Reproductively isolated ecotypes of killer whales Orcinus orca in the seas of the Russian Far East

Two ecotypes of killer whales—fish-eating and mammal-eating—have been found in the seas of the Russian Far East, but confirmation of their status required genetic studies of animals with known phenotype and foraging specialization. In this paper we combine the results of the analysis of nuclear genetic markers, isotopic composition of tissues and phenetic feature (shape of the saddle patch) of killer whales from different regions of Far Eastern seas. Analysis of allelic composition of 9 microsatellite loci of the nuclear DNA divided the samples into two distinct clusters with the divergence between them high enough to indicate reproductive isolation. The content of nitrogen stable isotope 15N in tissues of whales from the first cluster was significantly lower than that of the second cluster. The difference of δ15N values between individuals from different clusters was about 3‰, which corresponds to the difference between adjacent trophic levels. Apparently, the first cluster comprised fish-eating, and the second—mammal-eating animals. The ratio of saddle patch shape types also differed between the clusters. Whales from the first cluster had five types of patch shape in different proportions, while whales from the second cluster had only “smooth” saddle patches. The differences between the clusters were statistically significant. Thus, killer whales from the seas of the Russian Far East comprise at least two reproductively isolated clusters with stable ecological and morphological differences, that is, two different ecotypes—fish-eating and mammal-eating. Different ecotypes of killer whales should be managed separately during abundance surveys, monitoring, evaluation of human impact and estimates of total allowed takes from the wild populations.