Repeated transAtlantic dispersal catalysed a global songbird radiation
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ABSTRACTAimTurdusthrushes are one of the most speciose and widespread songbird genera, comprising nearly 70 species that combined have a nearglobal 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 longstanding paradigm of Beringian colonization or transAtlantic dispersal best explains modern distributions in the New and Old Worlds.LocationWorldwide, with emphasis on New WorldOld World biotic interchange.MethodsUsing a molecular phylogenetic hypothesis ofTurdusthrushes, 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.ResultsTurdusoriginated in Eurasia, and following the colonization of Africa underwent a series of five transAtlantic sweepstake dispersals. The data reject the alternative hypothesis that connections between Old and New WorldTurdusspecies can be attributed to movement through Beringia with subsequent extinction. Divergence estimates indicate that these dispersals all occurred near the MiocenePliocene boundary, 5 Ma. A significant phylogenetic correlation between migratory and flocking behaviour is evident in the genus.Main conclusionsThe initial divergence ofTurdusin the Old World was followed by a series of transAtlantic sweepstake dispersal events. These dispersals are temporally correlated with a specific palaeoclimatic system, which would have facilitated transport ofTurdusfrom 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 transAtlantic dispersals are evident inTurdusafter this time. Migratory movements by ancestral lineages in flocks, rather than as single individuals, suggest an increased likelihood of successfully colonizing new areas, postdispersal.
