Changes in centrum shape along the vertebral column in four species of partially sympatric dolphins from Southern South America: a 3D morphometric approach.

SILVANA DANS; ROLANDO GONZÁLEZ-JOSÉ; CLAUDIA BOY; MATÍAS MORA; MARIA CONSTANZA MARCHESI

Halifax

Conferencia; 22nd Biennal Conference on the Biology of Marine Mammals; 2017

Society for Marine Mammalogy

Dolphin vertebral column has been described as variably flexible. Centrum shape is one of the features that allow determination of stable and flexible areas in the column. Centra from stable areas are short anteroposteriorly and with large articular facets; opposite features would be signaling a potentially flexible area. The Commerson?s dolphin (Cephalorhynchus c. commersonii), the Peale?s dolphin (Lagenorhynchus australis), the dusky dolphin (L. obscurus) and the hourglass dolphin (L. cruciger) are closely related species with distributions restricted to the Southern Hemisphere. We describe changes in centrum shape along their vertebral columns. To our knowledge, this is the first 3D geometric morphometrics approach applied on dolphin vertebrae. For each species, eight different vertebrae were chosen. For each centrum, 18 landmarks were digitized with a Microscribe G2X. We explored shape variations among regions employing Principal Components Analyses. The beginning of the thorax had discoidal centrum shape (positive values in PC1), with a dorsoventral compression (negative values in PC2), resulting in a centrum facet wider than higher. Vertebrae in the mid-thorax had the less discoidal centra (negative PC1 values) along the column, having circular centrum facets (PC2 values close to cero). The rest of the regions are distributed between extreme PC1 values, with the mid-torso and the limit between mid and posterior torso being highly compressed anteroposteriorly. Tailstock vertebral centra are strongly compressed laterally, being centra taller than wider, this especially true for the Lagenorhynchus spp. tailstock centra. The degree of anteroposterior compression of the tailstock centra seems to be the main difference between species, being highly discoidal in C. commersonii when compared qualitatively to the three Lagenorhynchus species. In the studied species, centrum shape varies along the column, signaling areas of high stability and areas with high flexibility. Differences among species may be related to their swimming style and ecological habits.