Opsin switch reveals function of the ultraviolet cone in fish foraging

Abstract

Although several studies have shown that ultraviolet (UV) wavelengths are important in naturally occurring, visually guided behaviours of vertebrates, the function of the UV cone in such behaviours is unknown. Here, I used thyroid hormone to transform the UV cones of young rainbow trout into blue cones, a phenomenon that occurs naturally as the animal grows, to test whether the resulting loss of UV sensitivity affected the animal's foraging performance on Daphnia magna, a prey zooplankton. The distances and angles at which prey were located (variables that are known indicators of foraging performance) were significantly reduced for UV knock-out fish compared with controls. Optical measurements and photon-catch calculations revealed that the contrast of Daphnia was greater when perceived by the visual system of control versus that of thyroid-hormone-treated fish, demonstrating that the UV cone enhanced the foraging performance of young rainbow trout. Because most juvenile fishes have UV cones and feed on zooplankton, this finding has wide implications for understanding the visual ecology of fishes. The enhanced target contrast provided by UV cones could be used by other vertebrates in various behaviours, including foraging, mate selection and communication.

Pronounced heritable variation and limited phenotypic plasticity in visual pigments and opsin expression of threespine stickleback photoreceptors

“…Modulation of opsin expression has also been documented during development (Wood and Partridge, 1993;Szél et al, 1994;Xiao and Hendrickson, 2000;Cheng and Novales Flamarique, 2004;Takechi and Kawamura, 2005;Spady et al, 2006;Hoke et al, 2006;Applebury et al, 2007;Shand et al, 2008;Cottrill et al, 2009) and, to a lesser extent, following changes in habitat (Fuller et al, 2005;Shand et al, 2008;Cottrill et al, 2009;Hofmann et al, 2010;Fuller and Claricoates, 2011). Studies using fishes and rodents have demonstrated that opsin switching within individual cones is a major mechanism that restructures the chromatic organization of the retina and the colour sensitivity of these animals during development and at early life stages (Szél et al, 1994;Cheng et al, 2006;Novales Flamarique, 2013). By contrast, the mechanism(s) underlying, and functional significance of, environmentally induced changes in opsin expression are unknown.…”

UV wavelengths experienced during development affect larval newt visual sensitivity and predation efficiency

“…By contrast, we found additive, not interactive, effects of the immediate and developmental lighting environment on predation efficiency in newts. Regardless of developmental group, prey survival was higher in the UV2 testing environment, meaning that, as in fishes [2][3][4], the use of UV cues enhances predation efficiency in newt larvae. We also found that UV-deprived larvae foraged less efficiently than larvae reared with UV light.…”

“…When UV cues are not accessible, animals' foraging efficiency is directly negatively affected [2,3]. A recent study demonstrated that, at least in zooplankton predators, UV vision allows location of UV-absorbing food items at greater distances and angles [4].…”

Role of the iridescent eye in stickleback female mate choice

“…UV vision improves the foraging performance of some zooplanktivorous fishes because the crustaceans that they prey upon differentially absorb or scatter light in the UV and short wavelengths with respect to the water background (Browman et al, 1994;Novales Flamarique and Browman, 2001). Evidence for the role of a UV cone in enhancing the foraging performance of juvenile, zooplanktivorous, rainbow trout has recently been found (Novales Flamarique, 2013) and it is likely that the same target contrast enhancement mechanism, mediated by the UV cone, operates in sticklebacks. In support of this idea, recent estimates of stickleback foraging performance indicate increased activity when light backgrounds contain UV wavelengths (Rick et al, 2012).…”