Biodiversity, biogeography and phylogeny of Australian freshwater triclads

Grant, Lauryne Joan (2016) Biodiversity, biogeography and phylogeny of Australian freshwater triclads. PhD thesis, James Cook University.

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Freshwater triclads are a cosmopolitan group. Despite this, our knowledge of their biodiversity, biogeography and phylogeny is surprisingly poor. There has been steady progress worldwide towards remedying this; however, research on the biodiversity of Australian freshwater triclads has been dormant until recently. This project is the first study of the biodiversity, biogeography and phylogeny of Australian freshwater triclads, involving extensive and targeted sampling, contrasting with the more haphazard studies characteristic of the past. The project contributes greatly to our limited understanding of freshwater triclads in general, and the Australian species in particular.

This project began with extensive systematic work performed on a pre-existing, unstudied Australian collection. This work revealed several new species from three separate genera, representing a major contribution to the Australian fauna. New material was then collected from throughout Australia (the Northern Territory being the only notable exclusion), with over 500 sites visited and freshwater triclads discovered at over 400 of these. Molecular and traditional systematic techniques were used to describe new genera and species, draw conclusions concerning their phylogeny, and to examine patterns of geographical distribution and affinities with related taxa elsewhere in the world.

The taxonomic work, which forms the basis for the phylogenetic and biogeographic analyses, revealed a rich and diverse Australian fauna. In total, 16 new species and two new genera (with additional tentative new species and genera) have been described. The phylogenetic analysis, including both new genera and numerous new species, agreed with several previous analyses suggesting that the Dugesiidae shared a closer relationship with their terrestrial counterparts, than they did with other freshwater triclads (the Planarioidea). Where the current analysis disagrees with previous research is around the nature of this relationship. The current research suggests that the entire Geoplanoidea (freshwater and terrestrial) is a simple, monophyletic group within which the Dugesiidae sensu lato (s.l.) is paraphyletic. The consequence of this result is that the Geoplanidae arose from a freshwater ancestor. This outcome has prompted the development of a tentative new classification for the Geoplanoidea (the Dugesiidae s.l. and Geoplanidae) that more accurately reflects the state of our understanding for the group.

In relation to the generic relationships among the Dugesiidae s.l., there are several conflicts with recent morphological and molecular work (Álvarez-Presas et al. 2008; Álvarez-Presas and Riutort 2014; Sluys 2001). This may be related to the markers chosen for the current analysis (i.e. molecular and morphological). However, it is also possible that these discrepancies are due to the inclusion of new genera, unique to this study. One of the most interesting results is the position of eastern Romankenkius as the most ancient of the extant "dugesiid" genera. The position of Masaharus and the possible new genus (western Romankenkius) are also exciting developments, as they seem to represent links between freshwater and terrestrial genera, and occupy critical position within the paraphyletic Dugesiidae s.l.

Australia's position as the most diverse continent, for both genera and species, has been emphasised through the current research. Endemicity is also a feature of the Australian "dugesiid" fauna. These high levels of diversity and endemicity suggest that Australia was a center of diversity for the Dugesiidae s.l., at least in the Gondwanan era. Within Australia two biodiversity hotspots occur: the Australian Alpine region and the island of Tasmania. These two hotspots are the primary contributors to the status of Australia as the most diverse continent for the Dugesiidae s.l. Outside these areas, Australia is dominated by three widespread genera, Cura, Dugesia and the invasive Girardia.

Existing theory, relating to the current distribution of the Dugesiidae s.l. throughout the globe, suggests that the taxon must have diversified before the breakup of Pangaea (Ball 1974a; Ball 1975). Regardless of the actual sequence of diversification, by the Jurassic representatives of the Dugesiidae s.l. must have been broadly distributed to allow the distribution of its members throughout the Northern Hemisphere. Within Australia the biogeography of the Dugesiidae s.l. is defined by what are perceived to be older Gondwanan relics (e.g. Romankenkius, Spathula) in the southern highlands (Australian Alps and Tasmania) and by the more "modern" genera (Cura, Dugesia) throughout the remainder of the continent's waterways.

This study has highlighted the importance of the Australian continent in both freshwater and terrestrial triclad research and provided a substantive contribution to this field. However, there is a great deal more research to be done in relation to the origin of the freshwater and terrestrial Geoplanoidea. I believe that the next major step is a thorough investigation into the relationship between the Geoplanidae, specifically the Australian species, and the Dugesiidae s.l. families Spathulidae and Romankenkiidae and Masaharidae. Indeed, such efforts may also lead to the discovery of morphological synapomorphies for the newly described families, allowing the formalisation of the classification.

Practical applications of this research include the development of a key utilising the internal morphology. This would be of use to other taxonomists who may not specialise in this group. The sequencing of the cox1 region of the mitochondrial genome and 18S region of the nuclear genome for many new species and several new genera will be useful for future phylogenetic research, and will ideally contribute to an identification system utilising sequence data for the Dugesiidae s.l. (i.e. barcoding).

Item ID: 51512
Item Type: Thesis (PhD)
Keywords: Australia, biodiversity, biogeography, Cura, Dugesia, Girardia, homoplasy, morphology, Platyhelminthes, Romankenkius, Spathula, taxonomy, freshwater triclads, Tricladida
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Grant, Lauryne J., Sluys, Ronald, and Blair, David (2006) Biodiversity of Australian freshwater planarians (Platyhelminthes: Tricladida: Paludicola): new species and localities, and a review of paludicolan distribution in Australia. Systematics and Biodiversity, 4 (4). pp. 435-471.

Sluys, Ronald, Grant, Lauryne J., and Blair, David (2007) Freshwater planarians from artesian springs in Queensland, Australia (Platyhelminthes, Tricladida, Paludicola). Contributions to Zoology, 76 (1). pp. 9-19.

Date Deposited: 10 Nov 2017 04:29
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060302 Biogeography and Phylogeography @ 20%
06 BIOLOGICAL SCIENCES > 0604 Genetics > 060409 Molecular Evolution @ 30%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060808 Invertebrate Biology @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960807 Fresh, Ground and Surface Water Flora, Fauna and Biodiversity @ 100%
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