Assisted gene flow from outcrossing shows the potential for genetic rescue in an endangered salmon population

Abstract

Abstract Genetic rescue has emerged as an important tool to prevent extinction and improve fitness of declining populations. In principle, genetic rescue increases genetic variation in a population through translocation of unrelated individuals from an outside source population. Genetic rescue remains uncommon in conservation management due to concerns about the risk of outbreeding depression. Lack of data evaluating success of genetic rescue interventions has hampered willingness to use this technique to improve the genetic viability of inbred, bottlenecked populations. Here, we evaluate the success of a genetic rescue intervention within the endangered Central California Coast Coho Salmon Evolutionarily Significant Unit using ∼17 years of genetic and demographic data, including pre‐ and postoutcrossing with fish from a nearby watershed. We assessed fitness of outcrossed F1 and F2 progeny in a captive setting, and then used mark–recapture to estimate survival of juveniles released into streams. We found that outcrossing decreased relatedness among adults, and their hybrid progeny had higher fitness in both captive and stream settings relative to nonhybrids. Importantly, we did not observe evidence of outbreeding depression in either the F1 or F2 generations. This study highlights that genetic rescue can be a useful tool in the conservation of imperiled salmonids.

Keywords

• coho salmon
• conservation
• endangered species
• gene flow
• genetic rescue
• inbreeding depression