Genetic signatures of Bassian glacial refugia and contemporary connectivity in a marine foundation species

Abstract

Aim To examine the population genetic structure in Posidonia australis meadows, a marine foundation species capable of long distance dispersal (LDD), and the role of historical versus contemporary processes in shaping post Last Glacial Maximum (LGM) re‐colonization. Location Southeastern Australia including the Bass Strait Islands. Methods We generated multilocus genotypes and assessed spatial patterns of genetic diversity. Relationships among meadows were assessed in terms of historical sea level changes, oceanic boundary currents and contemporary seed dispersal based on a hydrodynamic model. Results There was strong regional spatial genetic structuring among P. australis meadows in south‐eastern Australia, which was congruent with three recognized marine biogeographical provinces [Peronian (eastern), Flindersian (western and southern), and Maugean (south‐eastern)]. The genetic data suggest Maugean meadows persisted in isolation during the LGM, with evidence for admixture and contemporary gene flow. Simulated dispersal events identified high rates of local and regional demographic connectivity, with evidence for occasional LDD events. Main conclusions The strong regional differentiation is consistent with long‐term barriers to dispersal persisting in the marine environment through many sea level fluctuations. Bass Strait Island meadows all have strong signals of genetic admixture. A weak but significant isolation by distance relationship is consistent with a historical signal and contemporary seed dispersal mostly within the Bass Strait.

Life‐history predicts past and present population connectivity in two sympatric sea stars

“…Meridiastra calcar also displayed relatively high levels of overall and regional genetic structure, especially compared to other asterinid species with planktonic development (Keever et al, 2009;Puritz & Toonen, 2011), but with little genetic differentiation among sites within regions, especially within NSW. Coalescent estimates of withinregion migration line up with recent models of nearshore offshore oceanographic currents (Teske, Sandoval-Castillo, van Sebille, Waters, & Beheregaray, 2015, 2016, such as the highly unbalanced gene flow seen from eastern to western Tasmania and the high rates of exchange between southern and central NSW. Across-region estimates of gene flow were generally much lower and corresponded better with offshore current patterns, suggesting that M. calcar larvae do, at times, Even with varying levels of genetic structure, M. calcar has unusually high levels of genetic diversity, especially for nuclear loci.…”

“…When sea levels fell to lower than 50 m below contemporary levels, a land bridge formed between Victoria and Tasmania in the present day area of Bass Strait. The emergence and subsequent submergence of the Tasmanian land bridge would have cut off circulation and gene flow between the Southern Ocean and the Tasman Sea, providing opportunities for reproductive isolation in refugia (Sinclair et al, 2016), differentiation via diversifying selection, and lineage extinctions . Several other species show strong genetic breaks or phylogenetic structure at this point (Ayre et al, 2009;Dawson, 2005;Sherman et al, 2008;Waters, 2008;Waters & Roy, 2003;York, Blacket, & Appleton, 2008 with peaks in relative glacial periods (Billups, 2004).…”

The First Isolation and Characterisation of the Protist Labyrinthula sp. in Southeastern Australia

“…For instance, it is known that marine flora and fauna in southeast Australia display strong regional genetic variations that suggest a lasting physical barrier to dispersal was present historically, and through several sea level change periods (Sinclair et al. ). These barriers resulted in what are known to be three biogeographical provinces (Peronian to the east, Flindersian to the south and west, and Maugean to the southeast) with clearly observed genetic variations that persist in both marine flora (Sinclair et al.…”

“…These barriers resulted in what are known to be three biogeographical provinces (Peronian to the east, Flindersian to the south and west, and Maugean to the southeast) with clearly observed genetic variations that persist in both marine flora (Sinclair et al. ) and fauna (Charlton‐Robb et al. ; DiBattista et al.…”

“…Alternatively, the distribution of the different Labyrinthula isolates may have been influenced by one or more as yet undetermined factors, such as physical or hydrological barriers, or shift in species abundance due to annual climatic variations. For instance, it is known that marine flora and fauna in southeast Australia display strong regional genetic variations that suggest a lasting physical barrier to dispersal was present historically, and through several sea level change periods (Sinclair et al 2016). These barriers resulted in what are known to be three biogeographical provinces (Peronian to the east, Flindersian to the south and west, and Maugean to the southeast) with clearly observed genetic variations that persist in both marine flora (Sinclair et al 2016) and fauna (Charlton-Robb et al 2015;DiBattista et al 2014;Miller et al 2016) of southeast Australia.…”