Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Polar bears are evolutionary older than previously known: ancestry traced back to 600,000 years ago

20.04.2012
A study appearing in the current issue of the journal “Science” reveals that polar bears evolved as early as some 600,000 years ago.
An international team led by researchers from the German Biodiversity and Climate Research Centre (BiK-F) shows the largest arctic carnivore to be five times older than previously recognized. The new findings on the evolutionary history of polar bears are the result of an analysis of information from the nuclear genome of polar and brown bears, and shed new light on conservation issues regarding this endangered arctic specialist.

Polar bears are uniquely specialized for life in the arctic. This fact is undispu-ted, and supported by a range of morphological, physiological and behavioural evidence. However, conducting research on the evolutionary history of polar bears is difficult. The arctic giant spends most of its life on sea ice, and typically also dies there. Its remains sink to the sea floor, where they get ground up by glaciers, or remain undiscovered. Fossil remains of polar bears are therefore scarce. Because the genetic information contained in each organism carries a lot of information about the past, researchers can study the history of the species by looking at the genes of today’s polar bears.

Analysis of the genetic information in the cell nucleus
Recent studies had suggested that the ancestor of polar bears was a brown bear that lived some 150,000 years ago, in the late Pleistocene. That research was based on DNA from the mitochondria - organelles often called the ‘powerhouses of the cell’. Researchers from the German Biodiversity and Climate Research Centre (BiK-F), together with scientists from Spain, Sweden and the USA, now took an in-depth look at the genetic information contained in the cell nucleus. Frank Hailer, BiK-F, lead author of the study explains: “Instead of the traditional approach of looking at mitochondrial DNA we studied many pieces of nuclear DNA that are each independently inherited. We characterized those pieces, or genetic markers, in multiple polar and brown bear individuals”.

Polar bears had much more time for adaptation and speciation than previously assumed
This genetic survey was well worth the effort - the information obtained from nuclear DNA indicates that polar bears actually evolved in the mid Pleistocene, some 600,000 years ago. This provides much more time for the polar bear ancestors to colonize and adapt to the harsh conditions of the arctic. Based on studies of mitochondrial DNA, polar bears had earlier been considered an example of surprisingly rapid adaptation of a mammal to colder climates. The polar bear’s specific adaptations, including its black skin, white fur, and fur-covered feet now seem less surprising. “In fact, the polar bear genome harbours a lot of distinct genetic information”, says Hailer, “which makes a lot of sense, given all the unique adaptations in polar bears”.

Maternally inherited (mitochondrial) DNA was showing a biased picture
Previous studies of mitochondrial DNA had indicated that polar bears are much younger as a species. The authors of the new paper in “Science” explain this apparent discrepancy with past events of hybridization between polar and brown bears - a process recently observed in the Canadian arctic. After their initial speciation, polar bears and brown bears came into contact again, maybe due to past climatic fluctuations. The mitochondrial DNA found in polar bears today was probably inherited from a brown bear female that hybridized with polar bears at some point in the late Pleistocene. It appears that much of the nuclear genome remained unaffected by hybridization, so polar bears retained their genetic distinctiveness. “Each part of the genome tells its own story. In our study we analysed nuclear DNA that is inherited from both parents. It provides a more detailed and accurate picture of the evolutionary history of a species than mitochondrial DNA that is inherited only from the mother”, says Axel Janke, BiK-F, senior author on the study who also headed the recent sequencing of the brown bear genome. He goes on to say: “Inferring a species’ evolutionary history based on mitochondrial DNA alone is like solving a puzzle with only a few of the many available pieces. You need to study many genetic markers (loci) to put together the full picture.”
Genome carries evidence of past climate fluctuations
The new genetic data indicate that polar bears went through tough times over the course of their 600,000 year-old evolutionary history. Polar bears show much less genetic diversity than brown bear. This is probably due to dramatic reductions in population size in the past. Maybe those times coincided with phases of climatic warming. Whether polar bears will be able to survive the current phase of sea ice melting is not clear. Firstly, human impacts are accelerating the rate of climate change, and the arctic could reach higher temperatures than in previous interglacial warm phases. In addition, numerous human-related issues are threatening the polar bear today. Polar bears colonizing coastal regions due to sea ice melting frequently encounter human habitat, and many bears are killed. Besides persecution, polar bears are also facing other - evolutionarily novel - threats, including pollution by persistent chemicals in the food chain. “If we were to lose polar bears in our era, we would have to ask ourselves what role we played in pushing them over the edge. They clearly were able to survive previous warm phases”, Hailer concludes upon the wider implications of the study.

