I did my Honours project on the population genetic structure of Powelliphanta land snails, and I am interested in issues of taxonomy and conservation in snails.
Molluscs as a group have the highest number of documented animal extinctions of any major taxonomic group (Lydeard et al. 2004). They suffer the dual disadvantage of extreme sensitivity to habitat modification and pollution, and under -recognition of taxonomic diversity. Shell morphology (a key taxonomic feature) has been found to be both highly plastic within species and convergent between species making taxonomy based on shell characteristics problematic. Genetic studies are often used clarify taxonomy and make conservation management decisions.
Powelliphanta are a genus of carnivorous snails belonging to the family Rhytididae (found in Australia and South Africa too). Most Powelliphanta are found in South Island where they occupy small ranges that make them especially vulnerable to habitat loss and predation and all members of this species are afforded high conservation status. My study focused on a group of Powelliphanta snails found on the West Coast of the South Island of New Zealand. In this area the snails are in highly fragmented populations, with a remarkably high number of putative taxa (>7) given the relatively small area (<112502km). How is this possible?
When looking at species units the critical causative factors are not geographical distances or even time but simply barriers to geneflow. The landscape on the west coast of the South Island is not uniform therefore if the landscapes heterogeneity provides sufficient areas of unsuitable habitat between populations this might limit geneflow between these populations. In fact the group of snails in this area are moslty at high altitude, above the tree line. Despite intensive searching, many of these snails have not been found in lowland areas between these high altitude populations. I want to find out if these putative taxa are distinct species which should be evident in the scale of their population genetic structure. As an alternative it is possible the current fragmented distribution is the result of habitat changes and introduction of mammal predators by people.
I am currently examining genetic and morphological variation in another group of land snails- Placostylus. Genetic analysis allows an estimate of recent past population composition and distribution, but additional information about persistence and form change comes from fossils. I am applying geometric morphometric analysis of shell shape to modern and Holocene fossils for Placostylus from Far North New Zealand. A nice feature is that fossils of known age (carbon dated) are available at or near existing modern population sites.
|
