The herring gull complex (Larus argentatus - Fuscus - Cachinnans) as a model group for recent holarctic vertebrate radiations

Abstract

Under what circumstances speciation in sexually reproducing animals can occur without geographical disjunction is still controversial. According to the ring species model, a reproductive barrier may arise through isolation-by-distance when peripheral populations of a species meet after expanding around some uninhabitable barrier. The classical example for this kind of speciation is the herring gull (Larus argentatus) complex with a circumpolar distribution in the northern hemisphere. An analysis of mitochondrial DNA variation among 21 gull taxa indicated that members of this complex differentiated largely in allopatry following multiple vicariance and long-distance colonization events, not primarily through isolation-by-distance. In a recent approach, we applied nuclear intron sequences and AFLP markers to be compared with the mitochondrial phylogeography. These markers served to reconstruct the overall phylogeny of the genus Larus and to test for the apparent biphyletic origin of two species (argentatus, hyperboreus) as well as the unexpected position of L. marinus within this complex. All three taxa are members of the herring gull radiation but experienced, to a different degree, extensive mitochondrial introgression through hybridization. The discrepancies between the mitochondrial gene tree and the taxon phylogeny based on nuclear markers are illustrated.