Allometric Growth and Scaling of Body Form of the Spadenose Shark (Scoliodon laticaudus).

Abstract

The versatility of the shark body form is suggested to be one of the key factors underlying their evolutionary success and persistence. Nevertheless, sharks exhibit a huge diversity of body forms and morphological adaptations. More subtly, it is increasingly evident that in many species, morphology varies through ontogeny. Multiple competing hypotheses exist explaining both the function of specific morphological structures and the interspecific distribution of these ontogenetic morphological shifts. However, existing studies are restricted to a small number of mostly large-bodied species. In this study, we report allometric scaling relationships from functionally important morphological structures in the spadenose shark (Scoliodon laticaudus). We find that a mosaic of isometric and allometric growth underlies the scaling trends in this species and that cases of allometry are consistent with an ontogenetic shift in diet. Moreover, our results refute suggestions that small-bodied sharks grow isometrically. Given the small number of existing studies of ontogenetic morphometry in sharks and the life-history/ecological characteristics of S. laticaudus, this study is a valuable contribution to our understanding of the adaptive value of ontogenetic morphological shifts in elasmobranchs.