Date of Award

2014

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Natural Sciences

Faculty

Health, Engineering and Science

First Advisor

Dr Annette Koenders

Second Advisor

Professor Pierre Horwitz

Abstract

The overall aim of this study was to explore the systematics and biogeographic patterns of the freshwater crayfish genus Engaewa Riek, a strongly burrowing freshwater crayfish restricted to the coastal corner of south-western Australia (SWA). The genus Engaewa is a Gondwanan relict with great potential as a marker of historical processes, due to its high habitat specificity and low dispersal ability. This study comprises an extensive taxonomic and phylogenetic revision of the genus Engaewa (using both molecular and morphological data), a detailed study of its distribution and uses the knowledge gained to explore biogeographic patterns in the biodiversity hotspot of SWA.

The molecular analyses undertaken in this project support the monophyly of the genus Engaewa. They also, combined with a re-evaluation of morphological characters, support the recognition of (at least) two new species in addition to the five currently described species. Diagnostic morphological characters for the current species and two additional previously undescribed species, along with an updated taxonomic key, are presented. Engaewa species possess a genetic structure that is highly unusual and is characterised by particularly low intra-population diversity, and very high interpopulation diversity on a scale seemingly not observed in freshwater crayfish before. Based on the updated species designations, the ecology, distribution and conservation status of each species level lineage are also reviewed in this study.

A biogeographic interpretation of the phylogenetic trees and population analyses/summary statistics from the genetic data is consistent with a scenario wherein lineages within this genus have undergone cyclical periods of expansion followed by contraction into refugia, in response to repeated changes in both climate and sea-level. This cyclical process concurs with the Taxon Pulse Hypothesis and has driven lineage diversification, via vicariant speciation, causing rapid bursts of speciation within the genus. This study has identified a number of refugia (from periods of inhospitable climate) centered on locations within the Cape-to-Cape region of SWA (i.e. between Cape Naturaliste and Cape Leeuwin) and on the south coast (specifically the region around the town of Walpole), which are supported by information from other taxa likewise adapted to mesic habitat, such as other freshwater crayfish, slaters, frogs, orchids and sedges. Not only does this study recognise biogeographic concordance between these taxa in SWA, it highlights a possible central role for Engaewa in creating habitat for other taxa.

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