High inter-population connectivity and occasional gene flow between subspecies improves recovery potential for the endangered Least Bell's Vireo

Increasingly, genomic data are being used to supplement field-based ecological studies to help evaluate recovery status and trends in endangered species. We collected genomic data to address 2 related questions regarding the Least Bell's Vireo (Vireo bellii), an endangered migratory songbird restricted to southern California riparian habitat for breeding. First, we sought to delineate the range limits and potential overlap between Least Bell's Vireo and its sister subspecies, the Arizona Bell's Vireo, by analyzing samples from the deserts of eastern California, southwestern Nevada, Utah, and Arizona. Second, we evaluated genetic structure among Least Bell's Vireo populations in coastal California and estimated effective population size. Clustering analyses based on 10,571 single-nucleotide polymorphisms (SNPs) from 317 samples supported 2 major groups that aligned closely to the previously defined subspecies ranges. The first cluster included birds in the Central Valley, all coastal drainages, and westernmost deserts of California, with no further sub-structuring among coastal drainages. Almost all birds from the Amargosa River in eastern California and eastward assigned to the second cluster; however, low levels of gene flow were detected across the subspecies groups, with greater rates of gene flow from Arizona Bell's Vireo to Least Bell's Vireo than the reverse. Admixed individuals occurred in the California deserts; and although smaller than coastal populations, desert populations may be important for maintaining and replenishing genetic diversity and facilitating the movement of potentially adaptive genes between subspecies. Within Least Bell's Vireo, local populations in coastal drainages comprised a single genetic population, with some evidence of close relatives distributed across drainages, suggesting that these could function as a well-connected metapopulation. These results are consistent with previous Least Bell's Vireo banding studies that reported high rates of dispersal among drainages. Effective population size for both subspecies was high, suggesting that adaptive potential has been maintained despite previous declines. center dot Maintenance of genetic diversity is essential for species to be able to persist and adapt to changing environmental conditions.center dot We examined dispersal and genetic diversity in the endangered Least Bell's Vireo, a migratory songbird dependent upon riparian habitat for breeding, and in its closest subspecies, the Arizona Bell's Vireo.center dot Analysis of blood samples collected from vireos throughout southern California, Nevada, Utah, and Arizona revealed that in general birds from the Mojave Desert west are Least Bell's Vireos, while those to the east are Arizona Bell's Vireos. However, we found low levels of gene exchange across subspecies and that 9% of birds in the desert region were of mixed ancestry.center dot Occasional dispersal and successful breeding across the California desert could be a source of novel adaptive genetic variation that could increase the capacity of Least Bell's Vireo to adapt to climate change across its range. Cada vez mas, los datos genomicos se utilizan para complementar estudios ecologicos basados en el campo y ayudar a evaluar el estado de recuperacion y las tendencias en especies en peligro. Recolectamos datos genomicos para abordar dos preguntas relacionadas a Vireo bellii pusillus, un ave canora migratoria en peligro de extincion restringida para su reproduccion al habitat ribereno del sur de California. En primer lugar, buscamos delinear los limites de los rangos de distribucion y la posible superposicion entre V. b. pusillus y su subespecie hermana, V. b. arizonae, mediante el analisis de muestras de los desiertos del este de California, suroeste de Nevada, Utah y Arizona. En segundo lugar, evaluamos la estructura genetica entre las poblaciones de V. b. pusillus en la costa de California y estimamos el tamano efectivo de la poblacion. Los analisis de agrupamiento basados en 10.571 polimorfismos de nucleotido unico provenientes de 317 muestras respaldaron dos grupos principales que se alinearon estrechamente con los rangos previamente definidos de las subespecies. El primer grupo incluyo las aves en el Valle Central, todos los drenajes costeros y los desiertos mas occidentales de California, sin una subdivision adicional entre los drenajes costeros. Casi todas las aves del Rio Amargosa en el este de California y hacia el este se asignaron al segundo grupo; sin embargo, se detectaron bajos niveles de flujo genico entre los grupos de subespecies, con tasas de flujo genico mas altas desde V. b. arizonae hacia V. b. pusillus que al reves. Se encontraron individuos mestizos en los desiertos de California; y aunque mas pequenas que las poblaciones costeras, las poblaciones del desierto pueden ser importantes para mantener y reponer la diversidad genetica y facilitar el movimiento de genes potencialmente adaptativos entre las subespecies. Dentro de V. b. pusillus, las poblaciones locales en los drenajes costeros constituyeron una sola poblacion genetica, con algunas evidencias de parientes cercanos distribuidos a traves de los drenajes, lo que sugiere que estos podrian funcionar como una metapoblacion bien conectada. Estos resultados son consistentes con estudios anteriores de anillado de V. b. pusillus que informaron altas tasas de dispersion entre los drenajes. El tamano efectivo de la poblacion para ambas subespecies fue alto, lo que sugiere que el potencial adaptativo se ha mantenido a pesar de las disminuciones previas.