Species barriers between Formica ants (F. aquilonia and F. polyctena)
Locating barrier loci in population genomic data is difficult due to the often complex demographic history of diverged taxa and heterogeneity in evolutionary forces across the genome. We take advantage of natural hybridization between two wood ant species (Formica aquilonia and F. polyctena) to identify regions of reduced long-term gene flow using demographically explicit scans of non-admixed genomes. In addition we identify candidate Bateson-Dobzhansky-Muller incompatibilities (BDMIs) through an imbalanced recombinant haplotype frequency analysis using a large sample of natural F. aquilonia × F. polyctena hybrid genomes. We find BDMIs scattered across the genome. Furthermore, BDMIs significantly overlap with long-term barriers, indicating that BDMIs have persisted despite divergence with gene flow. Intriguingly, the number of pairwise interactions a BDMI has correlates with its long-term barrier strength: hub-like BDMIs with many interactions reduce gene flow more effectively.