Beluga whale in Far Eastern seas: mtDNA lines assortment and distribution

Beluga whale in Far Eastern seas: mtDNA lines assortment and distribution

21 March 2014

To conduct a genetic research of beluga whale population inhabiting Russian Far East, we took skin remote biopsy samples as well samples taken from dead animals and from live animals during capture for educational and scientific purposes from the Okhotsk Sea beluga whales in the following regions: the Sakha-linsky Bay; Nikolaya, Ulbansky, Tugursky, and Udskaya Bays; off the west coast of Kamchatka in the Okhotsk Sea, and in the Bering Sea. Nucleotide sequences of the mitochondrial DNA (mtDNA), with a total length of 559 bp (proline tRNA gene – 62 bp, and control region – 497 bp) were determined for all animals tested; allelic compositions at 8 or 19 nuclear DNA microsatellite loci were determined for most of the animals tested.


Estimation of the distribution of the allele frequencies showed genetic isolation between the Okhotsk Sea and the Bering Sea stocks. It also showed a high level of genetic isolation between the stocks that summer in the western Okhotsk Sea (the Sakhalinsky Bay and the Shantar Region) and in the eastern Okhotsk Sea (the west coast of Kamchatka). Since the beluga whales from the Sakhalin-Amur and Shantar summer aggregations are members of the same population, they can be named the ―western-okhotsk population‖.


The mitochondrial lines distribution pattern that is being analysed in this paper reflects stable preferences in selection of summering areas (that were formed historically, during habitat enhancement), rather than the population structure. The same DNA fragment tested in 437 individuals was found to contain 24 nucleotide sequence variants (haplotypes).


All the 4 summering areas demonstrated statistically significant differences (p<0.000001) not only in the frequency of occurrence of particular haplotypes, but also in the mean genetic distances between the variants present in each study region. For example, the most frequently occurring haplotype for the Sakhalin-Amur aggregation was haplotype S022 and its derivatives (S011, S051, S001, S053, S063). This beluga whale aggregation is charac-terized by the highest degree of haplotype diversity and a rather high degree of nucleotide diversity. It should be noted that haplotypes having the same base sequence (of the 409-bp fragment) as haplotype S022 are often observed in beluga whales occurring along the both coasts of North America, up to the Svalbard Archipelago in the east.

 

The S022 haplotype was also the most frequent haplotype in the individuals of the Shantar aggregation, but within this aggregation there were statistically significant differences between belugas, depending on the bay (Языкова и др. this book). The differences consisted in an east-to-west increase in the presence of the S148 haplotype (that is essentially distanced from S022) and its derivatives (S148A, S327). These considerable differences between the dominant variants were the cause of samples from the Shantar aggregation.


As for the individuals that summer off the west coast of Kamchatka, haplotypes S148/K357 were found to be absolutely dominant in them. The haplotype prevailing in the Anadyr Estuary is haplotype C425 and its derivatives (they commonly occur in beluga whales of the Arctic Basin. However, the number of beluga whales with the K357 haplotype (that is dominant among belugas of west coast of Kamchatka) is also high. It is noteworthy that the S148/K357 haplotypes.

 

The situation observed is in many ways paradoxical. The composition of mitochondrial lines in the Sakhalin-Amur aggregation and their diversity are in the best ac-cordance with that of population of hypothetical Ice Age refugium, from where, at the end of the ice age, beluga whales began to move north, occupying more northern parts of the Pacific Ocean including waters along the northwestern coasts of the American continent. At the same time, we cannot consider the recent West Okhotsk Sea population (that includes the Sakhalin-Amur and Shantar stocks) to be the ancestor population for the whole North Pacific area, because this population includes individuals of different philogenetic line that is endemic to the Asian coast.

 

The research was done under the Beluga White Whale Program (the program is part of the Permanent expedition of Russian Academy of Science studying Red Book animals and other focus species of Russia) conducted by the Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences, with the support of the Russian Geographical Society and the project ― Current status of the Sa-khalin-Amur beluga aggregation (The Okhotsk Sea, Russia): sustainability assessment‖ (contractor: ― Dolphin and I‖ Ltd: rehabilitation and health center), with the financial support of Ocean Park Corporation (Hong Kong); and with the financial support of Georgia Aquarium Inc., SeaWorld Parks and Entertainment, Mystic Aquarium and Institute for Exploration, (USA); Kamogawa Sea World (Japan).

 


Meschersky I.G., Shpak O.V., Glazov D.M., Litovka D.I., Borisova E.A., Yazykova M.G., Rozhnov V.V.

 

References:

 


Borisova E.A., Meschersky I.G., Shpak O.V., Glazov D.M., Litovka D.I., Rozhnov V.V. 2012. Evaluation of effect of geographical isolation on level of genetic distinctness in beluga whale (Delphinapterus leucas) populations in Russian Far East.


Yazykova M.G., Meschersky I.G., Shpak O.V., Glazov D.M., Litovka D.I., Borisova E.A., Rozhnov V.V. 2012. Molecular genetic analysis of Sakhalin-Amur and Shan-tar beluga‘ (Delphinapterus leucas) summer aggregations in the Okhotsk Sea.


O‘Corry-Crowe G.M., Suydam R.S., Rosenberg A., Frost K.J., Dizon A.E. 1997. Phylogeography, population struc-ture and dispersal patterns of the beluga whale Delphinapterus leucas in the western Nearctic revealed by mito-chondrial DNA. Mol. Ecol., 6: 955-970.


O‘Corry-Crowe G. M., Lydersen C., Heide-Jørgensen M.P., Hansen L., Mukhametov L.M., Dove O., Kovacs K.M. 2010. Population genetic structure and evolutionary history of North Atlantic beluga whales (Delphinapterus leu-cas) fromWest Greenland, Svalbard and the White Sea. Polar Biol., 33: 1179-1194.