Under- and over-water halves of Gyrinidae beetle eyes harbor different corneal nanocoatings providing adaptation to the water and air environments

Abstract

Whirligig beetles (Gyrinidae) inhabit water surfaces and possess unique eyes which are split into the overwater and underwater parts. In this study we analyze the micro- and nanostructure of the split eyes of two Gyrinidae beetles genera, Gyrinus and Orectochilus. We find that corneae of the overwater ommatidia are covered with maze-like nanostructures, while the corneal surface of the underwater eyes is smooth. We further show that the overwater nanostructures possess no anti-wetting, but the anti-reflective properties with the spectral preference in the range of 450–600 nm. These findings illustrate the adaptation of the corneal nanocoating of the two halves of an insect's eye to two different environments. The novel natural anti-reflective nanocoating we describe may find future technological applications.

Antireflective nanocoatings for UV-sensation: the case of predatory owlfly insects

“…Together with our previous observation that nanocoatings-harboring overwater eyes of the whirligig beetles reflect less light than the smooth underwater eyes [8], this current communication on the optical properties of the owlflies’ eyes represents the second only direct proof of the antireflective function of insect nanocoatings.…”

Extraordinary diversity of visual opsin genes in dragonflies

“…This vertical heterogeneity of light conditions is ubiquitous across terrestrial and aquatic ecosystems, which have probably prompted the evolution of dorso-ventrally differentiated eyes known from diverse animals (39). The most striking cases are found in water surface dwellers, like whirligig beetles and four-eyed fish, whose dorsal half and ventral half of eyes are anatomically separated and functionally specialized for aerial vision and aquatic vision, respectively (17,43). Dorso-ventral structural differentiation of compound eyes has been reported not only in dragonflies but also in diverse actively flying or swarming insects, such as black flies (44), march flies (45), mayflies (46,47), owlflies (48), butterflies (49), and others (39,50).…”

Diverse set of Turing nanopatterns coat corneae across insect lineages

“…1G; E′ is a fragment of Fig. 1E; F′ is an image from a Gyrinus beetle [overwater eye (13)]; G′ is a fragment of Fig. S2B; and H′ is a fragment of Fig.…”

“…1D. Modeling parameters are given in Table S2 Detailed analysis of the physical (such as antireflective and antiwetting) properties of the diverse corneal nanostructures we present here is still to be performed, but the fact that both the nipple-type and maze-type nanostructures serve the antireflective function (2,13) suggests the functionality of the majority, if not all, of them. The variety of these nanostructures can serve as a highly promising model, obeying the Turing mechanism of pattern formation.…”

“…These nanostructures may carry antireflective, dirt-removing/ self-cleaning, and hydrophobic/antiwetting functions (2,(8)(9)(10)(11)(12). Later, some other insects were found to possess a very different type of corneal nanocoating, such as the antireflective maze-like 30-nm-high evaginations covering corneae of the overwater eyes of Gyrinidae beetles (13). An attempt to analyze the variety of corneal nanocoatings throughout the insect class was made in the classical study by Bernhard et al (5).…”