Genetic rescue benefits persist to at least the F3 generation, based on a meta-analysis

Many species have isolated, inbred populations that have a high risk of extinction from inbreeding depression. While inbreeding can be reversed by outcrossing (genetic rescue), doubts have been expressed about whether fitness benefits persist beyond the F1 generation. To address this issue, I used a meta-analysis to evaluate the effects of outcrossing of inbred populations on reproductive fitness in F1, F2 and F3 (and later) generations for population crosses screened as having a low risk of outbreeding depression. Outcrossing of inbred populations was significantly beneficial compared to the inbred parent in the F1, F2 and F3 (and later) generations, with 90.5%, 100% and 94.1% of comparisons beneficial, respectively. The median benefits of outcrossing on composite fitness (combined fecundity and survival) were 42%, 84% and 86% in the F1, F2 and F3 generations, respectively, and F2 and F3 effects were not significantly different from those in the F1. Further, pre-screening to detect possible outbreeding depression was highly effective. Consequently, outcrossing can be recommended to genetically rescue inbred populations, provided the risk of outbreeding depression has been assessed and found to be low. (C) 2015 Elsevier Ltd. All rights reserved.