Polymorphism and Evolutionary Dynamics in Terrestrial Gastropods

Terrestrial gastropods exhibit remarkable polymorphism in shell colour, pattern and form, making them a classic model for studying natural selection, genetic architecture and microevolution. Variation in shell phenotype often arises from a combination of tightly linked genes (supergenes) and unlinked loci, which together determine ground colour, banding and pigmentation. Geographic clines in morph frequencies reflect adaptation to thermal environments and vegetation cover, while predator–prey interactions further shape the distribution of conspicuous and cryptic forms. Recent advances in genomics and population sequencing have revealed that much of the raw material for rapid adaptation resides in ancient allelic variation maintained through past divergence and subsequent admixture. Behavioural and ecological studies demonstrate that morph-specific responses to temperature, humidity and predation modulate selective pressures, underscoring the multi-layered dynamics of polymorphism. These insights into shell polymorphism, speciation processes and demographic history have broad implications for understanding biodiversity resilience under global environmental change.

Research from Nature Portfolio

Recent studies have mobilised citizen science to quantify shell-colour distributions across urban-rural gradients, revealing that snails in urban heat islands disproportionately exhibit lighter morphs, a pattern consistent with thermal selection. Large-scale photographic data on tens of thousands of individuals indicate that shell-banding patterns interact with ground-colour to influence internal shell temperature and heat retention in novel urban environments. This approach highlights the power of community-driven sampling to detect real-time evolutionary responses to anthropogenic change.

Polymorphism and Evolutionary Dynamics in Terrestrial Gastropods publication trend

The graph below shows the total number of articles in polymorphism and evolutionary dynamics in terrestrial gastropods across all publications each year (not limited to Nature Index journals).

Technical terms

Polymorphism: The presence of two or more distinct phenotypes within a single interbreeding population, such as shell-colour and banding variants in land snails.

Supergene: A cluster of tightly linked genes that together control a complex trait, minimising recombination and maintaining favourable allele combinations.

Linkage map: A genetic map that orders markers along chromosomes by estimating recombination frequencies, aiding the localisation of trait-associated loci.

Genome resequencing: The high-throughput sequencing of multiple individuals’ entire genomes to uncover patterns of genetic variation and infer evolutionary processes.

Phenotypic cline: A gradual change in the frequency of a trait or allele across a geographic or environmental gradient, often driven by selective pressures.

References

1. Snail shell colour evolution in urban heat islands detected via citizen science. Communications Biology (2019).
2. Fine mapping of the Cepaea nemoralis shell colour and mid-banded loci using a high-density linkage map. Heredity (2023).
3. Whole-genome re-sequencing data to infer historical demography and speciation processes in land snails: the study of two Candidula sister species. Philosophical Transactions of the Royal Society B Biological Sciences (2021).
4. Discrete or indiscrete? Redefining the colour polymorphism of the land snail Cepaea nemoralis. Heredity (2019).
5. Evolution at two time frames: Polymorphisms from an ancient singular divergence event fuel contemporary parallel evolution. PLOS Genetics (2018).
6. Shell colour, temperature, (micro)habitat structure and predator pressure affect the behaviour of Cepaea nemoralis. The Science of Nature (2018).