Collaboration: Extreme earthworms, living at the volcano’s edge

Spitting geysers, boiling hot springs and toxic gasses – the volcanic complex of Furnas, on the island of Sao Miguel in the Azores, is an inhospitable place to live.



That is, except for the earthworm Pontoscolex corethrurus which has biologist Luís Cunha from the University of Cardiff questioning how it can thrive on the volcano’s edge.

Cunha couldn’t believe what he was seeing when he first discovered large populations of earthworms at the volcano: “Curiosity grabbed me and I wanted to know more, especially about where these worms came from and how they developed and adapted.” So he decided to study their genetic make-up and diversity. As it turns out, this extremely tough worm can teach us a lot about of adapting to changing climate.

First described 150 years ago in Southern Brazil, the earthworms were likely shipped from plantations in Brazil in crates of pineapples to the Azores. Pineapple greenhouses and the volcanic complex of Furnas are also the only two places where the worm can be found on Sao Miguel today. Other parts of the mid-temperate island seem to be too chilly for the tropical worm.

It makes sense that the P. corethrurus would feel at home in the hot and humid greenhouses on the island that are similar to its original environment. But why and how did it adapt to the extreme living conditions near volcanic geysers and craters? Which evolutionary forces were at work, and how did they influence the populations’ genetic diversity?

To find answers to these questions Cunha and his colleagues compared the populations living in the greenhouses and in the volcanic area. They used genetic markers both from mitochondrial DNA, the DNA of the in-cell power plants, and nuclear DNA, the genetic material in the nucleus of the cell.

It was here that Cunha ran into a problem: he needed to find the best method to filter his DNA samples. They needed filtering because they contained yet another form of DNA – from symbiotic bacteria – that Cunha wanted to exclude. He needed to find out whether it was best to do this before or after assembling the genome. Peers on ResearchGate agreed that he better do it before which helped Cunha and his team to move on quickly.

They found that the worms in the extreme environment were all very similar genetically. A large portion even showed polyploidy, which means that they had more than two chromosomes per set. This, Cunha believes, could be due to asexual reproduction, basically self-cloning. The next step for the team was to completely analyze this special genome, and Cunha says it wouldn’t have been possible without help from his peers: “ResearchGate was the vehicle to get the answers I was looking for and it’s the reason why we now have a complex polyploidy genome assembled.”

Another surprising observation that Cunha made was that the extremophile worms also showed a high degree of nuclear variability – some base pairs in their DNA were switched around. Potentially, Cunha believes, certain genetic changes had been passed on to the next generation because they worked better than the old make-up in the new environment.

Luis
Luís Cunha in his lab

One of these changes was seen in the worms’ skin. The epidermis of worms living in the hot zone was 50 percent thinner than of those worms living in the greenhouses. The team found this was correlated to a higher level of CO2 in the volcanic soil. Adapting to a hotter, more hostile climate is something the earthworms seem to be good at, and something we might be able to learn from them.

“The volcanic environment can be an environmental model for climate change, due to the increased acidity of the soils together with the high levels of CO2 and higher temperature,” Cunha says. By tracking down the genes that respond to such environmental changes we could infer, Cunha believes, what might happen to other animals in a warmer climate. Quite literally, Cunha says: “The biology around volcanos rocks!”

Images courtesy of Luís Cunha