In new research, ornithologists from Drexel University, the Delaware Museum of Nature & Science, and Burke Museum of Natural History and Culture conducted a taxonomic revision of the Catharus fuscater complex, a group of songbirds with a broad montane distribution in Central and South America.
They split Catharus fuscater into seven different species — including a newly-described species from eastern Panamá — and four subspecies.
“Genetic data have repeatedly confirmed the primary role of geographic barriers in the speciation process,” said lead author Matthew Halley and his colleagues.
“However, there is little consensus about where on the ‘speciation continuum’ to draw the line, between species and subspecies, when dealing with closely related taxa distributed on opposite sides of potential gene-flow barriers.”
“In the Neotropical highlands, hundreds of polytypic bird species have populations distributed across multiple mountain chains, which are isolated by deep river valleys, and adjacent populations may have divergent phenotypes and/or may not be phylogenetic sisters.”
“Describing and classifying this extraordinary diversity is necessary for conservation efforts, and to inform studies of the evolutionary origins and maintenance of avian biodiversity.”
“However, the process of integrntive taxonomy is not straightforward because of ideological conflicts related to species concepts and their application, and the need for broad geographic sampling of multiple traits.”
In their research, the researchers focused on the slaty-backed nightingale-thrush Catharus fuscater complex.
“The Catharus fuscater complex is composed of several disjunct populations that inhabit cloudy mountain rainforests, ranging from Costa Rica to Bolivia,” they explained.
“These birds are shy and more often heard than seen. Their song is a series of sweet, musical whistles.”
To document their differences, the scientists sequenced DNA from multiple populations, studied physical features like plumage color, iris color and bill color, and analyzed differences in their vocalizations.
They identified 10 genetically distinct populations that have been evolving independently for multiple glacial cycles.
Molecular clock suggests most lineages diverged in Early Pleistocene / Late Pliocene.
Populations were divergent in the acoustic structure of three different call types, which are presumed to be innately acquired (i.e., not learned), and there were subtle differences among populations in song structure, which is presumably learned.
“We propose an integrative taxonomic revision that recognizes seven species in the complex — including the Darién nightingale-thrush (Catharus arcanus), a newly described species from eastern Panama — and four subspecies, of which two — Catharus opertaneus tenebris and Catharus berlepschi nebulus — are newly described,” the scientists said.
Their paper was published in the September 2023 issue of the Zoological Journal of the Linnean Society.
Matthew R. Halley et al. 2023. Integrative taxonomy reveals hidden diversity in the Catharus fuscater (Passeriformes: Turdidae) complex in Central and South America. Zoological Journal of the Linnean Society 199 (1): 228-262; doi: 10.1093/zoolinnean/zlad031
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This article by Natali Anderson was first published by Sci.News on 16 October 2023. Lead Image: The slaty-backed nightingale-thrush (Catharus fuscater) in Costa Rica. Image credit: Simon Pierre Barrette / CC BY-SA 4.0 Deed.