PohnB6F1: a cross of wild and domestic mice that is a new model of extended female reproductive life span.

In the search for novel genetic diversity that affects the timing of life history traits, we investigated a wild-derived stock of mice (Pohn). Early generations showed extended reproductive life span; however, this phenotype diminished with propagation of the stock. Out-crossing latter generation Pohn mice to C57BL/6J (B6) mice produced PohnB6F1 hybrids with remarkably extended reproductive life spans-mean age at last litter of 647 +/- 32 days-longer than for the parental strains (70% longer than Pohn, 88% longer than B6) and longer than for highly heterogeneous crosses of laboratory mice. Litter size among young PohnB6F1 adults was similar to parental stocks, but their age-related decline in litter size was delayed by 150-200 days, resembling the earlier Pohn generations. Possibly, out-crossing Pohn mice unmasked cryptic alleles that promote extended female reproduction. This work establishes the PohnB6F1 hybrid as a new model for delayed reproductive aging.