The authors of the study are:
Frank Hailer (lead author), Verena E. Kutschera, Björn M. Hallström, Denise Klassert, Axel Janke (senior author) -- Biodiversity and Climate Research Centre (BiK-F), Frankfurt am Main, Germany. Jennifer A. Leonard -- Doñana Biological Station - CSIC, Seville, Spain. Steven R. Fain -- US Fish and Wildlife Service, Forensics lab, Ashland, OR, USA. Ulfur Arnason -- Lund University, Lund, Sweden.

Paper:
Hailer, F. et al. (2012). Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage. Science. DOI: 10.1126/science.1216424

For further information please contact:

Frank Hailer, Ph.D. (lead author)
LOEWE Biodiversity and Climate Research Centre (BiK-F)
phone +49 69 798 24733
frank.hailer@senckenberg.de

Prof. Axel Janke
LOEWE Biodiversity and Climate Research Centre (BiK-F) and Goethe University Frankfurt am Main
phone +49 69 7542 1842
axel.janke@senckenberg.de

or

Sabine Wendler
LOEWE Biodiversität und Klima Forschungszentrum (BiK-F), Pressereferentin
phone +49 69 7542 1838
sabine.wendler@senckenberg.de

LOEWE Biodiversität und Klima Forschungszentrum, Frankfurt am Main
With the objective of analysis the complex interactions between biodiversity and climate through a wide range of methods, the Biodiversität und Klima Forschungszentrum [Biodiversity and Climate Research Centre] (BiK‐F) has been funded since 2008 within the context of the Landes‐Offensive zur Entwicklung Wissenschaftlich ökonomischer Exzellenz (LOEWE) of the Land of Hessen. The Senckenberg Gesellschaft für Naturforschung and Goethe University in Frankfurt as well as other, directly involved partners, co‐operate closely with regional, national and international institutions in the fields of science, resource and environmental management, in order to develop projections for the future and scientific recommendations for sustainable action.

Sabine Wendler | Senckenberg
Further information:
http://www.bik-f.de
http://www.senckenberg.de

More articles from Studies and Analyses:

nachricht New model connects respiratory droplet physics with spread of Covid-19
21.07.2020 | University of California - San Diego

nachricht Risk of infection with COVID-19 from singing: First results of aerosol study with the Bavarian Radio Chorus
03.07.2020 | Klinikum der Universität München

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: ScanCut project completed: laser cutting enables more intricate plug connector designs

Scientists at the Fraunhofer Institute for Laser Technology ILT have come up with a striking new addition to contact stamping technologies in the ERDF research project ScanCut. In collaboration with industry partners from North Rhine-Westphalia, the Aachen-based team of researchers developed a hybrid manufacturing process for the laser cutting of thin-walled metal strips. This new process makes it possible to fabricate even the tiniest details of contact parts in an eco-friendly, high-precision and efficient manner.

Plug connectors are tiny and, at first glance, unremarkable – yet modern vehicles would be unable to function without them. Several thousand plug connectors...

Im Focus: New Strategy Against Osteoporosis

An international research team has found a new approach that may be able to reduce bone loss in osteoporosis and maintain bone health.

Osteoporosis is the most common age-related bone disease which affects hundreds of millions of individuals worldwide. It is estimated that one in three women...

Im Focus: AI & single-cell genomics

New software predicts cell fate

Traditional single-cell sequencing methods help to reveal insights about cellular differences and functions - but they do this with static snapshots only...

Im Focus: TU Graz Researchers synthesize nanoparticles tailored for special applications

“Core-shell” clusters pave the way for new efficient nanomaterials that make catalysts, magnetic and laser sensors or measuring devices for detecting electromagnetic radiation more efficient.

Whether in innovative high-tech materials, more powerful computer chips, pharmaceuticals or in the field of renewable energies, nanoparticles – smallest...

Im Focus: Tailored light inspired by nature

An international research team with Prof. Cornelia Denz from the Institute of Applied Physics at the University of Münster develop for the first time light fields using caustics that do not change during propagation. With the new method, the physicists cleverly exploit light structures that can be seen in rainbows or when light is transmitted through drinking glasses.

Modern applications as high resolution microsopy or micro- or nanoscale material processing require customized laser beams that do not change during...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“Conference on Laser Polishing – LaP 2020”: The final touches for surfaces

23.07.2020 | Event News

Conference radar for cybersecurity

21.07.2020 | Event News

Contact Tracing Apps against COVID-19: German National Academy Leopoldina hosts international virtual panel discussion

07.07.2020 | Event News

 
Latest News

Rare Earth Elements in Norwegian Fjords?

06.08.2020 | Earth Sciences

Anode material for safe batteries with a long cycle life

06.08.2020 | Power and Electrical Engineering

Turning carbon dioxide into liquid fuel

06.08.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>