Sexual selection matters in genetic rescue, but productivity benefits fade over time; a multi-generation experiment to inform conservation

Abstract

Globally, many species are threatened by population decline as a result of anthropogenic changes. Smaller populations are at greater risk of fragmentation, genetic isolation, and eventual inbreeding depression. As genetic load is expressed and adaptive potential is lost, risk of population extinction greatly increases. Genetic rescue, the controlled introduction of genetic variation, is a method used to potentially relieve such effects in small populations. However, without understanding how the characteristics of rescuers impact rescue attempts, in both the short- and long-term, interventions run the risk of being sub-optimal, or even counterproductive. Here, we use the Red Flour Beetle (Tribolium castaneum) to experimentally test the impact of rescuer sex, and sexual selection background, on population productivity. We record the impact of genetic rescue on population productivity in 24/36 replicated populations for ten generations following intervention. We find little or no impact of rescuer sex on the efficacy of rescue (P = 0.926) but show that a background of elevated sexual selection makes individuals more effective rescuers (P = 0.024). Importantly, in both experiments, rescue effects on productivity diminish 6-10 generations after the rescue event. Our results confirm that the efficacy of genetic rescue can be influenced by characteristics of the rescuers and, for the first time, that the level of sexual selection in the rescuing population is an important factor. We show that any increase in fitness associated with rescue may only last for a limited number of generations, suggesting implications for conservation policy and practice.