Year

2006

Degree Name

Doctor of Philosophy

Department

School of Biological Sciences

Abstract

The Lymnaeidae Rafinesque, 1815 are one of the most widespread groups of freshwater snails, however, they are characterised by a long and confused systematic history largely due to problems associated with shell plasticity. Recent molecular studies that have utilised DNA sequences have failed to adequately represent the Australasian lymnaeids. The aim of this study was to understand the systematics of the Australasian Lymnaeidae, using 16S and ITS-2 sequences in tandem with a anatomical and shell studies.

The native Australian and New Zealand lymnaeids are currently attributed to Austropeplea Cotton, 1942 and Kutikina Ponder and Waterhouse 1997, which are thought to be represented by three and one species, respectively. Results of this study indicate there are 5 distinct species across three genera. Phylogenetic analyses of the A. tomentosa (Pfeiffer, 1855) complex recovered two distinct species, A. tomentosa in New Zealand and A. huonensis (Tenison-Woods, 1876) in southern Australia. There was however incongruence between the anatomical and molecular phylogenies. Kutikina hispida was suggested to be closely related to the A. tomentosa complex, however, molecular phylogenies genes resolved K. hispida as sister to A. huonensis, with A. tomentosa being resolved as sister to the A. huonensis + Kutikina clade. Kutikina was therefore synonymised into Austropeplea based on the molecular phylogenies. Based on molecular and anatomical phylogenies, the more northern complex, A. lessoni (Deshayes, 1830) was more appropriately placed in the Peplimnea (Iredale, 1943), and was found to be represented by two distinct taxa, P. lessoni and P. affinis (Küster, 1862). Phylogenetic analysis of 16S, ITS-2 and anatomical characters recovered A. viridis (Quoy and Gaimard, 1832) as relatively divergent from other members of Austropeplea. Therefore, A. viridis was placed into Viridigalba Kruglov and Starobogatov, 1985.

Using 16S sequences and anatomical characters, a phylogeny of the Lymnaeidae was produced. The Australasian lymnaeids represented one of the most derived groups within the family in both the 16S and anatomical phylogenies. The North American and European lymnaeids were resolved at the base of the lymnaeid phylogeny, suggesting that these taxa represent the older groups within the family.

Phylogenies based on molecular sequences suggest that the Austropeplea lessoni complex is more closely related to lymnaeids from South East Asia than to other Australian lymnaeids. Furthermore, based on molecular and anatomical phylogenies, A. viridis is suggested as sister to the A. tomentosa complex. Therefore it is highly likely the A. lessoni complex and A. tomentosa complex have separate derivations. The monophyly of Radix Montfort, 1810 remains however unresolved.

Two theories of biogeography of the Australasian Lymnaeidae have been recently proposed and were examined in light of the new phylogeny. While it seems certain that the Austropeplea lessoni complex had a South East Asian origin, the origin of the A. tomentosa complex is still unclear. The close relationship of the A. tomentosa complex with Asian A. viridis plus the derived position of the group in the family, suggest a second invasion of Australia by lymnaeids from South East Asia. However, the basal position of the New Zealand A. tomentosa would suggest the group occurred here first and moved into Australia, thus suggesting a Gondwanan radiation of the A. tomentosa complex. The discovery of a lymnaeid fossil in Antarctica lends further weight to this theory.

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