Geographic variability of hybridization between red-breasted and red-naped sapsuckers

AbstractHybrid zones reveal the strength of reproductive isolation between populations undergoing speciation and are a key tool in evolutionary biology research. Multiple replicate transects across the same hybrid zone offer insight into the dynamics of hybridization in different environments, clarifying the role of extrinsic forces on the speciation process. Red-breasted and red-naped sapsuckers (Sphyrapicus ruber and S. nuchalis) have a long zone of contact over approximately 1,600 km from central British Columbia, Canada to central California, USA. We used Genotyping-by-Sequencing data from three independent sapsucker hybrid zone transects to compare hybridization dynamics between these species under variable geoclimatic conditions. We generated geographic clines of the genomic data to compare hybrid zone widths and used Random Forest models and linear regression to assess the relationship between climate and sapsucker ancestry along each transect. Our results show variation in the directionality of backcrossing, often indicative of moving hybrid zones. We note variable cline widths among transects, indicating differences in selection maintaining hybrid zone dynamics. Furthermore, Random Forest models identified different variables in close association with sapsucker ancestry across each transect. These results indicate a lack of repeatability across replicate transects and a strong influence of local environment on hybrid zone dynamics., MethodsPlease see the Natola et al. 2022 Evolution paper for methodology, and the README.md and tassel_filter_admixture_scripts.txt files for additional details. , Usage notesThe README contains a list of files used and the figures/contexts they appear in the publication text. The file tassel_filter_admixture_scripts.txt outlines steps to convert raw Illumina GBS reads to genotype files in the program Tassel, filter reads, and run ADMIXTURE on a remote server. Raw Illumina fastq.gz files can be downloaded from NCBI's Sequence Read Archive (SRA BioProject numbers PRJNA326842 - Northern, PRJNA896571 - Central, PRJNA521235 - Southern).