Plastral pigmentation symmetries in Western Hermann's tortoise (Testudo hermanni hermanni)

Abstract

Shape is a fundamental morphological descriptor, one method of its estimation being from digitally processed images. Elliptic Fourier method is an outline-based morphometrics that has some advantages: it does not require either landmarks or previous knowledge about the shape variation of the objects under study; it can visualize the contour of information and reconstruct the original shape; it can be mathematically normalized to size, rotation and starting point of the contour trace; and it can be conducted automatically using computer software. Hence, the variation can be decomposed into several mutually independent quantitative characteristics. In this manner, unacceptable errors based only on human visual judgment of shape, which is frequently deceptive and misled by size factors, can be effectively eliminated. In this study, we applied an elliptic Fourier analysis (EFA) to assess pigmentation pattern symmetries of plastron (ventral shell) of 52 western Hermann's tortoises (Testudo hermanni hermanni) studied from private breeders, and belonging to two different Mediterranean populations: Albera (Catalonia, NE Iberian Peninsula, n=14) and Balearic Islands (n=38). Low coefficients of regression appeared between carapace length and symmetrical and asymmetrical components. Based on this sample, it was shown that plastral pigmentation design does not present differences for either the symmetrical or the asymmetrical component. These results provide a baseline for further comparisons in variation of plastral pigmentation pattern based on EFA.