A phylogeographic and taxonomic assessment of the squirrel - mahogany glider complex

Ferraro, Paul Anthony (2012) A phylogeographic and taxonomic assessment of the squirrel - mahogany glider complex. Masters (Research) thesis, James Cook University.

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Abstract

Quaternary climate fluctuations, such as the contraction-expansion cycles of eastern Australia’s widespread forested biome, are widely cited as driving factors in speciation and extinction. Incorporating morphological and molecular data, I examined two representatives of an eastern Australian open forest species complex with contrasting distributional patterns, the geographically restricted mahogany glider (Petaurus gracilis) and its widespread congener, the squirrel glider (P. norfolcensis), with the aim of assessing existing taxonomic boundaries and establishing an accurate biogeographic narrative.

Current taxonomy of the squirrel – mahogany glider complex, as defined by existing distributional, behavioural and ecological data, support species status for each glider. However, molecular and morphological data presented in this study intimate a more nuanced evolutionary scenario. Mitochondrial (mtDNA) sequences assorted independent of taxonomy yet identified two partially overlapping, geographically oriented lineages, one restricted to north-eastern Australia and the other more widespread across eastern Australia. MtDNA substructure was also observed among south-eastern Australian squirrel glider populations. Although less clearly defined, geographic orientation among nuclear (nDNA) sequences was also detected. In contrast, morphological variation within the complex clearly differentiated the mahogany glider from the squirrel glider, with the former significantly larger. Minor morphological variation was also detected in squirrel glider populations in south-eastern Australia, mirroring mtDNA substructure.

Phylogeographic structure of the squirrel – mahogany glider complex was then compared to that of two co-distributed open forest congeners, namely the sugar (P. breviceps) and yellow-bellied (P. australis) gliders. MtDNA diversity was similarly structured across all species, with each represented by two divergent mtDNA lineages, although the depth of divergence differed. Biogeographic subdivisions in the squirrel – mahogany glider complex were more similar to those of the patchily distributed yellow-bellied glider than the widespread sugar glider. In the squirrel – mahogany glider complex, north-eastern Australian populations were clearly isolated from eastern and south-eastern populations by the Burdekin Gap, an expanse of dry, open woodland habitat well documented as a biogeographic barrier to open forest fauna. South-north introgression across the Burdekin Gap, not detected in other Petaurus gliders, was interpreted as evidence of intermittent open forest habitat connectivity in line with Quaternary contraction-expansion cycles. MtDNA substructure in south-eastern Australia was associated with the Hunter River Valley and Great Dividing Range, both biogeographic barriers to the sugar glider. MtDNA and morphological substructure also supports the recent recognition of the south-eastern Australian populations of the squirrel glider as a distinct evolutionary significant entity for conservation and management purposes.

In conclusion, results presented here do not reflect the clearly defined taxonomy of the squirrel – mahogany glider complex as currently recognised. When considering the taxonomic status of the mahogany glider, the available data permits two largely complementary interpretations. Firstly, the mahogany glider as a geographic variant of the widespread squirrel glider. The absence of reciprocal monophyly therefore represents evidence of ongoing gene flow between the two gliders, specifically between neighbouring populations, while the observed ecological and morphological differentiations are a consequence of the distinct environmental profile of the mahogany gliders’ coastal lowland habitat. Secondly, the data available does not preclude a scenario whereby the clear morphological divergence observed between the two gliders reflects character displacement driven by strong divergent selection across a steep moisture gradient. In this scenario, minor partitioning of phylogenetic diversity between the mahogany and squirrel gliders reflects incipient speciation of two allopatric species that are only recently isolated. It is arguably premature, however, to suggest changes to Petaurus systematics without data from more rapidly evolving loci and greater representation of north-eastern Australian populations of the squirrel – mahogany glider complex.

Item ID: 29137
Item Type: Thesis (Masters (Research))
Keywords: mahogany glider; squirrel glider; phylogeography; taxonomy; morphological divergence; species complex; squirrel-mahogany glider complex; open forests; environmental profile; Eastern Australia
Date Deposited: 03 Sep 2013 02:08
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060301 Animal Systematics and Taxonomy @ 33%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060302 Biogeography and Phylogeography @ 34%
06 BIOLOGICAL SCIENCES > 0604 Genetics > 060411 Population, Ecological and Evolutionary Genetics @ 33%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 50%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960805 Flora, Fauna and Biodiversity at Regional or Larger Scales @ 50%
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