Molecular systematics and biogeography of Antillean Thrashers, Tremblers, and Mockingbirds (Aves: Mimidae)

Auk, The, Jan 2001 by Hunt, Jeffrey S, Bermingham, Eldredge, Ricklefs, Robert E

ABSTRACT.-We constructed phylogenetic hypotheses for Greater and Lesser Antillean Mimidae, including five endemic species of tremblers and thrashers that represent the best plausible example of an avian radiation within the Lesser Antilles. Phylogenetic relationships were inferred from analysis of 3,491 base pairs (bp) of mitochondrial DNA (mtDNA) and roughly 780 bp of the nuclear-encoded myoglobin gene. We used a subset of mtDNA gene sequences and pcrRFLP analysis to evaluate the phylogeographic relationships among individuals representing island populations of the Brown and Gray tremblers (Cinclocerthia ruficauda and C. gutturalis), Pearly-eyed Thrasher (Margarops fuscatus), Scaly-breasted Thrasher (Margarops fuscus), and Antillean and continental populations of the Tropical (Mimus gilvus) and Northern mockingbirds (Mimus polyglottos). Phylogeographic analysis distinguished three strongly differentiated mtDNA Glades among tremblers, as well as distinct southern (St. Lucia and Martinique) and northern (Dominica to Montserrat) mtDNA lineages of the Scaly-breasted Thrasher. Minor geographic subdivision was also observed between continental and Antillean populations of the Tropical Mockingbird. Phylogenetic analyses of species-level Mimidae relationships that are based on mtDNA and nuclear sequences provide strong support for the monophyly and Antillean origin of a clade that consists of the tremblers, Pearly-eyed Thrasher, and Scaly-breasted Thrasher, but reject the monophyly of the genus Margarops. Phylogenetic analysis cannot confirm the monophyly of all endemic Antillean mimids because of the apparently contemporaneous diversification of the Antillean White-breasted Thrasher (Ramphocinclus brachyurus) with the continental Gray Catbird (Dumetella carolinensis) and Black Catbird (Melanoptila glabrirostris). However, an insertion and a deletion in the myoglobin intron 2 sequence support grouping the West Indian thrashers and tremblers, from which we infer that the endemic Lesser Antillean mimids are an indigenous radiation. Assuming a constant mtDNA clock for the Mimidae, the splitting of the Northern and Tropical mockingbird lineages is roughly contemporaneous with the separation of the three trembler Glades, as well as the two Scaly-breasted Thrasher Glades. Application of a mitochondrial DNA clock ticking at 2% sequence divergence per million years (Ma), suggests that the history of the endemic thrasher and trembler lineage in the West Indies extends back about 4 Ma, and the three distinct Glades of tremblers split about 2 Ma ago. Received 12 August 1999, accepted 8 August 2000.

AMONG BIRDS of the West Indies, few endemic radiations have resulted in sympatric daughter species, and certainly none are comparable to the radiations of Hawaiian honeycreepers (Drepanidinae) and Galapagos finches (Geospizinae). In the Lesser Antillean avifauna, the three endemic Mimidae genera Margarops, Ramphocinclus, and Cinclocerthia constitute the best plausible example of an autochthonous radiation. The five currently recognized species ic thrashers and tremblers, our phylogenetic analysis includes the migratory Gray Catbird (Dumetella carolinensis) of North America, the Black Catbird (Melanoptila glabrirostris) of northern Central America, the Blue Mockingbird (Melanotis caerulescens) of Mexico, and three Caribbean-basin species of mockingbird (Mimus; Fig. 2). Our taxonomic sampling of the Mimidae included Toxostoma (.T rufum and T. cinereum) and Oreoscoptes montanus, but our initial molecular-systematic results indicated that Dumetella and Melanoptila are closer relatives of the Antillean-endemic thrashers and tremblers. Accordingly, we deleted Toxostoma and Oreoscoptes from the present analysis.

The second objective of this study was to provide a phylogeographic description of each West Indian mimid species for which we have moderate samples and broad geographic representation. These species are the Scaly-breasted Thrasher (Margarops fuscus), Pearly-eyed Thrasher (M. fuscatus), Brown Trembler (Cinclocerthia ruficauda), Gray Trembler (C. gutturalis), and Tropical and Northern mockingbirds. Finally, our analyses provide a molecular-systematic perspective on the taxonomic status of Cinclocerthia and Margarops and on the evolutionary status of subspecies in both these genera.

We sequenced the full mitochondrial ATP synthase 6 and 8 genes for two or more individuals representing all species and multiple geographic populations of Lesser Antillean mimids. Phylogenetic analysis of the ATPase sequences formed the basis of our biogeographic appraisal of the two Margarops species, Cinclocerthia, and the two widespread Mimus species. Mitochondrial genotypes were also determined for additional Margarops fuscus and M. fuscatus individuals using RFLP analysis of PCR-amplified ATPase fragments. Following our initial phylogenetic analyses of Caribbean mimids, we selected 11 species (including outgroups) and a second genetically differentiated population of C. ruficauda for a more detailed molecular-systematic analysis. Our phylogenetic hypothesis for Caribbean mimid relationships is based on direct sequence analysis of 3,491 base pairs (bp) of mitochondrial DNA (mtDNA) and approximately 780 bp that represent the nuclear-encoded myoglobin intron 2 and short regions of flanking exons 2 and 3.