DEVELOPMENTAL STABILITY, FITNESS, AND TRAIT SIZE IN LABORATORY HYBRIDS BETWEEN EUROPEAN SUBSPECIES OF THE HOUSE MOUSE

The effects of hybridization on developmental stability and size of to oth characters were investigated in intersubspecific crosses between r andom-bred wild strains of the house mouse (Mus musculus domesticus an d M.m. musculus). Fluctuating asymmetry (FA) and trait size were compa red within and between parental, F-1, backcross, and F-2 hybrid groups . The relationship between FA and reproductive fitness within the F-1 hybrids was also studied. The results indicated that both FA and chara cter size levels differed significantly between the two subspecies. Th e F-1 hybrids and the recombined groups (backcrosses and F-2 hybrids) showed heterosis for both parameters. No significant differences in th e FA of fertile and sterile F-1 hybrid individuals were found. Compari son of the FA levels obtained in this study with those found in wild p opulations from the hybrid zone in Denmark showed that the levels of F A were lower in laboratory-bred samples than in the wild populations. This study provides further evidence that, in hybrids, the development al processes underlying most of the morphological trails we studied be nefit from a heterotic effect, despite the genomic incompatibilities b etween the two European house mice revealed by previous genetical and parasitological studies.