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Honest Communication Starts With Humidity

Flowering plants do not always communicate honestly with their pollinators. Often flowering plants benefit by decoupling floral advertisements and rewards in ways that both reduce floral investment by the plant but enhance cross-pollination.

However, scientists from Cornell University and the University of Arizona have identified a new signal that plays a role in "honest" communication between flowers and pollinators. Humidity gradients above flowers, produced partly by nectar evaporation, are perceived by insect pollinators and allow them to remotely sense the presence of nectar. These findings shed light on the mechanisms by which plants couple signal and reward and the circumstances under which they can reveal the presence of floral nectar.

The impact of this study goes beyond pollination ecology, as it explores the question of how context converts a universal environmental cue into a specific signal. The insights gained through this study should be of general interest to scientists who study mutualism, signal evolution, communication theory, sensory physiology and bioengineering.

Research on plant-pollinator communication has focused mainly on sensory and behavioral responses of pollinators to relatively static cues like flower color or shape, which at best advertise the potential to encounter floral nectar or pollen. However, the abundance of nectar in nature is dynamic, and pollinators will increase their reproductive success if they can make use of floral cues that more accurately indicate nectar presence in a flower.

Images (1 of )

  • a hawkmoth visits an evening primrose flower
  • within a tongue's length of an evening primrose, a hawkmoth detects and evaluates the flower's humidity gradient
  • evening primrose seen with the human eye and the humidity gradient the hawkmoth senses
A hawkmoth visits an evening primrose.
Robert A. Raguso, Cornell University
A hawkmoth visits two different species of evening primrose. The moth senses the presence of nectar without landing.
Robert A. Raguso, Cornell University
Evening primrose seen by the human eye (left) and the humidity gradient a hawkmoth perceives when nectar foraging.
Martin von Arx, Cornell University

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