Landscape genetics of the foundational salt marsh plant species black needlerush (Juncus roemerianus Scheele) across the northeastern Gulf of Mexico

Hayley R Tumas,Mark Woodrey,Campbell Nairn,Richard Chandler,Brian M Shamblin,Nathan P Nibbelink

doi:10.1007/s10980-018-0687-z

Hayley R Tumas, Mark Woodrey + Show 4 more

Open Access

https://doi.org/10.1007/s10980-018-0687-z

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Abstract

ContextCommon species important for ecosystem restoration stand to lose as much genetic diversity from anthropogenic habitat fragmentation and climate change as rare species, but are rarely studied. Salt marshes, valuable ecosystems in widespread decline due to human development, are dominated by the foundational plant species black needlerush (Juncus roemerianus Scheele) in the northeastern Gulf of Mexico.ObjectivesWe assessed genetic patterns in J. roemerianus by measuring genetic and genotypic diversity, and characterizing population structure. We examined population connectivity by delineating possible dispersal corridors, and identified landscape factors influencing population connectivity.MethodsA panel of 19 microsatellite markers was used to genotype 576 samples from ten sites across the northeastern Gulf of Mexico from the Grand Bay National Estuarine Research Reserve (NERR) to the Apalachicola NERR. Genetic distances (FST and Dch) were used in a least cost transect analysis (LCTA) within a hierarchical model selection framework.ResultsGenetic and genotypic diversity results were higher than expected based on life history literature, and samples structured into two large, admixed genetic clusters across the study area, indicating sexual reproduction may not be as rare as predicted in this clonal macrophyte. Digitized coastal transects buffered by 500 m may represent possible dispersal corridors, and developed land may significantly impede population connectivity in J. roemerianus.ConclusionsResults have important implications for coastal restoration and management that seek to preserve adaptive potential by sustaining natural levels of genetic diversity and conserving population connectivity. Our methodology could be applied to other common, widespread and understudied species.

Highlights

The majority of landscape genetic studies to date have focused on rare, threatened, or endangered species that either naturally exist in small, fragmented populations or have done so for an evolutionarily significant period of time (Storfer et al 2010)
Genetic and genotypic diversity results were higher than expected based on life history literature, and samples structured into two large, admixed genetic clusters across the study area, indicating sexual reproduction may not be as rare as predicted in this clonal macrophyte
A total of 576 samples were genotyped across sites, and 310 samples represented unique genotypes that were used in all subsequent genetic diversity analyses

Summary

Introduction

The majority of landscape genetic studies to date have focused on rare, threatened, or endangered species that either naturally exist in small, fragmented populations or have done so for an evolutionarily significant period of time (Storfer et al 2010). Genetic diversity in common, dominant plant species can have important and cascading effects on species diversity and processes throughout the ecosystem (Whitham et al 2003; Vellend and Geber 2005). In monotypic landscapes, genetic diversity of the foundational plant species is analogous to the role of species diversity in maintaining ecological health and ecosystem processes (Reusch and Hughes 2006; Hughes et al 2008). Such monotypic landscapes are typical in coastal ecosystems that tend to be dominated by single-species macrophyte communities, such as eelgrass (Zostera marina L.) in seagrass beds (Reusch and Hughes 2006). Positive effects of genetic diversity are especially important following disturbances, such as transplantation stress during restoration (Reynolds et al 2012) or a warming event (Reusch et al 2005; Ehlers et al 2008)

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