Seasonal polyphenism in wing coloration affects species recognition in rubyspot damselflies (Hetaerina spp.).

Understanding how phenotypic plasticity evolves and in turn affects the course of evolution is a major challenge in modern biology. By definition, biological species are reproductively isolated, but many animals fail to distinguish between conspecifics and closely related heterospecifics. In some cases, phenotypic plasticity may interfere with species recognition. Here, we document a seasonal polyphenism in the degree of dark wing pigmentation in smoky rubyspot damselflies (Hetaerina titia) - a shift so pronounced that it led early researchers to classify different forms of H. titia as separate species. We further show how the seasonal colour shift impacts species recognition with the sympatric congener Hetaerina occisa. Interspecific aggression (territorial fights) and reproductive interference (mating attempts) are much more frequent early in the year, when H. titia more closely resembles H. occisa, compared to later in the year when the dark phase of H. titia predominates. Using wing colour manipulations of tethered damselflies, we show that the seasonal changes in interspecific interactions are caused not only by the seasonal colour shift but also by shifts in discriminatory behaviour in both species. We also experimentally tested and rejected the hypothesis that learning underlies the behavioural shifts in H. occisa. An alternative hypothesis, which remains to be tested, is that the seasonal polyphenism in H. titia wing coloration has resulted in the evolution of a corresponding seasonal polyphenism in species recognition in H. occisa. This study illustrates one of the many possible ways that plasticity in species recognition cues may influence the evolution of interspecific interactions.