CONICET | Buscador de Institutos y Recursos Humanos

Commerson?s dolphin (Cephalorhynchus commersonii), Peale?s dolphin (Lagenorhynchus australis), dusky dolphin (Lagenorhynchus obscurus) and hourglass dolphin (Lagenorhynchus cruciger) are closely related species occurring in the Southern Hemisphere. Even though they are partially sympatric, they have evolved towards diverse foraging strategies, prey, and habitat preferences. Size variation occurs both among and within species. Our goal was to study the allometric patterns and ontogenetic trajectories in the vertebral column of these dolphins related to their ecology. We choose nine functionally homologous vertebrae in each column and digitized five different tridimensional configurations, containing 28 to 41 landmarks depending on the functional region under analysis. We explored different levels of allometry (static, ontogenetic, and evolutionary) using multivariate regressions of shape vs. log-transformed centroid size. We compared ontogenetic allometry regression vectors to evidence differences in growth patterns. Finally, we calculated Procrustes distances of shape configurations to determine the timing of shape shifts. Commerson?s dolphin showed the highest degrees of allometry, both static and ontogenetic; than Lagenorhynchus species. Differences in ontogenetic trajectories and timing of shape shifts allowed us to hypothesize that pelagic species that feed cooperatively would maintain a morphology related with greater stability, possibly similar to the oceanic ancestor proposed for these species. The macro-evolutive trends indicate a high degree of evolutionary morphological change, which could be associated to the rapid evolutionary radiation proposed for the group. This is the first time that allometric changes are studied in small cetaceans by means of 3D geometric morphometrics.

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