Growth regulation in Peromyscus species hybrids: a test for mitochondrial-nuclear genomic interaction

Interspecific hybridization of Peromyscus maniculatus (deer mouse) and P. polionotus (oldfield mouse) is accompanied by pronounced size differences between reciprocal F1 animals beginning in the fetus and continuing throughout life. Since the mitochondrial genome is inherited through the maternal line in Peromyscus, we tested the hypothesis that increased disparity between the species sources of mitochondrial and nuclear genomes within animals would exaggerate the reciprocal size effects through misregulation of growth, whereas species-compatible genomes were postulated to diminish the effect. Four series of backcrosses were established from females of the two reciprocal F1, while insuring continuity of the maternal mitochondrial composition at each generation. Size and weight measurements were made on neonatal, ten-day and six-month old animals through four or more backcross generations. Contrary to the hypothesis, deer mice with P. polionotus mitochondrial DNA, but 98% or more P. maniculatus nuclear composition, and animals with P. maniculatus mitochondria and principally P. polionotus nuclear genome regressed in mean size parameters to those of P. maniculatus and P. polionotus, respectively. Most of the regression was accounted for by the second backcross generation, and second and later backcross progeny did not differ significantly from the respective parental species controls. Maternal inheritance of mitochondrial DNA was confirmed by restriction enzyme analysis at the second and fifth backcross generation. Hybrid maternal effects in this Peromyscus cross are likely attributable to mechanisms other than nuclear-mitochondrial genomic interaction.