Sexual dimorphism in pollen foraging and sensory traits in Heliconius butterflies

Sexual dimorphism in foraging behaviour is widespread in insects and may arise from differences in nutritional demands, sensory systems, or cognition. In Heliconius , pollen-feeding is an evolutionary innovation among butterflies that supports extended lifespans and sustained reproduction. However, how foraging behaviour varies between the sexes and how it relates to sexually dimorphic traits remains poorly understood. We investigated sex-specific foraging strategies in wild Heliconius himera , a highland specialist from southern Ecuador, using field surveys and DNA metabarcoding. Females carried more pollen than males, consistent with higher nutritional demands. Yet both sexes used similar plant richness and composition, indicating that differences reflect foraging effort rather than shifts in plant choice. Gut samples revealed greater pollen diversity and a more consistent community profile than proboscis samples, suggesting they better capture cumulative foraging history. To place these behavioural differences in a sensory context, we quantified sexually dimorphic sensory traits. Males had larger eyes and more ommatidia, whereas females had larger mushroom bodies, brain regions that support associative learning and memory. These patterns are consistent with sexual dimorphism reported across Heliconius and may contribute to the observed sex differences in pollen foraging. Our findings highlight how sex-specific foraging differences may arise from effort on shared floral resources and co-occur with divergent sensory and neural investment, offering insights into the ecological basis of intraspecific variation in pollen use.