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

Abstract

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