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Changing climate may have ‘speeded up’ evolution

The tumultuous Pleistocene climate led to numerous migration, local extinction, and replacement events. North American mammoths crossed the Bering Strait and replaced those native to Siberia, before arriving in Europe. Image: Shutterstock/ Catmando.
The tumultuous Pleistocene climate led to numerous migration, local extinction, and replacement events. North American mammoths crossed the Bering Strait and replaced those native to Siberia, before arriving in Europe. Image: Shutterstock/ Catmando.

Environmental changes may have led to the emergence of resilient hybrids, scientists in Germany believe, raising the possibility that periods of climate flux can speed up evolution.

However, climate change also leads to large-scale extinctions because the environment changes too fast for species to adapt. As the present climate is changing very rapidly, researchers do not expect to see the same evolutionary adaptation in the future as has happened in the past.

The EU-funded GENEFLOW project looked at fossils of animals living during the Pleistocene period, a period which spanned from 2.5 million years to 12 000 years ago and was marked by frequent shifts between glacial and inter-glacial periods.

Due to the changing climatic conditions, animals often migrated between north and south, allowing researchers to explore gene flow – the extent to which genes are transferred from one species or population to another as animals mix.

‘We look at ancient DNA in the bones of species such as cave bears, mammoths, extinct elephants, wolves, hyenas, lynx or gray whales,’ said Professor Michael Hofreiter from the University of Potsdam, Germany, who is the principal investigator for GENEFLOW. ‘The question is: how do species adapt when there are environmental changes and there is migration?’

Unusually, Prof. Hofreiter’s team is focusing on DNA in the cell nucleus, which is passed along both the female and male line. Normally, researchers look at so-called mitochondrial DNA, which is located in the body of the cell and is passed down the generations through mothers only. This is advantageous when looking at the flow of genes between migrating animals, because male animals tend to be more mobile.

It has enabled the team to determine the complete genomes – an organism’s full set of DNA – of extinct species, and to see how these genomes have changed over time in different locations, shedding light on how climate change impacts biodiversity.

'The present human-caused climate change will not lead to similar extensive mixing and adaptation of populations.'

Prof. Eeva Furman, Finnish Environment Institute

Between species 

The first major results from the five-year GENEFLOW project should be published within six months. However, Prof. Hofreiter revealed: ‘What we have found is that gene flow is much more than we would have believed … There is evidence of a lot of gene flow between populations that were separate. There’s also evidence of gene flow between species.’

Gene flow makes creatures more resilient to climate change. ‘You have populations that live more in the south or more in the north,’ Prof. Hofreiter said. The genomes of these populations will be differently adapted to the local environment.

‘So if and when the climate changes, if it gets warmer, it is beneficial if you have gene flow from the south, to maintain a population.

‘In effect, evolution is being speeded up.’

Prof. Hofreiter points to modern day examples where species have interbred with beneficial results to the hybrid. For example, many European house mice are now resistant to the poison warfarin thanks to breeding with their Algerian peers.

Warfarin acts by interfering with the blood clotting process – meaning wounds continue to bleed. However, when the species were brought together – by humans – the Algerian mouse passed on a version of the VKORC1 gene – blocking the poisonous effects.

Often, hybrids suffer from physical problems, limiting survival, but in this case, the benefits to mice outweighed the drawbacks.

Skin, hair and nails

Another example of gene flow is between Neanderthals and humans, with some humans thought to carry 2 % of their archaic relative's DNA. Neanderthal genes are believed to help in making keratin, a protein used in skin, hair and nails, as well as strengthening the immune system.

‘In the same way, polar bears must have survived several inter-glacial periods – there may have been gene flow with brown bears,’ Prof. Hofreiter said. ‘We have to remember that 130 000 years ago it was so warm that we had elephants and hippos in parts of North Yorkshire.’

It shows that, rather than having fixed characteristics, a species should be seen as something that changes with the conditions.

‘The take-home message is that we must look at species as dynamic entities,’ said Prof. Hofreiter. ‘Rather than species dropping dead when the climate changes, when it gets hot, they will evolve by hybridizing.’

Professor Eeva Furman from the Finnish Environmental Institute coordinates the EU-funded OpenNESS project, which is investigating how ecosystems and natural assets could be secured under pressures such as climate change.

She says that while large-scale movements of animals during Pleistocene may have increased gene flow among populations and been beneficial for adaptation, she does not expect to see the same thing happen in the future.

‘The present human-caused climate change will not lead to similar extensive mixing and adaptation of populations, partly because movements of most species are greatly hindered in human dominated landscapes, and partly because the present climate warming is extremely rapid in comparison with Pleistocene climate fluctuations,’ she said.

‘There is much research showing that the negative effects of climate change will dominate and add to the threat of populations, species and ecosystem services.’

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