The Y-DNA and mtdna of Cres islanders in Croatia and the Pasiegos in Cantabria (Spain) further confirms my hypothesis about mtDNA I, U2, U3, U4 and W being linked to steppe haplogroups R1a and R1b. I might also add U5b and V.
Cres islanders were found to have an unusually high frequency of mtDNA U2e (20%) and W (12.5%), two haplogroups found in Central Asia, Pakistan and North-West India, and is associated with regions with a high frequency of R1a with a moderate amount of R1b.
I do not have the Y-DNA data for Cres, but this extensive study of Croatian Y-DNA and mtDNA has data for the neighbouring island of Krk (no, there is no vowel missing ). The samples in Krk, representing western Croatia, have the highest frequency of R1a (35.5%) and R1b (16.5%) nationwide. Krk has the particularity of having an startlingly high percentage of mtDNA I (11.5%) and W (7.5%), but also some U4 (3%) and U2 (1.5%). Better still, haplogroup A, of Siberian or East Asian origin, has been detected in Krk too. It is difficult to see how hg A could have got to Croatia if not through the Pontic steppe.
The Pasiegos of Cantabria are another isolated community whose DNA can enlighten us on the prehistory of Europe. A special study was dedicated to them by Maca-Meyer et al. and found a surprising pocket of hg R1a (18%, against 2% for Spain nationwide), but also of mtDNA I (6%), U3 (1.5%) and U4 (2.5%). There are also remarkably high frequencies of V (20.7%), U5 (16%) and T3 (7.3%), all common in north-east Europe.
V and U5 are also relatively common in Spain (5% and 5.5%), but not in such proportions. It is possible that both haplogroups were already in Spain during the Paleolithic, but that new people brought an additional layer of them later. Besides Spanish U5 is typically U5a, not the eastern U5b found in 3.7% of Pasiegos. It is undeniable that haplogroup U5 is more frequent in north-east Europe than Spain. It peaks in Finland (18%) and Estonia (16%), but is also high in Russia (12%) and Ukraine (11%).
Combined with a strong presence of R1a, this points at a direct migration from Russia/Ukraine to Cantabria. Other Cantabrians have a similarly high frequency of haplogroup V (21.5%) and U (22%), including U2 (2.5%), U3 (2.5%), U4 (4.5%) and U5 (11.5%). This proportion of U subclades is strongly reminiscent of southern Russia. The other Cantabrians have 8% of R1a (still very high for western Europe) and 58% of R1b.