In a unique 30-year-long experiment, scientists have watched the rough periwinkle (Littorina saxatilis) evolve in real time on Sweden’s Koster Islands. Following a toxic algae bloom in 1988 that decimated snail populations on one of the skerries (small rocky islets), marine ecologist Kerstin Johannesson from the University of Gothenburg reintroduced 700 snails of a different ecotype to study the process of evolution in action.
Johannesson chose snails adapted to crab-rich habitats, known as the Crab ecotype, rather than the original Wave ecotype, which had been suited to the wave-exposed environment of the skerry. This new population was observed over several dozen generations, gradually adapting traits similar to the former inhabitants despite starting with a distinct set of features.
In the Koster Islands, L. saxatilis snails exhibit different ecotypes based on the pressures they face. The Crab ecotype has thicker, larger shells to defend against predators, while the Wave ecotype, which lives on open rocks, has thinner, patterned shells to withstand waves. Over time, the transplanted Crab snails evolved smaller, smoother, and patterned shells, much like their Wave predecessors, a transformation visible in samples collected over the years.
The experiment also revealed genetic changes, including increased frequency of certain gene variants and chromosomal inversions that mirrored those of the Wave ecotype. Some genetic adaptation stemmed from latent traits in the Crab ecotype genome, while nearby Wave snails likely contributed genes to the evolving population.
Co-author Anya Westram highlights the broader implications: “This experiment shows that while some species can adapt to change if they have access to diverse gene pools, many others might struggle with rapid environmental shifts.”
The research, published in Science Advances, emphasizes the importance of preserving diverse natural habitats to maintain genetic variety and resilience in species facing climate change and other environmental pressures.
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