Evolutionary trajectories of multiple defense traits across phylogenetic
and geographic scales in Vitis
Abstract
Many investigations of plant defense theory fail to address how
trajectories of trait evolution vary across levels of biological
organization, even though the processes that shape trait correlations
have the strong potential to shift within versus across species, as well
as in different environmental and ecological contexts. 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
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 select traits vary 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.