Diversification and the adaptive radiation of the vangas of Madagascar

Abstract

The vangas of Madagascar exhibit extreme diversity in morphology and ecology. Recent studies have shown that several other Malagasy species also are part of this endemic radiation, even as the monophyly of the clade remains in question. Using DNA sequences from 13 genes and representatives of all 15 vanga genera, we find strong support for the monophyly of the Malagasy vangids and their inclusion in a family along with six aberrant genera of shrike-like corvoids distributed in Asia and Africa. Biogeographic reconstructions of these lineages include both Asia and Africa as possible dispersal routes to Madagascar. To study patterns of speciation through time, we introduce a method that can accommodate phylogenetically non-random patterns of incomplete taxon sampling in diversification studies. We demonstrate that speciation rates in vangas decreased dramatically through time following the colonization of Madagascar. Foraging strategies of these birds show remarkable congruence with phylogenetic relationships, indicating that adaptations to feeding specializations played a role in the diversification of these birds. Vangas fit the model of an 'adaptive radiation' in that they show an explosive burst of speciation soon after colonization, increased diversification into novel niches and extraordinary ecomorphological diversity.

Figure 1.

Phylogenetic relationships recovered using maximum likelihood (ML; GARLI). Vanginae are shown with red branches and the Vangidae are highlighted in bold. ML bootstrap support values are shown above nodes and Bayesian posterior probability values are below (or right) nodes on the ML tree. Yellow diamonds indicate where MP and ML topologies agree.

Figure 2.

Chronogram using penalized likelihood and ancestral area reconstruction using Lagrange. Nodes show the ancestral area(s) reconstruction with the highest likelihood of the descendant lineages on either side of split. Numbers at nodes prefixed with an ‘N’ refer to node numbers referenced in the text. For all nodes except N40, the reconstructions shown have about twice the relative probability (see the electronic supplementary material) as the next most likely. Coloured branches are used when all the descendant lineages are only found in a single area. Geographical areas are as follows: A (red), Madagascar; B (orange), Asia; C (green), Africa; D (blue), Australia; E (purple), Eurasia; F (yellow), Americas.

Figure 3.

The radiation of Vanginae and optimized foraging behaviour (table 1): black, gleaning; blue, sallying; red, probing. Illustrations of birds by Velizar Simeonovski.

Figure 4.

Tempo and mode of lineage diversification in Malagasy vangas. Black circles denote observed lineage-accumulation curve; grey circles are the locations of ‘missing’ speciation events estimated using the EM algorithm under the best-fit diversification model. ML estimate of speciation-through-time under exponential decline model is indicated by the dashed line.