Patterns and processes shaping phylogenetic history of an endemic Hawaiian bird radiation, ‘elepaio (AVES: Chasiempis )

The Hawaiian Islands, an isolated archipelago more than 3,000 kilometers from the nearest continent, are widely recognized as one of the best places to study causal mechanisms driving evolutionary change. Moreover, the clocklike production of new islands, each with known and discrete geological ages, makes investigating how paleogeological factors may influence species diversity particularly tractable. Here, we investigate phylogeny, divergence times, and intraspecific variation within an endemic Hawaiian bird lineage, the ʻelepaio (Aves: Chasiempis). We employed a Bayesian phylogenetic model that simultaneously accounts for lineage diversification, paleogeographic history, and molecular evolution to estimate divergence times. By utilizing information regarding the proximity of islands in different geologic epochs and the geologic age of island emergence, this process-based model allows for inference of time-calibrated phylogenies in cases that lack suitable fossil calibrations, as is common on oceanic islands. Using Ultraconserved Element (UCE) data, we recover a history for ʻelapaio that involves divergence from other Pacific Island lineages followed by colonization of the Hawaiian archipelago within the last several million years. Intraspecific sampling from thousands of loci provides further support for the recognized three species arrangement for the clade, with no evidence of intraspecific structure.