Figure S4: Innate AM Preferences. Larvae of all used genotypes were tested for their innate preference under relevant testing conditions. (A) AM preference of the same genotypes as in Fig. 1A-B under room light conditions. (B) AM preference of the same genotypes as in Fig. 1C either in darkness or green light. (C) AM preference of the same genotypes as in Fig. 1D under room light conditions. (D-E) AM preference of the same genotypes as in Fig. 2 in darkness (D) and under blue light (E). Data are presented with the median as middle line, the quartiles as box boundaries and the 10/90% quantiles as whiskers. Significant pairwise difference (MWU): ‡. “ns” indicate non-significant MWU or KW tests. All raw data and exact values of statistical tests are given in Table S1.

Learning where to find nutrients while at the same time avoiding toxic food is essential for survival of any animal. Using Drosophila melanogaster larvae as a study case, we investigate the role of gustatory sensory neurons expressing IR76b for associative learning of amino acids, the building blocks of proteins. We found surprising complexity in the neuronal underpinnings of sensing amino acids, and a functional division of sensory neurons. We found that the IR76b receptor is dispensable for amino acid learning, whereas the neurons expressing IR76b are specifically required for the rewarding but not the punishing effect of amino acids. This unexpected dissociation in neuronal processing of amino acids for different behavioural functions provides a study case for functional divisions of labour in gustatory systems.