Geometric morphometrics reveal complex shape variation patterns at different geographic scales in the patagonian gastropod Trophon geversianus

Abstract

Environments with strong gradients in physical conditions, such as rocky intertidal, induce animal morphological strategies to face them. The gastropod Trophon geversianus inhabit within the intertidal and subtidal habitats of Patagonian rocky shores. Although there is a wide knowledge of the phenotypic differences of this species regarding habitats (i.e., intertidal/ subtidal), little is known about the interaction between habitat and latitude. Here, we studied form variation (size and shape) by using 3D geometric morphometric of T. geversianus shells from alive gastropods and analyzed the phenotypic effect from micro-scale (habitat), macro-scale (latitude), and the interaction habitat-latitude (site). Lastly, we tested the classification accuracy of the shape variable for each predictor variable and a synthetic variable (from a cluster analysis). We found that habitats and sites had the greatest influence on shape variation. Moreover, we found that the largest shell sizes were more likely to be located in subtidal habitats. Also, the size differences between sites were not negligible. Finally, habitat demonstrated the highest classification accuracy for shape, even higher than genetically determined (sex) and synthetic variables. We found that the gastropods from the intertidal habitat presented a globular morph with shorter spire and larger relative size of the shell aperture, while subtidal gastropod showed an elongated morph, with smaller aperture and longer spire. We present evidence of the complexity of size and shape variation in T. geversianus, highlighting that site-dependence on shape variation must be considered in geometric morphometrics studies at a latitudinal scale.