Abstract
Variability in orientating behaviour of Talitrus saltator (Montagu, 1808) (Amphipoda; Crustacea) was investigated under natural conditions. Two populations were analysed from geomorphologically different Italian shores: a stable beach at Castiglione della Pescaia (Tyrrhenian Sea) and a more dynamic sandy shore intensively eroded by the sea at San Rossore (Ligurian Sea). Orientation was examined repeatedly on single animals on their native beach, releasing them on the sand with all cues available. Tests under controlled conditions were done inland, about 2 km away from the sea, in an experimental arena that permitted only vision of the sky and sun. The effect on orientation of some environmental (sun azimuth and meteorological variables) and intrinsic (sex, size, age and eye left/right asymmetry) factors was studied. Tests were done in spring and autumn, over several days in each season and at different times of the day. Using exploratory analysis and several multiple regression models, sun azimuth, wind direction and eye left/right asymmetry were found to be potential influences on orientation. These processes could explain the variation of orientation within a population that emerged from the choices of animals tested at different times of the day and under different meteorological conditions. The association with environmental variables and intrinsic factors demonstrated that the orientation adopted under natural conditions is dependent on a complex interaction of available cues and also on individual characteristics of the animal.
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