NATURAL HYBRIDIZATION OF 2 SUBSPECIES OF HOUSE MICE, MUSCULUS-DOMESTICUS AND MUS-MUSCULUS-CASTANEUS, NEAR LAKE-CASITAS (CALIFORNIA)

The house mouse Mus musculus is a polytypic species, distributed world wide, with three main subspecies: M. m. musculus in the North-East of Eurasia, M. m. castaneus in South-East Asia, and M. m. domesticus in E urope, the Near-East, and Africa. This last subspecies may also be fou nd in Australia and the Americas, where it was brought by European col onization Previous studies, however, have shown the presence of specif ic antiviral determinants of Asian origin in a mouse population at Lak e Casitas, California, In this study, an analysis of the variability a t 35 enzyme loci demonstrates the hybrid nature of this Californian po pulation intermediate between M. m. castaneus and M. m. musculus. Rest riction fragment length polymorphisms of two fragments of the mitochon drial DNA also confirm unambiguously the presence of two types of matr ilines in comparable frequencies in our sample. Nevertheless, the stud y of a subspecies-specific Y chromosome microdeletion in the Zfy2 gene reveals only the M. m. domesticus haplotype at Lake Casitas, a phenom enon comparable with the one observed in other hybrid zones of the M. musculus complex. These findings testify once more that genetic exchan ges between subspecies inside the broader M. musculus gene pool are st ilt possible.