Vertebral shape in Delphinidae within a phylogenetic frame

Abstract

Differences in vertebral morphology in cetaceans would be related to various functional abilities, promoting ecological diversity and adaptive radiation. We used three-dimensional landmark configurations as well as a calibrated phylogeny to explore vertebral morphology along the vertebral column of 24 dolphin species within a phylogenetic context. We employed various phylogenetic comparative methods to explore the presence and relevance of phylogenetic signal in vertebral morphology within Delphinidae, and to estimate to what extent vertebral modifications are constrained by phylogeny or could be linked to adaptation to particular habitats. Visual inspection of three different component analysis allowed us to evidence species with particular habitat requirements diverging greatly from their closest relatives. Differences between the angles of the first components of our analysis showed greater amount of variation not related to phylogeny in three regions, the anterior thorax (Th), the posterior thorax (ThTo), and the synclinal point (SP). Similarities between the angles in the mid-torso (Tm) and tail stock (TS) suggest as greater effect of phylogeny on vertebral morphology. Despite this, even in these regions, species with similar biomechanical requirements seem to be located relatively close disregarding phylogeny. Through Phylogenetic ANOVAS and tests for phylogenetic signal with different data sets (Procrustes coordinates, reductions of components), we found that both ecology and phylogeny have effect on vertebral morphology. Results showed statistical differences between the different ecological groups, in all regions but the anterior thorax (Th). Most regions showed weak but significant phylogenetic signal, with low z values. Vertebral morphology in Delphinidae may reflect habitat requirements within certain phylogenetic constraints, and this varies along the vertebral column. Further studies are needed to elucidate the factors behind vertebral morphology in these mammals of axial locomotion.