Recently lost connectivity in the Western Palaearctic steppes: the case of a scarce specialist butterfly

Palaearctic steppes evolved under the Cenozoic cold arid climate and megaherbivore pressure. A large portion of the biome persisted into the Holocene but has recently been subjected to human land use alternation. Pseudophilotes bavius (Lepidoptera: Lycaenidae) is a steppe specialist sporadically distributed in Eastern Europe and Pontic-Caspian region (from Transylvania to Southern Urals), the Balkans, the South-Eastern Mediterranean and Irano-Anatolian regions. We used samples covering the distribution area to assess the phylogeography and population genetics of the species based on one mitochondrial and four nuclear genes. The basal lineages are situated in the Irano-Anatolian region, forming two Evolutionary Units. The species radiated to the Balkans and Pontic-Caspian steppes probably when the climatic conditions became suitable after the mid-Pleistocene transition and formation of vast steppe biome. In these parts of the range, the species survived both glacial and interglacial periods in situ, forming a third Evolutionary Unit. In the Balkans, the individual populations are distinct and have probably been isolated for a long time, owing to the diversity of Balkan habitats. In the Pontic-Caspian region, population connectivity probably existed until recently, since the life history of the species is unlikely to include long-distance dispersal. The distribution could have become fragmented with the conversion of steppes into cropland during the past centuries. Future conservation will require proper knowledge of the distribution and habitat needs of the species. Management of inhabited sites should respect historical disturbance-succession dynamics.