Lecturer, Faculty of Medicine & Health Sciences
We undertake research in Evolutionary Relationships in the Pulmonate Land Snails and Slugs: Using molecular data to determine the deep evolutionary relationships among the pulmonate land snails and slugs, to estimate the ages of the major diversifications within the group, and to establish how the pulmonates colonised the land. We are also investigating population level variation within individual species of land snails and slugs, in particular the banded snail Cepaea hortensis, the Giant African land snail Achatina (=Lissachatina) fulica and the common garden snail Helix apsersa.
Another area of research is the Evolutionary Relationships in the Planktonic Foraminifera: Using genetic data to determine evolutionary relationships among species of foraminifera, to establish how much hidden diversity there is within individual foraminiferal morphospecies, and to investigate the distribution of genetic types across the oceans. The fossils of planktonic foraminifera are important indicators of past climate and our genetic data is being used to improve the current models for climate.
We also research Parasitic Nematodes: Studying the occurrence of nematode parasites in snail and slug hosts, with particular emphasis on Angiostrongylus cantonensis (which causes eosinophilic meningitis in humans) and the French Heartworm Angiostrongylus vasorum (a veterinary parasite that infects dogs).
Evolutionary Relationships in the Pulmonate Land Snails and Slugs (Pulmonata: Stylommatophora)
Land snails and slugs represent one of the largest invasions of the land, comprising some 30,000-35,000 species. They are major components of many ecosystems, and they include the vectors of many serious diseases. They have also become important models for studies on the mechanisms of evolution and are eminently suitable as subjects for biogeographic studies of early tectonic events.
Evolutionary Relationships and Taxonomy
Until recently, the origins and the deep-level evolutionary relationships of the major groupings of the land snails and slugs remained virtually unknown. Anatomical studies gave confusing and conflicting results, such that there appeared to be almost as many classifications as there were classifiers.
Working in the lab
Our recent molecular work has begun to unravel the evolutionary relationships within the land snails and slugs. We have sequenced part of the ribosomal RNA gene cluster for some 260 species of land snails and slugs in the Pulmonate suborder Stylommatophora. Although our molecular phylogeny largely agrees with the traditional taxonomy at the level of families, at deeper levels the molecular tree markedly disagrees with the traditional taxonomy. Remarkably, the Orthurethra (previously considered to be ancestral) appear to be relatively advanced, indicating that supposedly primitive features such as the orthurethran kidney are in fact derived. This finding is leading to a radical reinterpretation of early land snail evolution.
Adult Achatina achatina and baby
We are currently extending our molecular work on the Stylommatophora to include more taxa and to obtain new genes in order to provide independent confirmation of the relationships in the rDNA tree. In addition, we are expanding our phylogeny to include other non-stylommatophoran pulmonate groups. We ar
Recent genetic studies of the foraminifera have provided new insights into the evolution of the group. Our comparisons of small subunit (SSU) ribosomal (r) RNA sequences of the foraminifera with those of other eukaryotes have shown that the foraminifera apparently form one of the earliest diverging eukaryote lineages in the 'tree of life'. More work is needed to confirm this placement as the fast rate of evolution observed in foraminiferal SSU rRNA genes renders the group difficult to place in evolutionary trees. Our genetic studies of the foraminifera have also provided a great deal of information about evolutionary relationships within the group. Interestingly, the evolutionary transition between a benthic and a planktonic way of life appears to have occurred several times. Furthermore, planktonic spinose species (foraminiferans with spines) cluster separately from the planktonic non-spinose species. We are currently undertaking new molecular studies of the foraminifera utilising both the SSU rRNA gene and other nuclear genes in order to further investigate their placement in the 'tree of life' and the evolutionary relationships within the group. One of the most interesting outcomes of genetic studies of the planktonic foraminifera concerns the extent of differentiation within individual morphospecies. We have shown that most mophospecies of planktonic foraminifera show an exceptionally high level of genetic diversity in their SSU rRNA genes, and that many include more than one genetically distinct entity. Indeed, some of these genetic types may warrant classification as separate 'cryptic' species. This finding is of interest because of the role of foraminiferal microfossils in reconstructing past climates. For climate reconstruction it has been assumed that each 'morphospecies' is a single entity with a specific ecological (and thus climatic) preference. If the distinct genetic types within morphospecies are in fact adapted to different habitats, and exhibit different ecological and climate preferences, then the assumption that each morphospecies is characteristic of a particular climate would be wrong. If this is so, there may be significant errors in current models of climate reconstruction. Recent work suggests that different genetic types are indeed associated with different environments. If it does become possible to distinguish these newly recognised genetic types in the fossil record, the role of the foraminifera as indicators of past climate could be greatly enhanced. Land snails and slugs represent one of the largest invasions of the land, comprising some 30,000-35,000 species. They are major components of many ecosystems, and they include the vectors of many serious diseases. They have also become important models for studies on the mechanisms of evolution and are eminently suitable as subjects for biogeographic studies of early tectonic events.