Potential merger of ancient lineages in a passerine bird discovered based on evidence from host‐specific ectoparasites

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.

Biome stability predicts population structure of a southern African aridland bird species

“…Our findings of highly admixed individuals and high levels of contemporary gene flow suggest that the population differentiation we identified is disappearing as C. caffra populations merge. Although likely quite common, “despeciation,” “ephemeral speciation,” or “speciation in reverse” has only been studied in detail in a handful of species (Block, Goodman, Hackett, Bates, & Raherilalao, 2015; Garrick et al, 2014; Grant & Grant, 2006; Kearns et al, 2018; Ruskey & Taylor, 2016; Seehausen, 2006; Taylor et al, 2006). While many of these examples may have been further along on the speciation continuum (De Queiroz, 2007) than C. caffra , most are likewise considered to be “evolutionarily young.” In some of these instances, the loss of distinctive morphotypes provided the first indication that species were merging (Grant & Grant, 2006; Taylor et al, 2006).…”

Taxonomic revision of the Square-tailed Drongo species complex (Passeriformes: Dicruridae) with description of a new species from western Africa

“…Such a phenomenon, sometimes referred to as 'despeciation' or 'speciation in reverse', detected with the use of molecular sequence data is, now more commonly uncovered in empirical datasets (e.g. Webb et al 2011;Hogner et al 2012;Block et al 2015). In these cases, populations come into secondary contact after having been isolated for some time and exchange genetic material.…”

Asymmetric Response of Costa Rican White-Breasted Wood-Wrens (Henicorhina leucosticta) to Vocalizations from Allopatric Populations

“…Genetic divergence can be used to determine species limits if the evolution of reproductive isolation is correlated with evolutionary time such that species with large genetic distances (e.g., > 4% sequence divergence in mitcochondrial DNA (mtDNA) [ 7 ]) are unlikely to experience gene flow if they come into secondary contact. However, this may not always be the case [ 8 ] and there is some evidence that the evolution of reproductive isolation is particularly slow in the tropics [ 9 ].…”