The worm that outsmarted climate change

Biologist Katharine Clayton examines a specimen of 'Procerodes littoralis' found in Wembury Bay, UK University of Plymouth

This is the story of a marine worm, two scientists separated by a century, and a theory of life so new that it still has little evidence in its favor.

The theory states that, faced with a pressure that threatens their existence, there are species that find a way to survive.

The two women conducted the same experiment but separated by 106 years.

And the animal with which they experimented is a planarian that has adapted in this short period to the climatic stress caused by global warming.

The

is a gelatinous soft worm and as the name suggests, lives in the coastal coasts of western Europe and eastern US. In particular, abounds in tidal areas where there are water sweetest rivers with the salt of the sea.

Like other planarians it has such a regenerative capacity that it leaves the lizards and their tails in a game.

On the bias, in the carcass, lengthwise, widthwise or in small pieces, they are cut as they are, they end up recovering without showing scars.

In fact, this animal is the center of attention of scientists working in the field of cell regeneration.

The two scientists in this story studied the ability of

regenerate

in waters with different salinity.

The first to do so was Dorothy Jordan Lloyd, a marine biologist who pioneered research on the interaction between proteins and water.

In the summer of 1912 and the spring of 1913, Lloyd captured several dozen of these worms.

In the laboratory that the Marine Biological Association had in Plymouth (United Kingdom) she experimented with them.

That is, she cut them in half, put them in boats with different waters and observed if they recovered, how and when they did it.

Due to their habitat being tidal zones, these planarians have a broad tolerance to changing water conditions, with hyposaline low tide and hypersaline high tide.

Among Lloyd's goals was not determining the role of climate change in the regeneration of the worms.

Then there was no global warming.

The connection between the ability of these worms to heal, the salinity of the water, and climate change has now been made by Katharine Clayton, marine biologist at the University of Plymouth.

In the summers of 2016 and 2017, Clayton captured dozens of other

from the rocks at the mouth of the same stream that Lloyd did 100 years earlier.

He also dissected them from side to side with a scalpel and left them in jars with different concentrations of salt (from hyposaline of 3 grams per kilo of water, which is used to water the tomatoes, to hypersaline with 53 grams, which exceeds the concentration of the sea. Dead).

Their results, published in the scientific journal

, show how these marine planarians have increased their tolerance to saline extremes, particularly low-salt waters.

They also saw that, unlike what happened in 1914, there is not one optimal level, but several, in which the worms retain their ability to regenerate, which suggests that they have increased the range of salt tolerance without losing this ability in little more than a century.

"For 15 to 20 years there has been a theory called evolutionary rescue in which, in the face of accelerated climate change, animals evolve to survive," comments the professor of marine zoology at the University of Plymouth and supervisor of the research of Clayton, John Spicer.

“Many, including myself, doubt the possibility of such a rescue, especially in such a short space of time in terms of the evolution of the species.

But this study shows that it may be very possible in nature because, by comparing two identical experiments 100 years apart, the animal has changed its response [to the environment], its physiology, "he adds.

The evolutionary rescue theory was postulated in 1995. But aside from laboratory experiments, it has only been consistently tested in highly humanized settings.

One is medicine, with bacteria and viruses.

The best known example is the development of resistance to antibiotics.

In agriculture, the use of pesticides and fungicides has had the same effect, causing the most resistant or immune individuals to survive.

But in nature there are few cases of evolutionary rescue and also human-induced.

The best known are perhaps rats in the UK and rabbits in Australia.

The former almost disappeared from the British Isles after the widespread use of warfarin, an anticoagulant.

After years without seeing them, they reappeared everywhere: the rodenticide had favored those with genetic variants that made them overcome the action of warfarin.

Rabbits, a pest on the Australian mainland, were on the verge of extinction after the deliberate introduction of a virus, which killed 99% of them.

But, as with rodents, what they caused was a forced selection of the immune ones.

Another stressor is climate change, which threatens countless species.

Some estimate that between 400 and 500 species will be lost before the end of the century.

The most observed responses are specific adaptations, such as the ascent of plants to higher altitudes or the migration of many fish to latitudes more in line with their thermal range.

But there are hardly any proven examples that climate change is triggering evolutionary rescue episodes.

Hence the importance of these marine worms.

"The study offers evidence that they can be regenerated in less saline waters than those recorded 100 years ago," says Clayton, the study's lead author, in an email.

"This is important because they live in streams that end in the sea and if the area receives more freshwater contributions in the form of rain, the planarians are experiencing lower salinity, proof that they have adapted to increased rainfall," he adds .

And that's what has changed between the 1914 work and the current one.

After analyzing data from the nearest weather station collected since 1931, Clayton found that rainfall has continued to increase, while the number of days without rain has been reduced.

The biologist from McGill University (Canada) Graham Bell, author of several works on evolutionary rescue, recalls that "climate change will generate new sources of stress, such as ocean acidification."

For Bell, unrelated to the study of planarians, "whether or not populations are able to adapt quickly enough to enter an evolutionary rescue depends on abundance and the method of reproduction."

And he details it: “In general, large populations with sexual reproduction will be able to adapt more quickly.

Very large populations (like microbes) will adapt fairly quickly.

Very small populations, like those of many vertebrates, will be most at risk. "

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