Bowhead Whale Mysteries Uncovered By Genetic Study Using Modern And Ancient DNA

October 22, 2012 in Animals & Insects

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The first genetic analysis of bowhead whales, throughout their entire range, has just been completed. The study was done by using hundreds of unique samples taken from a wide variety of different modern populations and many archaeological hunting sites dating back thousands of years.

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The ancient DNA samples used by the researchers have been gathered over the past 20 years, primarily from: “old vessels, toys, and housing material made from baleen — preserved in pre-European settlements in the Canadian Arctic.” The new research has shed some light on the effects that whaling has had on genetic diversity, documenting the loss of several unique mitochondrial lineages in the recent past. The researchers comment that some of this loss may have been caused by the effects of increased sea ice during the ‘little ice age’.

“Our study represents the first genetic analysis of bowheads across their entire range,” said Elizabeth Alter, the study’s lead author and now a professor at City University of New York. “The study also illustrates the value of ancient DNA in answering questions about the impact of changing climate and human exploitation on genetic diversity in bowhead whales.”

The research was done by analyzing mitochondrial DNA taken from whales in all “four or five putative populations — the Canada-Greenland population (sometimes designated as two separate populations, the Baffin Bay-Davis Strait and Hudson Bay-Foxe Basin populations), Bering-Beaufort-Chuckchi Seas, the Okhotsk, and the Spitsbergen populations — for the purpose of gauging gene flow between those groups.”

The researchers also utilized ancient DNA gathered from some of the relics of the Thule people (thought to be the ancestors of the modern Inuit) on Somerset Island on the western side of Prince Regent Inlet, in their abandoned settlements. This site is estimated to have last been inhabited 500-800 years ago. The researchers also obtained older genetic samples from Spitsbergen (3,000 or so years old) that were used in the analysis.

The lab at AMNH’s Sackler Institute for Comparative Genomics was able to ‘isolate and amplify’ segments of mitochondrial DNA from these old samples. Mitochondrial DNA is essentially the maternal line DNA, it is only passed down from mother to daughter.

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The genetic analysis showed clear differences between the ancient and modern populations studied, and general loss of diversity. The loss of diversity includes “the recent disappearance of unique maternal lineages over the past 500 years, the possible result of habitat loss during the Little Ice Age (a period of climatic cooling that occurred between the 16th to 19th Centuries) and/or extensive whaling in the region.”

An unexpected and interesting finding of the research was that the frozen, and you would think impassable, inlets and straits that separate the Pacific and Atlantic populations, don’t actually separate the “ice-savvy and morphologically adapted bowheads.” The researchers found that the two populations are so closely related that it must be because individual whales can travel across the Arctic. The researchers make it clear though that however this is done is still completely unknown to them.

“The assumption that Arctic sea ice has separated bowhead whale populations over the past several thousand years is contradicted by the genetic analysis, which indicates that significant migration between Atlantic and Pacific populations has recently taken place,” said Dr. Howard Rosenbaum, Director of WCS’s Ocean Giants Program and senior author on the study. “The finding reveals much about the abilities of bowheads to find navigable routes through sea ice and helps illuminate hidden connections between populations.”

The researchers note that a better understanding of how shifting sea ice conditions and commercial whaling affect the whales is important for future decisions on their conservation or management. Especially now that the Arctic Ocean has begun rapidly losing its summer sea ice cover; opening it to increased shipping, fishing, and maritime tourism.

Some background on the bowhead whale:
It grows up to 70 feet in length and can weigh up to 133 tons in weight. It’s a baleen whale that lives almost entirely in Arctic and sub-Arctic waters. “The bowhead gets its name from its enormous arched head, which it occasionally uses to break through ice up to 60 centimeters thick in order to breathe. The species widely hunted for centuries by commercial whalers, who prized the species for its long baleen (used in corsets and other items) and its thick blubber (the thickest of any species of whale). The bowhead whale may also be among the most long-lived mammal species. In 2007, aboriginal whalers on the Alaskan coast landed a whale carrying a valuable clue about the animal’s probable age. The whalers discovered a harpoon point manufactured in the 1890s embedded in the whale’s blubber, indicating the animal may have survived an encounter with whalers more than one hundred years ago.”

There have been numerous reports of spear points dating back to the 1800′s being discovered in whale blubber. Current estimates suggest that they may live as long as 200 years, or longer.

The bowhead whale is currently ‘protected’ from commercial whaling by the International Whaling Commission since 1946. With the exception of limited subsistence whaling by some coastal communities. The Okhotsk Sea and Spitsbergen (Svalbard) populations of bowheads are currently listed on the IUCN Red List of Threatened Species as Endangered and Critically Endangered. And the Baffin Bay-Davis Strait stock and the Hudson Bay-Foxe Basin stock as Endangered and Vulnerable.

The new research was just published in the journal Ecology and Evolution.

Source: Wildlife Conservation Soceity

Image Credits: Brenda K. Rone NOAA/AFSC/NMML

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