Visual physiology underlying orientation and diel behavior in the sand beach amphipod Talorchestia longicornis
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2010-08-23
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Jonathan H. Cohen, Thomas W. Cronin, et.al, Visual physiology underlying orientation and diel behavior in the sand beach amphipod Talorchestia longicornis, The Journal of Experimental Biology 213, 3843-3851, DOI :10.1242/jeb.048686
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Abstract
Talitrid amphipods employ vision for zonal recovery behaviors on sand beaches and for entraining circadian activity rhythms.
Using a hierarchy of methods, we examined visual spectral and response–intensity functions in Talorchestia longicornis, a
species in which orientation and rhythm entrainment are wavelength-specific behaviors. Microspectrophotometry,
electroretinogram recording and behavioral assays were used to determine visual pigments, retinal spectral sensitivity and wholeanimal
spectral responsivity, respectively. Diel changes in absolute sensitivity were also investigated at retinal and whole-animal
levels. Two receptor spectral classes were identified, with values for visual pigment max of 427 and 518nm. Retinal spectral
sensitivity varied with electrode position along the distal–proximal axis. Chromatic adaptation of distal and proximal
photoreceptors resulted in sensitivity peaks at 430 and 522nm, respectively. In accordance with identified visual pigments and
spectral sensitivity, T. longicornis photobehavioral responsivity covered a broad range (420–580nm). Collectively, a dualpigment
visual system underlies wavelength-specific behavior in T. longicornis, with the short-wavelength pigment likely to
be localized in the distal R5 retinular cell. While response–intensity functions did not change over the diel cycle at the retinal
level, behavioral photoresponsiveness varied between day and night. At a wavelength used by T. longicornis for celestial
orientation (420nm), photobehavior was heightened at night, potentially aiding in nocturnal orientation. By contrast, at a
wavelength used to entrain its circadian rhythm (520nm) and for routine visual tasks, photobehavior was heightened during the
day, and spectral sensitivity matched to the twilight spectrum, facilitating crepuscular vision and entrainment by irradiance at
sunrise and sunset.