Data from: The relationship between microhabitat use, allometry, and functional variation in the eyes of Hawaiian Megalagrion damselflies

1. The evolution of visual systems is guided by the interaction of visual requirements imposed by habitat light heterogeneity, eye size, and physical limitations imposed by the resolution-sensitivity tradeoff. The physical constraints related to eye surface area result in a tradeoff between resolution, the ability of the eye to detect detail, and sensitivity, the ability to capture photons, so that both cannot be simultaneously maximized without increases to eye size. How this constraint interacts with ecology and whether it allows the fine tuning of the visual system to smaller scale habitat heterogeneity remains an understudied question in visual ecology. 2. Here we use closely related species of damselies in the Hawaiian genus Megalagrion which differ in ecology to test whether variation about the resolution-sensitivity tradeoff is the evolutionary result of scaling or differences in microhabitat use. We use regression analyses and phylogenetic comparative methods to examine the effects of size and microhabitat use on traits related to light sensitivity and visual resolution. 3. We find that eye size is tightly associated with body size in these damselies, but morphological traits related to light sensitivity and resolution are associated with microhabitat type. Furthermore, size and morphology relationships vary across microhabitats, and resolution tends to be more conserved than variation in light sensitivity. 4. Additionally, smaller species in visually challenging microhabitats have more regionalized eyes than species with larger eyes in open, well-lit areas. Thus, regionalization of the eye allows a decoupling of size and morphology/performance so that even small insect species can exploit visually challenging habitats. 5. These results suggest that variation in visual performance results from changes in eye geometry as well as size. These morphological changes are likely adaptive to differences in microhabitat indicating that variation in microhabitat use, even at small scales, can play an important role in the evolution of visual systems.