Glacial refugia of southern Australian echinoderms: past responses to climate change in the temperate marine environment

Abstract

© 2013 Dr. Kate Marilyn NaughtonDistributions of organisms are known to vary in response to glacial and interglacial climate cycling. While this process has been widely studied in terrestrial and aquatic environments, comparatively few have focused on marine invertebrates. The bulk of studies focus specifically on intertidal organisms, fish species and Northern Hemisphere coastlines, with fewer still addressing the dynamics of subtidal organisms and the Australian coastline. In this thesis, I address the question of population responses to glacial dynamics in a number of endemic southern Australian shallow-water echinoderm species, with the goal of expanding our understanding of the phylogeography of the region. The study region extends from Western Australia to northern New South Wales and includes Tasmania. The study is overall a comparative one, utilising multiple species and multiple genetic markers in order to track population dynamics over various time scales. Samples of all target species are initially screened for the presence of cryptic species and deep mitochondrial lineages, with the result that a high number of additional species are discovered and the initial sample size of target species is reduced. As intermittent barriers to gene flow are present on the southern coast of Australia, and as these vary in response to climate cycling, each species complex is investigated in terms of the timing of lineage production, examining the relationship of younger, allopatric lineages to older, sympatric lineages in the presence of intermittent barriers to gene flow. A large-scale comparative phylogeography of the southern coast is undertaken, examining intraspecific variation and congruent genetic breaks across ten species. A moderate level of phylogeographic congruence is apparent across these species and in this region. There was high support for all proposed biogeographic breaks. Finally, more recent dynamics are investigated by examining the distribution of intraspecific diversity and population expansion since the Last Glacial Maximum. These results suggest that, while expansions on the southern and western coasts tend to pre-date the Last Glacial Maximum, the south-eastern region of Australia is quite active in regard to post-LGM expansion