Ontogenetic shifts in body form in the bull shark Carcharhinus leucas

Abstract

Recent studies have uncovered mosaic patterns of allometric and isometric growth underlying ontogenetic shifts in the body form of elasmobranch species (shark and rays). It is thought that shifts in trophic and spatial ecology through ontogeny drive these morphological changes; however, additional hypotheses relating to developmental constraints have also been posed. The bull shark (Carcharhinus leucas) is a large‐bodied coastal shark that exhibits strong ontogenetic shifts in trophic and spatial ecology. In this study, we utilise a large data set covering a large number of morphological structures to reveal ontogenetic shifts in the body form of C. leucas, stratifying analyses by sex and size classes to provide fine‐scale, more ecomorphologically relevant results. Our results indicate shifts in functional demands across the body through ontogeny, driven by selective pressures relating to trophic and spatial ecology driving the evolution of allometry. We also find significant differences in scaling trends between life stages, and between the sexes, highlighting the importance of utilising large, diverse datasets that can be stratified in this way to improve our understanding of elasmobranch morphological evolution. Ultimately, we discuss the implications of these results for existing ecomorphological hypotheses regarding the evolution of specific morphological structures, and pose novel hypotheses where relevant.

Insights into ontogenetic scaling and morphological variation in sharks from near-term brown smooth-hound (Mustelus henlei) embryos

“…The prevalence of isometry as opposed to allometry in M. henlei embryos lends further credence to the idea that allometric shifts in shark body form result at least in part from ontogenetic niche shifts. Studies investigating ontogenetic shifts in body form in sharks typically relate these changes to differences in trophic or spatial ecology (Lingham-Soliar, 2005; Irschick and Hammerschlag, 2015; Fu et al, 2016; Irschick et al, 2017; Sternes and Higham, 2022; Gayford et al, 2023a; Gayford et al, 2023b; Seamone et al, 2023; Yun and Watanabe, 2023; Gayford et al, 2024). In many species, adults consume larger prey and spend a greater proportion of time in offshore, open-ocean environments – likely resulting in a shift in the selective pressures acting on individuals through ontogeny (Sternes and Higham, 2022; Gayford et al, 2023b).…”

“…It is only relatively recently however that ontogenetic shifts in morphology have been documented (e.g. Lingham-Soliar, 2005; Irschick and Hammerschlag, 2015; Fu et al, 2016; Irschick et al, 2017; Ahnelt et al, 2020; Sternes and Higham, 2022; Bellodi et al, 2023; Gayford et al, 2023a; Gayford et al, 2023b; Seamone et al, 2023; Yun and Watanabe, 2023; Gayford et al, 2024). These shifts are important not only from the perspective of functional ecology but help us to understand the selective forces underlying the evolution of elasmobranch morphology (Gayford et al, 2023b).…”