Cranial ontogeny in Lagenorhynchus australis and L. obscurus

DEL CASTILLO, DANIELA; VIGLINO, MARIANA; FLORES, DAVID A.; CAPPOZZO, HUMBERTO LUIS

San Francisco

Congreso; 21st Biennial Conference on the Biology of Marine Mammals; 2015

Society for Marine Mammalogy

Our goal was to investigate cranial morphology in Lagenorhynchus australis and L. obscurus by analyzing shape changes along their ontogenetic trajectories and compare them, using a 3D geometric morphometric approach. It may provide insights into their evolutionary history and interspecific variation. We analyzed craniums of complete ontogenetic series of L. obscurus (n=32) and L. australis (n=20) and digitized 55 cranial landmarks. We performed size-corrected PCA, to study differences in shape between species that are not size-related and regressions of shape into size to detect species-specific shape changes during ontogeny, and similar trends between them. We also performed a Procrustes Anova, to detect significance of different sources of variation, including directional asymmetry (DA) and regression of Asymmetric component of shape into size to study DA development. Size-corrected PCA revealed that L. obscurus displays a more elongated rostrum, external nares and infraorbital foramina more caudally displaced, posterior part of the skull relatively more compressed and temporal fossa proportionally smaller. Both ontogenetic trajectories described a lengthening of the rostrum, backward displace of infra orbital foramina and size reduction of external nares, relative compression of the posterior region of the braincase and dorsal displacement of temporal fossa. For specific ontogenetic trends, L. obscurus displayed stronger development of the rostrum than L. australis, besides, rostrum becomes narrower, while in L. australis rostrum widens. External nares showed a marked caudal displacement in L. obscurus, while in L. australis it was slighter. Significant DA was detected, and it did not change significantly during ontogeny. Some of the observed trends are associated with high prenatal development of the brain and telescoping, while other important differences in the rostrum and the robustness of the cranium may be related to differences in species habitat and foraging. Significant DA and the fact that it does not increase during ontogeny may be related to the importance of the sound producing apparatus since the beginning of postnatal life.