Evidence for natural selection and barrier leakage in candidate loci underlying speciation in wood ants

While speciation underlies novel biodiversity, it is poorly understood how natural selection shapes genomes during speciation. Selection is assumed to act against gene flow at barrier loci, promoting reproductive isolation and speciation. However, evidence for gene flow and selection is often indirect. Here we utilize haplodiploidy to identify candidate barrier loci in hybrids between two wood ant species and integrate survival analysis to directly measure if natural selection is acting at candidate barrier loci. We find multiple candidate barrier loci but surprisingly, proportion of them show leakage between samples collected ten years apart, natural selection favoring leakage in the latest sample. Barrier leakage and natural selection for introgressed alleles could be due to environment-dependent selection, emphasizing the need to consider temporal variation in natural selection in future speciation work. Integrating data on survival allows us to move beyond genome scans, demonstrating natural selection acting on hybrid genomes in real-time.