Whales, as specialized marine mammals, underwent profound biological changes in their transition from land to ocean, raising questions about the functionality of senses common to their terrestrial relatives. The investigation into whether whales possess the sensory structures needed for taste reveals that cetaceans have largely abandoned this classic mammalian sense. Their highly modified anatomy and genetic code reflect an evolutionary path where flavor detection became irrelevant to survival, favoring more efficient sensory systems for their aquatic environment. Understanding the sensory profile of these ocean dwellers requires examining the physical evidence on their tongues, the molecular remnants in their DNA, and their feeding strategies.
Anatomical Presence of Taste Buds
The tongues of whales offer the first physical evidence suggesting a significant reduction in the sense of taste compared to land mammals. Most mammals have papillae on the tongue surface that house specialized sensory organs known as taste buds. Whales, however, generally lack these structures. Examination of the oral anatomy in both toothed whales (Odontocetes) and baleen whales (Mysticetes) confirms a widespread absence or severe atrophy of these taste papillae.
For toothed whales, including dolphins and porpoises, the taste buds are either entirely missing or heavily reduced and non-functional. The tongue is often large, rigid, and adapted for moving prey quickly toward the throat, not for manipulating food. Baleen whales also possess tongues that are not structured for taste reception. Their massive and muscular tongues serve instead to help expel large volumes of seawater after filtering prey through the baleen plates.
Genetic Basis of Taste Perception
The genetic evidence provides a deeper explanation for the loss of taste in whales. Taste perception in mammals is governed by specific genes, particularly the TAS1R family, which code for the receptors of sweet, umami (savory), and bitter flavors. Genetic studies across multiple whale species, including both toothed and baleen lineages, have demonstrated a massive loss of functional taste receptor genes.
The genes responsible for sensing sweet, umami, and bitter tastes have been rendered non-functional, existing as pseudogenes. A pseudogene is a segment of DNA that resembles a functional gene but contains mutations that prevent it from producing a working protein. The gene associated with sour taste, Pkd2l1, has also been found to be pseudogenized in whales. This widespread loss of functionality is thought to have occurred in the common ancestor of all modern whales 36 to 53 million years ago. Whales are the first group of animals known to have lost four of the five primary taste modalities. The only exception is the gene for salty taste, which remains intact, but scientists hypothesize this is maintained for regulating sodium reabsorption and water balance, not flavor.
Feeding Mechanics in the Absence of Taste
The lack of traditional taste receptors is directly linked to the specialized feeding mechanics of cetaceans, which prioritize volume and speed over flavor evaluation. Toothed whales, which primarily hunt fish and squid, seize their prey and swallow it whole without chewing. This “grab-and-gulp” method means that the food spends virtually no time in the mouth, making flavor detection unnecessary.
Baleen whales employ a different but rapid strategy, relying on filter feeding. Species like the blue whale take in enormous amounts of water containing dense patches of small organisms like krill. A unique oral plug shifts to protect the respiratory tract as the whale engulfs the water, which is then filtered out through the keratinous baleen plates, leaving the prey behind. This process is optimized for capturing massive quantities of food and does not allow for the slow, sensory evaluation that taste provides.
Despite the loss of traditional taste, whales retain chemosensory capabilities in the water. Baleen whales, for instance, retain some elements of their olfactory system and may use waterborne chemical cues, like dimethyl sulfide (DMS) released by feeding krill, to locate food patches over long distances. This suggests that their sense of smell or a general chemical detection system acts as a substitute, guiding their feeding behavior toward areas of high prey density.