Genomic Insights into Hybridization and Speciation of Mitten Crabs in the <i>Eriocheir</i> Genus

Hybridization is a prominent and influential phenomenon with significant implications for adaptive evolution, species distribution, and biodiversity. However, the intricacies of how hybridization influences genomic structure and facilitates adaptive evolution remain poorly understood. By analyzing whole-genome data from seven populations within the Eriocheir genus across diverse geographic regions, we validated a complex hybridization history between Chinese and Japanese mitten crabs. This hybridization gave rise to two distinct ecological species: Hepu and Russian mitten crabs with unique genomic architectures and adaptations. Genes related to reproduction, development, and temperature adaptation exhibited divergent selection signals, potentially contributing to their phenotypic diversity and ecological niches. Meanwhile, genes associated with reproduction, namely Birc6, Bap31, and Poxn, displayed robust evidence of selective sweeps in Hepu mitten crab. Notably, the favored alleles for these genes originated from the parental lineages during the hybridization process. Furthermore, Hepu mitten crab is a homoploid hybrid species that originated from an ancient hybridization event, resolving its longstanding taxonomic controversy. Our study sheds light on the evolutionary history of mitten crabs and highlights the crucial role of hybridization in driving adaptation, range expansion, and diversification within the Eriocheir genus.