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

LOZA, CLEOPATRA M.; KRMPOTIC, CECILIA M.; GALLIARI, FERNANDO C.; ANDRÉS LAUBE, PEDRO F.; NEGRETE, JAVIER; SCARANO, ALEJO C.; LOUREIRO, JULIO; CARLINI, ALFREDO A.; BARBEITO, CLAUDIO G.

ZOOLOGY

ELSEVIER GMBH

Año: 2019 vol. 133 p. 66 - 80

0944-2006

Pinnipeds are semiaquatic carnivorans that spend most of their lives in water and use coastal terrestrial, or icepack, environments to breed, molt and rest. Certain characteristics of the ear have been linked to ecologicalaspects. In our contribution we focus on the study of the macroscopic and microscopic morphology of theexternal ear (with the exception of the osseous outer ear canal) of six species of Southern pinnipeds. In order torecognize the different components of tissues, sections were stained following several routine protocols. Inaddition, double-staining and enzymatic clearing (Alcian blue-alizarin red) was performed to assess the arrangementof skeletal elements in the OEC. The basic structure of the pinna in the southern otariids studiedmatch those previously analyzed for Northern Hemisphere species. The cartilage macro anatomy of the OEC ofMirounga leonina and Arctocephallus gazella is different from that of the Northern Hemisphere species, with onlyone plate of cartilage, but markedly different between them. The histology of the otariids OEC is homogeneousalong the entire extension, but phocids has three different regions (distal, middle, and proximal). The cartilagehistology of most phocids is also different from that of analyzed otariids, with an elastic cartilage that resemblesa myxoid-like tissue, but is not present in M. leonina, were the tissue around the OEC is very rich in adipocytes.The southern elephant seal M. leonina OEC has a combination of features similar to both the rest of the phocidsand to the otariids. An auditory organ that is functional both over and under water could be essential for socialbehavior in these species.