By: Emma Foster, Ana Alcantara, Apsara Gurung (Stonehill College, BIO 323 Evolution, Fall 2019)
While humans can taste a variety of flavors, this is not true for all mammals. Researches Dr. Kangli Zhu and other collaborators recently published the research article “The loss of taste genes in cetaceans,” and found that they are only able to detect one out of five sensations of taste. These tastes include sweet, salty, bitter, umami, and sour, but they can only taste salt. Taste is important to mammal adaptations, particularly in cetaceans, which are a group of organisms including whales, dolphins, and porpoises. Umami and sweet taste sensations are important for finding and eating nutritious protein- and energy-rich foods. Salt is also an attractive taste and helps animals maintain sodium levels. Bitter taste is beneficial for aversion to prevent ingestion of toxic or harmful foods. Sour taste also prevents the ingestion of potentially unripe or decayed foods.
Researchers used techniques including genetic analysis and phylogenies to trace back the evolution in taste. Genetic analysis was performed on blood and muscle samples and used to generate phylogenies. After sequencing the DNA from cetaceans and comparing it to other mammals, the researchers found that the taste receptors for sweet, sour, umami and bitter were non-functional due to premature stop codons. The salt-receptor is the only one that is functional.
It is possible that taste evolved with the transition of cetaceans from land to water approximately 52.5 million years ago. Ancient ancestors of cetaceans experienced changes in habitat and feeding behaviors, and the researchers suspect this is how cetaceans lost their ability to taste. This likely occurred as an accidental mutation and was carried along into all the species of cetaceans. Cetaceans live in the ocean, which is a salty environment, due to the high concentration of sodium. This high volume of salt might disguise the other taste sensations. This would decrease the dependence on flavor when searching for food. The cetaceans are no longer choosy in what tasty prey they eat, so they have access to a wider variety of food.
Podcast: https://soundcloud.com/user-669960307/salty-cetaceans/s-TMurg (with “just” repeat”)