Drought-induced changes in sex-specific floral chemistry reshape interactions with a nursery pollinator across life stages

Abstract

Nursery pollination systems provide unique models for studying the chemical ecology of plant-insect interactions, as specialized insects act as both pollinators and seed predators across life stages. How climatic stress alters the plant chemistry underlying these interactions remains unknown. To address this gap, we use the dioecious plant species Silene latifolia and its nursery pollinator Hadena bicruris. We investigated how water limitation affects visual floral traits, scent and nectar chemistry in male and female plants along with associated moth behaviour, as well as female seed chemistry along with associated larval performance. Water limitation broadly compromised floral traits, with particularly pronounced reductions in nectar metabolites in male plants eroding sexual dimorphism in nectar chemistry. Correspondingly, moths preferred well-watered flowers for oviposition and lost their adaptive preference for female flowers under water limitation, while feeding behaviour remained unaffected. Water limitation also compromised seed traits, including reductions in defence-associated metabolites. In parallel, larvae grew faster on seeds from water-limited plants despite consuming similar amounts. Our findings provide first evidence that climatic stress broadly compromises the multimodal phenotypes underlying nursery pollination, particularly chemical traits, and that these changes coincide with contrasting insect responses across life stages, with potential consequences for fitness and coevolution.