Geometric morphometric tools in the analysis of shell shape of twelve local populations of the invasive snail Achatina fulica Bowdich from the Philippines

Abstract

The shape of the giant African snail Achatina fulica Bowdich by visual examination seems to vary geographically. To test this observation, geometric morphometric analysis on a total of 976 A. fulica shells from several geographical locations in the Philippines was done. These were collected from the island of Bohol (Agapi, Ondol and Quinoguitan) and in the island of Mindanao - Davao City and Davao del Norte (Davao Riverside, Emily Homes, Las Arenas, New Corella, Nova Tierra and Panabo), Mindanao State University Main Campus, Mimbalut in Iligan City and Balangao, Zamboanga Sibugay. Images of the shells were captured, digitized and subjected to relative warp (RW), canonical variance (CVA) and linear regression analyses to determine whether populations in geographic isolation are phenotypically differentiated to serve as basis for the observation of geographical differentiation in A. fulica. Based on CVA, results showed differentiation of populations; however within population variability was also found to be high. This is in contrast with linear regression involving centroid shapes which revealed slight differentiation between populations. Based on RW analysis, results revealed shells of A. fulica have the following shapes - shells with elongated spire with narrow whorl and narrow aperture, elongated spire with narrow whorl and rounded aperture, short spire with wide whorl and rounded aperture, and short spire with wide whorl and narrow aperture. The findings in this study suggest that although there are notable morphological variations, it may not be substantial to conclude that speciation has taken place in this species.