Genetics
Credit: Lyle Walton
The field of genetics is one of the most rapidly advancing areas of study in polar bear research that is now providing insights into the ecology, evolution, and adaptive potential of polar bears. At its most basic level, the field of genetics is focused on the study of genes. Genes are composed of unique sequences of nucleotides that pair together (also called base pairs) to form an organism’s DNA. Genes code for proteins that influence the function of cells and act as a blueprint for the key biological processes of life. This genetic information is heritable from parent to offspring and is foundational to what makes a polar bear a polar bear. From their black skin to their translucent hair, polar bears evolved from brown bears because of changes in their genome that fixed certain traits (e.g., hair pigmentation) making them highly adapted to the Arctic marine environment. Original work on polar bear genetics was focused on understanding relatedness amongst different groups of bears using genetic markers called microsatellites, that are tandemly repeating sequences of nucleotides. More recently, single nucleotide polymorphisms (SNP’s) or single nucleotide variations in the genome have also been used to examine polar bear population genetics as well as to provide insights into variation in gene expression among subpopulations. These genetic markers can also be used to obtain unique genetic fingerprints for each bear allowing scientists to identify individuals in biopsy mark recapture studies as well as examine mating systems and the processes of natural and sexual selection.
Whole Genomes
The field of genomics has been rapidly advancing in response to technologies that were developed to map the human genome in effort to better understand how genes influence human health. As a reference, initial sequencing of the human genome took over 13 years and cost over 3 billion dollars. However, as a result of changes in the accessibility and cost of these technologies you can now get a whole genome sequence for a polar bear for $400-$500 dollars using just a small tissue sample. Thanks to these advancements, we now know that the polar bear genome is approximately 3.5 billion base pairs in length, with all those base pairs packaged into 37 pairs of chromosomes (humans have 23) that code for thousands of genes. Recent sequencing of whole genomes in brown bears and polar bears has revealed that genes associated with olfactory receptors, fatty acid metabolism and cardiac function were all critical in the evolution of polar bears. Examining whole genomes can not only provide a window into the past but also into the future, as pre-existing genetic variation in the polar bear genome will likely play an important role in the potential future adaptation of the species. Now that scientists have mapped the genetic architecture of the polar bear genome, future research will be focused on understanding which genes influence key biological processes like contaminants metabolism and fasting endurance to better understand how polar bears may be able to adapt and respond to emerging threats in the environment. Assessing, understanding, and conserving genetic variation in the world’s polar bear subpopulations will be a critical to the long-term conservation of the species.
Further Reading
- Laidre KL, Supple MA, Born EW, Regehr, EV, Wiig Ø, Ugarte F, Aars J, Dietz R, Sonne C, Hegelund P, Isaksen C, Akse GB, Cohen B, Stern HL, Moon T, Vollmers C, Corbett-Detig R, Paetkau, and Shapiro B. 2022. Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st-century sea-ice conditions. Science 376: 1333-1338.
- Malenfant RM, Davis CS, Richardson ES, Lunn NJ, and Coltman DW. 2018. Heritability of body size in the polar bears of Western Hudson Bay. Molecular Ecology Resources 18: 854-866.
- Paetkau D, Calvert W, Stirling I, and Strobeck C. 1995. Microsatellite analysis of population structure in Canadian polar bears. Molecular Ecology 4: 347-354.
- Rinker DC, Specian NK, Zhao S, and Gibbons JG. 2019. Polar bear evolution is marked by rapid changes in gene copy number in response to dietary shift. Proceedings of the National Academy of Sciences 116: 13446-13451.