Incomplete reproductive isolation and strong transcriptomic signature of hybridization between sympatric sister species of salmon

Global change is altering ecosystems at an unprecedented rate. The resulting shifts in species ranges and reproductive timing are opening the potential for hybridization between closely-related species which could dramatically alter the genetic diversity, adaptive capacity, and evolutionary trajectory of interbreeding taxa. Here, we used behavioural breeding experiments, in vitro fertilization experiments, and whole-transcriptome gene expression data to assess the potential for and consequences of hybridization between Chinook and Coho salmon. We show that behavioural and gametic prezygotic barriers between socioeconomically valuable Chinook and Coho salmon are incomplete. Postzygotically, we demonstrate a clear transcriptomic response to hybridization among F1 Chinook-Coho offspring. Genes transgressively expressed within hybrids were significantly enriched with genes encoded in the nucleus but localized to the mitochindrion, suggesting a potential role for mito-nuclear incompatibiliti...