intrapopulation phenotypic variability for many plant traits. This intrapopulation phenotypic variability was especially high, irrespective of environmental conditions, for those traits showing also high phenotypic plasticity. Within‐population variation represented 84% of the total genetic variation coinciding with certain individual plants keeping consistent responses for three plant traits (chlorophyll b and carotenoid contents, and dead shoot biomass) in the field and in common‐garden conditions. These populations have most likely undergone genetic bottleneck since their introduction from South America; multiple introductions are unknown but possible as the population from Vancouver Island was the most recent and one of the most genetically diverse. S. densiflora appears as a species that would not be very affected itself by climate change and sea‐level rise as it can disperse, establish, and acclimate to contrasted environments along wide latitudinal ranges.

Highlights

Invasive plant species can respond to environmental pressures in novel environments through genetic change at individual level, gene expression regulation and epigenetic processes (Richards, 2012), and phenotypic plasticity in response to different environmental conditions (Fuller et al, 2010; Miner, Sultan, Morgan, Padilla, & Relyea, 2005; Stomp et al, 2008)
Our results show that the populations of Spartina densiflora gradually invading the Pacific coast of North America along 12° of latitude from the late nineteenth century when it was first introduced to Humboldt Bay, until recently with the discovery of a new invasion in 2005 at Vancouver Island, are genetically very similar according to the chloroplast DNA sequences and the nuclear microsatellite loci investigated
Our results agree with those of Ayres et al (2008) who recorded low genetic diversity among S. densiflora plants in San Francisco Bay and Humboldt Bay, which is consistent with the origin of San Francisco Bay population as transplants introduced from Humboldt Bay (Faber, 2000)

Summary

| INTRODUCTION

Invasive plant species can respond to environmental pressures in novel environments through genetic change at individual level (local adaptation), gene expression regulation and epigenetic processes (Richards, 2012), and phenotypic plasticity in response to different environmental conditions (Fuller et al, 2010; Miner, Sultan, Morgan, Padilla, & Relyea, 2005; Stomp et al, 2008). Polyploidization, and especially hybridization, have been related to high levels of genetic diversity, epigenetic variation, and phenotypic plasticity (Braeutigam et al, 2013; Meyerson et al, 2016) and they are considered important in shaping the geographic range of plant species (Weiss-Schneeweiss, Emadzade, Jang, & Schneeweiss, 2013). In this context, few studies have evaluated the relationships between genetic differentiation and phenotypic plasticity of invasive plant species to novel, changing environments along wide latitudinal ranges. We hypothesized that (i) S. densiflora would show low genetic diversity and high phenotypic plasticity in response to contrasted environments and that they would be independent from each other, based on previous observations (Castillo et al, 2014, 2016; Grewell et al, 2016); (ii) due to the polyploid and hybrid nature of S. densiflora, at least certain foliar traits would show both high plasticity and high intrapopulation variability, as leaf (the organ of photosynthesis and transpiration) is highly sensitive to environmental conditions (Stephenson, Oliver, Burgos, & Gbur, 2006); and (iii) genetically based and environmental-based interpopulation differences in response to a changing environment would increase with geographic distance

| METHODS

GH MR HB SF

| DISCUSSION

Findings

CONFLICT OF INTEREST