Figure 1.

Phylogeny of vertebrate clades for which the ability to detect acid has been tested with a mapping of the valence of the reaction to acidic foods onto that phylogeny. Here ‘valence’ corresponds to whether or not a species likes (relative to some control) acidic foods or drinks at concentrations that are relevant to dietary preferences (see electronic supplementary material, table S2). Where possible, we focused on tests using citric acid (species names in bold). Citric acid can only be detected via sour taste, as opposed to other acids which can be detected via taste and aroma (acetic), tastes other than sour (l-aspartic) or astringency (tannic; see electronic supplementary material, table S1). (Online version in colour.)