2014 | 2013 | 2012 | 2011 | 2010 | 2009
12 November 2014
On a safari through the genome – genes offer new insights into the distribution of giraffes...
31 October 2014
Frankfurter Biodiversität und Klima Forschungszentrum (BiK-F) erhält Spitzenbewertung vom Wissenschaftsrat ...
23 October 2014
Vortrag „Long term dynamics in the Serengeti Ecosystem: Lessons for Conservation and Society “ ...
25 September 2014
Dengue fever and malaria in the Himalayas...
18 September 2014
Vorratshaltung beim Tannenhäher: Samenverstecke nutzen dem "gefiederten Förster" mehr als den Bäumen...
15 September 2014
The Biodiversity and Climate Research Centre opens its doors to the public...
11 September 2014
Pesticides are more toxic for soil organisms in dry soil and at enhanced temperatures ...
01 September 2014
Vortrag 4. September „The Climate Change Challenge and Opportunities“ ...
01 August 2014
More People Means More Plant Growth, NASA Data Show ...
25 July 2014
Erstmals Sandmücke in Hessen entdeckt...
09 July 2014
Climate change: Tropical species are most vulnerable to rising temperatures...
25 June 2014
Vogelschutz lohnt sich! – Vogelbestände in Osteuropa profitieren von neuer Gesetzgebung...
18 June 2014
Spanish slug – busting an invasion myth...
17 June 2014
The hidden history of rain: plant waxes reveal rainfall changes during the last 24,000 years...
11 June 2014
It’s complicated - new insights into the evolutionary history of bears ...
12 May 2014
A tale of survival – scientists reveals how fish were able to colonise poisonous springs...
08 May 2014
New ways for understanding the link between the uplift of the Tibetan Plateau and species diversity...
29 April 2014
Gehen oder bleiben? – Neue Emmy Noether-Gruppe erforscht die Klima-Anpassung von Vögeln ...
08 April 2014
Mapping ecosystem services: New method shows seed dispersal pathways of hornbills...
26 March 2014
Study yields 'Genghis Khan' of brown bears, and brown and polar bear evolution...
18 March 2014
Ants plant tomorrow's rainforest...
04 March 2014
Allergikern blüht etwas: Erhöhte Fitness der Beifußambrosie in Europa nachgewiesen ...
12 February 2014
Zukunftsthema Infektionskrankheiten – zwei neue Forschungsprojekte im Bereich Medizinische Biodiversität und Parasitologie...
05 February 2014
Aquatic Insects – a tremendous potential for research on diversification...
05 February 2014
Coffee: More biodiversity, better harvest ...
20 January 2014
Erfolgreiche Renaturierung von Gewässern: Das biologische Umfeld ist entscheidend...
Polar bears are evolutionarily older and genetically more distinct than previously known: ancestry traced back to 600,000 years ago
Frankfurt am Main, Germany, April 20, 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.
Polar bear – this arctic icon evolved some 600,000 years ago, much earlier than previously known. Copyright: Hansruedi Weyrich / www.weyrichfoto.ch
[Dowload in 300 dpi]
Their genome shows that polar bears have survived several past events of severe climate change..
Copyright: Alan Wilson / www.naturepicturesonline.com
[Download in 300 dpi]
To learn more about the evolutionary history of polar bears, scientists compared DNA from the cell nucleus to that of their closest relatives - brown bears. Copyright: Hansruedi Weyrich / www.weyrichfoto.ch
[Download in 300 dpi]
For further information please contact:
Frank Hailer, Ph.D. (lead author)
LOEWE Biodiversity and Climate Research Centre (BiK-F)
phone +49 69 798 24733
Prof. Axel Janke
LOEWE Biodiversity and Climate Research Centre (BiK-F) and Goethe University Frankfurt am Main
phone +49 69 7542 1842
LOEWE Biodiversität und Klima Forschungszentrum (BiK-F), Pressereferentin
phone +49 69 7542 1838
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
download PDF, 195 KB