Genetic purging of strongly deleterious mutations underlies black-necked crane's unusual escape from an extinction vortex

Many species are undergoing rapid demographic declines, necessitating an examination of the resulting genetic impacts. The prevailing small population paradigm posits an elevated genetic load and extinction risk. However, instances of fast recovery from severe population bottlenecks suggest alternative outcomes. To investigate this issue, we performed a population genomic analysis on the black-necked crane, analyzing 42 modern and 11 historical genomes. This study revealed substantial evidence of large-effect allele purging underlying the unexpectedly rapid population recovery following an abrupt bottleneck during the 1980s. Nevertheless, forward simulations supposing a prolonged bottleneck (e.g., five generations) predicted a reversion with negative prospects, implying that rapid population recovery served as both the cause and consequence of the species escaping from an extinction vortex. These findings shed light on a potential positive microevolutionary response to current widespread population collapses and underscore the urgency of implementing active and effective conservation strategies to reverse this trend before it becomes irreversible.