Optic flow and sea - land orientation in the sandhopper Talitrus saltator (Montagu)

Abstract

The problem sandhoppers face when they find themselves on the dry sand is to reach as quickly as possible the belt of moist sand near the water. In the present study, I ask whether, alongside many other orienting factors, sandhoppers use the optic flow they experience to maintain their bearing relative to the sea-land axis. Adult individuals of Talitrus saltator were released in a transparent Plexiglas bowl, horizontally placed between four walls with a pattern of vertical black and white stripes. The orientation of one pair of opposite walls was south-north, orthogonal to the sea-land axis of the home beach, whilst the second pair of walls was oriented east-west. The black and white striped pattern of opposite walls could be moved in pairs and in the same direction (speed=4.8 cm s −1 ). The results demonstrate that the optic flow sandhoppers experience when moving on the sea-land axis of their home beach influences their direction of travel and could help sandhoppers in maintaining a straight path to reach favourable ground by the shortest route.

Sky radiance and spectral gradient are orienting cues for the sandhopperTalitrus saltator(Crustacea, Amphipoda)

“…It is important to note that the spectral gradient was the only available cue in the experiments where the simulated sun was switched off. Thus, the reduction of the number of radially orientated individuals could be caused by the absence of any further reliable cues, such as the substrate slope and the surrounding landscape (Ercolini and Scapini, 1974;Craig, 1973;Hartwick, 1976;Ugolini et al, 1986Ugolini et al, , 2006Ugolini, 2014;Ugolini and Ciofini, 2016). It remains an open question why the sandhoppers exhibited a relatively low number of radially oriented individuals (50%) registered from the morning releases with the artificial sun switched on (Fig.…”

“…However, the sun and moon are not the only celestial cues used by this species. Beside astronomical cues, sandhoppers can use local cues, such as the slope of the substratum and the vision of the landscape as references to return to their belt of damp sand (Ercolini and Scapini, 1974;Craig, 1973;Hartwick, 1976;Ugolini et al, 1986Ugolini et al, , 2006Ugolini, 2014;Ugolini and Ciofini, 2016). In addition to the sun, sunlight scattering on atmospheric particles generates additional skylight cues, such as a polarization pattern as well as profiles of radiance and spectral distributions (e.g.…”

The crustacean model Parhyale hawaiensis

“…responding to gradients of light intensity and polarisation. Behavioural experiments in other talitrid amphipods support this notion (Ercolini and Scapini 1976, Forward et al 2009, Cohen et al 2010, Ugolini et al 2012, Cohen and Putts 2013, Ugolini 2014, Ciofini et al 2020. Simple behavioural experiments in Parhyale suggest that they have a phototactic response (Ramos et al 2019).…”