Sensory Biology of the Franciscana ( <i>Pontoporia blainvillei</i> , Pontoporiidae, Cetartiodactyla): Ontogenetic Modifications of Vibrissae and Vibrissal Crypts

The transition of cetaceans from a terrestrial to an aquatic environment involved a crucial sensory adaptation in environments with limited visibility. Vibrissae, important mechanoreceptors, undergo an ontogenetic transformation in odontocetes. Although most lose them early in life, their follicles persist as innervated vibrissal crypts, suggesting a continuous sensory function. In some species, these crypts could function as mechanoreceptors, electroreceptors, or even be involved in magnetoreception. The Franciscana (Pontoporia blainvillei) is a species restricted to the Southwestern Atlantic Ocean. It currently faces high mortality rates due to incidental capture in gillnets, which has led to its current classification as Vulnerable. This research describes the histomorphology of vibrissae and crypts in different developmental stages. The samples were processed using routine histological techniques, immunohistochemistry, and scanning electron microscopy. In neonates, the emerging and innervated vibrissae probably are important for lactation. Subsequently, the vibrissal hair is lost or involutes , being replaced in juveniles and adults by an innervated pseudohair that likely maintains a mechanoreceptive function, although its micromorphology also suggests a potential electroreception. The maturation of the echolocation system, which allows for a broader diet, coincides with these changes in the vibrissae. This suggests that the initial mechanoreceptive structures, linked to lactation, evolve to complement hearing and foraging within low-visibility environments.