Interglacials are driving speciation and intraspecific differentiation in the cold-adapted butterfly species groupBoloria pales / napaea(Nymphalidae)

Aim Cold-adapted species had their largest distribution areas during glacial periods, whereas the subsequent interglacials led to retreats of these taxa into mountain ranges and more northern regions, but existing data are not sufficient for generalizing these range dynamics. To improve our knowledge of the different phylogeographical patterns existing for cold-adapted species, we examined two closely related butterfly species of the genusBoloriawith alpine disjunct and arctic-alpine distribution respectively. Location Europe: High mountain areas and Scandinavia. Taxa Boloria palesandB. napaea. Methods We sequenced two mitochondrial (COI, ND1/trRNA/16S region) and two nuclear genes (wingless and EF-1 alpha) for 182B. palesspecimens from 37 localities and 60B. napaeaspecimens from 12 localities representing the whole distribution area of both species in Europe. We used existing and known calibration points to date the age of the relevant splits. Results While nuclear DNA showed no genetic structures, the mitochondrial loci revealed 91 haplotypes belonging to three well-differenced genetic lineages: (a) all samples ofB. napaeafrom the Alps and Scandinavia, (b) the samples ofB. palesfrom the Alps, Carpathians, High Tatra, Pirin Mountains, Dinaric Alps in Montenegro and the Apennines and (c) all samples ofB. palesfrom the Pyrenees. The time estimates for the splits between these three groups range from 1.3 to 0.84 million years ago (mya). The further within-groups differentiations are not older than 0.32 mya, but reveal a subtle pattern among and within mountain ranges. Main conclusions Allopatry during the mid-Pleistocene has led to differentiation into three major genetic groups, each of which possibly representing a separate species today. Especially within the today widespread mountain group (i.e. thepalessensu stricto group), repeated expansion out of their Alpine centre and a number of different peri-Alpine glacial distribution areas have produced the subtle genetic structure observed over the late Pleistocene. The two other groups also show substructures, but to a lesser degree, hence, calling for a less disrupted distribution pattern during the late Pleistocene. However, the arctic populations ofB. napaeaare not derived from the same source as the Alpine ones.

Automated summary

The study revealed three genetic lineages for Boloria pales and B. napaea in Europe, possibly representing separate species that differentiated during the mid-Pleistocene. The genetic structure observed over the late Pleistocene suggests repeated expansion and different peri-Alpine glacial distribution areas for the Alpine group of B. pales.