Data from: The power of evolutionary rescue is constrained by genetic load

Extinction risk of small isolated populations in changing environments can be reduced by rapid adaptation and subsequent growth to larger, less vulnerable sizes. Whether this process, called evolutionary rescue, is able to reduce extinction risk and sustain population growth over multiple generations is largely unknown. To understand the consequences of adaptive evolution as well as maladaptive processes in small isolated populations, we subjected experimental Tribolium castaneum populations founded with 10 or 40 individuals to novel environments, one more favorable, and one resource poor, and either allowed evolution, or constrained it by replacing individuals one-for-one each generation from a non-adapting large population to minimize both adaptive and non-adaptive evolutionary processes. After 8 generations we mixed a subset of surviving populations to facilitate gene flow, allowing us to estimate heterosis by comparing performance of mixed to unmixed groups and estimate potential effects of genetic load. Evolution reduced extinction rates, and increased population sizes in the first four to five generations compared to populations where evolution was constrained. Performance of evolving populations subsequently declined. Admixture restored their performance, indicating that high genetic load, which may have overwhelmed the beneficial effects of adaptation, was relieved with outcrossing. Our results show the immediate and substantial power of evolution in reducing extinction risk and increasing population sizes, but indicate that relying solely on adaptation from standing genetic variation may not provide long-term benefits to small isolated populations, and that active management facilitating gene flow may be necessary for longer-term persistence.