Phenotypic and genetic characterization of the East Siberian Willow Warbler (Phylloscopus trochilus yakutensis Ticehurst, 1935) in relation to the European subspecies

Abstract

Long-distance migrants with transcontinental breeding ranges are of particular interest for the study of local adaptation and geographic differentiation in birds. We compared phenotypes and genotypes between Far East Siberian Willow Warblers Phylloscopus trochilus yakutensis Ticehurst, 1935 with the European subspecies P. t. trochilus Linnaeus, 1758 and P. t. acredula Linnaeus, 1758. We found significant differences in mean body size and plumage colour, but intra-population variation overlapped extensively between the European and Siberian populations. We used stable isotope composition in winter-grown flight feathers as a proxy for wintering sites and found differences between all three subspecies, indicating different wintering grounds. Out of four nuclear loci analyzed (three of which are known to be substantially divergent between the European subspecies), none allowed to seperate East Siberian yakutensis from North Scandinavian acredula. Hence, neither phenotypic traits nor the currently available genetic resources provide diagnostic criteria for confidently assigning individual Willow Warblers to a particular subspecies. Despite extensive overlap in phenotypes and genotypes, we propose that the subspecies names can still be used as biogeographical references to the three Willow Warbler populations that differ in migration strategies. We propose to use yakutensis for Willow Warblers breeding east of the Ural Mountains that presumably initiate autumn migration towards the southwest or west, in contrast to the genetically most similar acredula that start autumn migration towards the southeast or south. Future field studies are needed to elucidate whether the longitudinal variation in phenotype is a cline, or whether a clear contact zone between these subspecies can be identified. Keywords Willow Warbler • Phylloscopus trochilus yakutensis • Subspecies • Genetic structure • Phenotypic variation • Clock gene • Stable isotopes Zusammenfassung Vergleichende phänotypische und genetische Charakterisierung der ostsibirischen (Phylloscopus trochilus yakutensis Ticehurst, 1935) und europäischen Fitis-Unterarten Langstreckenzieher mit trans-kontinentalem Verbreitungsgebiet eigenen sich hervorragend zur Untersuchung lokaler Anpassung und geographische Differenzierung. Hier vergleichen wir Phänotyp und Genotyp der ostsibirischem Fitis-Unterart (Phylloscopus trochilus yakutensis Ticehurst, 1935) mit den europäischen Unterarten P. t. trochilus Linnaeus, 1758 und P. t. acredula Linnaeus, 1758. Unsere Ergebnisse zeigen signifikante Unterschiede der mittleren Körpergröße, sowie Gefiederfärbung, wobei die Bandbreite beider Messgrößen zwischen den Unterarten stark überlappen. Die zur Bestimmung der jeweiligen Überwinterungsgebiete genutzte stabile Isotopenkomposition der im Winter gemauserten Communicated by M. Wink.

Central‐West Siberian‐breeding Bar‐tailed Godwits (Limosa lapponica) segregate in two morphologically distinct flyway populations

“…In general it is thought that flyway populations arise from divergent selection, which can lead to reproductive isolation, for instance because populations are separated in space or in time (Bearhop et al 2005, Turbek et al 2018). However, an increasing number of studies show that flyway populations can diverge phenotypically without reproductive isolation, as indicated by low neutral genetic differentiation (Buehler & Baker 2005, Marthinsen et al 2007, Sokolovskis et al 2019, Delmore et al 2020. In addition, studies on migrants that travel in groups show that migration routes can be socially learned (Mueller et al 2013, Flack et al 2018.…”