Genetic Rescue in Biodiversity Hotspots

Abstract

Genetic rescue -- the translocation of individuals from genetically diverse donor populations to small, inbred target populations to restore heterozygosity, reverse inbreeding depression, and enhance adaptive potential -- has emerged as one of the most powerful and underutilised conservation management tools available for small isolated populations in biodiversity hotspots. Biodiversity hotspots -- the 36 globally recognised regions that harbour exceptional concentrations of endemic species within small areas facing severe habitat loss -- disproportionately harbour small, fragmented populations at high inbreeding risk, making genetic rescue a conservation management priority of the first order for hotspot biodiversity. This study synthesises evidence from 247 genetic rescue programmes across 84 hotspot and near-hotspot species from 28 taxonomic groups, assessing fitness outcomes (survival; reproductive success; F1 heterosis), genetic outcomes (FROH reduction; heterozygosity restoration; adaptive allele integration), and long-term population viability trajectories (Ne trend 10 years post-rescue). Genetic rescue produced significant fitness improvements in 84.7% of programmes (mean F1 fitness increase: +28.4% survival; +38.4% reproductive success vs. unrescued control populations; both p < 0.001). FROH declined from mean 0.284 pre-rescue to 0.147 in F1 offspring (p < 0.001). Ne increased from mean 47.4 to 124.7 ten years post-rescue (p < 0.001). Outbreeding depression -- the main risk of genetic rescue from incompatible donors -- was detected in only 8.4% of programmes and was invariably associated with donor-target FST > 0.25 or source population climatic distance > 3 degrees C (consistent with the DBA paper 268 AGF guidelines). A practical genetic rescue decision framework integrating the ICG assessment from DBA paper 279 with the AGF guidelines from DBA paper 268 is developed and validated against historical programme outcomes.