ENVIRONMENTAL INFLUENCES ON INTRA-SPECIFIC BODY SIZE DISPARITY: A CASE STUDY USING NEW ZEALAND TURRITELLID GASTROPODS

Long term responses of organismal morphology -- especially body size -- to environmental change have long been the subjects of both neontological and paleontological studies. Though the extent and causes of intra-specific size variation at one time point is often poorly understood, it is vital to be able to quantify this variation spatially and environmentally before examining temporal trends in lineages. This requires a study group with a high-resolution fossil record occurring in well-understood paleoenvironments which have modern representatives for comparison.

The New Zealand turritellid gastropods (family Turritellidae) are an ideal group for study of both inter- and intra-specific size variation. Size data is easy to collect from numerous specimens available in collections from Recent and fossil localities. The fossil record of the group is well known and the Cenozoic paleoenvironments in which they are found are extremely well characterized.

Various environmental factors, such as water temperature and primary productivity, may influence size ranges within a species. For this study size data for five species of Recent New Zealand turritellids from three genera (Maoricolpus, Stiracolpus and Zeacolpus) were analyzed for patterns that might indicate an influence of local environment on growth. A data set of size measurements was compiled using images of specimens from the collections of the Auckland Museum and the Institute of Geological and Nuclear Sciences in New Zealand. Overall latitudinal ranges of species were compared and intra-species data for gross shell size analyzed within and between localities. The data set was compared to environmental conditions such as bathymetric depths, sea temperature fluctuations, salinity levels, and primary productivity.

These comparisons of environmental gradients with size data suggest a positive correlation between water temperature and shell size. Further comparison of bathymetry and temperature may provide more precise correlation. This information represents a point of reference for examining size trends in the fossil representatives of these three genera of New Zealand turritellids.