Electroreception in treehoppers: How extreme morphologies can increase electrical sensitivity.

The link between form and function of an organism's morphology is usually apparent or intuitive. However, some clades of organisms show remarkable diversity in their form, often exhibiting extreme morphologies, but with no obvious functional explanation. Treehoppers (Membracidae) are a family of insects that exemplify this, displaying an astounding morphological diversity, resulting in a plethora of extreme forms. The function of these morphological extremities and the reasons for their evolution have thus far remained largely enigmatic. However, this mystery can be considered in light of the capacity of many animals to detect electric fields in air via electrostatic actuation of mechanosensory structures on their body. Importantly, the strength of the electric field experienced by these mechanosensory structures is expected by physics to depend on the animal's geometry, with sharp and elongated features producing the highest electric fields. Therefore, we hypothesize that the extreme morphologies of treehoppers increase their electrical sensitivity. Here, we show that treehoppers, along with their predators and mutualists, produce electric fields and that the treehopper can detect electric fields, responding behaviorally. We also demonstrate that predatory wasps and mutualist bees differ significantly in their electrostatic profiles, pointing to the sophistication of electrical information potentially available to treehoppers. Biophysical, computational, and mathematical techniques are then utilized to provide evidence that the pronotum of treehoppers is the site of electroreception and that its extreme shapes may enhance its sensitivity to electricity.