Different timing of the adaptive radiations of North American and Asian warblers

Abstract

The timing of speciation events among warblers (small insectivorous woodland birds) in the Himalayas of India and in the White Mountains of New Hampshire, USA, is compared. Sequence divergence in the mitochondrial cytochrome b gene for 13 New World species in six genera averages 2.6%, which according to standard calibrations places most of the diversi¢cation in the early Pleistocene. In contrast, eight Himalayan species in the single genus Phylloscopus di¡er by an average of 10.7% in the same gene sequence. The New Hampshire warblers appear to have undergone a relatively recent burst of speciation and morphological evolution, but there is a detectable slowing of speciation rates (or increase in extinction rates) within the community towards the present. Other North American passerine groups that have been studied show no signs of explosive diversi¢cation in the Pleistocene. In these groups, pairs of sister species are often older than the entire warbler radiation. Boreal forest migrated south from very high latitudes towards the end of the Pliocene and this apparently created conditions ripe for explosive diversi¢cation among the warblers, but not for many other groups.

The Imprint of History on Communities of North American and Asian Warblers

“…Lovette and Bermingham (1999) inferred that the Dendroica underwent a burst of rapid speciation early in the radiation of the group. We confirmed this to be the case for just the Dendroica species on the phylogeny of figure 1, using the coalescent method described in Price et al (1998). We computed a statistic based on the ratio of terminal branch lengths to internal branch lengths and compared it to the simulated distributions shown in Price et al (1998); low P values imply overly long terminal branches.…”

“…Lovette and Bermingham (1999) include a much larger sequence base in their analyses of the Dendroica, and obtain very similar results in all respects to that based on just the cytochrome b molecule presented here. A previous study comparing the phylogenetic relationships of these two groups (Price et al 1998) was flawed due to the presence of nuclear homologs in the Dendroica sequences ("numts"; see Arctander 1995). Here, we reanalyse the timing of speciation events using the correct sequences, and the methods described in Price et al (1998).…”

“…A previous study comparing the phylogenetic relationships of these two groups (Price et al 1998) was flawed due to the presence of nuclear homologs in the Dendroica sequences ("numts"; see Arctander 1995). Here, we reanalyse the timing of speciation events using the correct sequences, and the methods described in Price et al (1998).…”

“…Long terminal branch lengths imply that there has been a "slowing down" of speciation events toward the present among the species included in the analysis. Further details of this method, including the simulated distributions against which the statistic can be evaluated, are presented in Price et al (1998). Both the tests described in this paragraph require clocklike trees.…”

“…The method assesses whether a focal lineage at an identified point in time has given rise to disproportionately many present-day descendants (Nee et al 1996). We estimated relative timing of speciation events within clades using an analysis based on coalescence (Price et al 1998). This method examines the ratio of terminal branch lengths to internal branch lengths against a simulated null distribution based on the neutral model.…”