Mitochondrial phylogeny of the genus Regulus and implications on the evolution of breeding behavior in sylvioid songbirds.

We tested four hypotheses about the relationships of the kinglets (genus Regulus)to seven closely related genera of the songbird superfamily Sylvioidea using mitochondrial DNA sequences. The kinglets were suggested to be closely related to the tits (Parus) or to the Old World Warblers (Phylloscopus) and were also suggested to constitute the, or at least one of the, most ancestral splits among the sylvioids. Our phylogenetic analysis grouped the kinglets as the sister group of a clade comprising Parus and Phylloscopus and including the genera Sylvia, Aegithalos, and Leptopoecile. Two of the taxa were placed more ancestral to the kinglets: Sitta and Certhia. We also identified the endemic kinglet species from the Canary Islands s the sister group of R. regulus. The superimposition of breeding behavior on the phylogeny suggests that hole nesting is ancestral and various other patterns of nest construction have evolved from it. The placement of Parus implies that hole nesting in the Paridae is likely to have originated secondarily. Further, Leptopoecile and Aegithalos, two genera for which a helper system of elder offspring in breeding was described, were resolved as a clade.