Stepping stone speciation in Hawaii’s flycatchers: molecular divergence supports new island endemics within the elepaio

Abstract

The elepaio (Chasiempis sandwichensis) is a monarch flycatcher endemic to the Hawaiian Islands of Kauai, Oahu, and Hawaii. Elepaio vary in morphology among and within islands, and five subspecies are currently recognized. We investigated phylogeography of elepaio using mitochondrial (ND2) and nuclear (LDH) markers and population structure within Hawaii using ND2 and microsatellites. Phylogenetic analyses revealed elepaio on each island formed reciprocally monophyletic groups, with Kauai ancestral to other elepaio. Sequence divergence in ND2 among islands (3.02-2.21%) was similar to that in other avian sibling species. Estimation of divergence times using relaxed molecular clock models indicated elepaio colonized Kauai 2.33 million years ago (95% CI 0.92-3.87 myr), Oahu 0.69 (0.29-1.19) myr ago, and Hawaii 0.49 (0.21-0.84) myr ago. LDH showed less variation than ND2 and was not phylogenetically informative. Analysis of molecular variance within Hawaii showed structure at ND2 (fixation index = 0.31), but microsatellites showed no population structure. Genetic, morphological, and behavioral evidence supports splitting elepaio into three species, one on each island, but does not support recognition of subspecies within Hawaii or other islands. Morphological variation in elepaio has evolved at small geographic scales within islands due to short dispersal distances and steep climatic gradients. Divergence has been limited by lack of dispersal barriers in the extensive forest that once covered each island, but anthropogenic habitat fragmentation and declines in elepaio population size are likely to decrease gene flow and accelerate differentiation, especially on Oahu.

Charting the course of reed-warblers across the Pacific islands

“…This progressive pattern has been observed in birds (Fleischer et al. , 1998; Vanderwerf et al. , 2009), mammals (Steppan et al.…”

Deep Diversification and Long-Term Persistence in the South American ‘Dry Diagonal’: Integrating Continent-Wide Phylogeography and Distribution Modeling of Geckos

“…However, because CE and NE lineages are not reciprocally monophyletic and show some admixture, they may have diverged through ecological speciation along environmental gradients, without physical barriers to prevent gene flow (Nosil 2008). The alternative of sympatric speciation is supported by an increasing body of evidence in marine vertebrates (Foote et al 2009; Crow et al 2010), where obvious barriers are less evident, but is also documented for terrestrial vertebrates (Niemiller et al 2008; VanderWerf et al 2010), and must also be considered as a possibility here.…”

Within-island diversification in a passerine bird

“…We suggest that the evolution of low dispersal ability in the Reunion grey white-eye, combined with periods of geographical isolation, ecological opportunity and sexual selection, could have been key in explaining why this lineage has diversified within such a small island, well below the minimum spatial scale considered suitable for divergence in highly mobile organisms like birds [44]. There is currently no other convincing evidence of intra-island speciation, including incipient speciation, on islands smaller than 10 000 km 2 [75], and, more generally, little evidence on islands smaller than Madagascar (600 000 km 2 ) [6,29,76,77]. Recent studies have shown that more variation exists among the different geographical forms of the Reunion grey white-eye than would be expected under drift for both morphological and plumage colour traits [34,42].…”