Figure 3
Evolutionary associations were detected in two pairs of traits according to Pagel’s test76 of correlated evolution: (1) flavonoids and chalcones and (2) p-alkenyl phenols and kavalactones/butenolides. Filled shapes indicate presences and unfilled shapes indicate absences of flavonoids (circles), chalcones (squares), p-alkenyl phenols (diamonds), and kavalactones/butenolides (triangles), respectively. The shapes used in the phylogenetic plots (a,c) are repeated below (b,d) to depict four states comprising all combinations of presences and absences in the pair of traits. Arrows represent transition rates between states. (b) As both models of contingent change provided good fits to the flavonoid and chalcone data, both sets of transition rates are displayed, with the first set of values (bolded) corresponding to the best supported model (chalcone evolution contingent on flavonoid state) and the second set of values corresponding to the alternative contingency model (flavonoid evolution contingent on chalcone state). (d) The best fit model to the p-alkenyl phenol and kavalactone/butenolide data was one of interdependent evolution, where p-alkenyl phenol evolution is dependent on the state at the kavalactone/butenolide trait, and vice versa. Panel (e) illustrates the enzymatic processes and branch points along biosynthetic pathways that give rise to the four classes of metabolites. Chalcones are immediate biosynthetic precursors of flavonoids, where the inherent reactivity of the chalcone moiety permits cyclization to the flavonoid scaffold. Subtle structural changes to the flavonoid scaffold caused by late-stage oxidation can produce protoflavonoids, a rare class of metabolite with potent cytotoxic activity. In contrast, the pathways of p-alkenyl phenols and kavalactones diverge much earlier and embark on distinct chain elongation pathways that lead to long-chain lipophilic substituent characteristic of the p-alkenyl phenols in one case, and lactones (kavalactones and butenolides) in the other case.
