Phenotypic selection of the freshwater snail, Campeloma decisum.

Abstract

Phenotypic selection in the snail species Campeloma decisum is found by observing characteristics such as an individual's size, growth rate, and ability to manipulate available resources. Populations of C. decisum, live and dead samples, were collected from both Douglas and Burt Lake. It is suggested that if only genetic drift is occurring, we should see no significant difference between the live and dead samples. However, if natural selection is occurring, we should see a significant variance in phenotype. We made measurements of shell length, width, age, and aperture length and width. From these measurements we made calculations of overall growth rate, juvenile growth rate, recent growth rate, whorl tightness, aperture to shell ratio, slenderness of the shell, and aperture shape. We obtained results for the populations as a whole, and for each of the three individual populations we collected. Overall, whorl tightness, aperture to shell ratio, and aperture shape showed a significant difference between the live and the dead snails. In Grapevine Point we found a difference in juvenile growth rate and slenderness of the shell, while at Pine Point we discovered a difference in overall growth rate, juvenile growth rate, whorl tightness, and aperture shape. Finally, at Burt Lake we found a significant difference in whorl tightness, aperture shape, and aperture to shell ratio. These varying results lead us to speculate that natural selection is taking place for certain characteristics within a population of C. decisum in different areas.