Figure 1.

Two contrasting hypotheses about the differentiation and colonization history of the herring gull complex. Large ovals show hypothetical ancestral refugia. Arrows indicate inferred colonization routes. (A) Mayr's model [4], proposed that herring gulls originated in the Aralo-Caspian region (cachinnans), from where gulls spread in three directions (1) west via the Mediterranean into the Atlantic giving rise to Mediterranean (michahellis) and Atlantic (atlantis) yellow-legged gulls; (2) east toward Inner Asia giving rise to Mongolian gull (mongolicus) and (3) north to the Arctic Ocean (heuglini). Along the north Eurasian coasts, the ancestral population expanded into two opposite directions: (a) west across Scandinavia towards Britain and Iceland differentiating into dark-mantled lesser black-backed gulls (fuscus), and (b) east all the way to the North Pacific, giving rise to progressively paler-mantled forms vegae (eastern Siberia), and into North America (glaucoides and smithsonianus). Mayr proposed that, following the last Glacial Maximum, North American herring gulls (smithsonianus) subsequently crossed the North Atlantic and invaded Europe, where they gave rise to the pale-mantled European herring gull (argentatus) that now overlaps with the dark-mantled lesser black-backed gulls (fuscus) [4,9]. Note that Mayr did not include marinus and hyperboreus in his original model. (B) Alternative model based on results of Liebers et al. [8]. Two ancient refugia are inferred. Taxa derived from Atlantic refugium are shown in green, those derived from Aralo-Caspian refugium in red. No invasion of herring gulls from North America to Europe occurred. Marinus developed reproductive isolation in allopatry (probably in north-eastern North America) before making secondary contact with North American smithsonianus and Eurasian argentatus/fuscus. Two separate colonisation events from the Atlantic into the Mediterranean led to the differentiation of armenicus and michahellis.

Sternkopf et al. BMC Evolutionary Biology 2010 10:348   doi:10.1186/1471-2148-10-348
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