Abstract
Umami is one of basic tastes that humans and other vertebrates can perceive. This taste is elicited by L-amino acids and thus has a special role of detecting nutritious, protein-rich food. The T1R1 + T1R3 heterodimer acts as the principal umami receptor. The T1R1 protein is encoded by the Tas1r1 gene. We report multiple inactivating (pseudogenizing) mutations in exon 3 of this gene from four phocid and two otariid species (Pinnipedia). Jiang et al. (Proc Natl Acad Sci U S A 109:4956-4961, 2012) reported two inactivating mutations in exons 2 and 6 of this gene from another otariid species. These findings suggest lost or greatly reduced umami sensory capabilities in these species. The widespread occurrence of a nonfunctional Tas1r1 pseudogene in this clade of strictly carnivorous mammals is surprising. We hypothesize that factors underlying the pseudogenization of Tas1r1 in pinnipeds may be driven by the marine environment to which these carnivorans (Carnivora) have adapted and may include: the evolutionary change in diet from tetrapod prey to fish and cephalopods (because cephalopods and living fish contain little or no synergistic inosine 5'-monophosphate that greatly enhances umami taste), the feeding behavior of swallowing food whole without mastication (because the T1R1 + T1R3 receptor is distributed on the tongue and palate), and the saltiness of sea water (because a high concentration of sodium chloride masks umami taste).