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Evolutionary tales of maskrays (Neotrygon, Dasyatidae), flatheads (Platycephalidae, Scorpaeniformes) and tuskfishes (Choerodon, Labridae)

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Puckridge, M (2013) Evolutionary tales of maskrays (Neotrygon, Dasyatidae), flatheads (Platycephalidae, Scorpaeniformes) and tuskfishes (Choerodon, Labridae). PhD thesis, University of Tasmania.

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Abstract

The tropical Indo-West Pacific (IWP) is the most biologically diverse marine region
on earth with a number of competing hypotheses proposed to explain the evolutionary events
responsible for this area’s biotic complexity. These hypotheses are based on varying
interpretations of species distributions radiating from the Indo-Australian Archipelago (IAA)
at the centre of the region. The IAA represents a geologically dynamic area formed by
colliding tectonics; mechanisms relating to tectonic activity are therefore commonly
considered responsible for the biodiversity here.
In the present study, a) maskrays of the genus Neotrygon (Dasyatidae), b) flatheads of
the family Platycephalidae (Scorpaeniformes) and c) tuskfishes of the genus Choerodon
(Labridae) were studied with respect to their taxonomy, phylogeny and phylogeography.
These groups are characterized by having demersal life histories and a high proportion of
narrow-ranging endemics. Furthermore, some of the widely distributed species across the
region are suggestive of either recent jump-dispersal events or fragmentation of once pantropical
populations. The sampling effort in this study focused on exploring diversity among
species, and within selected taxa, by obtaining multiple individuals across species’
distribution ranges, where possible. Molecular phylogenies, coupled with molecular clock
approximations, were employed to a) assess nominal species validity b) DNA barcode
Evolutionarily Significant Units (ESUs) and c) explore the geological and evolutionary
processes responsible for observed trends in diversity and species distribution in maskrays,
flatheads and tuskfishes. Both mitochondrial and nuclear molecular markers were used in this
study. The chosen markers amplified consistently across species, showed high content of
phylogenetic signal and were able to resolve closely related species, thus allowing the
inference of robust phylogenies and molecular clock dating.
Parallel genealogical trajectories have been recovered within rays of the genus
Neotrygon and platycephalin flatheads (the most comprehensively sampled subfamily of
Platycephalidae). These congruent spatial and temporal patterns suggest that species
differentiation predominantly occurred across the tropical IAA throughout the mid to late
Miocene. The most widely distributed and derived forms in these groups – Neotyrgon kuhlii
and Platycephalus indicus – were found to consist of cryptic species complexes with
considerable lineage diversity across their IWP range. Phylogeographic comparisons with
other, less well sampled platycephalid species confirm that diversification patterns are
consistent across multiple species, suggesting species diversity in shallow water marine fauna
may be grossly underestimated. In contrast, tuskfishes of the genus Choerodon showed
unclear phylogeographic structuring. However, mixed ancestral and derived lineages,
endemic to Australian waters, suggest the Australian region has acted as both a refuge for
lineage survival and source of radiation in this group since the mid-Miocene. Patterns are consistent with centrifugal speciation, a process that may be common across marine groups
here.
In conclusion, the tectonic suture zones across the Australian and Eurasian Plates
have played an essential role in triggering the area’s mega-diversity and biotic complexity.
Tectonic rafting, the establishment of new habitats in the form of shallow seas, tropical
coastlines and island arcs, together with glacio-eustatic sea level oscillations, have likely
favoured rapid species diversification through vicariance and allopatric speciation. The
imprint of these large-scale geological and climatic events has been retained within the
evolutionary history of maskrays, flatheads and tuskfishes. These uncovered patterns may
represent a common trend for many other marine taxa with similar ranges and geographical
distributions.

Item Type: Thesis (PhD)
Keywords: Phylogeography, biodiveristy hotspot, cryptic species, marine specialation, phylogenetics
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Date Deposited: 19 Feb 2014 03:55
Last Modified: 15 Sep 2017 01:06
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