Combined demographic, ecological and genetic tools reveal connectivity within a fragmented butterfly population

Protected species require targeted studies to establish population sizes, their dispersal capacity and the possible genetic bottleneck effect that could impair the future of the remaining populations. In this study, we used the genotyping-by-sequencing technique (SNP: single nucleotide polymorphism) combined with Capture-Mark-Recapture (CMR) method to measure the dispersal ability and subpopulation sizes of the protected butterfly Zerynthia polyxena in 14 sites of NW Italian Alps. The study species form a metapopulation divided into several small subpopulations (ranging from 90 to 859 estimated subpopulation sizes). The species showed low mobility, likely due to habitat fragmentation, with individuals travelling an average of 80 m from their original capture site. SNPs highlighted high observed heterozygosity, low genetic substructuring at short distances, and large genetic differentiation only for individuals found in sites located at 46 km distance, suggesting high gene flow at short distances and limited gene flow between distant populations. Although CMR data did not detect movement beyond 700 m, the genetic results revealed remarkable connectivity among nearby subpopulations. The results indicate that gene flow still exists among the subpopulations despite the fragmented habitat. Considering that the species is locally threatened by habitat loss due to the planning of a European high-speed railway, our data suggest that it is not too late to adopt conservation measures. In conclusion, combining genetic and ecological studies can be utilised to design proper conservation plans for protected and threatened insect metapopulations.