Phylogenetic patterns of tolerance to herbivory and underlying suite of traits: phylogenetic signal and trade-offs

When herbivory is inevitable, plants can cope with it through tolerance, buffering its negative effects on plant fitness. Macroevolutionary patterns of tolerance to herbivory may improve our understanding about its evolution. Here, we explore the phylogenetic patterns of tolerance to herbivory and underlying functional traits, as well as the potential evolutionary constraints in the forms of fitness costs and a trade-off with resistance across the genus Datura. We performed a common garden experiment with simulated herbivory (defoliation) and analyzed data within a phylogenetic comparative explicit framework. Significant phylogenetic signal was detected only for certain tolerance underlying traits: specific leaf area and chlorophyll content, but no overall phylogenetic signal for tolerance was observed. No trade-off between tolerance and resistance was detected although a negative relationship between tolerance and plant fitness in the absence of damage was found. Our results provide evidence for an absence of correspondence between phylogeny and interspecific plant defense variation, even though some underlying traits were influenced by phylogeny. We propose that the relationship between resistance and tolerance can arise as complementary defenses to variable herbivory pressures mediated by plants' internal resource allocation while the cost of tolerance may imply a trade-off with growth or reproductive potential.