Data from: Testing for latitudinal gradients in defense at the macroevolutionary scale

Plant defences against herbivores are predicted to evolve to be greater in
warmer climates, such as lower latitudes where herbivore pressure is also
thought to be higher. Instead, recent findings are often inconsistent with
this expectation, suggesting alternative hypotheses are needed. We tested
for latitudinal gradients in plant defence evolution at the
macroevolutionary scale by characterizing plant chemical defences across
80 species of the evening primroses, spanning both North and South
America. We quantified phenolics in leaves, flowers and fruits, using
advanced analytical chemistry techniques. Dominant individual ellagitannin
compounds, total concentrations of ellagitannins, flavonoids, total
phenolics, and compound diversity were quantified. Variation in these
compounds were predicted with latitude, temperature, precipitation, and
continent using phylogenetic generalized least squares multiple regression
models. Latitude did not strongly explain patterns for the chemical
defences. Instead, fruit total ellagitannins, oenothein A and total
phenolics were greater in species inhabiting regions with colder climates.
Using analytical chemistry and 80 species in two continents, we show that
contrary to classic predictions, concentrations of secondary metabolites
are not greater at lower latitudes or in warmer regions. We propose higher
herbivore pressure in colder climates and gradients in resource
availability as potential drivers of the observed patterns.