Genetic toolkit gives periwinkles seashore advantage


10 August 2018 by Amy Huxtable

Periwinkles, struggling to survive the seashore battleground, have developed a genetic toolkit to help them adapt to different environments, a new study shows.

This toolkit has enabled the snail to develop different characteristics according to whether it lives mainly on parts of the seashore where crabs are a constant threat, or in rocky places where it is disturbed by waves.

A team of researchers in Sheffield and Sweden, funded by NERC and the Swedish Research Council, investigated hundreds of rough periwinkles collected from seashores on the west coast of Sweden. They noted each shell's form and its exact position on the shore and then analysed their genomes to try to find out how these adaptations occurred to give the snails the best chance of survival.

The results showed the snails' characteristics changed significantly at the point on the shore where the crabs disappear and the wave action gets stronger.

Anja Westram, postdoctoral researcher at the University of Sheffield, who led the analysis, explained:

Either side of the habitat transition, the snails look like different species. Snails on the boulder shore have thicker shells which are a better defence against crabs. The smaller cliff shells have a wide opening so the snail's foot can attach more securely to rocks to defend against waves. And across 10-20 meters of shore in between these areas we found all kinds of intermediate forms.

But when the team analysed the periwinkles' genetic data to try to discover how these changes occurred, they uncovered some surprising results.

They identified around 1,000 genes that differed between snails in the 'crab' and 'wave' environments but, instead of being spread throughout the genome, most of them were clustered in specific regions across just three chromosomes. The researchers concluded that the chromosomes were holding together sets of genes to help the snails adapt to different environments.

Professor Roger Butlin of the University of Sheffield's Department of Animal and Plant Sciences, who led the study, said:

This study gives us a fascinating insight into how animals and plants might cope when faced with contrasting environments. Rather than many genes having to respond separately to natural selection, this creates a ready-made 'toolkit' on these three chromosomes that has allowed the snail to adapt more rapidly.

The seashore in Sweden could only have been colonised by the periwinkles some time after the end of the last ice age, around 5,000 to 6,000 years ago. As periwinkles reproduce annually, that means these adaptations must have occurred within 5,000 to 6,000 generations - a rapid change in evolutionary terms.

The team is now looking at other shores around Europe to investigate how widely the same adaptive toolkit is used by the periwinkles. They are also looking at other species of periwinkle to find out more about how the sets of genes were put together.

Professor Butlin said:

Our aim is to better understand the origin of the species, but also to understand how quickly animals and plants are able to cope with environmental challenges.

To read the full paper visit Evolution Letters - external link.

The teams are based at the University of Sheffield and the University of Gothenburg in Sweden.