Color signaling and visual behavior in Hawaiian Megalagrion damselfies
Many organisms use visual information to detect objects and to communicate with conspecifics. Color signals in particular can be important, however, effective transmission of information can be difficult in forests and any light environment that is heterogeneous. The forest canopy can filter light, and objects in the habitat reflect light differently so that patches of light can vary in color and intensity. Thus, we may expect species living in variable light habitats to behaviorally maximize their color signal efficacy to overcome such difficulties. Hawaiian damselflies of the genus Megalagrion provide an excellent model for examining color signaling in variable light habitats. Megalagrion damselflies use a wide range of breeding habitats that vary in light and males likely use coloration as both inter- and intrasexual signals. Here, we examine whether Hawaiian damselflies use coloration as a signal, and if so, whether signalers and receivers use perch position to improve the effectiveness of visual signals. Behavioral tests demonstrated that different colors elicit distinct behavioral responses from male damselflies, and behavioral responses vary across species, indicating that these damselflies use color as a signal. Furthermore, we show that at least some species perch to maximize their visibility, providing evidence that these damselflies may use behavior to improve their color signaling. Field measurements of light microhabitat use multi-species communities demonstrate adaptation to light levels in these damselflies, which is corroborated by an analysis of visual performance based on eye geometry. We find little evidence for ecological character displacement. We find that adaptive evolution in the visual system has played an important role in the evolutionary diversification of these Hawaiian damselflies.