Polar bears and brown bears were still mating long after they split into two separate species, according to a new study.
The two species are known to have split between 1.3 and 1.6 million years ago, but new genomic evidence suggests they inherited traits from each other much more recently.
Scientists from the United States, Mexico and Finland have analyzed the genomes of 64 modern polar and brown bears, as well as that of an ancient polar bear that lived up to 130,000 years ago.
While the proof of hybridization has been found in the brown and polar bear genomes, the latter bearing a particularly strong signature of brown bear DNA.
As global warming continues to melt Arctic sea ice, the two species of bears may encounter each other more frequently, their shared evolutionary history may become more meaningful.
This may influence how the Arctic-adapted polar bear adapts to life in a warmer climate, which its brown bear cousins are already more prone to.
Subfossil jawbone of a polar bear that lived 115,000 to 130,000 years ago in the Norwegian archipelago of Svalbard. A genomic study includes analysis of DNA extracted from a tooth attached to this jawbone, which showed evidence of hybridization in polar and brown bears
Researchers estimate that polar bears and brown bears began becoming separate species between 1.3 and 1.6 million years ago. The interbreeding of polar and brown bears previously made it difficult to determine how long ago the two species separated
“We find evidence of interbreeding between polar bears and brown bears predating an ancient polar bear that we studied,” said Dr. Charlotte Lindqvist, associate professor of biological sciences at the University at Buffalo College of Arts and Sciences.
“Furthermore, our results demonstrate a complicated and intertwined evolutionary history in brown and polar bears, with the main direction of gene flow from polar bears to brown bears.
“This reverses a hypothesis suggested by other researchers that gene flow was unidirectional and passed to brown bears during the height of the last ice age.”
This hybridization of the two types of bears reflects the complexities also seen in the evolutionary history of humans.
Scientists once thought that modern humans and Neanderthals simply separated into separate species after evolving from a common ancestor.
Next, researchers found Neanderthal DNA in modern Eurasians, implying that at some point modern human populations received an influx of Neanderthal genes.
They also found evidence of modern human DNA in the Neanderthal genome, demonstrating that interbreeding can affect the genomes of both species.
Dr Lindqvist continues: “The formation and maintenance of species can be a messy process,
“What happened with polar bears and brown bears is a good analog to what we learn about human evolution: that the division of species can be incomplete.
“As more and more ancient genomes have been recovered from ancient human populations, including Neanderthals and Denisovans, we find that there was ongoing multidirectional genetic mixing as different groups of archaic humans mated with ancestors of modern humans.
“Polar bears and brown bears are another system where you see this happening.”
Genomes analyzed in a new bear study include that of this bear, pictured here in 1995 on Alaska’s North Slope. Scientists wondered if this bear could be a brown bear-polar bear hybrid, but the new research reveals that “This bear is not a hybrid, just a tan bear,” says Charlotte Lindqvist, a biologist at the University at Buffalo.
The researchers analyzed the genomes of 64 modern polar and brown bears, including several new genomes from Alaska, a state where both species are found, to get their results.
Researchers from the University of Buffalo in the United States, the National Genomics Laboratory for Biodiversity in Mexico and the University of Oulu in Finland analyzed the genomes of 64 modern polar and brown bears, including several new genomes from Alaska, a state where both species are found.
They also produced a newmore complete genome of a polar bear that lived 115,000 to 130,000 years ago in the Norwegian archipelago of Svalbard.
Ancient polar bear DNA was extracted from a tooth attached to a subfossil jawbone – the skeletal remains of a bear that isn’t ancient enough to be considered a true fossil.
Using this dataset, the researchers estimate that polar bears and brown bears began becoming separate species between 1.3 and 1.6 million years ago.
Interbreeding of polar and brown bears, as well as limited fossil evidence of polar bears, have previously made this age difficult to identify.
Scientists have also concluded that polar bears suffered a dramatic population decline after becoming their own species.
This in turn reduced variation in the gene pool and left polar bears with far less genetic diversity than brown bears.
Polar bears were eventually found to carry more evidence of brown bear DNA than the reverse, despite the two species hybridizing.
Previous research has suggested the opposite may be the case.
Kalle Leppälä, postdoctoral researcher from the University of Oulu, said: “It is exciting to see how DNA can help reveal the history of ancient life.
“The direction of gene flow is more difficult to determine than its mere presence, but these patterns are key to understanding how past adaptations transferred between species to give modern animals their current characteristics.”
Dr Luis Herrera-Estrella of the Texas Tech Department of Plant and Soil Science added: “Population genomics is an increasingly powerful toolkit for studying plant and animal evolution and the effects of activity. human and climate change on endangered species,
“Bears provide no more simple speciation stories than human evolution. This new genomic research suggests that groups of mammalian species may hide complicated evolutionary histories.
The findings were published today in the Proceedings of the National Academy of Sciences.
Humans and Neanderthals were frequent lovers: DNA tests show the two species interbred ‘several times’ over 35,000 years
According to a 2018 study, early humans had sex with Neanderthals and other early cousins far more often than expected.
DNA tests on ancient remains show the two species interbred at ‘several points in time’ over the 35,000 years they shared the plains of Eurasia
The researchers said interbreeding began soon after humans came into contact with Neanderthals after they began moving out of Africa around 75,000 years ago.
Previous studies have shown that around 2% of our DNA is made up of Neanderthal genes, passed down through mating with our ancestors.
Data from the 1,000 Genomes Project – which mapped the DNA of 1,000 people around the world – suggests a more promiscuous relationship
It was a complex web of sexual encounters in which individuals had sex with members of their own group – and different hominids
Recent studies have revealed that the Denisovans, another extinct relative, also had sex with Neanderthals and humans on numerous occasions.
Using AI (artificial intelligence), researchers have found that the different DNA patterns in modern humans are explained by numerous periods of interbreeding between Neanderthal, East Asian and Asian populations. ‘Europe.
Evidence comes from samples such as an ancient human skull belonging to an individual dubbed Oase 1 which was unearthed in Romania in 2002
The Denisovans (artist’s impression), another extinct relative, had sex with Neanderthals and humans on numerous occasions
#Polar #bears #brown #bears #continued #mate #long #species #split
