Our sense of taste is determined by a set of genes that encode taste receptors. In response to different types of compounds, these proteins initiate cascades of signals that result in behavioral or physiological reactions. For example, while sweet and salty compounds tend to stimulate appetites, bitter and sour ones tend to evoke aversion. In a review of bitter taste receptor genes (the TAS2R gene family) in 661 vertebrate genomes, Higgins et al. (2025) find that amphibians have a uniquely large number of these genes – up to 248 in Rana sylvatica – while other vertebrates may only have a handful. The number of TAS2R genes could not be explained by genome size expansion, or by nearby transposable element content. Instead, the relatively large number of TAS2R genes seems to be related to their physical location on the ends of chromosomes, where recombination events are frequent and can cause duplications, as well as their tendency to be in gene clusters, which could also promote gene duplication during recombination events. They also find that TAS2R genes are expressed in the brain, liver, stomach, and skin, and that some are sensitive to bitter compounds such as toad toxins. Thus, amphibians could be using these proteins as general chemoreceptors throughout their entire body and the TAS2R gene family may act as a previously unrecognized physiological regulator system in amphibians and other animals. Their results reveal future research avenues into how TAS2R genes might help regulate toxin production and metabolism or responses to toxin exposure, providing insights both into how amphibians modulate their own toxicity and why certain compounds produce adverse or allergic reactions.

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