Color Change from male-mimic to Gynomorphic: a New Aspect of Signaling Sexual Status in Damselflies (Odonata, Zygoptera)

Body color variations are used by many animal species to communicate their sexual state and are believed to have evolved through sexual selection. In damselfly species (Odonata, Zygoptera), females sometimes come in different color morphs: gynomorphs and male-like andromorphs, pursuing different reproductive strategies. These distinct female color morphs are usually mature females and their color remains stable throughout the female’s life. Here, we show for the first time that blue andromorph females of the Australian damselfly Ischnura heterosticta, are still sexually immature, and change their body color to green-grey gynomorph when they are ready to mate. The color change occurs within 24h and is irreversible. Males of I. heterosticta rarely recognize blue andromorphs as potential mates, but mistake them for other males. The andromorphs thus avoid male sexual harassment, giving them the advantage of additional time to forage and sexually mature. The color change to gynomorph signals the readiness to mate, and the former andromorphs have equal mating success after the color change as other gynomorph females. Our results demonstrate that andromorph I. heterosticta use a complete and unique body color change from male-mimic to gynomorphic to signal sexual maturity and regulate reproduction. Our discovery gives rise to a novel hypothesis regarding maintenance of female-limited polymorphism in Ischnura damselflies via this color change mechanism.