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. Replacement individuals spent one generation in the target novel environment before use to standardize effects due to the parental environment. After 8 generations we mixed a subset of surviving popu...