Genetic differentiation of the marbled white butterfly, Melanargia galathea , accounts for glacial distribution patterns and postglacial range expansion in southeastern Europe

Isolation of Mediterranean species in the southern European peninsulas during the cold
glacial phases often resulted in differentiation of several genetic lineages confined to the
respective peninsulas. However, whilst there is good genetic evidence for multiple refugia
in Iberia, there are only limited data available for the Balkans. Therefore, we wish to examine
the hypothesis of a strong genetic structuring within southeastern Europe for the existence
of multiple Balkan differentiation centres and/or several leading edges. As a model we use
the marbled white butterfly,
Melanargia galathea
. We studied 18 allozyme loci of 564 individuals
from 16 populations distributed over a large part of southeastern Europe. The single
populations showed moderately high genetic diversity and no northward decline of genetic
diversity was detected. The overall genetic differentiation between populations was considerable
(FST 7.0%). Cluster analysis discriminated three genetic groups: (i) a western flank
in the former Yugoslavia, parts of eastern Austria and Hungary; (ii) an eastern flank with
populations from Bulgaria and Romania (south of the southern Carpathians and eastern
Carpathians); and (iii) the eastern Carpathian Basin. Hierarchical variance analysis distributed
53% of the variance among populations between these three groups. One sample from the
Greek–Bulgarian border clustered within the eastern flank, but showed some tendency
towards the eastern Carpathian Basin populations. Two populations from Carinthia clustered
together with the eastern Carpathian Basin ones and a population from Styria showed an
intermediate genetic composition between the three groups. Most probably, the eastern and
the western flank groups are due to postglacial range expansion from the northeastern and
the northwestern edges of the glacial differentiation centre (so-called leading edges). The
eastern Carpathian Basin group may have resulted from postglacial expansion from northern
Greece through valley systems of the central Balkan peninsula, maybe even expanding
westwards north of the Balkan mountains reaching some parts of eastern Austria (e.g. Carinthia).
Therefore, the Balkanic refugium of
M. galathea
may or may not have been continuous
along the coastal areas of the Mediterranean, but must have been strongly genetically structured.