| The glacial refugia hypothesis indicates that during the height of the Pleistocene glaciations the temperate species that are today widespread across western Europe must have survived in small and climatically favorable areas located in the southern peninsulas of Iberia, Italy and the Balkans. This hypothesis was investigated with the tawny owl (Strix aluco), a relatively sedentary, nonmigratory bird that is currently widespread throughout Europe. Populations from all putative refugia as well as from northern Europe were sampled and individuals were analyzed using both mitochondrial and nuclear markers. A total of 1425 by of mitochondrial control region sequences and seven microsatellite loci were sequenced and genotyped from 187 individual owls distributed among 14 populations. High congruence was obtained in the detection of three groups of tawny owls in western Europe that corroborate the three Pleistocene refugia, although additional assumptions were required with the microsatellite data. Both mitochondrial and microsatellites recovered the Balkans' origin of northern populations of tawny owls due to post-glacial expansion, as well as extensive gene flow between northern Italy and adjacent mid-latitude populations. Estimates of population divergence times between refugial populations, as computed with mtDNA data, were similar, but one order of magnitude smaller between Greece and northern Europe. Based on a wide range of mutation rates and generation times, divergence between refugia appears to date to the Pleistocene. Two hybrid zones, corresponding to the meeting of the different refugial populations (Iberia-Balkans) and (Italy-Balkans) were detected with both marker classes but the precise location of the contact zones differed between markers. When corrected for differences in effective population size, mtDNA showed less structure than did the microsatellites, which is consistent with female-biased dispersal, typical of avian taxa. The mitochondrial and microsatellite results were largely congruent, and when they differed it was often (but not always) due to differences in natural history, behavior, and molecular biology. |
