| Summary: | Evolutionary radiations of colonists on archipelagos provide valuable insight into mechanisms and modes
of speciation. The apparent diversification of Galapagos mockingbirds (Nesomimus) provoked Darwin’s initial conception
of adaptive radiation, but the monophyly of this historically important exemplar has not been evaluated with
molecular data. Additionally, as with most Galapagos organisms, we have a poor understanding of the temporal pattern
of diversification of the mockingbirds following colonization(s) from source populations. Here we present a molecular
phylogeny of Galapagos and other mockingbird populations based on mitochondrial sequence data. Monophyly of
Galapagos mockingbirds was supported, suggesting a single colonization of the archipelago followed by diversification.
Our analyses also indicate that Nesomimus is nested within the traditional genus Mimus, making the latter paraphyletic,
and that the closest living relatives of Galapagos mockingbirds appear to be those currently found in North America,
northern South America, and the Caribbean, rather than the geographically nearest species in continental Ecuador.
Thus, propensity for over-water dispersal may have played a more important role than geographic proximity in the
colonization of Galapagos by mockingbirds. Within Galapagos, four distinct mitochondrial DNA clades were identified.
These four clades differ from current taxonomy in several important respects. In particular, mockingbirds in the eastern
islands of the archipelago (Espan˜ola, San Cristo´ bal, and Genovesa) have very similar mitochondrial DNA sequences,
despite belonging to three different nominal species, and mockingbirds from Isabela, in the west of the archipelago,
are more phylogenetically divergent than previously recognized. Consistent with current taxonomy is the phylogenetic
distinctiveness of the Floreana mockingbird (N. trifasciatus) and close relationships among most mockingbirds from
the central and northern region of the archipelago (currently considered conspecific populations of N. parvulus).
Overall, phylogeographic patterns are consistent with a model of wind-based dispersal within Galapagos, with colonization
of more northerly islands by birds from more southern populations, but not the reverse. Further radiation
in Galapagos would require coexistence of multiple species on individual islands, but this may be prevented by
relatively limited morphological divergence among mockingbirds and by lack of sufficient habitat diversity in the
archipelago to support more than one omnivorous mimid.
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