The Tactile Senses of Marine Mammals

Abstract

The successful return of mammals to aquatic environments has presented numerous sensory challenges to overcome. Aquatic habitats reduce the utility of vision and the type of chemoreception important in terrestrial perception. In several orders, the sense of touch assumed greater importance, especially when enhanced by the development of vibrissal (sensory hair) systems. Species of two extant orders, Sirenia and Cetacea, have lost all of their hairs except for vibrissae. In the former, these hairs cover the entire bodies of the two families, Trichechidae and Dugongidae. Hairs in adult cetaceans are more constrained (e.g., they appear in some river dolphins and baleen whales) and are restricted primarily to rostral regions. Pinnipeds and sea otters retained their pelage, but in addition have elaborated their mystacial and other facial vibrissae. High numbers of vibrissal receptors, associated dense innervation, prominence of neural tracts, and hypertrophy of brain areas associated with touch suggest an importance of tactile senses for aquatic mammals. Experimental testing has demonstrated the exquisite tactile sensitivity of many marine mammal species. Sensory hairs contribute to that tactile sensitivity in both haptic and mechanosensory contexts. Several, if not most, pinniped species, seals and sea lions, can track prey based on mechanoreception alone. It remains unclear to what degree non-vibrissal skin receptors contribute to tactile sensation in most marine mammals. In this review we will discuss the neurobiological and behavioral evidence for the tactile senses of marine mammals.