Molecular evidence for the loss of three basic tastes in penguins

Abstract

Sensing its biotic and abiotic environmental cues is critical to the survival and reproduction of any organism. Of the five traditionally recognized senses of vertebrates, taste is dedicated to the differentiation between nutritious and harmful foods, triggering either appetitive or rejective behaviors. Vertebrates typically can detect five basic taste qualities: sweet, umami, bitter, sour and salty. Remarkable progress in understanding the molecular basis of taste has opened the door to inferring taste abilities from genetic data. Based on genome and relevant gene sequences, we infer that the sweet, umami, and bitter tastes have been lost in all penguins, an order of aquatic flightless birds originating and still occupying the coldest ecological niche on Earth, the Antarctic.

Figure 1. Taste loss in penguins

Species tree of 27 birds and human showing presence (check marks) and absence (crosses) of sweet, umami, bitter, sour, and salty tastes in penguins (shaded) and outgroups, inferred from genes for taste receptors (shown at the top of the figure). Neither check mark nor cross is given to a species when there is no genetic/genomic data for such an inference. Species with available genome sequences are shown in black, whereas those without available genome sequences are shown in grey. The red-throated loon Gavia stellata is considered a putative bitter non-taster due to the pseudogenizations of Tas2r1 and Tas2r2 that are independent from the penguin-specific pseudogenizations. Note that the umami taste receptor has been repurposed to detect sweet in the hummingbird Calypte anna [10]. As a result, C. anna possesses the sweet taste, in addition to a weak umami taste. See also FigureS1 and Tables S1.