Differences in genetic variability between two ecotypes of the endangered myrmecophilous butterfly Phengaris (=Maculinea) alcon– the setting of conservation priorities

.  1. The endangered butterfly Phengaris alconexists in two ecotypes(P. ‘alcon’ and P. ‘rebeli’), which inhabit contrasting biotopes(wet and warm/dry grasslands respectively) and use different larval food plants. The initially flower-bud-feeding caterpillarscomplete their development as social parasites of Myrmica ants, and the specificity of these relationships shows geographical variation. 2. We studied the genetic structure of 16 populations (365 individuals) of both ecotypesin eastern Europe, sampling P. ‘rebeli’ in two disjunct areas in Lithuania and southern Poland, and P. ‘alcon’ on Polish localities between them. We analysed the cytochrome c oxidase subunit I(COI) mitochondrial gene, the EF1-α nuclear geneand five polymorphic microsatellite loci. 3. All individuals shared an identical COI haplotype, which we hypothesise may be linked to a selective sweepassociated with the presence of the WolbachiaB strain in allpopulations. 4. For nuclear markers, we did not find a clear pattern reflecting divisioninto twoputative ecotypes. However, ecotypesdiffered significantly in their genetic variability, i.e., the P. ‘rebeli’ ecotypewas less polymorphic, and its populations were much more differentiated (FST: 0.632 for EF1-α and 0.504 for microsatellites) than the P. ‘alcon’ ecotype(0.177 and 0.082, respectively). 5. Our microsatellite data suggest that all populations of P. ‘alcon’ form a single clade but that P ‘rebeli’ can be split into either six or two clades. The former model would indicate many independent origins, especially in the mountainous areas of southern Poland. The latter, not mutually exclusive, grouping clearly reflects the use of different host ants.