REPRODUCTION IN THE WATER-VOLE (ARVICOLA- TERRESTRIS), POLYMORPHIC FOR THE AGOUTI LOCUS

Reproduction of three coat-color genotypes:brown, AA (homozygotes for the wild type agouti allele); melanic, a(e)a(e) (homozygotes for the a utosomal recessive extreme nonagouti allele); and black-brown, Aa(e) ( heterozygotes)-in the water vole was investigated under laboratory con ditions. Nine possible kinds of crosses were identified. The Aa(e) and a(e)a(e) females had higher fertility than brown AA females, while ma les of all three group displayed similar fertility. AA and a(e)a(e) fe males started breeding earlier and bore larger litters, Unlike melanic females, heterozygous females had stable high fertility indices indep endent of male genotype. In the melanic form, female receptivity, litt er size, and postnatal viability of offspring were the highest in the (a(e)a(e) x AA) crosses, which resulted in exclusively heterozygous pr ogeny.