Damselfly Compound Eye in the Stream Habitat: Biological Design for Object Detection in a Dark Complex Habitat

摘要

Habitats characterized by high spatial variation in absolute light levels and spectral quality present a challenge to animals that rely on visual orientation and visual target discrimination. Insects, in particular, face several difficulties in visual performance related to the small absolute size and simplicity of visual components comprising their compound eyes, including the lack of a focusing mechanism, relatively limited light capture and course spatial resolution. Therefore, an understanding of the morphological and behavioral means by which insects overcome these limitations in order to perform highly demanding visual tasks can provide insight into both ecological specialization and artificial visual system optimization. We investigated optical geometry, perch orientation and microhabitat selection in the Hawaiian damselfly Megalagrion xanthomelas, a sit-and-wait predator that intercepts aerial prey among heterogeneous vegetation bordering streams and wetlands. We found that while the eyes of Megalagrion xanthomelas are roughly spherical, maximum visual acuity appears concentrated in an oblong region shifted below the equatorial frontal plane. This optical geometry corresponds well with typical orientations of damselflies resting on perches and suggests an arrangement maximizing detection of prey or conspecifics traveling along stream margins. We discuss the visual morphology and behavior of Megalagrion xanthomelas in relation to available light environments and in comparison to the visual systems of other species.