Evolution at Rocket Speed: "Hopeful"

From big and scared to small and brave – evolution has moved at lightning speed on a small island in the Koster Sea on the West coast of Sweden.

The beach snail’s rapid adaptation after a forced change of environment amazes researchers. In 30 years, it has changed both its appearance and behavior to survive.

Kerstin Johannesson, professor of marine ecology at the University of Gothenburg, thinks this gives hope.

– It gives us some hope in the times we live in now. We are changing the environment at an alarming rate, she says, referring to climate change and environmental pollution.

Many species are affected when the surrounding environment changes. For some species, the solution may be to move.

But this is not always possible. The fact that they could adapt gives us hope.

Killed in an algal bloom

When an unusually severe algal bloom hit the West Coast in 1988, wiping out the population of shore snails living in the surf on a small islet, she took the opportunity to start an experiment.

She replaced the extinct shells with a different variety of gastropod mollusc, which was moved to the cob. The move was only a few hundred metres within the same archipelago, but it was a jarring change of scenery, which she thought would be difficult for the new snails to survive.

They were designed to cope with an existence surrounded by hungry crabs: they were equipped with a large and strong shell and at the same time were extremely cautious, always ready to be attacked by a crab.

Instead, they found themselves in an environment where the challenge was to withstand strong ocean waves. Their predecessors, who died in the algal bloom, had been adapted to this life – they were small, had thin shells and had to act boldly to constantly find places to suck in the surf.

Long-term adaptation

The fully grown, relocated snails died after the move. But by then, the female snails had given birth to half-millimetre-sized offspring. Some of these mini snails survived and were able to reproduce, thanks to dormant genes on standby.

– The initial sorting killed many of the small ones, but a few survived and gradually they became more and more numerous, says Kerstin Johannesson.

After about 30 generations, the adaptation to the new environment has gone so far that the crab shells now resemble their predecessors on the cob in every detail.

– A precondition for such an adaptation is that there is genetic variation, says Kerstin Johannesson. ‘Some of the large crab shells carry the genes needed to become a small wave shell.

– When you move them, these genes will be very, very useful. Their offspring will have an advantage and survive.

Changing world

This shows the importance of genetic variation for a species to survive in a changing world, she emphasises.

This is why, for example, the Swedish wolf population becomes vulnerable if the wolves are few and all wolves are related to each other. This reduces the likelihood that they will carry the breadth of different traits needed in a situation where the environment is changing.

– You can think of the cod in the Baltic Sea or any other species that would normally naturally be very many individuals, but where we have pushed them back and they are not so many anymore, then you reduce their chances of surviving environmental changes, says Kerstin Johannesson.

Darwin’s ideas

The snail study, published in the scientific journal Science Advances, is one of the first of its kind.

In the US, similar rapid adaptations to a new environment have been highlighted in studies on fish. In one case, a volcanic eruption reshaped the environment. Fish from the sea came in and adapted to life in a newly formed lake. In the other, researchers followed how a species of fish adapted when the river water they lived in became heavily polluted.

– The fact that this happens at all is not surprising, because these are Darwin’s ideas from start to finish: natural selection changing organisms. That it can happen so quickly is what is surprising, says Kerstin Johannesson.