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.
Highlights
The widespread merger of formerly isolated lineages – sometimes referred to as despeciation or speciation in reverse – is hypothesized to be possible for vertebrates under certain conditions, which often involve human alteration of habitat or introduction of non-native species (Rhymer and Simberloff 1996; Seehausen 2006; Seehausen et al 2008)
The mtDNA sequences lack stop codons and indels within coding regions and double peaks in sequence chromatograms, and phylogenetic results of all three mtDNA markers are congruent when analyzed separately, both suggesting that the X. zosterops phylogeography is not the result of numts
In addition to contributing to the study of vertebrate speciation, in birds, this work adds to limited data concerning avian phylogeography on Madagascar
Summary
The widespread merger of formerly isolated lineages – sometimes referred to as despeciation or speciation in reverse – is hypothesized to be possible for vertebrates under certain conditions, which often involve human alteration of habitat or introduction of non-native species (Rhymer and Simberloff 1996; Seehausen 2006; Seehausen et al 2008). Despite many documented instances of introgression between vertebrate taxa in secondary contact, examples of complete lineage mergers, as indicated by total genetic mixing, are rare. The only genetically documented examples of complete lineage mergers in vertebrates, to our knowledge, involve recently diverged lake a 2015 The Authors. Other likely instances of complete genetic mixing of previously isolated lineages have been described but have not been analyzed using genetic data (Rhymer and Simberloff 1996; Seehausen et al 1997). In all of these cases, the lineages involved are evolutionarily young, having diverged since the Pleistocene. Documenting the scope of this timescale would contribute to the understanding of vertebrate speciation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
