7 research outputs found
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
Frequency of Yellow <i>C. nemoralis</i> recorded as population averages in quarter degree cells of latitude and longitude.
<p>(a) the modern and historic datasets combined (b) the modern dataset and (c) the historical dataset. The Key shows the division of the frequency of the Yellow morph by intervals of 0.2.</p
Summary of the results of General Additive Modeling of shell polymorphism in <i>Cepaea nemoralis</i> in the combined dataset of historical and 2009 samples collected throughout Europe.
<p>Statistics shown are coefficients (α) and t-values for unsmoothed terms and F-values for smoothed terms. P-values are approximate. n = sample size (number of populations), Dev% is the percent deviance accounted for by the model. Mid-banded frequency is calculated as a percentage of banded. Coefficient values are not given for the terms entered as smooth functions, because such function cannot be described by a single coefficient.</p>†<p>In this case the model omitting Habitat as an independent variable fits slightly better in terms of deviance than the model including Habitat, so no test statistic or p value can be calculated.</p
Definitions of independent variables used in the statistical analysis.
<p>Definitions of independent variables used in the statistical analysis.</p
A collection of snails from a polymorphic population of <i>Cepaea nemoralis</i> in Poland.
<p>This illustrates the variety of shell colours (Yellow, Pink, Brown) and banding (0, 1, 5) typically found. Photograph by Robert Cameron.</p
Paired sample analysis for sites sampled within 20 km of each other in the historical and modern datasets.
<p>n = number of pairs.</p
Frequency of morphs in four habitat types, as predicted from the models in <b>Table 2</b>.
<p>Standard errors are shown. (a) Yellow, all differences between habitats are significant P<0.001; (b) Mid-banded, differences between dune habitat and all others are significant P<0.001. Other differences are not significant; (c) Unbanded. All differences are significant except for that between grassland and woodland. (P<0.001 for all comparisons involving dune, P = 0.023 for woodland v hedge, P = 0.027 for hedge v grassland). All P values in these comparisons were corrected for multiple testing using Bonferroni.</p