Selection and survivorship in the freshwater snail Campleoma decisum.

Abstract

In this study, we investigated selection for survivorship in the freshwater snail Campeloma decisum. Two primary evolutionary trends were observed for C. decisum: selection for smaller shell size, and smaller aperture area. Differences in living and dead population means revealed a selection for decreased weight, overall length, overall width, aperture length, number of whorls, shell volume, and aperture area. Selection for an increase in distance from last growth bar to aperture and aperture area to shell volume was also observed. Our results from an analysis of variance difference (F-test) suggested the occurrence of either directional or stabilizing selection in the living and dead populations for weight, overall length, overall width, aperture length, aperture width, shell shape, shell volume, aperture area, and growth rate. Overall selection is toward a smaller overall shell length for self-defense and protection, however, increasing shell size is important reproductively.