HYBRID VIGOR AGAINST PARASITES IN INTERSPECIFIC CROSSES BETWEEN 2 MICE SPECIES

The resistance and susceptibility to the intestinal pinworm Aspiculuri s tetraptera, a natural parasite of the house mouse Mus musculus, is e xperimentally analysed using both the F-1 from wild-type mice of the t wo subspecies (M. m. domesticus and M. m. musculus) and the F-1 from d ifferent laboratory inbred mice. The results show that: (i) the F-1 fr om wild-type mice harbour a lower parasite load than the parental mice , suggesting a phenomenon of hybrid vigour; and (ii) the F-1 from inbr ed mice harbour parasite loads similar to the resistant parent, sugges ting that resistance is inherited as a dominant feature in these labor atory mice. This analysis supports the hypothesis that recombinations occurring between the two mouse genomes (i.e. M. m. domesticus and M. m. musculus) are responsible for the hybrid dysgenesis observed in the natural hybrid zone between the two mice subspecies.