Filling the gaps in the origin and biogeography of the Turdus thrushes

What is it about?

Although the biogeographic history of thrushes (Turdidae) has been extensively studied, a concise discussion of this topic is still lacking. Therefore, in this study we aimed to investigate: (1) the evolutionary origin of the migratory behaviour of the Turdus thrushes in a biogeographic context including (2) trans-Atlantic dispersal events, (3) possible colonization routes into the Nearctic, and (4) relationships among life history traits, ecological factors, and migratory strategies within the most comprehensive taxon set of 72 Turdus thrushes to date. We estimated the ancestral ranges of the studied species, primarily by comparing main biogeographic models (dispersal-vicariance, dispersal-extinction-cladogenesis, BayArea models), and performed phylogenetic generalized least squares analyses to identify relationships among distribution patterns, diet, body measurements, clutch size, and migratory behaviour. We found that the most probable ancestral regions for all Turdus species were located in the East Palearctic realm, followed by early colonization of the western Palearctic and Africa, and that several trans-Atlantic movements occurred between 11 and 4 million years ago, which is earlier than previously thought. Migration emerged as an ancestral behaviour of the genus Turdus, and differences in clutch size and main food types were significant between migratory and non-migratory species. Correlated evolution was found between migration and along-latitudinal mobility, main food type, and the shift in main food type between the seasons. We conclude that along-latitudinal movements may have evolved earlier, simultaneously with the radiation of the Turdus thrushes, followed by the appearance of meridional migration, associated with orographic and climatic changes. The increased clutch sizes observed in migratory species and documented here for thrushes could serve as an important mechanism to compensate for losses due to mortality during migration.

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