Evolutionary trajectories of multiple defense traits across phylogenetic and geographic scales in Vitis

Abstract

The processes driving defense trait correlations may vary within and between species based on ecological or environmental contexts. However, most studies of plant defense theory fail to address this potential for shifts in trait correlations across scales. In this work, we tested for correlations between multiple defensive traits (secondary chemistry, carbon to nitrogen ratio, domatia, leaf toughness, trichomes, and pearl bodies) across a common garden of 21 Vitis species and eighteen genotypes of the species Vitis riparia to identify when and where patterns of defense trait evolution persist or break down across biological scales. Additionally, we asked whether Vitis defense trait investment correlates with environmental variables as predicted by plant defense theory, using environmental metrics for each Vitis species and V. riparia genotype from the GBIF and WorldClim databases. We tested for correlations between defense trait investment, herbivore palatability, and environmental variables using phylogenetically informed models. Beyond a few likely physiological exceptions, we observed a lack of significant correlations between defense traits at both intra- and interspecific scales, indicating that these traits evolve independently of each other in Vitis rather than forming predictable defense syndromes. We did find that investment in carbon:nitrogen (at both scales) and pearl bodies increases with proximity to the equator, demonstrating support for plant defense theory's prediction of higher investment in defenses at more equatorial environments for some, but not all, defense traits. Overall, our results challenge commonly held hypotheses about plant defense evolution, namely the concept of syndromes, by demonstrating that strong correlations between defense traits are not the prevailing pattern both across and within Vitis species. Our work also provides the first comprehensive evaluation of the evolutionary divergence in approaches that Vitis, a genus with significant agricultural value, have evolved to defend themselves against herbivores.