HISTORICAL BIOGEOGRAPHY AND MORPHOLOGICAL-DIFFERENTIATION OF STREPTOCEPHALUS-TORVICORNIS (WAGA) SINCE THE WURM-III GLACIATION

We argue that the Wurm III glaciation eradicated possible European pop ulations of S. torvicornis, and that today, a reconquest of Europe tak es place on two fronts. A western wave has reached the Pyrenees, an ea stern one now occupies most of eastern and northern Europe. The wester n route probably started in the Maghreb, the eastern one in the Levant and the Ponto-Caspian. Animals in the west had to move north by cross ing, at right angles, a series of east-west oriented river valleys and progressed slowly; animals in the east could move up river valleys ex tending north and north-east, and moved quickly. Italy was not occupie d, because S. torvicornis is a warm stenotherm, and by the time the cl imate had warmed sufficiently for it to reach the southern shore of th e mediterranean (ca 6000 BP), the gap with Italy was probably too larg e for a crossing. Cold-loving species (of the genera Branchipus, Chiro cephalus) conversely, could freely flow across the Central Mediterrane an at low sea-levels (ca 12 000 BP), and now occur in Italy (and the r est of Europe) as well as in Northern Africa. A prediction of our hypo thesis is that the pioneer populations in Spain and Central Europe sho uld have been isolated longest. This is tested and confirmed by their comparative morphology, and two subspecies, S. t. towicornis and S. t. bucheti are reinstated. A gap across the Nile Valley where only S. ru bricaudatus seems to occur, deserves further study.