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

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 twenty-one 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.