Well-travelled snails hitch a ride around the globe
A group of land-snail species have been shown to belong to one big family, despite living on far-flung islands some 9,000 kilometres apart. The discovery, made by comparing their DNA sequences, raises the intriguing question of how they accomplished their extensive ocean-going journeys — with migratory birds being the leading contenders for ferrying them around the globe.
Snails of the genus Balea are found throughout Europe and the Azores, a remote group of islands in the middle of the North Atlantic. Similar snails are also found on the Tristan da Cunha archipelago in the South Atlantic, but naturalists had assigned them to a different species because of their sheer distance from the Northern Hemisphere species.
But, by comparing the genetic sequences of these snails, researchers led by Richard Preece have discovered that all of the more than 20 species of Balea arose from a single, relatively recent common ancestor.
As the researchers explain in a Brief Communication in last week’s Nature, this means that they represent a single genus that has spread over incredible swathes of open ocean. This supports the possibility that the molluscs may have been transported by birds — a phenomenon that fascinated Charles Darwin during his studies on the origin of species.