9301687 REX The primary objective of this project is to critically evaluate size trends in deep-sea gastropods in the context of an optimality model of body size. The evolution of body size is a problem of fundamental interest, and one that has an important bearing on community structure and conservation of biodiversity. The most obvious and pervasive characteristic of the deep-sea benthos is the small size of most species. The numerous attempts to document and explain size patterns in the deep sea have focused on variation among species or whole faunal components, and have led to conflicting and contradictory results, In general, there has been a failure to recognize that studying size as an adaptation to the deep-sea environment must include analyses within species using measures of size that are standardized to common growth stages. Also, most studies have not applied appropriate statistical methods for either demonstrating or comparing size trends. Sebens' optimality model of body size in marine invertebrates provides a useful conceptual framework for exploring the evolution of size in deep-sea species. It predicts that optimal body size should decrease with depth under circumstances where decreased nutrient input lowers food intake rates and increases costs of foraging; but it also allows for the evolution of size above the optimum when larger size confers a competitive advantage. A preliminary analysis within eight species of deep-sea gastropods reveals a clear trend for size to increase with depth in both larvae and adults. Based on this preliminary analysis and Sebens' optimality model, this project will test the hypothesis that there are within- and among- species components to size-depth trends. Using a single taxonomically coherent family of ecologically similar species (the Turridae) and the analysis of covariance, this project will test four specific predictions: 1. that size will increase with depth within species, but that the slopes of size-depth relations will decrease with depth, 2. that size will decrease among species as they replace one another along a depth gradient, 3. that there will be a latitudinal gradient in size, with larger species found at higher latitudes, and 4. that size-depth regressions in regions of higher production will have higher elevations than those in regions of low productions. This project will provide the first accurate analysis of geographic variation in size within deep-sea species, and will contribute significantly to our basic understanding of size as an adaptive response to the deep-sea environment. ***
