Plant–plant signalling reduces herbivore damage in two Arabidopsis thaliana populations with contrasting life histories

Volatile organic compounds (VOCs) mediate plant–plant signalling and may contribute to phenotypic differentiation among populations. However, how signalling responses and VOC–life-history associations vary among locally adapted populations remains poorly understood. We conducted a greenhouse experiment using two genetically and phenologically divergent (i.e. rapid and slow cyclers) Iberian populations of Arabidopsis thaliana. We exposed emitter plants to Spodoptera exigua herbivory and quantified VOC emissions, subsequent herbivore damage in neighbouring conspecific receivers, and associations between VOC emissions and life-history traits. We detected no overall population difference in measured VOC profiles. Herbivory explained little variation in VOC profiles, and evidence for a treatment-induced shift in mean emission profiles was inconclusive. In the rapid cycler population, later-flowering maternal lines had higher constitutive emissions of several VOCs and higher total emissions, but these associations were not detected in herbivore-induced plants. Exposure to herbivore-induced emitters reduced receiver damage in both populations, with no detectable population difference in the treatment response. These findings indicate that plant–plant signalling increases resistance to herbivory in both populations despite their contrasting life histories. Furthermore, they suggest that herbivory may reshape associations between VOC emissions and life-history traits, such as flowering phenology, differently among populations.