Variation of multiple plant defences and herbivory reveal different patterns of adaptation across a productivity gradient

Plants with large geographic distributions experience varying biotic and abiotic conditions across their range that can influence plant defence traits among populations. Whether populations inhabiting warmer, wetter, and more productive regions face greater pressure and results in higher investment in defence compared with populations from cooler, drier, and less productive regions remains uncertain.

Here, we quantified defence traits and herbivory on Solanum carolinense L . across a large climate and productivity gradient. We sampled populations spanning the entire north–south range (29–44° N) of S. carolinense (33 populations; ~15 plants per population) and employed a common garden experiment (15 populations; ~5 plants per population). We examined whether climate predicts (1) plant defence traits (specific leaf area, trichome density and glycoalkaloid concentration), (2) herbivore damage, and (3) the correlation of traits and herbivore damage in field and common garden plants.

Trichome density and herbivore damage were higher for S. carolinense at the centre of its range, while glycoalkaloid concentrations were negatively associated with warmer, wetter climates both in the field and in the common garden. In the field, plants with higher glycoalkaloid production experienced reduced herbivory, while in the common garden plants with greater SLA received more damage.

Synthesis. Overall, these findings suggest that different types of defensive traits within a single species may follow different ecological and evolutionary trends and highlight the need for trait‐specific considerations when applying plant defence hypotheses at the intraspecific level.