Fig. 1

Structural features and distribution of flavonoids in seasonal diets. A Basic scaffold of flavonoids and representative aglycone monomers detected in dietary bamboos of giant pandas. Flavonoids are constituted of two aromatic rings (A, B) linked through three carbons that usually form an oxygenated heterocycle (C ring) (a C6-C3-C6 skeleton named phenylchromane). This C ring is characteristic of each flavonoid subfamily. The basic structure of the individual flavonoids is modified by hydroxy, methoxy and alkyl groups attached to the A- and B-rings. For each representative aglycone with numbers in parentheses, the structural formula and the common name are indicated. B Comparison of the diversity of flavonoid monomers in bamboo leaves versus shoots. C Comparison of the abundance of flavonoids in bamboo leaves versus shoots. The unrooted tree on the left shows the hierarchical clustering among diet samples by hierarchical clustering based on the Bray-Curtis distance. The bubble chart on the right shows the distribution of all flavonoids. The sizes and colors of the circles indicate the abundance and food type in different seasons, respectively. The absence of a bubble at one node indicated no flavonoid was detected in the corresponding sample. The subjects of indexes are listed in Table S2. Ampersand denotes flavonoids with precise structural identification. Most flavonoids were identified as in the glycoside forms. C, C-glycoside; O, O-glycoside; C, O, C, O-di-glycoside; NA, no glycosyl. For B and C, four groups represented samples of two types of bamboo diets (leaves and shoots) from two populations of giant pandas (wild and captive ones): WL, wild pandas with leaves of the bamboo B. fargesii as diet; WS, wild pandas with shoots of the bamboo B. fargesii as diet; CL, pandas in captivity fed on the leaves of B. fargesii; CS, pandas in captivity fed on shoots of the bamboos P. amarus and P. nidularia, corresponding to subclass CS_I and CS_II, respectively. The green and purple colors represent the bamboo leaf and shoot individually. And both the group information and colors were the same as in Figs. 2 and 3