Climate change is NOT to blame for polar bear hybrids
One of the many damaging effects of put forward by scientists is that shrinking habitats are causing polar and grizzly bears to mate more. This hybridisation could dilute polar bears' DNA which will further drive down the animals' already dwindling numbers, experts suggest. But a new study reveals that this inter-breeding is natural and is in fact not a consequence of global warming. Scroll down for video Pizzly, grolars or 'cappuccino bears' are common names of grizzly/polar hybrids. 'Such hybrids among bears are not as rare as we have hitherto assumed,' said study lead author Professor Dr Axel Janke of the Senckenberg Biodiversity and Climate Research Center in Frankfurt. It had previously been assumed climate change causes grizzlies or 'brown bears' to invade northern regions while polar bears are pushed onto the sea ice later than usual. The new results show however that an abundant flow of genes among different bear species occurred plenty of times in the past. This means hybrids are not necessarily linked to climate change, they say. 'Bears can form hybrids in different combinations,' said Dr Janke. 'We knew this from zoos. In the wild, so far this was only observed for polar bears and brown bear as well as Asiatic black and sun bear,' he said. Scientists sequenced the entire genomes of four bear species, making it possible to analyse the evolutionary history of all bears. It shows that the exchange or 'flow' of genes between species by hybridisation is possible between most bear species - not only polar and grizzly bears. 'With these new data of the sun bear, sloth bear, Asiatic black bear and spectacled bear, we now have the genomes of all known bear species,' Dr Janke said. The new genomic data show that there must have also been gene flow between the polar and sun bears in the past. However, the two species live in completely distinct geographical areas and so have never met. The researchers are able to explain this contradiction by suggesting that an 'intermediate host' has passed the genes on in various directions. The grizzly is an ideal candidate for this role as its geographic distribution overlaps with that of all other bear species. Its genome was found by the team to contain polar bear genes. 'By hybridization the brown bear could pass these polar bear genes on to other bear species in Asia,' Dr Janke said. The detected gene flow among bears also questions the scientific concept of a species. The current definition assumes that either different species cannot produce offspring in the wild or that hybrid offspring are sterile. The best-known example of this is the mule a hybrid between a horse and a donkey. However, it has been observed that grolars, the hybrids between polar and grizzly bears, are often fertile. Dr Janke said: 'We have to ask ourselves: Does the species concept still hold true, given there is evidence of gene flow not only in bears, but also in other animals?'