Genetic diversity and relatedness in aquaculture and marina populations of the invasive tunicate Didemnum vexillum in the British Isles

M B Prentice,S R Vye,J E Ironside,P W Shaw,S R Jenkins

doi:10.1007/s10530-021-02615-3

Abstract

Introductions of invasive, non-native species in the marine environment are increasing as human activity within coastal areas rises. Genetic datasets are useful tools to identify source populations, track routes of invasions, and illuminate the role of genetic variation in the establishment and subsequent spread of novel introductions. Here, a microsatellite dataset is used to estimate the genetic diversity and population structure of 7 introduced Didemnum vexillum populations in Britain and Ireland, 4 of which are associated with aquaculture and 3 with marinas. Genetic differentiation observed between these populations indicates human-mediated transport as the main mechanism underlying the population structure of D. vexillum in Britain and Ireland. In addition to elucidating patterns of population structure we found that aquaculture sites showed significantly higher genetic diversity (measured as allelic richness) in comparison to the marina sites. We discuss these findings in relation to the history of each invasion, the complex life history of D. vexillum, and available evidence of the relative invasiveness of these populations. Our results show numerous interesting patterns which highlight further research avenues to elucidate the complex factors underlying the global spread of this successful invader.

Highlights

Examining patterns of genetic diversity in invasive non-native species (INNS) can provide important mechanistic insights into the pathways of invasion and assist future management (Wellband et al 2017)
Of our sample subset sequenced at the COI gene (N = 71), all were identified as D. vexillum with 99–100% identity matches to at least 1 D. vexillum sequence in the NCBI GenBank database
Comparisons of genetic diversity metrics (HO, allelic richness (AR), gene diversity and FIS) for populations grouped by habitat revealed a significant difference in AR between aquaculture and marina habitats, regardless of whether Kent was included (p = 0.025) or excluded (p = 0.025) from the analysis

Summary

Introduction

Examining patterns of genetic diversity in invasive non-native species (INNS) can provide important mechanistic insights into the pathways of invasion and assist future management (Wellband et al 2017). Newly introduced populations of INNS were expected to exhibit low levels of genetic variation due to genetic drift, a result of population bottlenecks and founder events following transport from their native range (Dlugosch and Parker 2008; Crawford and Whitney 2010) Despite these expectations, many successful introductions of INNS have retained high genetic diversity (Lavergne and Molofsky 2007; Crawford and Whitney 2010; Wellband et al 2017), likely the result of high propagule pressure (Simberloff 2009), multiple introduction events (e.g., Kolbe et al 2004; Dlugosch and Parker 2008), and/or stratified dispersal (Darling and FolinoRorem 2009; Tobin and Blackburn 2008; BerthoulySalazar et al 2013). Not all populations of an INNS have equal potential for becoming invasive (Allendorf and Lundquist 2003), and instances of marine INNS with both invasive and non-invasive populations have been reported (e.g., Osman and Whitlatch 2007)

Methods

Results

Conclusion