Phylogeography of Drosophila subobscura from North Atlantic islands inferred from mtDNA A+T rich region sequences.

Drosophila subobscura has been used extensively in the past, in numerous studies focused on the colonization history of natural populations (Afonso et al., 1990; Brehm and Krimbas, 1987; Khadem et al., 1998; Krimbas, 1993; Latorre et al., 1992; Pascual et al., 2001; Pinto et al., 1997; Prevosti, 1974; Prevosti et al., 1984). A native Paleartic with circum-Mediterranean distribution, the species reaches the southern limits of its distribution in Morocco and is also present in the North Atlantic Archipelagos of Azores, Canaries and Madeira. In the two later archipelagos an ancestral lineage gave rise to the endemics Drosophila guanche and Drosophila madeirensis, respectively (Gonz alez et al., 1983; Gonzalez et al., 1990; Krimbas and Loukas, 1984; Moncl us, 1976, 1984) all together forming the subobscura cluster. A recent combined analysis of nucleotide sequences indicated that D. madeirensis is the sister taxa of Drosophila subobscura (O Grady, 1999) and this was supported by mtDNA A+T rich region sequences (Brehm et al., 2001). The vast geographical distribution of D. subobscura makes it an excellent species for phylogeographic studies assessing past colonization events. It is known that D. subobscura from Crete resembles much more populations from Israel and Tunisia than those from mainland Greece, probably due to the last European glaciation which did not extend into the Middle East and North Africa (Krimbas, 1993). Extant North Atlantic island populations are supposed to be long isolated from those of the mainland and were not