Figure 6.

Proposed speciation model of T. altaicus. The hybridization between T. tibetanus and T. himalayensis occurs in the sympatric zone during the Quaternary Early glacial period, and then reproduces F1 generation. The F1 hybridizes with T. himalayensis and reproduces F2 during the interglacial period, and then several generations of introgression allowed hybrids to inherit numerous loci from T. himalayensis, which can be combined via gene flow through hybridization. Competitive exclusion between them gives rise to the introgression zone shift along with the Tien Shan and makes Fn (hybrids) to be an ancestor for T. altaicus. Hybrids (Fn generations) can potentially be adaptive and favored in a new habitat via adaptive introgression and can lead to a separate hybrid taxon (hybrid speciation). Finally, competitive exclusion and ecological opportunity can explain that hybrid species (the ancestor of T. altaicus) colonize the Altai–Sayan–Hangay Mountains during the glacial period, and then, geographical isolation and adaptive radiation have driven hybrids to be a novel species—T. altaicus