The Physiological, Ecological, and Evolutionary Basis of Polychromatic Ultraviolet Sensitivity In Stomatopod Crustaceans

The eyes of stomatopods are the most functionally diverse photoreceptor array found in nature. These marine crustaceans possess at least sixteen spectral types of photoreceptors, as well as sensitivity to various forms of polarized light. These visual aptitudes are the product of a variety of unique anatomical, neurological, molecular, and optical modifications to the retina and optical components of the eye. The sixteen peak sensitivities of their photoreceptors are spread evenly from 310 nm in the deep ultraviolet to 700 nm in the far-red. While the optics, visual pigments, and behavioral sensitivity of these photoreceptors have been examined in great detail at human-visible wavelengths, little is known about the UV receptors beyond their electrophysiological spectral sensitivities. Here, I present a physiological explanation for the five narrowly tuned ultraviolet receptor types in the retina of the stomatopod, Neogonodactylus oerstedii, including opsin transcript expression, visual pigment absorption, and the discovery of a unique ultraviolet-specific optical filter pigment set found in the crystalline cones of the midband. Additionally, I present a survey of these filters in twenty-one additional species of stomatopods, including data on their diverse absorbance spectra, a reconstruction of their evolution in the order, and the factors influencing their spectral tuning. Furthermore, this broad survey identifies additional ultraviolet filters in the peripheral ommatidia, suggesting an even greater level of photoreceptor spectral specialization than was previously estimated in these animals. Finally, I present behavioral evidence for ultraviolet sensitivity in stomatopods, as well as ultraviolet reflectance patterns associated with their threat displays, that may represent a covert deep-ultraviolet communication system