Research on large-scale mutations provides new knowledge about evolution

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The periwinkle snail, Littorina saxatilis, is found in different ecotypes with characteristics tailored to its own habitat. On the Swedish west coast there are "crab snails" and "wave snails". The crab snails live on rocky shores and have developed a shell and a behaviour that protects them from hungry shore crabs. Wave snails, which are found on wave-exposed rocky shores, are smaller, have a large foot, and can crawl into crevices and hold on when waves crash in.

Recently, research has discovered a number of inversions in the genome of the periwinkle snail that seem to be crucial for the evolution of the ecotypes. An inversion is a large-scale chromosomal change that forms when a piece of a chromosome breaks off and changes direction. In his thesis, James Reeve has taken a closer look at the inversions of periwinkle snails. By investigating how common they are in snails in different habitats, he was able to draw conclusions about the snails' adaptation to the local environment and the development of ecotypes.

Inversions contribute to local adaptation

"I have found links between inversions and environmental conditions, such as wave exposure or the steepness of shore slopes. This suggests that the inversions play a key role in the snails' ability to adapt to different environments and develop ecotypes", says James says.

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James Reeve also found that in varied environments, ecotypes can develop very locally. In a ten-metre-wide gully, he found snails with characteristics typical of crab snails, despite living very close and potentially mating with wave snails.

"This shows the importance of viewing local adaptation and evolution on a scale relevant to the organism. Afterall, these snails only move around in a 2-3 meters area over their lifetime."

Knowledge on how biodiversity is formed

Research on how species evolve and adapt to their environment through evolution gives us knowledge about the biodiversity we see today, says James Reeve. It is about understanding how biodiversity is formed and maintained.

"At an applied level, we can use this information to make predictions about how species will evolve in the future. This is important in the context of climate change as it can be used for designing smarter long term conservation strategies".

Analysed thousands of snails 

The thesis includes extensive fieldwork in which James Reeve collected thousands of snails along shores in northern Bohuslän but also in the UK and Spain. For each snail, he has noted various environmental factors such as wave exposure, how high-on-shore the snail lived and how steep the shore was. The snails have been DNA sequenced to identify the inversions, and then analysed to find statistical correlations with environmental factors.

"It was very challenging to try to keep track of everything. I had to make many decisions about how to split the data and which variables to include. But we can learn a lot about evolution and speciation by analysing this type of data".

Text: Susanne Liljenström