Mitochondrial evidence for genetic diversity and low phylogeographic differentiation in the Marsh Warbler Acrocephalus palustris (Aves: Acrocephalidae)

Abstract

We analyzed the levels of genetic variability in a long-distance migratory reed warbler, the Marsh Warbler Acrocephalus palustris, by using nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I gene (COI; 611 nucleotides [nt]). We obtained sequences from 229 individuals from ten sampling sites that include breeding, wintering, and migrating birds. Overall, 44 haplotypes were detected, which reflect high levels of genetic variation in this species, but most of this variation corresponds to individual differences within collecting sites. We also analyzed 829 nt of cytochrome b (cyt b) from 49 selected individuals of different sampling sites to evaluate the reliability of the COI results. Our analyses based on both mtDNA loci could not detect any population subdivision or phylogeographic structure, indicating high levels of gene flow between breeding sites (Nm = 13.69). The split between the Marsh Warbler and its sister species, the Eurasian Reed Warbler Acrocephalus scirpaceus, could be dated for the Lower Pliocene (about 3.8 million years ago). The time to the most recent common ancestor (TMRCA) among Marsh Warbler haplotypes was estimated as 0.45 million years, indicating their bottleneck during the last glacial periods. Low nucleotide diversity, a shallow phylogenetic tree, a star-like haplotype network, and a unimodal mismatch distribution point to a sudden increase of the effective population size (probably after the last glaciation period) and a recent range expansion likely from a single refuge.