Data from: Citizen science reveals unexpected continental-scale evolutionary change in a model organism

Organisms provide some of the most sensitive indicators of climate change
and evolutionary responses are becoming apparent in species with short
generation times. Large datasets on genetic polymorphism that can provide
an historical benchmark against which to test for recent evolutionary
responses are very rare, but an exception is found in the brown-lipped
banded snail (Cepaea nemoralis). This species is sensitive to its thermal
environment and exhibits several polymorphisms of shell colour and banding
pattern affecting shell albedo in the majority of populations within its
native range in Europe. We tested for evolutionary changes in shell albedo
that might have been driven by the warming of the climate in Europe over
the last half century by compiling an historical dataset for 6,515 native
populations of C. nemoralis and comparing this with new data on nearly
3,000 populations. The new data were sampled mainly in 2009 through the
Evolution MegaLab, a citizen science project that engaged thousands of
volunteers in 15 countries throughout Europe in the biggest such exercise
ever undertaken. A known geographic cline in the frequency of the colour
phenotype with the highest albedo (yellow) was shown to have persisted and
a difference in colour frequency between woodland and more open habitats
was confirmed, but there was no general increase in the frequency of
yellow shells. This may have been because snails adapted to a warming
climate through behavioural thermoregulation. By contrast, we detected an
unexpected decrease in the frequency of Unbanded shells and an increase in
the Mid-banded morph. Neither of these evolutionary changes appears to be
a direct response to climate change, indicating that the influence of
other selective agents, possibly related to changing predation pressure
and habitat change with effects on micro-climate.