Abstract
The Southwestern Willow Flycatcher (Extimus traillii extimus) is an endangered subspecies of the Willow Flycatcher (Extimus traillii) and breeds exclusively in the dwindling riparian habitats in Southwestern US. The northern border between the southwestern subspecies and the subspecies to the north, E. t. adastus, isn’t clear because populations are not continuous along the border and environmental conditions like temperature and elevation differ. Introgression zones are areas where interbreeding between subspecies occurs when there is no physical barrier separating them. Our research objective was to see if subspecies breeding populations were consistent with the boundary lines and if there are zones of introgression. We genotyped blood samples from 13 breeding population of willow flycatchers at sites near the subspecies border in Arizona, Nevada, and Utah. We used STRUCTURE (Version 2.3.3) to determine the number of distinct genetic populations and Rubias (Version 0.3.0) to assign each individual to a known genetic cluster. The northern sites which are in the predicted range of E. t. adastus were assigned to a different population than individuals from the southern sites within the E. t. extimus range, as expected. Most individuals from both the southern and northern sites were assigned to the Southwestern genetic cluster. One site, Meadow Valley Wash, which is near the subspecies border was assigned to a third genetic population, though it was still in the E. t. adastus predicted range and individuals there were assigned to four different genetic clusters. Our results from STRUCTURE and Rubias didn’t reveal a conclusive boundary, but Meadow Valley Wash appears to be an introgression zone between four different genetic clusters. Future research should focus on determining ecological factors that are most important to the distribution of the endangered subspecies and for Meadow Valley Wash.
Included in
Introgression Zones and Boundary Lines between Breeding Populations of Two Subspecies of Willow Flycatcher
The Southwestern Willow Flycatcher (Extimus traillii extimus) is an endangered subspecies of the Willow Flycatcher (Extimus traillii) and breeds exclusively in the dwindling riparian habitats in Southwestern US. The northern border between the southwestern subspecies and the subspecies to the north, E. t. adastus, isn’t clear because populations are not continuous along the border and environmental conditions like temperature and elevation differ. Introgression zones are areas where interbreeding between subspecies occurs when there is no physical barrier separating them. Our research objective was to see if subspecies breeding populations were consistent with the boundary lines and if there are zones of introgression. We genotyped blood samples from 13 breeding population of willow flycatchers at sites near the subspecies border in Arizona, Nevada, and Utah. We used STRUCTURE (Version 2.3.3) to determine the number of distinct genetic populations and Rubias (Version 0.3.0) to assign each individual to a known genetic cluster. The northern sites which are in the predicted range of E. t. adastus were assigned to a different population than individuals from the southern sites within the E. t. extimus range, as expected. Most individuals from both the southern and northern sites were assigned to the Southwestern genetic cluster. One site, Meadow Valley Wash, which is near the subspecies border was assigned to a third genetic population, though it was still in the E. t. adastus predicted range and individuals there were assigned to four different genetic clusters. Our results from STRUCTURE and Rubias didn’t reveal a conclusive boundary, but Meadow Valley Wash appears to be an introgression zone between four different genetic clusters. Future research should focus on determining ecological factors that are most important to the distribution of the endangered subspecies and for Meadow Valley Wash.