Wing coloration and courtship behaviour of the damselfly Calopteryx japonica

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Damselflies of the genus Calopteryx japonica feature two types of colour polymorphism in their wings. The wings of both immature and mature females have a brown-greyish, gynochrome colour. The wings of the immature male also have the gynochrome colour, but the mature male wings have a bright blue-green, androchrome colour, due to iridescent wing veins. We found that the adult males in their territory attack other mature males, but not females and immature males, suggesting that males visually distinguish the androchrome colour. In choice experiments, we presented four different tethered models to territorial males. The territorial male attacked the mature male model, and showed reproductive behaviour display towards the mature female model. Covering the wings of a mature male model with grey spray resulted in a complete disappearance of the aggressive behaviour of the territorial males. On the other hand, female models with wings covered by bright blue-green particles, thus mimicking a mature male, were attacked by territorial males. The results indicate that the bright blue-green iridescence of the wings of C. japonica males plays a significant role in male territorial behaviour.