Genetics - Theses
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ItemTaxonomy, biogeography and population genetic structure of the southern Australian intertidal barnacle fauna( 2008)Barnacles are a unique organism in that they have both a planktonic larval stage followed by an irreversibly sessile adult stage. Widely distributed throughout the world, they have been studied by many prominent scientists, with much of the work undertaken focusing on ecology and taxonomy. However, most of the taxonomic work had been undertaken based on morphological characteristics, with phylogenetic studies only undertaken more recently. Many of these studies have failed to include Australian species, most of which are endemic to the continent. Newly produced and Genbank records of mitochondrial DNA sequence were used to confirm the taxonomic status of Australian species. The status of most species was confirmed, with a few notable exceptions. In particular, data analysis suggested the existence of cryptic species within Elminius modestus. In addition, the divergence between these three species and Elminius kingii was great enough to warrant the introduction of a new genus, Austrominius. This genus now contains three species, A. modestus, A. adelaidae and A. covertus. The two-phase life history of barnacles also made them the ideal organism for the study of the dynamics of the southern Australian marine environment. Three marine biogeographic provinces are recognised in the region, with both historical and contemporary ecological factors predicted to be responsible. In order to investigate the biogeography and hydrography of the region, both mitochondrial sequence data and microsatellite data were used to investigate the phylogeography and population genetic structure of Catomerus polymerus. The mitochondrial data showed a deep phylogeographical split, dividing the species into eastern and western lineages. Dating this split using a molecular clock indicated that the repeated emergence of the Bassian Isthmus during glacial periods was most likely responsible, having provided a barrier to gene flow between the two lineages. However, subsequent gene flow during interglacial periods prevented the lineages from diverging into two separate species. Analysis of the microsatellite data indicated that the species comprised four groups or subregions; one in South Australia, one in New South Wales and eastern Victoria, one in central Victoria, and one in western Victoria and Tasmania. Further analysis of the data indicated that these subregions could be due to the influence of the major ocean currents (Leeuwin, East Australian and Zeehan currents), and the reduction in gene flow across two biogeographic breaks (Ninety Mile Beach, The Coorong). This correlates reasonably well with the previously recognised biogeographic provinces. Finally, mitochondrial data were used to examine the phylogeography of two species of barnacle, Chthamalus antennatus and Chamaesipho tasmanica. In contrast with the study of C. polymerus, these species did not show any significant structure across their entire distribution. There are a number of possible explanations for this, with most relating to the longevity and durability of the larvae. However, it is also possible that these species could colonise southern Tasmania during the glacial periods, thereby being unaffected by the present of the Bassian Isthmus, and maintaining a single panmictic population.