Experimental change of the orientation of two populations of Talitrus saltator (Crustacea Amphipoda Talitridae) from Cap Bon (north-eastern Tunisia)

Studio dell'orientamento rispetto al sole e al paesaggio di popolazioni di anfipodi sulle coste tunisine: esperimento di trasferimento su una spiaggia diversamente orientata. The orientation of sandhopper populations is adapted to the direction of the shoreline of the sandy beaches where they live; this behaviour was shown to be inherited in some Mediterranean populations. The question was open whether this behaviour could be adaptively modified in case of changing shoreline or passive transfer to a new differently oriented shoreline. The Cap Bon beaches in north-eastern Tunisia are particularly interesting because they belong to two different Mediterranean Basins, the central and the eastern one, and their supra-tidal populations do not come together. This work verified the effect of experimental change of the shoreline direction in two populations of Talitrus saltator from Cap Bon (north-eastern Tunisia) through a displacement experiment. We transferred samples of T. saltator from two different localities (Korba and Ratiba) from their original beach to the familiar one and tested their solar and landscape orientation on the new beach that had an almost opposite direction with respect to the previous one. The comparisons of the results on the home beach and the new one confirmed the use of the solar compass in both populations, as well as the importance of landscape view and optical local sky factor in adjusting the escape direction. In both populations, an increase of scatter was observed on the new beach, especially when individuals could see the landscape. Also, a clear behavioural difference between the two populations was recorded, being Ratiba population not significantly oriented to the shoreline when tested on the unfamiliar beach, while Korba population maintained its home direction also on the new beach.