Résumé
We used DNA sequence data of the mitochondrial control region and cytochrome b gene to assess phylogenetic relationships among 32 gull species and two outgroup representatives. We tentatively estimated divergence times from transversional substitutions calibrated against DNA-DNA hybridization data. Several strongly supported species groups are identified, but the relationships between these species groups and the rooting of the gull tree remain unresolved. Geographical range extension appears as a factor of speciation, but several related, well-differentiated species seem to have evolved within comparatively restricted areas. Some plumage characters used in the past for delimiting species groups appear inappropriate. The dark hooded species, for instance, do not constitute a natural assemblage. Molecular data also allowed the identification of several striking plumage convergences that had obscured the true relationships between gull species until now. For example, the dark tropical gulls analysed here each belong to totally different clades and are independent examples of convergent plumage evolution under common environmental constraints. The reverse situation also happened, with two arctic-distributed species, the ivory gull (Pagophila eburnea) and the Sabine's gull (Xema sabini), appearing as sister taxa despite completely different plumage features. Molecular data have thus significantly improved our understanding of gull evolution.