Uncover the secret of the species of bears

It is clear to anyone that an African elephant Garden snails are of different species, but the lines are blurry around the closely related animals. In fact, many biologists point out that there is no clear definition of what a “species” really is.

It turns out that speciation is a much more complex and chaotic process than previously thought.

recent study, published In the Proceedings of the National Academy of Sciences (PNAS), in separating polar bears and brown bears into different species, and found that the process of speciation is not quite as straightforward as we think.

Scientists have known for some time that the demarcation of polar and brown bears did not prevent them from mating with each other. The findings presented in the paper include an extensive data set – including genetic sequences of ancient polar bear teeth – to gain insight into the split between species.

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Fossil jawbone of a polar bear that lived 115,000 to 130,000 years ago in the Norwegian archipelago of Svalbard. Credit: Credit: Carsten Sunde/Natural History Museum/University of Oslo

The research has implications beyond bears. The findings are similar to discoveries relating to the evolution of our species, and to speciation on a larger scale.

“What species? That is the question,” laughs Peter Kauman, Senior Curator of Biosystems at the Museum of Queensland Network and Senior Research Associate in the Center of Excellence for Coral Reef Studies at James Cook University. “Sex is a concept, and it’s important to understand that it’s a human construct. We need species to understand the world we live in and the biodiversity of our planet, but nature and evolution don’t necessarily care about what we think a species is. As scientists we have different notions of what species are.”

“Many people use the concept of a biological species – the ability of two individuals to successfully produce fertile, viable offspring – but this is not always the case. The polar bear and the brown bear, although uncommon, participate in interbreeding across the two species.

“Many people use the concept of biological species – the ability of two individuals to successfully produce fertile, viable offspring – but this is not always the case.”

Peter Cayman, Queensland Museum Network

“Because I am a geneticist, or a bioinformatician, I tend towards what we call the concept of ‘evolutionary species.’ This is all about using family trees or molecular phylogenetic trees to understand how individuals are related to each other within a group or across species. But that doesn’t always give the right answer either.”

Cayman said Cosmos That PNAS paper highlights how new analytical tools are changing the way we study evolution and genetics. In turn, this provides opportunities for us to better understand the basics of a species and where organisms fit into an ecosystem.

“We’re really entering the sci-fi end of things,” Kauman says. “We have a desktop sequencer that can sequence the genome in 48 hours or less. It’s the same size as an iPhone. The data we’re producing now is what future technology will depend on. All you have to do is look at the response to the COVID pandemic – we can get the genetic data and analyze it.” Very quickly.. Overnight you get new trees for the different COVID strains and understand how new strains emerge.

“It’s the same thing in biodiversity analysis. All of these things add up to how we can analyze this data very quickly and understand how different species interact, especially how they will change under a climate change scenario.”

Museums are a goldmine for these types of analysis, especially with this changing technology. Like analyzing DNA from fossils, we are able to analyze DNA from samples collected 80 to 100 years ago. We are able to obtain DNA that can solve different mysteries.”

“We are able to analyze DNA from samples collected 80 to 100 years ago. We are able to obtain DNA that can solve different mysteries.”

Peter Cayman, Queensland Museum Network

An example of the power of new analysis techniques, particularly those involving ancient DNA, appears in our evolving understanding of our own evolution.

Scientists once believed that a common ancestor simply divided into modern humans and Neanderthals. But researchers have found Neanderthal DNA in modern Eurasian peoples. This means that modern human groups received a gene flow from Neanderthals at some point in their common evolutionary history.

It was only later that scientists realized that this genetic overlap also complemented Neanderthal groups with modern human genes, the researchers explained in the PNAS paper, which included scientists from the United States, Finland, Norway, Denmark, Singapore and Mexico. In other words, crossbreeding is complex and not necessarily a single method.

“Species formation and conservation can be a chaotic process,” says study co-author Charlotte Lindqvist, associate professor of biological sciences at the University at Buffalo and expert in bear genetics.

“We found evidence of interbreeding between polar bears and brown bears that predated the ancient polar bear we studied,”

Charlotte Lindqvist, University at Buffalo

“What happened with polar bears and brown bears is a subtle analogue of what we are learning about human evolution: that species division can be incomplete,” she says. “As more and more ancient genomes are recovered from ancient human groups, including Neanderthals and Denisovans, we see that multi-directional genetic admixture is occurring as different groups of ancient humans interbred with the ancestors of modern humans. Polar bears and brown bears are another order where you see this happens “.

