Can’t taste, or don’t care? Greater Caribbean manatees (Trichechus manatus manatus) fail to display preferences for or aversions to the five basic taste qualities

Marine mammals such as cetaceans and pinnipeds are known to have largely lost their sense of taste, probably due to their transition from a mixed to a strictly carnivorous diet and from masticating plant-based food to swallowing their animal prey whole. In contrast, nothing is known so far about the functionality of the sense of taste in sirenians, the only extant herbivorous marine mammals. Using two-bottle preference tests of short duration (2 min), we therefore assessed the gustatory responsiveness of three adult male Greater Caribbean manatees (Trichechus manatus manatus) to food-associated substances representing the five canonical taste qualities. Further, we assessed if the manatees display a preference for the taste of freshwater over that of seawater. We found that the manatees showed no significant preference for or significant avoidance of any of the taste stimuli when presented at concentrations that are detectable for most mammal species tested so far. This was true both when using seawater or freshwater as the solvent and as the alternative stimulus. The manatees also showed no significant preference for freshwater over seawater. These results are not consistent with anatomical findings that reported manatees to possess a high number of taste buds and with genetic findings suggesting the taste receptor genes of manatees to be intact. Further, they do not align with the notion that access to freshwater sources is an important feature of their habitat. Our results suggest that the herbivorous dietary specialization of manatees may not have prevented a reduction in their sense of taste. However, at this point we cannot decide whether the manatees can't taste or don't care about taste.