The periwinkle snail showed evolution in real time
Can a species survive if thrown into a completely new habitat? Yes, if the species has dormant genes ready to deal with the new conditions. In a new study by researchers from the University of Gothenburg, a periwinkle snail shows rapid evolution taking place in just 30 years.
Climate and other environmental changes are altering the habitats of many species, and one question biologists are asking today is whether species in nature are able to adapt to the new living conditions at the same rate as the conditions change. Slow evolution as Darwin envisaged it is hardly enough.
In 1988, there was a major algal bloom on the Swedish west coast. On one small skerry, the entire population of the species periwinkle snail was wiped out. This was a population of ‘wave snails’ adapted to life in the surf; they were small, had thin shells and acted boldly to constantly find places to attach themselves. That's when researcher Kerstin Johannesson saw her chance to perform an evolutionary experiment.
Shy snails
“On a neighbouring island, there was another population of the periwinkle snail that had a given enemy in the form of crabs. On crab-rich beaches, the snail has a large and strong shell, and they are very shy because the slightest shadow that moves could be a crab and then it is best to be enclosed in the shell. I moved over 700 ‘crab snails’ to the deserted skerry in 1992,” says Kerstin Johannesson.
Her expectation was that the change of environment to the skerry would quickly wipe out the ‘crab snails’ as they were adapted to a completely different environment. And indeed, within a few weeks, all the adults disappeared, but at the same time they had also released thousands of half-millimetre sized fry, some of which managed to survive. Over the years, the snails changed in size, shape and colour. What were originally large and robust ‘crab snails’ hells began to look more and more like small and fragile ‘wave shells’ as new generations of snails were born.
Tracing genetic changes
Now, an international team of researchers has mapped the changes in characteristics and used DNA sequencing to trace the genetic changes that have occurred over the 30 or so generations since the snails were placed on the skerry.
“It is astonishing. Virtually all characteristics have changed so that the periwinkle snails today resemble ‘wave snails’ in every detail. From the DNA analyses, we can see that large so-called supergenes that code for the various characteristics have been replaced from the crab variant to the wave variant,” says Kerstin Johannesson.
However, DNA not involved in adaptation to different environments shows that the new snails of the small island are not ‘true’ wave snails’ but have a different origin. The researchers conclude that it is mainly natural selection and not chance that governs adaptation when the environment changes. Another lesson is that if there is a lot of genetic variation within a species, there is potential for this type of rapid adaptation.
Predicting what will happen
“Since we already knew that the supergenes had an important function in coding for the various traits that waves and crab snails have, we can predict the changes that occurred,” says Kerstin Johannesson.
Scientific article in Science Advances: Predicting rapid adaptation in time from adaptation in space: A 30-year field experiment in marine snails
Contact: Kerstin Johannesson, Professor of Marine Ecology at the Department of Marine Sciences, University of Gothenburg, phone: +46 766 22 96 11, e-mail: kerstin.johannesson@gu.se