From 20 to 2? Landmark-based geometric morphometrics reveal negligible wing-shape divergence between 20 subspecies of the Apollo butterfly, Parnassius apollo (Lepidoptera, Papilionidae), in the Carpatho-Pannonian region

For effective conservation management of endangered taxa, it is important to define operational units for conservation. In the absence of detailed genetic analyses, morphology-based taxonomy is often used as a surrogate. The Apollo butterfly, Parnassius apollo, is one of the most endangered butterfly species in Europe (considered as a flagship species) with 26 subspecies rank taxa described from the Carpatho-Pannonian region (Central Europe), often based on old, one-by-one descriptions. We applied landmark-based geometric morphometrics on wing shape to determine the number of morphologically distinguishable groups in the region, based on 949 males and 477 females from 20 Carpatho-Pannonian putative subspecies (both extant and potentially extinct). We found a single division between the Eastern Carpathian populations (described as two subspecies: ssp. transsylvanicus and ssp. rosenius) and the rest of the populations (including our outgroup from the Swiss Alps). Since P. apollo was not observed in the Eastern Carpathians in the last two decades, and the currently known extant populations in the Carpatho-Pannonian region are all located in the Northern Carpathians, our results support a single conservation unit in the region. We suggest that (i) extensive monitoring is needed to reveal whether the unique Eastern Carpathian populations have really gone extinct and (ii) more taxonomical/phylogenetic studies on Central European P. apollo are needed for establishing the taxonomy of the species and efficient conservation strategies. We emphasize that modern integrative taxonomy is not only important for clarifying taxonomical issues, but also for providing basis for sound conservation management.