Genetic variation in Holocene bowhead whales from Svalbard

Abstract

Bowhead whales (Balaena mysticetus) are distributed in the Arctic in five putative stocks. All stocks have been heavily depleted due to centuries of exploitation. In the present study, nucleotide sequence variation of the mitochondrial control region was determined from bone remains of 99 bowhead whales. The bones, 14C dated from recent to more than 50,000 bp, were collected on Svalbard (Spitsbergen) and are expected to relate to ancestors of the today nearly extinct Spitsbergen stock. Fifty-eight haplotypes were found, a few being frequent but many only found in one individual. The most abundant haplotypes of the Spitsbergen stock are the same as those most abundant in the extant Bering-Chukchi-Beaufort (BCB) Seas stock of bowhead whales. Although F(ST) indicates a slight but statistically significant genetic differentiation between the Spitsbergen and the BCB stocks this was not considered informative due to the very high levels of genetic diversity of mitochondrial DNA haplotypes in both bowhead whale stocks. Other measures such as K(ST) also indicated very low genetic differentiation between the two populations. Nucleotide diversity and haplotype diversity showed only minor differences between the Spitsbergen and BCB stocks. The data suggest that the historic Spitsbergen stock--before the severe bottleneck caused by whaling--did not have substantially more genetic variation than the extant BCB stock. The similar haplotypes of the Holocene Svalbard samples and the current BCB stock indicate significant migration between these two stocks and question the current designation of five distinct stocks of bowhead whales in the Arctic.

Ancient DNA reveals that bowhead whale lineages survived Late Pleistocene climate change and habitat shifts

“…Ancient DNA analysis of radiocarbon-dated balaenid subfossils identified the occurrence of a true Arctic species, the bowhead whale, south of 59°N during the Pleistocene, which is then replaced by the right whale during the Holocene. Insert shows a map of the study area and locations of the samples used in this study: Late Pleistocene bowhead whale subfossil samples (blue squares); Early Holocene bowhead whale subfossil samples 22 (blue circles); and Early Holocene right whale subfossils (purple circles).…”

“…We compared the Late Pleistocene samples with two data sets from the Arctic dated to the Early Holocene 19,22 to determine whether the southern lineages repopulated the Arctic following the rapid climate change that occurred between these sampling periods. The first comparison with 34 samples from Svalbard 22 , which is almost directly north of the locations of our Late Pleistocene subfossils, revealed four shared haplotypes and no significant differentiation (F ST ¼ 0.008, P ¼ 0.252) between the two time periods (Fig. 3).…”

“…The Late Pleistocene bowhead whale sequences were compared with a data set of 99 Holocene bowhead whale sequences from subfossils collected from Svalbard in the Arctic 22 . The skyline plot estimated from these sequences (Fig.…”

“…These samples originated from an area south of 59°N, over 1,000 km south of the current Arctic range of the bowhead whale [11][12][13][14][15][16][17][18][19][20][21][22] . We successfully genetically identified the species of 27 ancient samples, of which 15 were bowhead whales ( Supplementary Fig.…”

“…Sea ice does, therefore, not appear to have been a barrier to movement between stocks, even those in different ocean basins, during warmer periods of the Holocene 20,21 . Previous aDNA studies have found that genetic diversity was maintained throughout the Holocene, despite bowheads being heavily exploited across their range by whalers 20,22 . Modelled projections based on Holocene data suggest that effective female population size increased in the Late Pleistocene 20,23 .…”