Sharks Have Bitter Receptors, but They Don’t Use Them for Tasting, Study Shows

Sharks are among the oldest living vertebrates, having evolved for more than 400 million years. They are known for their keen senses of smell, hearing, and electroreception, but what about their sense of taste?

A new study has revealed that sharks and rays have a receptor for bitter taste, which may have implications for their feeding behavior and ecology.

Bitter Taste Receptors in Cartilaginous Fish

(Photo : MICHELE SPATARI/AFP via Getty Images)

Bitter taste receptors are a family of proteins that detect bitter compounds, often associated with toxins or plant defenses. In mammals, these receptors are encoded by the TAS2R gene family, which consists of 25 functional genes and 11 pseudogenes in humans.

Bitter taste perception plays a vital role in animal behavior and fitness, as it enables animals to avoid exposure to harmful substances.

However, bitter taste receptors are not only found in the mouth, but also in other tissues, such as the pancreas and the gastrointestinal tract, where they may have other functions related to metabolism and immunity.

The evolution of bitter taste receptors has been influenced by the dietary habits and ecological niches of different species.

For example, carnivores tend to have more bitter taste receptors than herbivores, as they encounter more bitter compounds in their prey.

However, the origin and diversity of bitter taste receptors in non-mammalian vertebrates are poorly understood.

A research team from the University of Cologne, in collaboration with colleagues from the Leibniz Institute for Food Systems Biology in Freising, has discovered a receptor for bitter taste in twelve different cartilaginous fish (sharks and rays).

Cartilaginous fish are a group of vertebrates that have a skeleton made of cartilage instead of bone. They are the closest living relatives of the bony fish, from which the tetrapods (four-limbed vertebrates) evolved.

The researchers used a combination of genomic, transcriptomic, and functional analyses to identify and characterize the bitter taste receptor in cartilaginous fish.

They found that the receptor belongs to the TAS2R family, but is not orthologous to any of the mammalian TAS2R genes.

Instead, it is a novel member of the TAS2R family that arose from a gene duplication event before the split of cartilaginous and bony fish. The researchers named this receptor TAS2R-Sh, for shark.

The researchers also tested the ability of TAS2R-Sh to respond to various bitter compounds, such as quinine, caffeine, and salicin.

They found that TAS2R-Sh is sensitive to a wide range of bitter substances, but has a preference for salicin, a natural compound found in willow bark and other plants. Salicin is also the precursor of aspirin, a widely used anti-inflammatory drug.

Also Read: Blue Sharks Use Eddies for Fast Track to Food

Implications for Shark Ecology and Conservation

The discovery of a bitter taste receptor in sharks and rays has several implications for their ecology and conservation.

Firstly, it suggests that sharks and rays have a more complex taste system than previously thought, and that they may be able to discriminate between different types of prey based on their taste.

This could affect their feeding preferences and strategies, as well as their interactions with other predators and competitors.

In addition, it indicates that sharks and rays may have evolved a mechanism to cope with the ingestion of bitter and potentially toxic substances, such as marine toxins or pollutants.

This could have implications for their health and survival, especially in the face of environmental changes and human impacts.

Thirdly, it provides a new molecular marker for studying the evolution and phylogeny of cartilaginous fish, as well as their divergence from bony fish and tetrapods.

This could help to resolve some of the unresolved questions and controversies in the evolutionary history of vertebrates.