Genetic determination and plasticity in the sun orientation of natural populations ofTalitrus saltator

As has been previously shown, talitrid crustaceans have an inherited compass which causes them to head in a direction appropriate to their original shoreline (even after several generations in the laboratory), while learnt components can improve the correctness of orientation in natural conditions. In order to extend this analysis to a greater range of populations and to show differences in the determination of direction finding behaviour, seven natural populations ofTalitrus saltator (Montagu) from differently oriented shores of the Ligurian (Marina di Vecchiano, Pisa), Tyrrhenian (Castiglione della Pescaia and Tombolo di Feniglia, Grossetto) and Adriatic (Casal Borsetti, Ravenna; Torre Fantine, Marina di Lesina and Lido di Siponta, Foggia). Italian coasts were compared for their rigidity-plasticity in sun orientation. The study was conducted from 1982 to 1985. Differences were given in relation to the dynamics of the shorelines, the stability of which changes over the years due to natural and artificial causes. Furthermore, in order to reveal something about the genetic determination of the compass, mass-crosses between geographically distant populations (Ligurian-Tyrrhenian on one side and Adriatic on the other) were performed, and the F1 and F2 inexpert offspring tested for sun orientation. The results show a partial or total disruption of the compass in cross offspring which is discussed in the light of oligogenic and polygenic transmission mechanisms.