New clues about the evolution of bitter taste perception found in sharks

In a new study led by the University of Cologne, scientists have made a remarkable discovery about the taste perception abilities of sharks and rays. 

The research team, including Dr. Maik Behrens, Tatjana Lang, and Dr. Sigrun Korsching, identified a receptor for bitter taste in these cartilaginous fish, challenging previous assumptions that such receptors were exclusive to bony vertebrates.

Significant discovery

The receptor, part of the taste receptors type 2 (T2R) family, is known to help humans identify bitter and potentially toxic foods. 

This discovery in cartilaginous fish like sharks and rays is significant as it indicates the presence and functional importance of T2R receptors in a broader range of species than previously understood.

Toxic compounds

“Many animal and plant species synthesize toxic compounds as deterrent, often recognized by bitter taste receptors (T2Rs),” wrote the study authors. 

“Here, we have identified a singular T2R in cartilaginous fishes and determined its ligand repertoire in two shark species.”

Focus of the study 

Until recently, molecular research on sharks faced challenges due to their large genomes, making sequencing complex and time-consuming. 

However, advancements in techniques have now made it possible to delve deeper into the gene sequences of many cartilaginous fishes.

What the researchers learned 

The team’s investigation covered seventeen cartilaginous fish genomes, out of which twelve contained genes for the T2R taste receptors. Intriguingly, only one T2R gene, named T2R1, was present in each species. 

This singularity suggests that T2R1 might represent the original form of these bitter taste receptors, remaining unchanged by gene duplication and specialization over time.

New insights

“These findings give us new insights into the evolution of these receptors: We can look back almost 500 million years on the molecular and functional origin of an entire family of bitter taste receptors. Because that is how old the last common ancestor of cartilage and bony fish is,” said Professor Korsching. 

Detecting bitter substances 

Further experiments introduced the T2R1 gene from the bamboo shark and the catshark into immortalized cell lines, revealing that these sharks can detect bitter substances similar to those perceived by humans, like colchicine or bile acid. 

Out of ninety-four human bitter substances tested, eleven were able to activate the sharks’ receptors.

Vertebrate evolution 

Remarkably, some of these substances also activated the bitter taste receptors of the coelacanth, a species known as a “living fossil” among bony fish. This finding, from a previous study, highlights the astonishing conservation of this function throughout vertebrate evolution.

Professor Korsching summarized the significance of this research by stating: “The extent to which this function has been conserved is astonishing, i.e., through the entire evolution of vertebrates.” 

Study implications 

This discovery not only sheds light on the evolutionary history of taste receptors but also opens new avenues for understanding how taste perception has shaped the survival and behavior of diverse species across millions of years.

The study is published in the journal Proceedings of the National Academy of Sciences.

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