Ethological mechanisms of the maintenance of coat color polymorphism in the population of the Northern red-backed vole (Myodes rutilus) in the vicinity of Novosibirsk

The population of the Northern red-backed vole (Myodes rutilus) from the vicinity of Novosibirsk’s Akademgorodok is polymorphic for coat coloration (some individuals have an unusual blak rump). Experimental studies have shown that mature males with an aberrant coloration outperform standard males in adaptive characteristics such as body mass and exploratory activity, rank higher in the social hierarchy, have the optimal balance between amicability and aggressiveness, and are more attractive for receptive females. All these features give the aberrant males a selective advantage in a high population density and intensive social competition as early as the beginning of the mating season. As a result, they produce more offspring carrying this trait in the population. However, the early-born aberrant progeny also matures early and starts its reproduction; thus, it is eliminated in the autumn. In a sparser population, the aforementioned advantages are less significant, and the proportion of the aberrant form remains unchanged by the end of the reproductive season. Thus, the ethological mechanisms determining the male competitive capacity and female mating preferences contribute to the maintenance of the dynamic coat-color polymorphism in the Northern red-backed vole population.