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Fig. 1 Phylogenetic tree visualizing vertebrate T2R evolution. Top panel, complete T2R repertoires from 22 species are shown color coded as indicated. Some colors refer to closely related species as shown. The tree was generated using a maximum-likelihood method, for details see Materials and Methods. Note the high branch support (shown as %) even in basal nodes. Most gene birth events occur late as visualized by a small degree of color mixing within the tree. Note the axolotl gene pair within the large coelacanth clade. Ancestral genes discussed in the main text are indicated by a1–a5. T2Rs selected for deorphanization are indicated by numbers in colored circles, red circles for zebrafish genes, blue for coelacanth, with numbers referring to the gene name, for example number 34 represents T2R34. The evolutionary relationships of the 22 species investigated are approximated in the bottom panel by a phylogenetic tree constructed with the respective species opsin orthologs, for details see Materials and Methods. Species color code same as above. Species are indicated by two letter abbreviations; Dr, Danio rerio, zebrafish; La, Latimeria chalumnae, coelacanth; for other names see supplementary figure S1, Supplementary Material online. The number of putatively functional T2Rs is given below the species acronym, second row of numbers refers to pseudogenes. Circled numbers refer to estimates for the number of ancestral genes.