Integrative phylogeography and ecological niche analysis reveal insight into the evolutionary history and taxonomy of the Black-throated Gray Warbler (Setophaga nigrescens)/Filogeografia integrativa y analisis de nicho ecologico revelan una perspectiva en la historia evolutiva y la taxonomia de la reinita Setophaga nigrescens

The Black-throated Gray Warbler (Setophaga nigrescens) is a migratory songbird with a widespread and continuous distribution in the North American West. Previously published morphological data support the designation of 2 putative subspecies based on subtle differences in plumage and song; however, whether these patterns are clinal or discrete has yet to be determined. Furthermore, given that patterns of morphological variation occur across multiple distinct habitats and geographical boundaries, underlying population genetic structure may be present. To investigate this question and explore the evolutionary history of S. nigrescens, we conducted the first range-wide phylogeographic analysis of this species using genetic (mitochondrial DNA [mtDNA], ND2 gene sequences), morphological (body measurements), and environmental (niche modeling) data. Overall, our results identified 2 major mtDNA clades. One clade occurs east of the Cascade-Sierra ranges throughout the southwestern, Great Basin, and Rocky Mountain regions in North America (Interior clade), while a second widespread clade is comprised of birds that span the Pacific Northwest, and also across the Great Basin and southwest into the Rocky Mountains (Coastal clade). Divergence time estimates suggest a Pleistocene epoch vicariance event. Environmental niche models predict habitat modification and fragmentation from glacial-interglacial cycles, which were frequent over the Pleistocene. Range expansion northwards following the Last Glacial Maximum was identified from neutrality tests and shifts in suitable habitat from the Mid-Holocene to present-day conditions, where both clades arc likely experiencing secondary contact. We found support for nonequivalent environmental niches among both clades based on a spatial analysis of environmental variables, with the Coastal clade showing greater tolerance to both temperate and xeric climatic conditions across the North American West; however, the environmental space occupied by both clades was more similar to each other than expected by chance. High levels of geographic overlap and a lack of discrete patterns in morphology suggest few contemporary reproductive barriers to gene flow. Received 12 July 2023. Accepted 27 February 2024. Key words: gene tree, mitochondrial DNA, morphology, niche divergence, niche modeling, Pleistocene vicariance, subspecies delimitation. La reinita Setophaga nigrescens es un ave canora migratoria con una distribucion amplia y continua en el Oeste Norteamericano. Datos morfologicos previamente publicados apoyan la denominacion de 2 subespecies putativas basadas en diferencias sutiles en plumaje y canto; sin embargo, aun no se determina si esos patrones son cunales o discretos. Ademas, dado que los patrones de variacion morfologica ocurren en multiples habitats separados con limites geograficos definidos, podria estar presente una estructura poblacional genetica subyacente. Para estudiar esta pregunta y explorar la historia evolutiva de 5. nigrescens, condujimos el primer analisis filogenetico de todo el rango de distribucion de esta especie usando datos geneticos (ADN mitocondrial [mtDNA], secuencias geneticas ND2), morfologicos (medidas corporales) y ambientales (modelamiento de nicho). En general, nuestros resultados identificaron 2 ciados mayores de mtDNA. Un ciado se encuentra en las cordilleras Cascade-Sierra hacia el sudoeste y las regiones de Great Bassin y Rocky Mountain en Norte America (ciado Interior), mientras que un segundo ciado se compone de aves que se enceuntran en el Pacifico noroeste, ademas de a traves del Great Bassin y el sudoeste de las Rocky Mountains (ciado Costero). Los tiempos de divergencias estimados sugieren un evento de vicarianza en la epoca del Pleistoceno. Modelos de nicho ambiental predicen una modificacion y fragmentacion del habitat durante ciclos interglaciales, que eran frecuentes en el Pleistoceno. Una expansion de rango hacia el norte a partir del Ultimo Maximo Glacial frie identificada de pruebas de neutralidad y cambios de habitat favorables de condiciones del Holoceno medio a las actuales, donde ambos ciados posiblemente experimentaron contacto secundario. Encontramos apoyo para nichos ambientales no equivalentes entre ambos ciados basados en el analisis especial de variables ambientales, donde el ciado Costero mostro mayor tolerancia tanto a temperatura como a condiciones climaticas xericas a traves del Oeste Norteamericano; sin embargo, el espacio ambiental ocupado por ambos ciados era mas similar entre ellos que lo esperado por el azar. Altos niveles de sobrelapamiento geografico y una falta de patrones discretos morfologicos sugieren pocas barreras reproductivas contemporaneas al flujo genico. Palabras clave: ADN mitocondrial, arbol genetico, delimitacion de subespecies, divergencia de nicho, modelamiento de nicho, morfologia, vicarianza en el Pleistoceno.
Evolutionary biologists have long been interested in investigating how historical and contemporary processes have influenced patterns of biodiversity across the globe. In particular, the historical events associated with Pleistocene glaciations [...]