EXPLAINING LOCALIZED VARIATION IN CERION SHELL MORPHOLOGY ON SAN SALVADOR ISLAND, THE BAHAMAS

Cerion is a remarkably diverse genus of terrestrial pulmonate snails that has attracted over 50 years of scientific investigation. The genus is characterized by distinctive variation in shell morphology between adjacent populations in the absence of reproductive isolation, and its peculiar distribution across the islands of the Caribbean has resulted in a vast body of literature from researchers in paleontology, geology, and evolutionary biology. The goal of this observational study is to investigate possible mechanisms behind the maintenance of populations of Cerion with distinct shell types in localized areas on San Salvador Island, The Bahamas. Morphometric measurements including shell height, shell width, whorl count, and rib count will be taken for all individuals found within a 40x10 meter transect residing on specific vegetation (n=1,210). Variance calculations from these measurements will determine the variability between any single individual and other Cerion: 1) in the “neighborhood” (vertical distance of 10cm), 2) on the tree as a whole, 3) within the patch of trees, and 4) within the site. Dispersal measurements are also being calculated for 332 tagged individuals over a seven-month period. Morphometric and dispersal data are then being analyzed to determine possible correlations between these parameters and the varying population densities within the study site. Morphologic trends and population density preferences may arise from this data that can help to shed light on the puzzling spatial distribution and morphologic diversity of this genus. We predict that Cerion from high-density areas will show a preference for less dispersal as a result of relaxed selective pressure for finding a mate, and that this preference will ultimately result in less morphologic variability in high density patches.

Additional Abstract Information

Student(s): Benjamin S. Stanley

Department: Biology

Faculty Advisor: Dr. Christine L. May

Type: Oral

Year: 2013