Wing Membrane Thickness, Allometric Scaling and Wing Interference Patterns in Damselflies - A Target of Sexual Selection?

Damselflies (Odonata: Zygoptera) have evolved highly developed visual systems for mate recognition, flight and prey detection. Wing Interference Patterns (WIPs), which are colors generated by thin-film interference in the wing membrane, could function as visual signals and play a role in sexual selection. Because the color of these signals depends on membrane thickness, a potential conflict exists between changes in wing area and the need to maintain a consistent signal. We examined how wing membrane thickness scales with wing area in two damselfly species, Ischnura elegans and Enallagma cyathigerum . Using hyperspectral imaging, we found that while wing area was highly variable, membrane thickness showed low intraspecific variability. We found no evidence for any significant correlation between wing thickness and wing area or any support for sexual selection operating on these traits. Low intraspecific variation of the membrane thickness results in a consistent Wing Interference Signal (WIS), which is useful for species identification with remote sensing approaches.