Out of the Alps: The Biogeography of a Disjunctly Distributed Mountain Butterfly, the Almond-Eyed Ringlet Erebia alberganus (Lepidoptera, Satyrinae)

Many studies on the biogeography of thermophilic and arctic-alpine species were performed during the past. Only little is known about species with intermediate characteristics. We analyzed the molecular biogeography of the butterfly Erebia alberganus (30 populations, representing 1106 individuals), sampled over the Alps, Apennines (Italy), and the Stara Planina (Bulgaria) using allozyme electrophoresis (17 loci). Genetic analyses revealed 3 major splits, with the strongest between the Stara Planina populations and all other populations, and a weaker split between the Alps and the Apennines. Individuals from the Apennines were genetically nested within the Alps group. The Alps cluster was segregated into 3 groups: the Southwestern, Western/Central, and Eastern Alps. The genetic diversities were highest for the Alps populations and significantly lower in the 2 isolates (Apennines, Stara Planina). The remarkable genetic split between Stara Planina and all other populations and the genetic distinctiveness of the former cluster might be interpreted as an ancient colonization event of this Balkan mountain range. The Apennines populations derive from a more recent expansion out of the Southwestern Alps. After surviving the Würm ice age most probably in the central Apennines, accompanied by genetic modification of some of these populations, northward expansion might have started from the western parts of the central Apennines reaching the northern Apennines during the early postglacial. The subtle genetic differentiation found among the Alps populations probably reflects 3 geographically disjunct Würm glacial centers located at the western slopes of the Southwestern Alps, at the southern slopes of the Central Alps, and in the Southeastern Alps.