Scientists find evidence of gene flow across most bear species

April 19 (UPI) -- New genomic research suggests mosts bears breed across species boundaries and are capable of producing fertile hybrids.

Scientists have long assumed species hybridization is unsustainable and typically yields infertile offspring. For example, a mule, the offspring of a horse and donkey, can't reproduce. Polar-grizzly hybrids -- often called grolars, pizzly bears or "cappuccino bears" -- are often fertile.

Recently, scientists from the Senckenberg Research Institute and Natural History Museum in Germany completed the genomic sequencing of four new bear species.

"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," Axel Janke, a scientist at the Senckenberg Biodiversity and Climate Research Center in Frankfurt, said in a news release.

The results -- detailed in the journal Scientific Reports -- revealed evidence of interspecies gene flow, or gene exchange, throughout ursine evolution.

Several studies have suggested bear hybridization is the product of climate change -- warmer temperatures push brown bears northward into polar bear territory. But the new research suggests bear hybridization has been prevalent for thousands of years.

The research also showed gene flow between polar and sun bears, despite significant geographical separation between the two species. Only an intermediary host, like brown-polar hybrids, can explain the shared genetics.

Photo by Vikas Kumar, et al./Scientific Reports

"By hybridization the brown bear could pass these polar bear genes on to other bear species in Asia," Janke said.

Reproductive exclusivity or isolation have long been used as a defining marker of special distinction, but the latest research calls such logic into question.

"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?" Janke said. "Therefore, what do we need to protect for the future -- species or genomic diversity?"

Janke believes the answer is genomic diversity.

"What we must preserve... is genetic variation to protect diversity and to allow adaptation to future environmental changes," he said.