Genomics of Sable (Martes zibellina) × Pine Marten (Martes martes) Hybridization

The sable (Martes zibellina) and pine marten (Martes martes) are two Palearctic mustelids with long-recognized hybrids (kidases), whose fertility was controversial for years. Early genetic studies confirmed the existence of hybrids beyond F1, but limited marker resolution prevented detailed characterization of hybrid ancestry. Both species were hunted for centuries, but anthropogenic pressures during the 20th-century caused severe bottlenecks in the sable. Hunting bans and large-scale reintroduction programs restored sable populations across much of its range, including the sympatric zone, potentially affecting hybridization. We resequenced 30 individuals from most of the sables' range and the Eastern part of pine marten's. Among samples, we found a broad spectrum of hybrid types with mosaic recombinant chromosomes that confirm hybrid fertility and indicate crossover is not suppressed in kidases. This necessitates re-evaluation of previous research, as we detected notable discrepancies between short tandem repeat-based ancestry and whole-genome analysis. We revealed mitochondrial DNA introgression from sables into most pine martens, indicating displacement of native pine marten mitochondrial sequences. Pine marten heterozygosity is relatively low (∼0.5 to 0.6 hetSNPs/kbp), while sable's diversity (∼1.5 to 1.8 hetSNPs/kbp) is unexpectedly high given its demographic history, likely reflecting successful reintroduction programs. We dated species divergence at 1.52 [confidence interval (CI): 1.05 to 2.06] Mya, and identified candidate genes potentially associated with hybrid fertility issues. This study is the first to elucidate marten hybridization at the whole-genome level, opening new research directions for understanding hybridization among Holarctic martens, the genetic consequences of reintroduction programs, and comparative adaptomics.