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Biogeography and systematics of the Tasmanian mountain shrimps of the family Anaspididae (Crustacea: Syncarida)

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Andrew, Jane (2005) Biogeography and systematics of the Tasmanian mountain shrimps of the family Anaspididae (Crustacea: Syncarida). Research Master thesis, University of Tasmania.

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Abstract

The family Anaspididae is a relictual Gondwanan group of malacostracan crustaceans now surviving
only in cool waters and caves of Tasmania. Its most widespread species, Anaspides tasmaniae, is also
the most morphologically plesiomorphic of the order Anaspidacea, and shows very little development
since Triassic fossil anaspid forms. A number of issues relating to the systematics and taxonomy of the
family Anaspididae have been raised since the first discovery of the extant species. In particular, the
separate species status of Anaspides spinulae has been questioned. The level of genetic differentiation
among populations of Anaspides tasmaniae has never been ascertained, but has been presumed to be
high due to the long periods of isolation between populations. The relationships between the three
anaspid genera are also of interest as they elucidate the early evolution of the family in Tasmania.
In order to clarify the systematics of the genus Anaspides, an allozyme and mitochondrial
DNA study of populations of Anaspides tasmaniae, A. spinulae, Paranaspides lacustris,
Allanaspides helonomus and Allanaspides hickmani was undertaken. Anaspides populations
were sampled over the entire geographic range of the genus and a wide variety of habitats,
including caves. Genetic affinities ascertained from the allozyme and 16S mtDNA analyses were
largely congruent. The allozyme study also provided information on within-population processes and
the mtDNA analysis provided confidence levels on phylogenies and molecular clock estimates for
divergence times. The results showed that: • Anaspides spinulae was not supported as a species separate from A. tasmaniae.
• Cave populations do not form a distinct genetic group despite the common loss of
pigmentation. All cave populations sampled shared genotypes with the nearest epigean
populations.
• Populations of Anaspides tasmaniae (including A. spinulae) were characterised by generally
low levels of within-population genetic variation, with many instances of fixed differences
and private alleles, and often high levels of among-population genetic differentiation.
• The genus Anaspides contains three distinct geographical groups all of which were supported
genetically as separate species. These are found in the south (Huon area), the southwest and
the Central Plateau / Derwent areas. It is proposed that these groups be considered as separate
species requiring detailed description.
• Differentiation among Anaspides populations within the Central Plateau was significantly less
than that within the southern and southwestern group. Speciation appears to be continuing in
isolated populations, particularly in the southwest. • The Central Plateau group has a core group of 8 populations, and 5 populations on the fringe
of the Plateau that are more distant. An isolation by distance test found a significant
correlation between inter-population structure and geographical distance.
• The southern group of Anaspides showed the same high level of differentiation from the other
two Anaspides groups as from Paranaspides. This level of differentiation is similar to genuslevel
divergence in other crustacean groups. As a result, it is recommended that the southern
Anaspides group be described as a new genus. A thorough examination of morphological
characters should be undertaken in order to establish the southern Anaspides as a new genus.
• The emergence of Allanaspides was found to be the earliest divergence from the anaspid
lineage, estimated at about 43 million years ago by molecular clock calculations. The
separation of Paranaspides lacustris and the southern group of Anaspides, and the divergence
of the two Allanaspides species is likely to have occurred between about 20 and 25 million
years ago. The Central Plateau and southwest groups appear to have diverged approximately
10 million years ago. The estimated time at which the last common ancestor occurred within
geographical groups is approximately 6 my for the southwestern group, 3.5 my for the
southern group and 2 my for the Central Plateau.
• Biogeographical explanations for divergences in the family Anaspididae are suggested. These
include climatic warming in the Eocene, increasing aridity in the late Oligocene and Miocene,
various geological faulting and tectonic events in the Tertiary and the invasion of Tasmanian
freshwaters by fish predators. Vicariant speciation in the Tertiary appears to have been the
major influence on evolution in the Anaspididae, with Pleistocene glaciation and/or recent
warming possibly forcing populations into cave refugia. There is evidence that glacial
meltwater may have allowed some populations to mix, having a homogenising effect on
genotypes, and possibly overlaying more ancient relationships between populations.

Item Type: Thesis (Research Master)
Keywords: Shrimps, Shrimps
Copyright Holders: The Author
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Copyright the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Additional Information:

Thesis (M.Sc.)--University of Tasmania, 2005. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:54
Last Modified: 11 Mar 2016 05:54
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