“We found evidence of interbreeding between polar bears and brown bears that predates the ancient polar bear we studied,” Lindqvist adds. Furthermore, our results show a complex and interwoven evolutionary history between brown and polar bears, with the main orientation of gene flow into polar bears from brown bears. This reflects the hypothesis proposed by other researchers that gene flow was unidirectional and going into brown bears around the height of the last Ice Age. “

64 recent genomes of polar and brown bears have been studied by researchers.

“It’s exciting how DNA can help reveal the history of ancient life,” said co-first author Kali Lipala, a mathematics researcher from Finland’s University of Oulu. “The direction of gene flow is more difficult to determine than just its presence, but these patterns are essential to understanding how past adaptations passed between species to give modern animals their current traits.”

The genomes included many new genes from Alaska, where both species were found. A new and more complete ancient polar bear genome has been analyzed. DNA was extracted from a tooth attached to a jawbone (not completely fossilized) found in the Norwegian archipelago of Svalbard. The bear lived 115,000 to 130,000 years ago.

Cauman was particularly impressed by the inclusion of the fossil’s subgenome in the study, which he says is “extremely rare.”

“We usually analyze contemporary genetic samples from living species, living lineages, while here we were able to include the fossil lineage. It really highlights the extent to which speciation persists.”

“It’s not just a switch where, over a certain period of time, two groups become separate species overnight. It really shows that they can interact and when they come back into contact, there is potential to share genetic material.”

“The direction of gene flow is more difficult to determine than just its presence, but these patterns are essential to understanding how past adaptations passed between species to give modern animals their current traits.”

Kali Lipala, University of Oulu

“I’m so jealous! I have a background in studying fish and corals, and it would be nearly impossible to get similar data from fossil fish! This comes with the advances we’re seeing in these genetic methods.”

“Being able to get viable DNA from a fossil 10 years ago was almost unheard of. It’s not just these fossils that can be analyzed – think of all the museum specimens preserved in formalin or new preservation techniques. Getting DNA Ancestors have a new and revolutionizing field in how these speciation patterns are studied.”

Using the expanded data set, the team estimated that polar bears and brown bears began splitting into distinct species between 1.3 and 1.6 million years ago. Lindqvist says that interbreeding and limited fossil evidence made it difficult to pinpoint this timing.

Polar bears, soon after becoming a separate species, experienced a significant decline in their numbers, perpetuating a genetic bottleneck. The new research indicates that this resulted in much lower genetic diversity than is found in brown bears.

Researchers have found a remarkably similar story among bear species such as that found between modern humans and Neanderthals. Their analysis found evidence of hybridization in the genomes of both polar bears and brown bears. The flow of genetic information from other species is particularly strong in polar bears. Previous research suggested that this was the opposite.

The team believes its findings may be of interest in studies of the impact of climate change on threatened species.

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In April 2021 Live Science Grolar Bear, a mixture of Grizzly Bear and brown bear, has been reported. Credit: Arterra/Universal Images/Getty

Polar bears, which have adapted to the icy north of the Arctic, have been found to capture genetic material from brown bears, which are adapted to life in lower and warmer latitudes. As global warming sees a decrease in Arctic sea ice, the two bears may overlap more frequently as their ranges overlap. This makes it interesting to study their shared evolutionary history, Lindqvist says.

“Population genomics is an increasingly powerful toolkit for studying plant and animal evolution and the effects of human activity and climate change on endangered species,” says team leader Luis Herrera Estrella, of the National Biodiversity Genomics Laboratory and Texas Tech University in Mexico. we. “Bears provide no more simple stories about speciation than do human evolution. This new genetic research suggests that groups of mammalian species can hide complex evolutionary histories.”

“The implication of the results is that the ancestral polar bear lineage may be able to get some new gene from this expanding northern brown bear and possibly help it adapt to a changing climate,” Kauman says. The implication is that if he does it once, he can do it again.


Read also: We may be looking at the wrong climate change data… and it might be worse than we thought

“This has implications for a lot of other species. But I think it’s important to understand that we use the past to try to predict the future a lot here. But it does show that there is this interaction between species and it can have all these different outcomes that we might not expect.”

Cowman believes that the techniques presented in the PNAS paper reflect an evolution in our ability to delve into these problems of speciation, although he suggests that speciation remains an unsolved mystery. “I guarantee you that one day, scientists unite under the concept of a common or universal species, nature and evolution will say ‘hold my beer’ and show us something completely different,” he says. “I think for me, that is the beauty of it all. It is so much fun, and it can be frustrating at times, the study of evolution and speciation.”