POLAR BEAR GENOME

POLAR BEAR RESPONSE TO GLOBAL WARMING: Insights from shotgun sequencing of the Polar Bear Genome

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 Obiettivo del progetto (Objective)

'The polar bear (Ursus maritimus) is the top predator of the northern hemisphere polar regions and the human iconic symbol of the Arctic and climate change itself. Due to projections of accelerated global environmental changes leading to dramatic reductions in range size over the next 50–100 years, global warming is believed to be the most important long-term threat to the polar bear’s future survival. However, these current projections are based on short-term ecological, behavioural, and genetic studies, and no scientific studies exist that directly quantify the effect of climate-induced environmental changes on the species. This study will apply novel shotgun sequencing methods to build a genome-wide SNP (single nucleotide polymorphism) library of the polar bear genome, initially using modern populations, and subsequently transferring these methods to subfossil samples. By projecting the temporal genetic data against precise estimates of past climatic events derived from Arctic ice and lake cores, we will be able to estimate the precise timing, duration, and effects of past demographic changes. By understanding the significance of how environmental perturbations affected the species in the past, the first informed predictions can be made of how polar bears, and ultimately other Arctic marine mammals, will respond to the ongoing global warming that is threatening their ecosystem. This study will generate the first population genomic dataset of its kind, using both ancient and modern samples. The refinement of current laboratory methods and the development of analytical methods during the statistical analysis of the data will significantly contribute to the fields of evolutionary genetics and ancient DNA. In addition, the study will make an important contribution to polar bear research by answering the fundamentally important question of how polar bears responded to past climate changes.'

Introduzione (Teaser)

Polar bears (Ursus maritimus) are the top predator in the High Arctic, one of the most inhospitable environments on the planet. For many, this iconic animal has become symbolic of climate change, which represents the greatest long-term threat to its survival.

Descrizione progetto (Article)

The POLAR BEAR GENOME (Polar bear response to global warming: Insights from shotgun sequencing of the polar bear genome) project will develop a library of the polar bear genome. The study uses novel shotgun sequencing methods to sequence DNA strands and build a genome-wide single nucleotide polymorphism library of modern polar bear populations.

Researchers have generated 80 complete polar bear genomes and 10 high-coverage brown bear genomes. These were studied in order to determine the age of polar bears as a species and the joint demographic history of brown and polar bears since the two species diverged. Researchers also investigated which genes have been under the strongest positive selection.

The results were published in the journal http://www.cordis.europa.eu/docs/results/253/253376/periodic1-cell2014.png (Cell) in May 2014 as the cover story. They reveal that the polar bear is a very young species, which diverged from the brown bear less than half a million years ago.

Estimating a correct age is vital to understanding how polar bears adapted to the High Arctic. The divergence date coincides with the longest interglacial in the preceding half million years; an interglacial being a period of warmer global temperatures lasting thousands of years.

It is believed that brown bear populations were able to expand northwards, but as conditions shifted towards a colder climate, a population was marooned in the north. The bears were forced to adapt very quickly and diverged from the main population to become the polar bears of today.

Polar bears differ fundamentally from brown bears in ecology, behaviour and morphology, and their recent divergence represents an unprecedented level of rapid evolution in a large mammal. The species has since undergone dramatic physiological and phenotypic changes that enable them to live out on the Arctic sea ice.

A major project finding was that of genes associated with the development of adipose tissue, traits fundamental to a species surviving primarily on seal blubber. Polar bears have substantial adipose deposits under the skin and around organs, and cholesterol levels in blood plasma are extreme.

In humans, such high cholesterol levels would risk cardiovascular disease; therefore, polar bears represent a model organism for studying rapid adaptation to a new environment and a high calorific diet. This offers great potential for future research.