Fitness benefits of genetic rescue despite chromosomal differences in an endangered pocket mouse.

Two-thirds of Earth's species have undergone population declines, leaving many vulnerable to genomic erosion and inbreeding depression. Genetic rescue can boost the fitness of small populations, but perceived risks of outbreeding depression can limit its use. We quantified these trade-offs in hundreds of endangered Pacific pocket mice (Perognathus longimembris pacificus) by combining whole-genome sequences with fitness data. The impacts of genomic erosion in remnant populations were reversed in an admixed breeding program, suggesting the potential benefits of genetic rescue. However, differences in chromosome numbers increase the risk of genetic incompatibilities. Fitness analyses suggested that although admixed karyotypes may have reduced fertility, non-admixed mice with low heterozygosity and high genetic load had even lower fitness, pointing to a greater risk of extinction if populations remain isolated. Editor's summary: As habitats become increasingly fragmented and populations continue to decline, more and more species face genetic threats associated with small population sizes. Although introduction of individuals from related populations can introduce genetic variability and thus "rescue" populations with low heterozygosity and high inbreeding, such introductions can also lead to outbreeding depression. Looking at populations of endangered pocket mice, Wilder et al. found that breeding of individuals with different karyotypes did lead to lower fitness; however, their fitness was still higher than those breeding with closely related individuals. —Sacha Vignieri [ABSTRACT FROM AUTHOR]