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The banded brown-lipped snail (Cepaea nemoralis) and the white-lipped snail (Cepaea hortensis) can be found in a wide range of different habitats all across Europe and display a huge variety of individual shells. Photo: André Künzelmann, UFZ
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Citizen Science Project Demonstrates Rapid Evolution in Banded Snails
Changes can force animals to speedy evolutionary adjustments. This is the conclusion an international team of researchers has drawn from evaluating historical and current data regarding shell colours and patterns of more than half a million specimens of grove or brown-lipped banded snails (Cepaea nemoralis), one of the most common species of land snail in Europe. The current data were collected through the citizen science project "Evolution MegaLab", in which thousands of volunteers in 15 European countries participated and thus rendered this the hitherto biggest data collection of this kind.
The Banded Snail: Ideal because of the existence of historical data from the beginning of the twentieth century onwards.
Animals and plants are amongst the most sensitive indicators of global change. Particularly species with a high reproduction rate are in principle able to genetically adapt to changed conditions of life within a short period of time. However, there are hardly any historical genetic data available from a larger area of distribution which could demonstrate such rapid evolution. A rare exception to this rule is the brown-lipped banded snail (Cepaea nemoralis), the shell of which displays an exceptional diversity of colours and patterns and which has been intensively researched already since the beginning of the twentieth century.
The banded snail is a master of adaptation: It can be found in the most diverse habitats ranging from coastal dunes to alpine forests and it is well known that the diversity in this snail's shells is connected to adapting to different habitats and predators. The high incidence of this distinctive species in gardens and cities made it the ideal object of study for a large-scale field study on evolution. On 12 February 2009, the 200th anniversary of the birth of Charles Darwin, the Museum für Naturkunde - Leibniz Research Institute for Evolution and Biodiversity at the Humboldt University Berlin, the Nature and Biodiversity Conservation Union NABU and the Helmholtz Centre for Environmental Research initiated the German version of the Europe-wide citizen science project. "Evolution MegaLab" was one of the winners of the Volkswagen Foundation's competition "Evolution heute" (Evolution today) and was awarded funding of around 97,000 Euro.
Volunteers collected data on some 3000 populations
Whereas biologists needed nearly a century to collect data on around 6000 populations of the species, volunteers helped to collect data on some 3000 populations within ten years, the majority of which was entered into the internet platform www.evolutionmegalab.org during the Darwin Year 2009. On the platform, information regarding the data collection and eventually also the results were displayed. At the same time, all volunteers were asked to participate in a quiz to ensure that they would not confuse the targeted species with similar kinds of snails. The hobby biologists' knowledge surprised even the professional scientists: Only one percent of data turned out to be faulty and was removed in order not to distort the final result. Professor Jonathan Silvertown from the Open University (OU) in Great Britain, who had the idea for this study, happily states that, "This is one of the largest evolutionary studies ever undertaken". "Through mass observation we wanted to give the general public, including families and school children, the opportunity to do real science and to experience the fun and excitement of discovery for themselves."
Rapid Evolution: Snails with a single dark spiral across their shell now are more common
According to data from the European Environment Agency EEA for the year 2010, the average temperature across mainland Europe rose by 1.3 degree Celsius over the course of the twentieth century. "We expected that this rise in temperature would result in an increase of lighter coloured shells and a decline in dark shell colours", explains Dr Christian Anton, UFZ-based coordinator of the project for Germany. The researchers were able to verify an increase in light coloured yellow shells that least warm up when exposed to the sun - however, only in snails inhabiting dunes. Apparently, snails in other habitats simply crawl to find shadow when they get too hot. "Yet we were surprised to find that the proportion of snails with only one dark band on their shell increased well across Europe. This is rapid evolution, indeed."
Driving Factors: Predators or Climate Change?
The scientists assume that this adaptation is connected either to small-scale changes in the environment or is due to the natural enemy of this species of snails, the song thrush. "Considering how many people are interested in observing birds, a citizen science project on the development of bird populations could shed light on this question", says Anton.
On average, half a century separates the historical and the current data collection activities. This corresponds to approximately 15 to 20 generations of these small snails with such diverse shells. Owing to the commitment of thousands of volunteers, researchers could confirm that this diversity is a result of adaptation to different environmental conditions. It also demonstrated how fast evolution can take place, when the environment changes.
