UV photoreceptors in the compound eye of Daphnia magna (Crustacea, Branchiopoda). A fourth spectral class in single ommatidia

Abstract

The spectral sensitivities of individually stimulated ommatidia in the compound eye of Daphnia magna were measured using a fast spectral scan voltage-clamp technique with extracellular recording. Chromatic adaptation was used to reveal the contributions of individual spectral classes of photoreceptors to the ommatidial sensitivity. Ommatidia in the dorsal and ventral regions of the compound eye were tested. Four spectral classes of photoreceptors were found in each ommatidium, among them a previously undetected class with peak sensitivity in the ultraviolet. The wavelengths of peak sensitivity were at 348, 434, 525, and 608 nm for the dorsal ommatidia. The three longer wavelength classes agreed well with those found previously by intracellular recording (Schehr 1984). Only small differences in wavelength and magnitude of peak sensitivity were found between the four classes in the dorsal versus ventral ommatidia.

The Coevolution of Blue-Light Photoreception and Circadian Rhythms

“…Recent laboratory studies by Storz and Paul (1998) demonstrate that Daphnia responds to visible light (420-600 nm) with positive phototaxis, whereas ultraviolet light leads to negative phototaxis. Sensitivity was maximal at 340 nm, which corresponds closely to the value expected from the UV photoreceptors of its compound eye (Smith and Macagno 1990). These results were confirmed under field conditions by Leech and Williamson (2001), who demonstrated a vertical migratory response to UV radiation under full-spectrum solar irradiation.…”

What role does UV‐B radiation play in freshwater ecosystems?

“…If effect, they will remain in habitats that they perceive as benign while UV-B radiation inflicts its damage. Although some invertebrates, such as the freshwater cladoceran Daphnia (Smith and Macagno 1990) and larvae of the sand dollar Dendraster (Pennington and Emlet 1986), have UV-B-sensitive photoreceptors and respond appropriately to selective increases in UV-B radiation, other invertebrates such as the cuphausiid Thysanoessa (Damkaer and Dey 1983) and the freshwater midge Cricotopus (Bothwell et al 1994), are unable to detect UV-B radiation and may be vulnerable to solar ambush. Scssile organisms may bc particularly vulnerable to solar ambush because they cannot respond behaviorally to fluctuations in UV-B radiation as in, for example, the hypothesized coral bleaching by UV-B in marine ecosystems during calm, sunny periods (Gleason and Wellington 1993).…”

Toward a more comprehensive theory of zooplankton diel vertical migration: Integrating ultraviolet radiation and water transparency into the biotic paradigm

“…Another key element has been the discovery of UV photoreceptors in the widespread freshwater cladoceran Daphnia magna with peak sensitivity in the UV-A at 348 nm (Smith and Macagno 1990). More recent laboratory studies with monochromatic light carefully adjusted for intensity among treatments revealed that D. magna was negatively phototactic to UV with the strongest response between 300 and 400 nm (340-nm peak) and positively phototactic to 420-600-nm visible light (Storz and Paul 1998).…”