Taxonomy and phylogeny of reed warblers (genus Acrocephalus) based on mtDNA sequences and morphology

Abstract

The mitochondrial cytochrome b gene of the majority of Acrocephalus species (76 individuals) was amplified by PCR and sequenced directly. Nucleotide sequences (1068 base pairs) were used to reconstruct phylogenetic relationships within the genus Acrocephalus as well as between Acrocephalus and other sylviid warblers, particularly Hippolais. Acrocephalus and Hippolais share ancestry and cluster in a monophyletic clade. Hippolais appears to represent a polyphyletic assemblage since H. icterina figures as the sister taxon to Acrocephalus, whereas "Hippolais" pallida and caligata cluster within Acrocephalus. The following Acrocephalus clades could be recognized: (1) Large reed warblers form a clade consisting of a monophyletic Palearctic-Australasian subgroup (arundinaceus, stentoreus brunnescens, orientalis, australis, and vaughani) and a monophyletic Afrotropical subgroup (brevipennis, rufescens, gracilirostris, sechellensis, and newtoni). A. griseldis holds an isolated position at the base of the large reed warbler clade. Within the small reed warblers, two probably monophyletic clades are apparent: (2) the striped species (with bistrigiceps, melanopogon, paludicola, and schoenobaenus), and (3) the small plain-coloured complex (consisting of dumetorum, palustris, scirpaceus, s. fuscus, baeticatus, and avicenniae plus the neighbouring agricola-complex with agricola, tangorum, and concinens). The relationship between these groups cannot be resolved. The molecular data clarify the status of some taxa, the systematic position of which has been controversial. A morphometric analysis (PCA) of 20 external characters confirmed the basic complexes, and unveiled adaptations of general importance among clades. At species level, we found less congruence between molecular and morphological data, which can be interpreted as a consequence of specializing adaptations and convergence. The major complexes established by molecular and morphometric analyses are further supported by distributional, acoustical, and oological affinities. A sound phylogenetic framework of the genus makes it now possible to examine the distribution of ecological and behavioural characters and to differentiate informative or convergent characters. Acrocephalus may be split into four previously recognized genera with the following names: Acrocephalus for the large, Calamodus for the striped, Notiocichla for the small plain, and Iduna for the brownish "Hippolais" species.