GENETIC DIFFERENTIATION AND PHYLOGENETIC-RELATIONSHIPS OF BONELLI WARBLER PHYLLOSCOPUS-BONELLI AND GREEN WARBLER P-NITIDUS

The mitochondrial genetic differentiation and molecular phylogenetic r elationships of western and eastern Bonelli's Warblers (Phylloscopus b . bonelli, P.b. orientalis) and Green Warbler Phylloscopus nitidus wer e investigated. The cytochrome b gene was amplified by polymerase chai n reaction and 1038 nucleotides were sequenced directly in these and s everal other Phylloscopus species plus Sylvia atricapilla and Acroceph alus scirpaceus. The mitochondrial genetic distance between eastern an d western Bonelli's Warblers was as large (8.3-8.6%) as between each o f them and the Wood Warbler P. sibilatrix. Compared to the amount of m tDNA differentiation between other closely related species and subspec ies of birds, the divergence between the Bonelli's warblers is far gre ater than among typical subspecies. Together with the distinct differe nces in calls and structure of song elements the genetic data support full species status of the two taxa. The cytochrome b sequence of P. n itidus differed by 2.5-3.1% from P. trochiloides, to which it is most closely related. This divergence is also larger than between most subs pecies of birds studied so far at this locus and is consistent with th e placement of P. nitidus as an allospecies within the superspecies P. [trochiloides]. We discuss population-genetic scenarios for a potenti ally accelerated rate of mtDNA differentiation in relatively small, ge ographically isolated populations that might help to explain the large sequence divergence observed. A phylogenetic tree was constructed by maximum parsimony and neighbour-joining. Chiffchaff P. collybita and W illow Warbler P. trochilus are sister species and together form the si ster group of Bonelli's and Wood Warblers. As expected, Arctic Warbler P. borealis was found to be the sister species of the Greenish Warble r complex (including nitidus), whereas the relationships of P. (inorna tus) humei relative to the other species could not be resolved. Among the taxa studied, those without wing-bars belong to a phylogenetically older clade than those with wing-bars. MtDNA sequence data promise to be very useful in quantifying the genetic differentiation and phyloge netic relationships among closely related species, especially in morph ologically poorly differentiated genera like phylloscopus.