Sexual Differentiation ofOctopus hubbsorum(Mollusca: Cephalopoda) Using Body Dimensions and the Shape and Size of the Stylets: A Traditional and Geometric Morphometric Analysis

Abstract

Sexual differences in size and morphology are conspicuous features of dioecious organisms like octopuses. In this study, we analyze differences on body dimensions and the size and shape of Octopus hubbsorum Berry, 1953 stylets, using traditional and geometric morphometrics to ascertain if both methods can recognize differences between males and females. Traditional morphometrics revealed differences in body and stylet sizes because the females were bigger than the males, and the total body weight was the most related body measure with all the stylets measures. Due to the shape of the stylets we used two landmarks and 40 semilandmarks, and for the semilandmarks alignment we used two methods: minimization of bending energy (min BE) and minimization of Procrustes distance (min D), to test if the method to align semilandmarks influenced the analysis. Differences were found between the two methods, such as the mean shape, the percentage of predicted organisms to their corresponding sex in discriminant function analysis (DFA), and the relationships between stylet shape and body size as well as centroid size of the stylets; however, the deformation grids were similar between the two methods and their canonical variate analysis (CVA) found significant differences in mean shape of the stylets of males and females. These results demonstrated the morphometric sexual dimorphism in O. hubbsorum using body dimensions and the size and shape of the stylets.