Snails mastered the art of air travel thousands of years before humans, according to a study by researchers from the Smithsonian Tropical Research Institute and their colleagues.
The paper by Osamu Miura and coauthors is to be published in a forthcoming issue of the Proceedings of the Royal Society B: Biological Sciences.
The authors focused their study on two closely related species of horn snails: the Pacific horn snail (Cerithideopsis californica) and the Atlantic horn snail (C. pliculosa). As their names imply, these snails are found on either coasts of the Central American isthmus, where they inhabit intertidal mudflat and mangrove habitats.
The authors collected snails from 29 populations from California to Panama on the Pacific coastline and from Texas to Panama on the Atlantic coastline of the Central American isthmus. They then partially sequenced five mitochondrial genes from these snails for analysis.
Their study indicated that the snails crossed the seemingly insurmountable geographical barrier of dry land not once but twice: from the Pacific to the Atlantic about 750,000 years ago and again from the Atlantic to the Pacific about 72,000 years ago.
The authors hypothesised that the snails crossed the Central American isthmus stuck to the legs, clinging on the bellies, or even inside the stomachs of migrating shore birds. Lest the third possibility seems implausible, previous studies have shown that the snails can survive ingestion by shore birds. The shorebirds regularly cross Central America over two migration flyways: the Isthmus of Tehuantepec in southern Mexico, and the Isthmus of Panama.
According to author Ryan Hechinger, "There is a chance that the hitchhiking snails benefited native populations by bringing in new genes that helped them resist common parasites that castrate the snails and keep them from reproducing."
This idea of hitchhiking is not new: Charles Darwin had postulated that invertebrates, including marine snails, could be dispersed long distances by birds, although there has been little evidence that this occurs for marine animals. The result of this study thus provides evidence that not only is such passive dispersal possible for marine organisms, but that it can occur across seemingly insurmountable barriers.
For more information, see the paper: Miura, O, ME Torchin, E Bermingham, DK Jacobs and RF Hechinger (2011) Flying shells: historical dispersal of marine snails across Central America. Proceedings of the Royal Society B: Biological Sciences, doi:10.1098/rspb.2011.1599
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