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

We argue that the Wurm III glaciation eradicated possible European populations of S. torvicornis, and that today, a reconquest of Europe takes place on two fronts. A western wave has reached the Pyrenees, an eastern one now occupies most of eastern and northern Europe. The western 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 crossing, at right angles, a series of east-west oriented river valleys and progressed slowly; animals in the east could move up river valleys extending north and north-east, and moved quickly. Italy was not occupied, because S. torvicornis is a warm stenotherm, and by the time the climate had warmed sufficiently for it to reach the southern shore of the mediterranean (ca 6000 BP), the gap with Italy was probably too large for a crossing. Cold-loving species (of the genera Branchipus, Chirocephalus) conversely, could freely flow across the Central Mediterranean at low sea-levels (ca 12 000 BP), and now occur in Italy (and the rest of Europe) as well as in Northern Africa. A prediction of our hypothesis is that the pioneer populations in Spain and Central Europe should 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. rubricaudatus seems to occur, deserves further study.