Adaptations to a semiaquatic lifestyle in the external ear of southern pinnipeds (Otariidae and Phocidae, Carnivora): Morphological evidences

LOZA, C. M.; CECILIA M. KRMPOTIC; FERNANDO C. GALLIARI; LAUBE, F. A.; NEGRETE, J.; SCARANO, A. C.; LOUREIRO, J.D.; ALFREDO A. CARLINI; CLAUDIO G. BARBEITO

ZOOLOGY

ELSEVIER GMBH

Año: 2019 vol. 133 p. 66 - 80

0944-2006

Pinnipeds are semiaquatic carnivorans that spend most of their lives in waterand use coastal terrestrial, or ice pack, environments to breed, molt and rest. Certaincharacteristics of the ear have been linked to ecological aspects. In our contribution wefocus on the study of the macroscopic and microscopic morphology of the external ear(with the exception of the osseous outer ear canal) of six species of Southernpinnipeds. In order to recognize the different components of tissues, sections werestained following several routine protocols. In addition, double-staining and enzymaticclearing (Alcian blue-alizarin red) was performed to assess the arrangement of skeletalelements in the OEC.The basic structure of the pinna in the southern otariids studiedmatch those previously analyzed for Northern Hemisphere species. The cartilagemacro anatomy of the OEC of Mirounga leonina and Arctocephallus gazella is differentfrom that of the Northern Hemisphere species, with only one plate of cartilage, but2markedly different between them. The histology of the otariids OEC is homogeneousalong the entire extension, but phocids has three different regions (distal, middle, andproximal). The cartilage histology of most phocids is also different from that of analyzedotariids, with an elastic cartilage that resembles a myxoid-like tissue, but is not presentin M. leonina, were the tissue around the OEC is very rich in adipocytes. The southernelephant seal M. leonina OEC has a combination of features similar to both the rest ofthe phocids and to the otariids. An auditory organ that is functional both over and underwater could be essential for social behavior in these species.