A Test of the Long‐Term Efficiency of Genetic Rescue With <scp>Drosophila melanogaster</scp>

Genetic rescue is considered a promising but underutilised conservation strategy to mitigate inbreeding depression and restore genetic diversity. Yet, empirical evidence supporting its long-term efficacy is limited to studies investigating short-term effects. Here, we conducted an experiment with Drosophila to test the long-term efficiency of genetic rescue across generations. A wild population was captured to found a genetically diverse mass-bred base population (BP) in the laboratory. Smaller populations of 50 individuals each (N50) were then founded from the BP and maintained for 31 generations. Three sets of lines of eight individuals each were founded from these N50 populations: non-rescued (control), rescued with BP males, and rescued with N50 males. These lines were maintained for 33 generations. Pupae productivity analysis showed substantial purging in N50 populations and adaptation to laboratory conditions in the BP. Rescued-BP lines showed a higher productivity and lower extinction rates compared to non-rescued lines. Whole-genome sequencing of individuals from a non-rescued line and a rescued-BP line revealed fewer deleterious alleles, lower genetic diversity, and higher inbreeding in the rescued line, suggesting efficient rescue. Our results enlighten the importance of introducing new genetic variation allowing for adaptation to increase survival even in small populations despite the simultaneous introduction of an inbreeding load, particularly when facing global changes affecting environmental conditions of both donor and recipient populations.