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Figure 1. Phylograms and sample distribution maps of Xanthomixis zosterops and its associated Myrsidea.
(A) ML phylogram of X. zosterops from 1979 bp of mtDNA (ND3, cyt-b, and ATP6), collapsed to unique haplotypes. Nodes labeled with cyt-b corrected and p-distance (in parentheses) divergences and with nodal support (MP/ML/PP, *=100/100/1.0). Map shows distribution of X. zosterops mtDNA clades, with pie charts showing proportion of each clade among samples from a given area. Numbers next to pie charts are sample sizes.
(B) ML phylogram of all Myrsidea feather lice collected from X. zosterops, based on 379 bp of mtDNA (COI). Numbers at tips represent the X. zosterops clade from which the individual was collected. Nodes labeled with corrected and p-distance (in parentheses) divergences and with nodal support (MP/ML/PP, *=100/100/1.0). Map shows geographic distribution of Myrsidea samples.
Internal pie charts represent proportion of Myrsidea collected from each of the four X. zosterops mtDNA clades. Numbers next to pie charts are sample sizes. || DOI: 10.1002/ece3.1639
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Abstract
The merger of formerly isolated lineages is hypothesized to occur in vertebrates under certain conditions. However, despite many demonstrated instances of introgression between taxa in secondary contact, examples of lineage mergers are rare. Preliminary mtDNA sequencing of a Malagasy passerine, Xanthomixis zosterops (Passeriformes: Bernieridae), indicated a possible instance of merging lineages. We tested the hypothesis that X. zosterops lineages are merging by comparing mtDNA sequence and microsatellite data, as well as mtDNA sequence data from host-specific feather lice in the genus Myrsidea (Phthiraptera: Menoponidae). Xanthomixis zosterops comprises four deeply divergent, broadly sympatric, cryptic mtDNA clades that likely began diverging approximately 3.6 million years ago. Despite this level of divergence, the microsatellite data indicate that the X. zosterops mtDNA clades are virtually panmictic. Three major phylogroups of Myrsidea were found, supporting previous allopatry of the X. zosterops clades. In combination, the datasets from X. zosterops and its Myrsidea document a potential merger of previously allopatric lineages that likely date to the Pliocene. This represents the first report of sympatric apparent hybridization among more than two terrestrial vertebrate lineages. Further, the mtDNA phylogeographic pattern of X. zosterops, namely the syntopy of more than two deeply divergent cryptic clades, appears to be a novel scenario among vertebrates. We highlight the value of gathering multiple types of data in phylogeographic studies to contribute to the study of vertebrate speciation.
Keywords: Birds; despeciation; ectoparasites; Madagascar; microsatellites
Conclusion
In addition to contributing to the study of vertebrate speciation, particularly in birds, this work adds to limited data concerning avian phylogeography on Madagascar. The focus of most phylogeographic studies on Madagascar has been amphibians, reptiles, or mammals, with only four utilizing extensive population-level sampling in birds (Fuchs et al. 2007, 2013; Cruaud et al. 2011; Goodman et al. 2011). This study represents the densest and largest sampling yet presented for a Malagasy endemic bird and the first for a species within one of Madagascar's endemic avian radiations. Although bird communities show differences between lowland and montane forests, this differentiation between habitats has not been suggested to play a direct role in bird diversification on the island. Studies on other vertebrates have highlighted cryptic taxa geographically split by elevation in humid forests (e.g., Olson et al. 2004), but X. zosterops provides the first example of this biogeographic pattern in birds.
As well as being informative about avian biogeography in Madagascar, this study illustrates the importance of lowland humid forest to preserving extant biodiversity on the island. This has been highlighted in other vertebrate taxa, but it has been underemphasized in birds. Low-elevation forests in the central east and southeast have not received attention as a center of endemism in birds, but the X. zosterops results show their importance. Further phylogeographic studies on Malagasy birds may yet uncover similar patterns and unknown cryptic taxa.
Finally, we highlight the value of gathering multiple types of data in phylogeographic studies to contribute to the study of vertebrate speciation. In this instance, data from mtDNA, nuclear DNA, and ectoparasites were necessary to better understand the complicated evolutionary history of X. zosterops. We also emphasize the importance of sampling across a taxon's distribution to provide greater insight into the biodiversity of a region and to reveal unknown patterns of regional endemism. These aspects contribute to more accurate and comprehensive biogeographic theories and provide important details for developing conservation programs.
Nicholas L. Block, Steven M. Goodman, Shannon J. Hackett, John M. Bates and Marie J. Raherilalao. 2015. Potential Merger of Ancient Lineages in A Passerine Bird discovered based on Evidence from Host-Specific Ectoparasites.
Ecology and Evolution. 5(17); 3743–3755.
DOI:
10.1002/ece3.1639
