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GENomic evolution In Ecological Speciation

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Genetics and speciation in snails

An EU team studied the genetics of speciation in land snails. The current diversity of shell shapes results from previous episodes of environmental change, favouring different morphologies that have been preserved in the genome.

Climate Change and Environment
Fundamental Research

Although Charles Darwin’s famous book was called ‘The Origin of Species’, it never discussed the actual origin of species. Subsequent generations of ecologists have filled in the details, revealing that the process involves various types of genetic partitioning of populations. The EU-funded project GENIES (Genomic evolution in ecological speciation) examined the processes of speciation in greater depth. The team studied Murella muralis, a land snail. Snails are generally excellent subjects for the topic because their populations are widespread, yet individuals seldom move far, which controls for migration. M. muralis has a high morphological diversity and even greater genetic diversity. Using the ultimate in gene-sequencing technologies, the study examined how the species’ genes change during speciation. Researchers also associated the morphological variation with patterns of particular genes. They identified the genes most important for speciation, and how such genes are affected by environmental factors. Results indicate that environmental changes act on different levels of the genome. Such changes simultaneously promote and constrain differentiation. Researchers concluded that the snails’ shell shape diversity results from adaptation to contrasting environments. Previous environmental changes contributed to numerous shell shapes and separate genetic lineages. Various forms of evidence revealed repeated population mergers and separations, promoting active divergence and gene flow. The team furthermore concluded that independent gene regions within the genome experienced separate selection. Such divergent selection can show genome-wide effects, even during early stages of speciation. Sources of standing variation may facilitate the emergence of genome-wide reproductive isolation, followed by adaptive radiation. Hence, speciation with gene flow is more likely given a transition from the effects of selection of individual genes to large portions of the genome. Analysis revealed that population-level differences in shell shape contribute to the degree of genomic differentiation. Geographically isolated organisms sometimes showed patterns of isolation by adaptation, where divergent selection on traits impeded gene flow. The GENIES project demonstrated the potential for genetic diversity to facilitate species survival given environmental change. The work has important implications for ‘evolutionary rescue’ projects, which aim to minimise the impact of environmental change.

Keywords

Genetics, speciation, land snails, GENIES, genomic evolution, Murella muralis

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