Salinity and hydrological barriers have little influence on genetic structure of the mosquitofish in a coastal landscape shaped by climate change

Binod Regmi,Whitney J B Anthonysamy,Michael E Douglas,Paul L Leberg,Marlis R Douglas

doi:10.1007/s10750-016-2786-7

Abstract

Gradients in salinity and vegetation have been dramatically altered along shoreline of the northern Gulf of Mexico by both natural (i.e., erosion, fluctuating sea levels) and anthropogenic (i.e., dredging, habitat restoration) drivers. We gauged the impacts of salinity gradients and open water barriers on the genetic structure of a common marsh resident, western mosquitofish (Gambusia affinis) by sampling 15 populations along 440 km of Texas/Louisiana coast. We characterized 602 individuals (~40/population) using seven microsatellite loci and our results reflected significant isolation by distance (IBD) among populations, but without the hypothesized genetic substructure from local adaptation. Large tracts of open water, thought to inhibit mosquitofish movement, were apparently not significant deterrents of dispersal. There was no evidence of a significant relationship between salinity gradients and genetic divergence. Although mosquitofish dispersal is sufficiently limited to result in a strong pattern of IBD, it is high enough to maintain the connectedness of populations. Our results suggest that limited gene flow, combined with large effective size, creates conditions suitable to adaptation to local environment, suggesting that mosquitofish and other marsh residents with similar life histories will be able to adapt to changes occurring in coastal environments.

Highlights

Global climate change is a challenge for ecosystem conservation as it reshuffles environmental conditions and biodiversity gradients as a result of in situ adaptation, distribution shifts, and extirpation (Bellard et al, 2012; Parmesan et al, 2013)
We identified the marshlands separated by these rivers as east Texas (ETX), western Louisiana (WLA), central Louisiana (CLA), and eastern Louisiana (ELA) (Fig. 1; Table 1)
We found no significant correlations between salinity and either He (r = 0.33, P [ 0.20) or allelic richness (Ar) (r = 0.30, P [ 0.25)

Summary

Introduction

Global climate change is a challenge for ecosystem conservation as it reshuffles environmental conditions and biodiversity gradients as a result of in situ adaptation, distribution shifts, and extirpation (Bellard et al, 2012; Parmesan et al, 2013). As one of most pressing aspects of climate change, sea level rise has manifest consequences for ecological systems (Bordbar et al, 2015). Estimates of absolute sea level rise do not reflect local conditions that can alter the consequences for coastal regions (Bordbar et al, 2015). The coastal wetlands of southeastern Louisiana are recognized as highly susceptible to even small changes in absolute sea level rise (Day et al, 2000). As relative sea levels increase, saltwater intrusions proliferate, and marshes become fragmented by open water with elevated salinities (Boesch et al, 1994; Day et al, 2000)

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