Taste perception is one of our basic five senses. It can tell us what is edible or what is not, what is nourishing for our bodies and what can be potentially harmful. For example, being unable to recognize food with the right amount of nutrients could lead to malnutrition in the long run, while being unable to detect poisonous or toxic foods could result in near instantaneous death. Thus the ability to taste food can be a life-and-death matter.
Most marine and terrestrial vertebrates including humans have five basic tastes—sour, sweet, bitter, salty and umami (savory). These flavors are detected by taste receptor—proteins on the upper surface of the tongue. Cetaceans—dolphins and whales—appear to be an exception. These animals appear to have lost the ability to taste any flavors, except for salty. Most of the genes that are supposed to produce proteins necessary for taste perception are riddled with mutations. Only the genes responsible for detecting salty flavors are still functional. One suggested reason behind the mutations is that these animals swallow their prey whole, and as such don’t need to perceive flavor, which is usually released by chewing. Young dolphins and whales however do have a small number of taste receptors, but the receptors decrease in number or even disappear completely with age.
Bottlenose dolphins however appear to be capable of perceiving at least four of the five basic tastes i.e., sweet, salt, bitter and sour. However, in is unclear whether or not this has an impact on their natural behavior.
To investigate this, Bouchard and his colleagues devised a spontaneous choice experiment to test whether or not captive bottlenose dolphins could prefer a natural fish taste stimulus (fish) to a control stimulus (spring water). Four dolphins—two adult male (aged 22 and 24 years old) and two juvenile females (aged 4 and 7 years old) were used in the experiment. The two stimuli were presented to the dolphins using floating taste diffusers built from modified chlorine diffusers for outdoor swimming pools.
Each spontaneous choice experiment consisted of placing the two diffuser on opposite sides of a lagoon pool equidistant from a starting position, and then allowing a dolphin to freely interact with the diffusers. The movements and attractive behaviors of the dolphins were recorded using two digital cameras.
The researchers found that juvenile females spent more time interacting with the fish diffuser than with the control diffuser, indicating that they were able to discriminate between the fish mixture and the control. Thus they were attracted by the fish mixture. The adult males on the other hand showed no preference between the fish mixture and the control. This is probably because of the age-related loss in the number of taste receptors in this species.
This finding shades light on our understanding of the role of chemoreception in the behavioral ecology of bottlenose dolphins. This also means that zoos and aquariums should incorporate chemical cues in their environmental enrichment programs if they are to effectively maintain the physiological and psychological health of captive dolphins.
References:
Bertrand Bouchard, Thomas J. Lisney, Sylvie Campagna, Aurélie Célérier (2017). Do bottlenose dolphins display behavioural response to fish taste? Applied Animal Behaviour Science 194, 120-126, ISSN 0168-1591, https://doi.org/10.1016/j.applanim.2017.05.013
