Citizen Science Reveals Unexpected Continental-Scale Evolutionary Change in a Model Organism

Abstract

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.

Solar radiation stress in climbing snails: behavioural and intrinsic features define the Hsp70 level in natural populations of Xeropicta derbentina (Pulmonata)

“…Due to sunlight reflectance, it was postulated that brighter coloured shells generally heat up slower than darker shell patterns (YomTov 1971;Dittbrenner et al 2009). However, current results of our group show that there are no differences in the thermal capacity of the different morphs in T. pisana, another Mediterranean helicoid snail species living in the same habitat as X. derbentina (Scheil et al 2012). Since in X. derbentina the increase in shell pigmentation is strongly and negatively correlated with size, we assume that shell colouration pattern distribution could depend on the individual's age.…”

Hsp70 and lipid peroxide levels following heat stress in Xeropicta derbentina (Krynicki 1836) (Gastropoda, Pulmonata) with regard to different colour morphs

“…Asterisks show significant differences between the colour categories within an exposure group: 0.01< p≤0.05 (*), 0.001<p≤0.01 (**); p≤0.001 (***) derbentina populations change their composition of colour morphs during the years and how different local temperatures may influence the morph frequencies within a population of these snails. However, the phenomenon of morph frequency fluctuations throughout the years has been reported for other helicoid land snails before (Cowie 1992;Johnson 2011;Silvertown et al 2011). As summarized by Ozgo and Schilthuizen (2012), the shell colour of Cepaea nemoralis was found to be associated with a gene locus coding for the different background shell colours in this species, while the banding was found to be associated with another locus, linked to the colour coding one.…”

Supergenes and their role in evolution

“…The determination of shell pattern is genetic (Cain et al, 1968), and polymorphism is known to be maintained in populations over long periods of time (Silvertown et al, 2011). Evidence for the selective forces maintaining the polymorphism is mixed, with several selective factors having a role (Studies on Cepaea, 1968), including differential predation, climatic selection, heterosis (Cook, 2007) or random processes (Bellido et al, 2002).…”