Tectonic collision and uplift of Wallacea triggered the global songbird radiation

Abstract

Songbirds (oscine passerines) are the most species-rich and cosmopolitan bird group, comprising almost half of global avian diversity. Songbirds originated in Australia, but the evolutionary trajectory from a single species in an isolated continent to worldwide proliferation is poorly understood. Here, we combine the first comprehensive genome-scale DNA sequence data set for songbirds, fossil-based time calibrations, and geologically informed biogeographic reconstructions to provide a well-supported evolutionary hypothesis for the group. We show that songbird diversification began in the Oligocene, but accelerated in the early Miocene, at approximately half the age of most previous estimates. This burst of diversification occurred coincident with extensive island formation in Wallacea, which provided the first dispersal corridor out of Australia, and resulted in independent waves of songbird expansion through Asia to the rest of the globe. Our results reconcile songbird evolution with Earth history and link a major radiation of terrestrial biodiversity to early diversification within an isolated Australian continent.

Figure 1. Time-calibrated phylogeny of songbirds.

Topology based on concatenated maximum likelihood analysis of 4,155 UCE loci and date estimates based on fossil-derived calibrations. Nodes with squares around ancestral range indicate 70% or greater maximum likelihood bootstrap support, circles indicate <70% bootstrap support. All nodes are supported by posterior probability greater than 0.98 in Bayesian analyses. Geological events are indicated by vertical grey bars and labelled below. Stars indicate nodes calibrated for dating analyses. Coloured squares at tips indicate distribution of clade for that exemplar and correspond to coloured world map (A, Australia; B, New Zealand; C, New Guinea; D, Wallacea; E, S and SE Asia; F, Africa; G, New World; H, Palaearctic; I, Madagascar). Ancestral areas at internal nodes inferred with DEC+j model and New Guinea excluded as an ancestral area before 15 Myr ago. Palaeogeographic reconstructions adapted from Hall depict the distribution of land and sea across Wallacea and northern Australasia during early songbird diversification. Abbreviations: Plio.=Pliocene; Pleis.=Pleistocene. See (Supplementary Fig. 6) for dating with alternative calibrations.