A field study of chemical senses in bottlenose dolphins and pilot whales

Abstract

For most marine vertebrates, chemical cues provide crucial information during navigation and foraging, but their use by cetaceans is still poorly understood. In contrast to baleen whales, toothed whales (odontocetes) are scarcely equipped for chemoreception: they lack the conventional anatomical structures (i.e., olfactory epithelium, nerves and bulbs) involved in olfaction and have reduced taste buds on the tongue. Several behavioral studies have however shown that captive dolphins can perceive chemical solutions, including odorants, in their oral cavity. To investigate whether odontocetes could use infochemicals in their foraging ecology, we implemented a behavioral response experiment in wild bottlenose dolphins and long-finned pilot whales. We tested dimethyl sulfide (DMS) as a potentially attractive stimulus since it is a chemical signature of highly productive marine areas, known to attract several marine predators including fishes and seabirds.We assessed cetacean responses to DMS exposure by analyzing their movements and surface behaviors recorded by onboard observers. In both species, results did not reveal any significant attraction or behavioral reaction toward DMS when compared to a control chemical stimulus, apart from a short-distance response in bottlenose dolphins. These results suggest that while odontocetes may perceive DMS in water, it apparently does not play a significant role in their foraging ecology. Testing potentially more attractive compounds such as prey extracts with the present method and analyzing surface, underwater and acoustic responses would provide further insights on odontocete feeding behavior. It would also provide valuable clues to studies on the anatomical structures involved in their chemosenses.

Physiology of the tongue with emphasis on taste transduction

“…Whereas in the hummingbird, a specialized nectar feeder, the umami receptor has been repurposed to detect carbohydrates ( 78 ). Cetaceans (whales and dolphins) have reduced gustatory range reportedly only detecting salt and a limited range for bitter ( 79 ). However, aquatic chemosensation is also still poorly understood but is equally if not more complex than that of mammalian tongue perception with the chemotactile sensation of the octopus as a prime example of that complexity ( 80 ).…”

Neuroanatomy of the Cetacean Sensory Systems

“…Odontocetes have reduced but functional chemosensory capacities, as shown by anatomical, genetic, and behavioural studies. They are able to detect certain substances in air or water, although the physiology of the sensory systems involved is not well understood [ 214 ]. For a brief summary of chemoreception in dolphins, see [ 5 ].…”

“…Regarding function, humpback whales have been shown to detect krill over a distance of several hundred metres [ 228 ], while odontocetes might detect chemicals but over short distances, considering that chemoreception does not play a significant role in foraging behaviour [ 214 ]. Besides prey detection, a sense of smell might also be useful for other purposes, such as the detection of conspecifics, or even to extract information on conspecific reproductive states through their breath exhalations [ 222 , 229 ].…”

Open questions in marine mammal sensory research

“…Olfaction and gustation (i.e. chemoreception in general), are largely understudied and many questions as basic as ‘What (if anything) can cetaceans smell or taste?’ are still unclear ( Bouchard et al, 2019 ; Bouchard et al, 2022 ; for review see Kremers et al, 2016 ). The proposed perspective on marine mammal sensing, including aquatic and aerial sensing, will require examining adaptations that allow for amphibious sensing in all marine mammal species.…”