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The Common Chiffchaff Phylloscopus collybita is an abundant, polytypic Palearctic bird. Validity of some of its subspecies is controversial and birds from some parts of the species range remain unclassified taxonomically. The relationships among populations from different geographic areas have not been sufficiently explored with molecular data. In this study we analyzed the relationships among the four species in the 'chiffchaff complex' (Common Chiffchaff, Iberian Chiffchaff P. ibericus, Canary Islands Chiffchaff P. canariensis and Mountain Chiffchaff P. sindianus), and the patterns of intraspecific geographic variation in the mtDNA ND2 gene and intron 9 of the Z-linked aconitase gene (ACO1I9) across the Common Chiffchaff range, including a recently discovered population breeding on Mt. Hermon (Anti-Lebanon mountains). Our data supported the monophyly of the chiffchaff complex and its current systematics at the species level. Within the Common Chiffchaff, the Siberian race P. c. tristis was the most differentiated subspecies and may represent a separate or incipient species. Other Common Chiffchaff subspecies also were differentiated in their mtDNA, however, lineages of neighboring subspecies formed wide zones of introgression. The Mt. Hermon population was of mixed genetic origin but contained some birds with novel unique lineage that could not be assigned to known subspecies. All Common Chiffchaff lineages diverged at the end of the Ionian stage of Pleistocene. Lineage sorting of ACO1I9 alleles was not as complete as that of mtDNA. Chiffchaff species were mostly distinct at ACO1I9, except the Common and Canary Islands Chiffchaffs that shared multiple alleles. An AMOVA identified geographic structure in Common Chiffchaff ACO1I9 variation that was broadly consistent with that of mtDNA ND2 gene. The genetic and other data suggest the chiffchaff complex to be a group of evolutionarily young taxa that represent a paradigm of 'species evolution in action' from intergrading subspecies through to apparently complete biological speciation., Competing Interests: The authors have declared that no competing interests exist.

Hewitt's paradigm for effects of Pleistocene glaciations on European populations assumes their isolation in peninsular refugia during glacial maxima, followed by re-colonization of broader Europe during interstadials. This paradigm is well supported by studies of poorly dispersing taxa, but highly dispersive birds have not been included. To test this paradigm, we use the dunnock ( Prunella modularis ), a Western Palaearctic endemic whose range includes all major European refugia. MtDNA gene tree, multilocus species tree and species delimitation analyses indicate the presence of three distinct lineages: one in the Iberian refugium, one in the Caucasus refugium, and one comprising the Italian and Balkan refugia and broader Europe. Our gene flow analysis suggests isolation of both the Iberian and Caucasus lineages but extensive exchange between Italy, the Balkans and broader Europe. Demographic stability could not be rejected for any refugial population, except the very recent expansion in the Caucasus. By contrast, northern European populations may have experienced two expansion periods. Iberia and Caucasus had much smaller historical populations than other populations. Although our results support the paradigm, in general, they also suggest that in highly dispersive taxa, isolation of neighbouring refugia was incomplete, resulting in large super-refugial populations., (© 2018 The Author(s).)