Data from: Reduced male fertility is common but highly variable in form and severity in a natural house mouse hybrid zone

Reduced hybrid fertility is a common feature of reproductive barriers separating recently diverged species. In house mice (Mus musculus), hybrid male sterility has been studied extensively using experimental crosses between subspecies.

Here, we present the first detailed picture of hybrid male fertility in the European M. m. domesticus – M. m. musculus hybrid zone. Complete sterility appears rare or absent in natural hybrids but a large proportion of males (~30%) have sperm count or relative testis weight below the range in pure subspecies, and likely suffer reduced fertility. Comparison of a suite of traits related to fertility among subfertile males indicates reduced hybrid fertility in the contact zone is highly variable among individuals and ancestry groups in the type, number and severity of spermatogenesis defects present.