Genomic data confirms that mutation cannot restore genetic diversity lost through population bottlenecks

Toby Gregory Laszlo Kovacs , Simon Y. W. Ho, Carolyn J. Hogg, Catherine E. Grueber

Maintaining within-species genetic diversity is a critical goal of biodiversity conservation as it determines a species’ ability to adapt to environmental change. Without human intervention, isolated populations can only recover genetic diversity post-bottleneck through the accumulation of new mutations over evolutionary timescales. Using recent estimates of mutation rates from major genomic datasets across the tree of life, we modelled the recovery of genetic diversity post-bottleneck. We found that mutation rates do not affect the recovery rate of genetic diversity, which instead is determined by the effective population size (Ne). For example, regardless of the mutation rate, an isolated population with Ne = 500 that experiences a 50% reduction in heterozygosity would require ~2,300 generations to return to 95% of its pre-disturbance level. In contrast, a bottleneck can lead to a 50% reduction in heterozygosity very quickly, taking just 30 generations for bottlenecks of Ne = 20. We also demonstrate that allelic richness responds quickly following the recovery of Ne but argue that this is unlikely to correspond to the recovery of evolutionary potential. Our results reinforce that recovery via mutation alone is too slow to be effective within conservation timeframes, providing an evolutionary context to genetic diversity loss.