We show defense syndromes in European willows

Plants employ diverse anti-herbivore defenses, forming syndromes of multiple traits. These include direct defenses like toxic compounds and trichomes, and indirect defenses like volatile organic compounds that can attract predators of herbivores. Syndromes provide complementary defenses against various herbivores through trade-offs among plant traits such as nutrient content, chemical, and physical defenses.

Our study in Oecologia examined 16 lowland willow species in central Europe, analyzing physical traits, chemical defenses, and resource acquisition traits. We found two main clusters defined by structurally related compounds, and a third group spread across these clusters. Trade-offs mainly involved salicinoids, flavonoids, and proanthocyanidins that shared metabolic pathways and may compete for their precursor compounds. Individual traits rather than syndromes explained more variation for all three herbivore feeding guilds. Additionally, several traits that characterized the syndromes play additional roles in willows other than defense from herbivory. Overall, our results thus suggest that the recovered willow syndromes probably did not solely evolve as anti-herbivore defenses.

Principal coordinate analysis (PCoA) diagrams showing correlations between willow individuals (circles), individual traits, and three trait syndromes on CANOCO5. Individual willow samples are color coded by species as shown in the legend. The recovered PCoA axes were used as response variables. Individual traits were used as supplementary variables and are shown as arrows. Traits that showed significant phylogenetic signal and were more similar among the related species than expected under a conserved model of evolution are in black arrows. Traits that showed significant phylogenetic signal and were less similar among the related species than expected under a conserved model of evolution are in red arrows. Traits that did not show a significant phylogenetic signal are shown as dashed arrows. HS syndrome, LS syndrome, and mixed group (M) are shown as symbols (square, diamond, and triangle, respectively) and were included as a supplementary variable in the PCoA. Phylogenetic axes with significant effects on trait similarity among the willows were used as covariables. See Table 1 for trait abbreviations. Species are coded as follows: ACU = Salix acutifolia, CAP = S. caprea, CIN = S. cinerea, DAP = S. daphnoides, ELE = S. eleagnos, FRA = S. fragilis, MYS = S. myrsinifolia, MYR = S. myrtilloides, PEN = S. pentandra, PUR = S. purpurea, REP = S. repens, ROS = S. rosmarinifolia, SIL = S. silesiaca, TRI = S. triandra, VIM = S. viminalis. 

For more, see Jing´s recent paper:
 https://doi.org/10.5281/zenodo.11164786.