Escalation (macroevolutionary increase) or divergence (disparity between relatives) in trait values are two frequent outcomes of the plant-herbivore arms race. We studied the defences and caterpillars associated with 21 sympatric New Guinean figs. Herbivore generalists were concentrated on hosts with low protease and oxidative activity. The distribution of specialists correlated with phylogeny, protease and trichomes. Additionally, highly specialised Asota moths used alkaloid rich plants. The evolution of proteases was conserved, alkaloid diversity has escalated across the studied species, oxidative activity has escalated within one clade, and trichomes have diverged across the phylogeny. Herbivore specificity correlated with their response to host defences: escalating traits largely affected generalists and divergent traits specialists; but the effect of escalating traits on extreme specialists was positive. In turn, the evolution of defences in Ficus can be driven towards both escalation and divergence in individual traits, in combination providing protection against a broad spectrum of herbivores.

Elevational gradients affect the production of plant secondary metabolites through changes in both biotic and abiotic conditions. Previous studies have suggested both elevational increases and decreases in host-plant chemical defences. We analysed the correlation of alkaloids and polyphenols with elevation in a community of nine Ficus species along a continuously forested elevational gradient in Papua New Guinea. We sampled 204 insect species feeding on the leaves of these hosts and correlated their community structure to the focal compounds. Additionally, we explored species richness of folivorous mammals along the gradient. When we accounted for Ficus species identity, we found a general increase in flavonoids and alkaloids. Elevational trends in non-flavonol polyphenols were less pronounced or showed non-linear correlations with elevation. The abundance of insect herbivores decreased with elevation, while the species richness of folivorous mammals showed an elevational increase. Insect community structure was affected mainly by alkaloid concentration and diversity. Although our results show an elevational increase in several groups of metabolites, the drivers behind these trends likely differ. Flavonoids probably provide figs with protection against abiotic stressors, such as UV-irradiation. In contrast, alkaloids affect insect herbivores and may provide protection against mammalian herbivores and pathogens. Concurrent analysis of multiple compound groups alongside ecological data is an important approach for understanding the selective landscape that shapes plant defences.

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Proanthocyanidins (PAs) are highly bioactive plant specialized metabolites. One of their most characteristic features is their ability to precipitate proteins. In this study, eleven plant species were used to study the structure–activity patterns between PAs and their protein precipitation capacity (PPC) with bovine serum albumin. To obtain a comprehensive selection of PAs with highly variable procyanidin to prodelphinidin ratios and mean degree of polymerizations, nearly 350 subfractions were produced from the eleven plant species by semi-preparative liquid chromatography. Their PA composition was defined by tandem mass spectrometry and high-resolution mass spectrometry, and their PPC was measured with a turbidimetry-based well-plate reader assay. The distribution of the PPC within plant species varied significantly. The mean degree of polymerization of the PAs had a strong correlation with the PPC (r = 0.79). The other structural features were significant from the PPC point of view as well, but they contributed to the PPC in different ways in different plant species. Retention time, prodelphinidin proportion, and mean degree of polymerization explained 64% of the measured variance of the PPC.

Color is a major sensorial characteristic of red wines. Numerous monomeric and some small oligomeric pigments have been characterized from red wines but the contribution of larger oligomeric pigments to the color intensity has not been established by direct measurements. We measured the color intensity of 317 commercial red wines and semiquantified the malvidin glycosides and eight different adduct groups derived from the malvidin glycosides by ultra-performance liquid chromatography–tandem mass spectrometry. Two of these groups were oligomeric pigments consisting of proanthocyanidins and malvidin glycosides with either direct or methylmethine linkages. The carboxypyranomalvidins and the oligomeric pigments were found to be major contributors to the color intensity. Besides the concentrations, the sizes of the oligomeric pigments had a positive and significant connection to the color intensity. The 1-year-old wines were studied separately and, even in the youngest of wines, the adducts of the malvidin glycosides were the major contributors to the color intensity.