[Reproduction of the water voles (Arvicola terrestris) polymorphic for the aguti locus]

Reproduction of three coat-color genotypes:brown, AA (homozygotes for the wild type agouti allele); melanic, aeae (homozygotes for the autosomal recessive extreme nonagouti allele); and black-brown, Aae (heterozygotes)-in the water vole was investigated under laboratory conditions. Nine possible kinds of crosses were identified. The Aae and aeae females had higher fertility than brown AA females, while males of all three group displayed similar fertility. AA and aeae females started breeding earlier and bore larger litters. Unlike melanic females, heterozygous females had stable high fertility indices independent of male genotype. In the melanic form, female receptivity, litter size, and postnatal viability of offspring were the highest in the (aeae x AA) crosses, which resulted in exclusively heterozygous progeny.