Fig. 2: Gut metabolite abundances and isotope labelling reveal the host origin of S. alvi substrates.

a, Abundances of selected metabolites in the guts of MF bees increase from emergence (day 0) to adult age (day 6). All metabolites except for caffeate and lactate were less abundant when extracted directly from an equivalent amount of pollen consumed per bee over 6 days. All bees were from the same hive. Quantitates from pollen extract were adjusted on the basis of average total pollen consumption per bee (Methods). Bars represent mean + s.d. for each metabolite, n = 8 for each condition. b, The ¹³C metabolite enrichment (%) in bee guts shows that carboxylic acids and non-essential amino acids become highly labelled on feeding [U-¹³C₆] glucose to MF bees. Dark and light bars indicate, respectively, presence and absence of pollen in the diet. The solid line denotes the natural ¹³C enrichment (1.108%), while the dashed line denotes the ¹³C enrichment of sugar water solution fed to bees. Bars show the mean + s.d. from n = 4 bee guts that were analysed for both dietary groups. All bees were from the same hive. A single mass feature was manually selected and plotted for metabolites with many analysed features, with a preference for features containing the most carbon atoms. See ‘Code availability’ section for data quality filtering steps.