Examination of ten thousand years of mitochondrial DNA diversity and population demographics in bowhead whales ( Balaena mysticetus ) of the Central Canadian Arctic (original) (raw)
Related papers
Marine Mammal Science, 2012
Mitochondrial DNA (mtDNA) sequences were analyzed from 106 bowhead whale (Balaena mysticetus) specimens dating 471 ± 44 14 C B.P.-10,290 ± 150 14 C B.P. to evaluate whether historical changes in distribution and connectivity were detectable in levels of diversity and population structuring in the Central Canadian Arctic. The species has maintained levels of mtDNA diversity over 10,000 yr comparable to other nonbottlenecked large whale species. When compared to data from the Holocene East Greenland/Spitsbergen and contemporary Bering-Chuckchi-Beaufort populations, differentiation was low (F ST ≤ 0.005, ST ≤ 0.003) and no temporal or geographical genetic structuring was evident. A combination of analyses suggests that the population has expanded over the past 30,000 14 C yr. This genetic signature of expansion could result from population growth, admixture of multiple gene pools, or a combination of both scenarios. Despite known climatic change that altered bowhead distribution and led to isolation of populations, there is no detectable population structuring or change in genetic diversity during the Holocene. This may be due to long generation time, occasional population connectivity and a historically large global population. These characteristics warrant caution when interpreting contemporary bowhead whale DNA data, as it is unlikely that any population will be in mutation-drift equilibrium.
Genetic variation in Holocene bowhead whales from Svalbard
Molecular Ecology, 2007
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 FST 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 KST 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.
Sea ice is believed to be a major factor shaping gene flow for polar marine organisms, but it remains unclear to what extent it represents a true barrier to dispersal for arctic cetaceans. Bowhead whales are highly adapted to polar sea ice and were targeted by commercial whalers throughout Arctic and subarctic seas for at least four centuries, resulting in severe reductions in most areas. Both changing ice conditions and reductions due to whaling may have affected geographic distribution and genetic diversity throughout their range, but little is known about range-wide genetic structure or whether it differed in the past. This study represents the first examination of genetic diversity and differentiation across all five putative stocks, including Baffin Bay-Davis Strait, Hudson Bay-Foxe Basin, Bering-Beaufort-Chukchi, Okhotsk, and Spitsbergen. We also utilized ancient specimens from Prince Regent Inlet (PRI) in the Canadian Arctic and compared them with modern stocks. Results from analysis of molecular variance and demographic simulations are consistent with recent and high gene flow between Atlantic and Pacific stocks in the recent past. Significant genetic differences between ancient and modern populations suggest PRI harbored unique maternal lineages in the past that have been recently lost, possibly due to loss of habitat during the Little Ice Age and/or whaling. Unexpectedly, samples from this location show a closer genetic relationship with modern Pacific stocks than Atlantic, supporting high gene flow between the central Canadian Arctic and Beaufort Sea over the past millennium despite extremely heavy ice cover over much of this period.
Although the majority of eastern North Pacific (ENP) gray whales migrate to feeding grounds in the Bering and Chukchi Seas, some terminate the migration in more southerly areas such as British Columbia (BC). Long-term sighting studies in Clayoquot Sound (CS), BC, indicate that approximately 35-50 individuals exhibit long-term fidelity to this site. To determine the sex composition (based on genetic sexing) of CS gray whales and to assess whether matrilineal site-fidelity occurs in CS, we collected skin biopsy samples from 16 CS individuals ('residents') and 41 samples from other areas (representative of the overall population in the ENP: 'non-residents'). A total of 27 polymorphic sites defined 24 haploytpes among the 57 samples sequenced for HV1 of the mtDNA control region. The nucleotide and haplotype diversities of these samples were 0.017 (SE = 0.0012) and 0.94 (SE = 0.0019), respectively. Neighbor-joining analysis revealed five lineages each of which contained haplotypes that were observed in both residents and non-residents. Residents did not differ significantly from non-residents, and no significant sex-ratio bias was found. These data suggest a level of diversity that is inconsistent with a severe historical bottleneck, and given the available sample size, do not indicate matrilineally directed fidelity to Clayoquot Sound.
Scientific Reports, 2022
The East Greenland-Svalbard-Barents Sea (EGSB) bowhead whale stock (Balaena mysticetus) was hunted to near extinction and remains Endangered on the International Union of Conservation of Nature Red List. The intense, temporally extensive hunting pressure may have left the population vulnerable to other perturbations, such as environmental change. However, the lack of genomic baseline data renders it difficult to evaluate the impacts of various potential stressors on this stock. Twelve EGSB bowhead whales sampled in 2017/2018 were re-sequenced and mapped to a previously published draft genome. All individuals were unrelated and void of significant signs of inbreeding, with similar observed and expected homo-and heterozygosity levels. Despite the small population size, mean autosome-wide heterozygosity was 0.00102, which is higher than that of most mammals for which comparable estimates are calculated using the same parameters, and three times higher than a conspecific individual from the Eastern-Canada-West-Greenland bowhead whale stock. Demographic history analyses indicated a continual decrease of N e from ca. 1.5 million to ca. 250,000 years ago, followed by a slight increase until ca. 100,000 years ago, followed by a rapid decrease in N e between 50,000 and 10,000 years ago. These estimates are lower than previously suggested based on mitochondrial DNA, but suggested demographic patterns over time are similar. The bowhead whale (Balaena mysticetus) is the only baleen whale that lives its entire life in Arctic and subarctic regions, often in association with sea ice 1. Four bowhead whale stocks are currently recognized: (1) the Bering/ Chukchi/Beaufort Seas (BCB) stock; (2) the Okhotsk Sea (OKH) stock; (3) the Eastern Canada-West Greenland (ECWG) stock; and (4) the East Greenland-Svalbard-Barents Sea (EGSB) stock, earlier referred to as the Spitsbergen stock 2. The bowhead whale, as a species, is listed as Least Concern in the International Union of Conservation of Nature (IUCN) Red List. However, the EGSB stock, which is distributed from the East Greenland Sea across the northern Barents Region into Russia (including Severnaya Zemlya and Franz Josef Land waters), is classified as Endangered 2. There has been ongoing discussion regarding the census size of the EGSB stock. This population was thought to be large prior to the onset of extensive hunting, which commenced circa 1611. Estimates of the preharvest stock size range from 25,000 to 100,000 individuals 3. When hunting ceased in 1932, the population was thought to be depleted to near extinction 4,5. Recent estimates of the current size of this stock have ranged from a few tens 6 to several hundred individuals 7. In support of these low estimates, only a few bowhead whale sightings
Canadian Journal of Zoology-revue Canadienne De Zoologie, 1999
The North Atlantic right whale (Eubalaena glacialis) inhabits five areas along the east coast of North America at different times of the year. During 17 years of field observations, it has been found that only 59% of the newborn calves are brought to the Bay of Fundy nursery area. To examine whether this is because of population structuring, the mitochondrial DNA (mtDNA) control region haplotypes were determined for 269 individuals. Seven polymorphic sites were found to define five haplotypes. Calves were divided into two groups based on whether or not they were brought to the Bay of Fundy nursery. Significant genetic structuring of mitochondrial haplotypes was found between these groups (p = 0.002). Mothers that have had more than three calves demonstrated significant fidelity (p = 0.005) to the Bay of Fundy, suggesting that philopatry is the basis for the genetic structuring. Although this study clearly identifies the existence of two subpopulations and an alternative nursery area(s), the location(s) of the alternative area(s) is unclear and remains an important issue for the conservation of the species.