Morphometric versus genetic variation in the Eurasian Reed Warbler Acrocephalus scirpaceus in Italy

Capsule: The Eurasian Reed Warbler Acrocephalus scirpaceus from breeding sites in Italy has little genetic variability in the mitochondrial cytochrome b gene but shows morphological variation suggesting isolation of some populations. Aims: To investigate the morphometric and genetic trait variation of Eurasian Reed Warbler populations at a large temporal and spatial scale. Methods: We analysed morphometric traits and the mitochondrial cytochrome b (cyt b) gene of samples collected over 25 years, from populations at seven sites across the Italian peninsula and islands. Results: While we found no genetic differences, we detected significantly smaller body sizes in individuals breeding in Sicily and Sardinia compared to those from mainland Italy. There were also significant body size differences between two Sicilian populations: one larger breeding on the southern coast and the other smaller at an inner highland site. Conclusion: The morphometric data, together with the site fidelity of individuals, are consistent with there being isolation of some populations. Specifically, our results are consistent with an example of polyphenism, morphological plasticity, in the populations of the main Italian islands, Sicily and Sardinia.