What’s the News: British scientists searching for signs of climate change in banded snail shells have completed one of the largest evolutionary studies ever, a massive survey across 15 European countries. Their research associates? More than 6,000 snail-hunting volunteers.
How the Heck:
Banded snails are sensitive to the sun, and lighter-colored shells reflect more sunlight than darker shells, helping them keep cool. The scientists in charge of the study, run by Open University, hypothesized that the 1.3° C climb in temperature since the 1950s would have given lighter snails an evolutionary advantage. Armed with shell color data from the '50s through the '90s, they set out to see if the number of light snails had grown.
To get samples from the present day, they enlisted the help of volunteers through the Evolution Megalab project, launched in honor of Darwin’s 200th birthday in April 2009. Volunteers registered on the site, learned to identify the different colors of snail shell, and set out scrounging around hedges and weeds over the course of six months. They submitted data sheets online, marking where they had found the snails on Google Maps so scientists could tell what habitat they were in—grassland, hedgerow, woodland, or sand dunes.
Looking at the frequency of shell colors over time, the scientists found that light shells had not grown more prevalent. But when they looked at a subset of old samples and new samples that had been collected very near each other, in hopes of seeing changes in specific populations of snails over time, they found that light shells had increased in the sunniest habitat, sand dunes. Snails could move into shade to escape increasing heat in wooded habitats, the scientists suggest, while in the dunes cover might be scarcer and light color more advantageous.
Unexpectedly, the study discovered that banded snails had actually been growing more banded, with more stripes on their shells. This had nothing to do with changing climate—after all, the dark bands would make the snails more susceptible to sun, not less—but the team thinks that it could be related to changes in the bird populations that prey on the snails. The bands serve as camouflage in wooded areas and would be dangerous in open spaces like the dunes. But if the numbers of song thrushes, a primary snail predator, are decreasing, snails could wear their bands anywhere without suffering evolutionary damage.
The Future Holds: More volunteer studies, this time perhaps focusing on bird-watching rather than snail hunting. Are there fewer song thrushes than there used to be? Do the changes in their populations reflect the changes in snail shell patterns? Only more studies will tell. Reference: Silvertown J, Cook L, Cameron R, Dodd M, McConway K, et al. (2011) Citizen Science Reveals Unexpected Continental-Scale Evolutionary Change in a Model Organism. PLoS ONE 6(4): e18927. doi:10.1371/journal.pone.0018927