(a) Two genes encoding chitinase and β-hexosaminidase enzymes show signatures of positive selection in the attine ancestor, whereas three chitin-synthase genes are positively selected in the ancestor of the higher attine cultivars. (b) Expression of the same genes in worker tissues showing very high expression in labial glands situated in the prothorax. Shared letters indicate that tissues do not differ significantly in gene expression level (n=4, Tukey’s honest significant difference, P>0.05). High expression in the mesosoma minus labial glands might reflect expression in additional tissues with contributions from residual fragments of the labial glands. (c) The positively selected attine ant (n=7) chitinase and β-hexosaminidase proteins have significantly higher isoelectric points than the orthologous proteins in other myrmicine ants (n=5, phylogenetic ANOVA, both P<0.03). (d) The conserved catalytic chitinase domain (GH18) of attine ants with its lost C-terminal chitin-binding domain (CBM) and dots indicating the positions of four amino acid residues that experienced positive selection in the ancestor of all attine ants (black) or in the ancestor of the higher attines only (grey). In contrast, the full β-hexosaminidase domain architecture is intact with both GH20 and GH20b2 domains, and nine sites positively selected in the ancestor of all attine ants (black dots).