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 alcon exists in two ecotypes (P.similar to alcon and P.similar to rebeli), which inhabit contrasting biotopes (wet and warm/dry grasslands respectively) and use different larval food plants. The initially flower-bud-feeding caterpillars complete 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 ecotypes in eastern Europe, sampling P.similar to rebeli in two disjunct areas in Lithuania and southern Poland, and P.similar to alcon on Polish localities between them. We analysed the cytochrome c oxidase subunit I (COI) mitochondrial gene, the EF1-a nuclear gene and five polymorphic microsatellite loci. 3. All individuals shared an identical COI haplotype, which we hypothesise may be linked to a selective sweep associated with the presence of the Wolbachia B strain in all populations. 4. For nuclear markers, we did not find a clear pattern reflecting division into two putative ecotypes. However, ecotypes differed significantly in their genetic variability, i.e., the P.similar to rebeli ecotype was less polymorphic, and its populations were much more differentiated (FST: 0.632 for EF1-a and 0.504 for microsatellites) than the P.similar to alcon ecotype (0.177 and 0.082, respectively). 5. Our microsatellite data suggest that all populations of P.similar to 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.