GEOMETRIC MORPHOMETRIC ANALYSES OF SHELL SHAPE CONTRIBUTIONS TO PREY SELECTIVITY: PREDATION IN THE NATICID GASTROPOD AND VENERID BIVALVE SYSTEM OF BIOTIC INTERACTIONS

Variable life habits, and to a lesser extent shell ornamentation and armor, have been acknowledged to pose some contribution to predation resistance in bivalves throughout their evolutionary history. These factors include deep burrowing, cementation, boring into hard substrates, shell microstructure and more. Of these changes in life habit and behavior, many have a preservable record as a component of shell shape. In long-term and closely-constrained biotic interactions, such as the agonistic relationship between venerid bivalves and their predators (i.e. shell-drilling gastropods), directional changes in shell shape and form may be heritable phenotypic responses to selection pressure by predators. In this project, I diagnose the major contributions of shell shape and morphological diversity (disparity) as they relate to predator avoidance and escape. I report an assessment of morphologic variation, by utilizing both landmarks (discrete homologous points) and digitized shell outlines, among Neogene venerid genera from the Indo-Pacific. I constrain these analyses in a broad stratigraphic and geographic context, taking into account the frequency of drilling predation as a function of morphological variation.

Morphometric analyses of venerid genera demonstrate that taxa are randomly distributed throughout shape space with respect to geographic and temporal distributions. However, when predation instances (i.e. drilled specimens) are superimposed on the ordination in shape space, a bias in prey selectivity is observed.