Outline-based geometric morphometric analysis of shell shapes in geographically isolated populations of Achatina fulica from the Philippines

Abstract

The invasive giant African land snail, Achatina fulica collected from different geographical locations in the Philippines exhibit qualitative differences in shell shape and banding pattern configurations. To be able to describe quantitatively the differences in shapes in relation to banding patterns and geographical locations, this study used outline-based geometric morphometrics analysis, the elliptic Fourier analysis. Snails were collected from 15 different geographical locations in the Philippines and were categorized under 14 different banding patterns. The shells were photographed, digitized using tpsDig software and subjected to elliptic Fourier analysis. Results showed the variations were mainly observed on the lateral and longitudinal length aspect of the shell. A total of 16 major shape configurations were observed through variation in shell shape, aperture size, and aperture margin shape. One important finding of this study suggested some degree of intrapopulational variations as shown by the scatterplots which may suggest phenotypic plasticity in the species. Although the scatter plots revealed some degree of overlaps among populations, Kruskal-Wallis test, phenetic and cluster analysis showed significant differences among populations. The differences can be due can be due to many possible factors including genetic, biotic and abiotic factors since geographic distance cannot be attributed to the differences observed among populations.