Genetic rescue and the maintenance of native ancestry

Abstract

Genetic rescue (GR) is an important tool in conservation biology for the management of highly inbred populations. However, GR comes at a potential cost: the reduction in native genomic content. The degree to which adaptive evolution for new immigrant alleles lead to complete or partial replacement of the native genome, depends on recombination rates, genome size, effective population sizes, and distributions of fitness effects. As one of the most well-studied examples of an inbred species that exchanged genetic material with a less inbred species, we use Neanderthals and humans as an example. Using simulations, we show that for parameters realistic for these species, the increase in fitness caused by GR is mirrored by an almost proportional reduction in the fraction of the native genome preserved. The main reason is that the effect of selection will be strongest in the first few generations during which time there is only little break-up, by recombination, of the immigrant chromosomes. We also show that in the presence of a strong and short-lived bottleneck with recessive mutations, GR leads to a stronger increase in fitness than in the presence of additive effects or a more prolonged bottleneck.