Fig. 6

a Schematics of avian carotenoid network (66 compounds, 97 enzymatic reactions) in species under this study (Additional file 3: Appendix S2). Green circles show dietary carotenoids. b Evolutionary consequences of network vulnerability. Avian carotenoid network in which diameter of each node represents the number of species with that carotenoid compound. Compounds and reactions found in <5 species are not shown. Colors show the proportion of species in which a compound is dietary, intermediate or expressed in plumage. For dietary nodes (those with some proportion of green), frequency of plumage expression (red) shows the number of species that deposit this dietary compound unchanged, without metabolic conversion. Similar frequencies of dietary, intermediate and plumage compounds across species is most consistent with the “boom-bust” cycle of network use, where substantial occupation of network by species with elongated metabolic pathways is alternating with species that have only starting (dietary) nodes