Photoperiod controls wing polyphenism in a water strider independently of insulin receptor signaling

Insect wing polyphenism has evolved as an adaptation to changing environments and a growing body of research suggests that the nutrient sensing insulin receptor signaling pathway is a hot spot for the evolution of polyphenisms, as it provides a direct link between increased growth and the available nutrients in the environment. However, little is known about the role of insulin receptor signaling in polyphenisms which are controlled by seasonal variation in photoperiod. Here, we demonstrate that wing length polyphenism in the water strider Gerris buenoi is determined by photoperiod and nymphal density, but not by nutrient availability. Exposure to a long-day photoperiod is highly inducive of the short-winged morph whereas high nymphal densities moderately promote development of long wings. Using RNA interference we demonstrate that, unlike in several other species where wing polyphenism is controlled by nutrition, there is no detectable role of insulin receptor signaling in wing morph induction. Our results indicate that the multitude of possible cues that trigger wing polyphenism can be mediated through multiple genetic pathways in insects.