Study explains the evolution of taste receptors in mammals

Is evolution responsible for people’s inability to resist a salty chip? Scientists from North Carolina State University (NC State University) have found that variations in the basic composition of foods and the elemental demands of animals can explain the development of appealing tastes, such as umami, sweet, and salty.

Study explains the evolution of taste receptors in mammals
Image Credit: North Carolina State University.

Taste tells people a lot of things about foods before they are consumed and digested, and certain tastes relate to the elemental composition of foods. An aged steak, for instance, activates the umami taste receptors because it has a high amount of elemental nitrogen, which is found in amino acid molecules.

Nitrogen is required for survival but despite this fact, it is often found in low proportions in relation to animals’ needs. Similarly, sodium is restricted in many natural foods—imagine life before supermarkets. So, if people require sodium to thrive—as all creatures do—they are more likely to have developed a taste for, and seek out salty foods.

Nutritional imbalances, even at the elemental level, can limit the growth and metabolism of animals. We posited that animals should have evolved the ability to taste, and enjoy, certain elements and nutrients that are most likely to be limiting for growth, due to their low concentrations in typical foods.”

Lee Demi, Study Co-Author and Postdoctoral Researcher, Department of Applied Ecology, North Carolina State University

Demi and collaborators investigated this concept by comparing the body elemental constitution of three animal species (such as fish, insects, and mammals) to the elemental composition of plants—the foundation of most food webs. The team hypothesized that animals who consume food containing specific elements that are unpredictable or rare may probably have taste receptors that reward them for identifying those same elements.

Because animals have very limited ability to change their elemental composition, the old adage that ‘You are what you eat’ doesn’t really apply. Rather, animals are rewarded with pleasing tastes for ‘eating what they are’, at least from an elemental composition perspective, which helps reduce the prospect of dietary nutrient limitation.”

Lee Demi, Study Co-Author and Postdoctoral Researcher, Department of Applied Ecology, North Carolina State University

This is especially crucial for herbivorous and omnivorous animals that eat a range of different foods of varying nutritional quality. In this context, taste becomes a tool that helps consumers prioritize the types of foods they should seek out and eat, so that they don’t spend time on foods that contain fewer essential components.

Similarly, taste can caution consumers to stay away from foods that contain an excessive amount of the required element. Therefore, eating a handful of chips is more appealing than consuming a handful of table salt.

The intricacy of humans’ taste systems can be predicted by where they are in the food chain. Some top predators, such as orcas, have lost numerous taste receptors over the evolutionary period. The new research suggests that predators are less likely to have severe elemental deficiencies in their diet when compared to omnivores or herbivores.

Predators face less selection pressure to sustain elaborate taste systems because their prey already meets their fundamental demands. These top predators, however, have retained their taste for salt, which may be dangerous if ingested in excess.

Affinity for certain foods must have strong evolutionary drivers, because without taste, animals would be forced to overconsume everything in the hopes of hitting the magic ratio of elements needed for growth and development. They would need to eat way too much and end up excreting huge quantities of those things they need less of, which is not efficient.”

Benjamin Reading, Study Co-Author and Professor, Department of Applied Ecology, North Carolina State University

In addition, the researchers identified substantial evidence of the evolution of convergent taste in fish, insects, and mammals. Despite being apart on the genealogical tree, each group has evolved tastes that prioritize the same rare elements, such as nitrogen, sodium, and phosphorus.

Phosphorus is particularly intriguing because this recently discovered taste is most strongly linked to phosphate, which is also the primary form of phosphorus in many nucleic acids, ATP, phospholipids, etc. Phosphate is the most readily available form of phosphorus for uptake by plants, and often the primary growth-limiting element in organisms and ecosystems. So, links between the elemental form, taste receptors, organismal needs, and ecosystem are really direct,” stated Brad Taylor, a co-author of the study and professor in NC State’s Department of Applied Ecology.

Despite the extensive research on the neurological mechanism of taste, this is the first-ever study to look at the taste as an evolutionary mechanism for efficient foraging. According to the researchers, this may open a new area of research about how taste can indicate the way animals affect their habitats through nutrient cycling, foraging, and other ecological principles.

Source:
Journal reference:

Demi, L. M., et al. (2021) Understanding the evolution of nutritive taste in animals: Insights from biological stoichiometry and nutritional geometry. Ecology & Evolution. doi.org/10.1002/ece3.7745.

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