Although many vertebrate and invertebrate animals detect taste of sugars and avidly consume them, receptors for sugars evolved independently in these two lineages. The vertebrate T1R receptors are not found in invertebrates[47] and are not related to a Drosophila taste receptor for a sugar trehalose encoded by the Gr5a gene.[48-53] Numbers of the T1R genes in different vertebrate species range from complete absence in the frog to five in some fishes.[40,47,54-63] Ligands for the T1R receptors have been experimentally confirmed only for a few species (mostly humans and rodents), but it is likely that their orthologues in other species have similar ligand specificities. Therefore, species differences in sweet taste preferences could be due to variation in the T1R genes.
