Abstract: The peppered moth Biston betularia L., widely distributed across the Northern Hemisphere, represents an ideal organism for exploring phylogeographic patterns and evolutionary history. In this study, we integrated molecular, morphological, and distributional data of this species to reconstruct its phylogenetic relationships, estimate divergence times, infer the geographic origin, and trace dispersal routes. Molecular analyses identified six monophyletic lineages (HM, NC, HD, E, NA I, and NA II). With the exception of the sympatric North American lineages NA I and NA II, the remaining lineages exhibit allopatric distributions across Eurasia. Ancestral area reconstruction and approximate Bayesian computation (ABC) analyses supported a southern Xizang origin within the Himalayan Mountains, consistent with the “Xizang-origin hypothesis.” The colonization of North America occurred twice via the Bering Land Bridge during the Pleistocene glaciation. Collectively, the current genetic pattern is best explained by gradual allopatric differentiation following long-distance dispersal and subsequent isolation. Furthermore, we reconstructed the global dispersal history of B. betularia. These results indicated that in situ speciation within the Himalaya may be more common than previously recognized, challenging the notion that Himalayan fauna are predominantly considered “immigrant.” This study enhances our understanding of Himalayan zoogeography and biodiversity through the resolved evolutionary history of a widely distributed species.

Key words: allopatric differentiation, genetic pattern, Xizang-origin hypothesis, ABC analysis, phylogeographical structure