Visual physiology underlying orientation and diel behavior in the sand beach amphipod Talorchestia longicornis

Abstract

SUMMARYTalitrid 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 518nm. 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 522nm, respectively. In accordance with identified visual pigments and spectral sensitivity, T. longicornis photobehavioral responsivity covered a broad range (420-580nm). 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 (420nm), photobehavior was heightened at night, potentially aiding in nocturnal orientation. By contrast, at a wavelength used to entrain its circadian rhythm (520nm) 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.

Regionalization in the compound eye ofTalitrus saltator(Crustacea, Amphipoda)

“…As expected (Cohen et al 2010), both the waveforms of corneal negative- and positive responses were observed, however our data obtained from a proximal area were not stable showing both negative- and positive-responses. Therefore, we only used the corneal positive waveform obtained the electrode placed on the surface layer of crystalline cone (just below the cornea).…”

Spectral sensitivity, spatial resolution, and temporal resolution and their implications for conspecific signalling in cleaner shrimp

“…In the fiddler crabs Uca thayeri and Uca pugilator, values of logk are 13.9 and 14.8, thus only slightly higher than the values we observed here (reported in Cohen and Frank, 2006). The beach-dwelling amphipod Talorchestia longicornis shows only slightly lower values of logk (dark-adapted 11.89 log photons cm −2 s −1 /light-adapted 11.97 log photons cm −2 s −1 ) than cleaner shrimp, as well as slightly longer response latencies (darkadapted 30.3 ms /light-adapted 27.7 ms) (Cohen et al, 2010). Thus, measures of sensitivity and response latency in our three species of cleaner shrimp were consistent with those of other studied crustaceans that live in a high-light environment.…”

The skylight gradient of luminance helps sandhoppers in sun and moon identification

“…Other factors are probably involved, such as the period of the day and some spectral characteristics of the two astronomical cues (e.g. Cohen et al, 2010). Finally, our results do not exclude the perception and use by sandhoppers of other celestial factors, e.g.…”