DOI: 10.5061/dryad.kwh70rz4p
title: Historic and contemporary biogeographic perspectives on range-wide spatial genetic structure in a widespread seagrass

description: This raw data set contains multilocus genotypes for 1,312 individual
 samples from 44 locations. Aim: Historical and contemporary
 processes drive spatial patterns of genetic diversity. These include
 climate-driven range shifts and gene flow mediated by biogeographical
 influences on dispersal. Assessments that integrate these drivers are
 uncommon, but critical for testing biogeographic hypotheses. Here, we
 characterise intraspecific genetic diversity and its spatial structure
 across the entire distribution of a temperate seagrass to test marine
 biogeographic concepts for southern Australia.
 Location: Temperate Australian coastal waters
 Methods: Predictive modelling was used to contrast the
 current Posidonia australis distribution to its
 historical distribution during the Last Glacial Maximum (LGM).
 Spatial genetic structure was estimated for 44
 sampled meadows from across the geographical range of the species
 using nine microsatellite loci. 
 Results: Historical and contemporary distributions were similar,
 with the exception of the Bass Strait. Genetic clustering was consistent
 with the three currently recognised biogeographic provinces and largely
 consistent with the finer-scale IMCRA bioregions. Discrepancies
 were found within the Flindersian province and southwest IMCRA bioregion,
 while two regions of admixture coincided with transitional bioregions.
 Clonal diversity was highly variable, but positively associated with
 latitude. Genetic differentiation among meadows was significantly
 associated with oceanographic distance. Main conclusions: Our
 approach suggests how shared seascape drivers have influenced the capacity
 of P. australis to effectively track sea level changes associated
 with natural climate cycles over millennia, and in particular,
 the recolonisation of meadows across the Continental Shelf following the
 LGM. Genetic structure associated with IMCRA bioregions reflects
 the presence of stable biogeographic barriers, such as oceanic upwellings.
 This study highlights the importance of biogeography to infer the role of
 historical drivers in shaping extant diversity and
 structure.  
description: Ribbon weed (<em>Posidonia australis </em>Hook.f.), a
 widespread temperate seagrass, was sampled from across its distribution.
 This includes ~5000 km of the west, south, and east Australian
 coastlines. Field methods
 and laboratory methods have been described in earlier
 publications: Sinclair EA, Krauss SL,
 Anthony JM, Hovey RK, Kendrick GA (2014) The interaction of environment
 and genetic diversity within meadows of the seagrass <em>Posidonia
 australis</em> (Posidoniaceae). <em>Marine Ecology Progress
 Series</em> 506: 87-98. https://doi.org/10.3354/meps10812 Sinclair EA, Anthony J, Coupland GT, Waycott M, Barrett MD, Barrett RL, Cambridge ML, Wallace MJ, Dixon KW, Krauss SL, Kendrick GA (2009) Characterisation of polymorphic microsatellite markers in the widespread Australian seagrass, <em>Posidonia australis</em> Hook. f. (Posidoniaceae), with cross-amplification in the sympatric <em>P. sinuosa</em>. <em>Conservation Genetics Resources</em> 1: 273-276. https://doi.org/10.1007/s12686-009-9067-y