Isolation, marine transgression and translocation of the bare-nosed wombat (Vombatus ursinus).

Alynn Martin,Sam Banks,Christopher P Burridge,Tamieka A Fraser,Scott Carver,Adam Polkinghorne,Kirstin Proft

doi:10.1111/eva.12785

Abstract

Island populations can represent genetically distinct and evolutionarily important lineages relative to mainland conspecifics. However, phenotypic divergence of island populations does not necessarily reflect genetic divergence, particularly for lineages inhabiting islands periodically connected during Pleistocene low sea stands. Marine barriers may also not be solely responsible for any divergence that is observed. Here, we investigated genetic divergence among and within the three phenotypically distinct subspecies of bare‐nosed wombats (Vombatus ursinus) in south‐east Australia that are presently—but were not historically—isolated by marine barriers. Using genome‐wide single nucleotide polymorphisms, we identified three genetically distinct groups (mainland Australia, Bass Strait island, and Tasmania) corresponding to the recognized subspecies. However, isolation by distance was observed in the Tasmanian population, indicating additional constraints on gene flow can contribute to divergence in the absence of marine barriers, and may also explain genetic structuring among fragmented mainland populations. We additionally confirm origins and quantify the genetic divergence of an island population 46 years after the introduction of 21 individuals from the Vulnerable Bass Strait subspecies. In the light of our findings, we make recommendations for the maintenance of genetic variation and fitness across the species range.

Highlights

Islands are frequently the location of populations that can be pheno‐ typically distinguished from those elsewhere (e.g., Harmon & Gibson, 2006; Schlotfeldt & Kleindorfer, 2006), and contribute to global bio‐ diversity through the effects of isolation on genetic divergence and speciation (Wilson et al, 2008)
Phenotypic distinction of lineages on continental shelf islands may be problematic to interpret if the peripheral geographic setting of these islands con‐ fers environmental differences (Mullen, Vignieri, Gore, & Hoekstra, 2009), in addition to potential influences of island size alone
This is a question of broad conservation interest, as continental shelf islands are common and host high biodiversity, most notably in South‐East Asia, and Europe (e.g., England and many islands of the Mediterranean), North America (e.g., Newfoundland), South America (e.g., Falkland Islands) and Australia (e.g., Tasmania; Burridge, 2012)

Summary

| INTRODUCTION

Islands are frequently the location of populations that can be pheno‐ typically distinguished from those elsewhere (e.g., Harmon & Gibson, 2006; Schlotfeldt & Kleindorfer, 2006), and contribute to global bio‐ diversity through the effects of isolation on genetic divergence and speciation (Wilson et al, 2008). Historical sea‐level rise associated with the end of the last gla‐ cial maximum (LGM) potentially played a significant role in the bio‐ geography of south‐eastern Australia This event isolated Tasmania and an array of islands from continental Australia during the flood‐ ing of Bass Strait, protecting some populations from causes of ex‐ tinction that are present on the mainland (e.g., invasive predators; Kinnear, Sumner, & Onus, 2002), and shaping the population genetic structure of others (Firestone, Elphinstone, Sherwin, & Houlden, 1999; Toon, Mather, Baker, Durrant, & Hughes, 2007). Discovery of genetically distinct populations across the wombat range will assist in determining spatial units that warrant independent management and support ongoing conserva‐ tion planning for this Australian marsupial

| METHODS

| DISCUSSION

Findings

CONFLICT OF INTEREST