‘Ring species’ or ‘circular overlaps’ present a unique opportunity to reconstruct the history of speciation. They occur when a chain of gradually diverging populations encircles a geographic barrier. Interbreeding occurs between neighbouring populations, but the two ends of the chain eventually meet as reproductively isolated species. They thus allow us to follow the process of geographic speciation step by step, and also demonstrate that speciation may occur even in the presence of gene flow. Yet despite their significance, very few genuine examples of ring species have been documented to date.
In a new study published in BMC Biology William Monahan and colleagues suggest a way to discover new examples of ring species, through a global topographic model that utilises information on the geographic barriers involved in the formation of known ring species to predict where other candidate barriers might be found.
Darren Irwin, in an accompanying commentary for BMC Biology, discusses how the model could be extended to incorporate geographic and environmental features not included in the current model, and examines their relative importance in known examples of ring speciation.
Heidi Seears, Assistant Editor, BMC Biology