Scents and Sense Ability: The evolution and role of chemical cues in the pollination and herbivory of Passiflora

Abstract

Pollination and herbivory play a critical role in both wild ecosystems and agricultural ones, factoring in to their maintenance, evolution, and ecology. Insects, for whom chemical cues are often more important than those of other modalities, are primary drivers of both of these processes. We investigated the role and evolution of scent in the pollination and herbivory of Passiflora, a large genus of flowering plants for which relationships with pollinators and herbivores are comparatively well-documented. To understand these processes from the perspective of both plant and animal, we used integrative methods including phylogenetics, sensory electrophysiology, analytical chemistry, and machine learning to investigate. On the pollination side, we find convergent evolution in floral morphology and floral scent, that these traits evolved in tandem to attract a given type of pollinator across Passiflora, and that these traits have the power to predict pollinator type. We further show that such floral scent changes may be biologically relevant to available pollinators using electrophysiological methods. Though future work is required to confirm the generality of this finding in additional plant and pollinator clades, this is a critical step to better understanding the role that chemical cues play in pollinator attraction, and the evolutionary synergy they may have with morphological traits in flowering plants. In contrast, on the herbivory side, we find no relationship between herbivore and leaf scent. The chemical make-up of leaf scent is not explained by herbivore identity in Passiflora species. Furthermore, we do not find distinct sensory responses to leaf scents from host plants versus non-host plants in herbivorous insects. However, in exploratory work we do find some other factors that may explain patterns in herbivory, such as geographic distribution, which may warrant additional investigation in this system.