INCREASED VARIATION IN CELLULAR DNA CONTENT AT A HYBRID ZONE - HYBRID BREAKDOWN IN PEROMYSCUS-LEUCOPUS

A natural hybrid zone of the white-footed mouse (Peromyscus leucopus) was studied to determine variation in cellular DNA content. The parental populations are distinguished by pericentric inversions in three chromosome pairs. Fifty-seven individuals were examined from localities in Oklahoma and Texas. Localities represented the two parental populations and a location from the center of the hybrid zone. Samples of spleen tissue were examined by flow cytometry, and the mean coefficient of variation of the northeastern sample was significantly lower than that of either the hybrid or the southwestern sample. We found no significant difference between hybrid and southwestern populations. In some individuals, we found evidence of mosaic cell populations indicated by overlapping G, peaks. We conclude that hybrid breakdown can result in natural hybrids as an increased variation in cellular DNA content that is detectable by flow cytometry. In the P. leucopus hybrid zone, the effect is not symmetrical in both directions.