The extent of hybridization between bull trout (Salvelinus confluentus) and brook trout (S. fontinalis) across Alberta’s Eastern slopes

Identifying hybridization provides insight into risks associated with non-native species. Bull trout (Salvelinus confluentus), a charr native to Alberta, face population declines across their range and one risk may include hybridization with non-native brook trout (S. fontinalis). However, the extent of introgressive hybridization throughout Alberta is not well understood. Therefore, we aimed to quantify bull x brook trout hybridization in three ways: 1. the observed hybrid presence across Alberta, 2. the proportion of post-F1 hybrids (e.g., F2 and backcrossed), and 3. the hybrid proportion relative to brook trout in well-sampled watersheds. Using two panels of >1,000 diagnostic Single Nucleotide Polymorphisms, we identified 35 F1 and 7 post-F1 hybrids (n = 42 total) across 10 HUC 8 watersheds. Our findings show hybridization throughout the bull trout range, however, with few post-F1 hybrids found, little evidence of extensive hybrid introgression was observed. The misidentification rate was low (2.1%), but 20 of 25 misidentifications involved confirmed hybrids, suggesting a higher misidentification rate (47.6%). This work improves the understanding of hybridization risks on at-risk bull trout in Alberta.

Methods
Genetic information on individual Salvelinus spp. samples (n=1200) collected across Alberta's Eastern Slopes. Files are data formatted for ADMIXTURE 1.3 software analyses.