Repeated transAtlantic dispersal catalysed a global songbird radiation
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Aim: Turdus thrushes are one of the most speciose and widespread songbird genera, comprising nearly 70 species that combined have a near-global distribution. Herein, we use molecular phylogenetic, molecular clock and behavioural evidence to examine the historical biogeography of the genus. Ancestral area reconstructions in conjunction with divergence estimates and palaeoclimatogical data are used to test whether the long-standing paradigm of Beringian colonization or trans-Atlantic dispersal best explains modern distributions in the New and Old Worlds. Location: Worldwide, with emphasis on New World-Old World biotic interchange. Methods: Using a molecular phylogenetic hypothesis of Turdus thrushes, we reconstructed ancestral area relationships utilizing the five major continental or regional areas occupied by species in the genus. We also examined the evolution of behaviours on the phylogeny, and estimated the timing of major lineage divergences via a molecular clock. Results: Turdus originated in Eurasia, and following the colonization of Africa underwent a series of five trans-Atlantic sweepstake dispersals. The data reject the alternative hypothesis that connections between Old and New World Turdus species can be attributed to movement through Beringia with subsequent extinction. Divergence estimates indicate that these dispersals all occurred near the Miocene-Pliocene boundary, 5 Ma. A significant phylogenetic correlation between migratory and flocking behaviour is evident in the genus. Main conclusions: The initial divergence of Turdus in the Old World was followed by a series of trans-Atlantic sweepstake dispersal events. These dispersals are temporally correlated with a specific palaeoclimatic system, which would have facilitated transport of Turdus from the Caribbean to the Old World across the Atlantic. Uplift of the Central American Seaway 4.7 Ma effectively shut down the palaeoclimatic system, and no additional trans-Atlantic dispersals are evident in Turdus after this time. Migratory movements by ancestral lineages in flocks, rather than as single individuals, suggest an increased likelihood of successfully colonizing new areas, post-dispersal. 2009 The Authors Journal compilation 2009 Blackwell Publishing.
