Abstract
The quality of visual information that is available to an animal is limited by the size of its eyes. Differences in eye size can be observed even between closely related individuals, yet we understand little about how this affects vision. Insects are good models for exploring the effects of size on visual systems because many insect species exhibit size polymorphism. Previous work has been limited by difficulties in determining the 3D structure of eyes. We have developed a novel method based on x-ray microtomography to measure the 3D structure of insect eyes and to calculate predictions of their visual capabilities. We used our method to investigate visual allometry in the bumblebee Bombus terrestris and found that size affects specific aspects of vision, including binocular overlap, optical sensitivity, and dorsofrontal visual resolution. This reveals that differential scaling between eye areas provides flexibility that improves the visual capabilities of larger bumblebees.
Highlights
What an animal can see within its environment is restricted by its visual field, or the total angular region of the world from which light can be absorbed by its photoreceptors
To test our hypothesis that the differential scaling of compound eyes will primarily improve the visual capabilities in only a small region of the visual field, we developed a novel method based on constructing 3D models of apposition compound eyes that were imaged with x-ray microtomography (Baird and Taylor, 2017)
Analysing the 3D structure of insect eyes to determine a holistic description of their visual capabilities provides insight into how the morphology of eyes has evolved to sample visual information from the world
Summary
What an animal can see within its environment is restricted by its visual field, or the total angular region of the world from which light can be absorbed by its photoreceptors. To detect specific objects within this visual field, the eyes need spatial resolution, which is achieved through (and limited by) the arrangement of individual receptors that sample the spatial distribution of light (Land and Nilsson, 2012). Having an eye with spatial resolution allows an animal to detect differences in the intensity of the light reaching it from different directions, and this information is crucial for the myriad of visually guided behaviours exhibited by different species (Cronin et al, 2014). The eyes of other species have evolved specializations that enable them to acquire critical information from important regions of the world, such as elongated regions of acute vision for detecting the horizon (Dahmen, 1991) and ‘bright zones’ of high optical sensitivity for discriminating passing prey or potential mates against a bright background (Straw et al, 2006).
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