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Evolutionary tales of maskrays (Neotrygon, Dasyatidae), flatheads (Platycephalidae, Scorpaeniformes) and tuskfishes (Choerodon, Labridae)
thesisposted on 2023-05-27, 06:58 authored by Puckridge, M
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 ‚Äö- Neotyrgon kuhlii and Platycephalus indicus ‚Äö- 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.
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