Escaping bottlenecks: The demographic path to genetic recovery in koalas (Phascolarctos cinereus)
Summary
Population bottlenecks can lead to evolutionary dead ends by eroding genetic diversity and intensifying inbreeding. Although theory predicts possible escape routes, direct observations of this process are rare. Using whole-genome data from 418 koalas, we found that populations with higher genetic diversity harbored the greatest mutational loads and had declining effective population sizes (Ne), whereas historically bottlenecked but recovering populations displayed reduced mutational load,
Content
# Escaping bottlenecks: The demographic path to genetic recovery in koalas (Phascolarctos cinereus)
*Published: 2026 Mar 5*
Population bottlenecks can lead to evolutionary dead ends by eroding genetic
diversity and intensifying inbreeding. Although theory predicts possible escape
routes, direct observations of this process are rare. Using whole-genome data
from 418 koalas, we found that populations with higher genetic diversity
harbored the greatest mutational loads and had declining effective population
sizes (Ne), whereas historically bottlenecked but recovering populations
displayed reduced mutational load, exhibited increasing Ne, and regenerated new,
rare variants. We concluded that this pattern was due to rapid demographic
expansion, which reshuffled genetic variation through recombination and affected
Ne more quickly than it did conventional diversity metrics. Our findings suggest
that recovery of bottlenecked populations can occur through rapid demographic
growth and that this can reestablish evolutionary potential in threatened
populations.
DOI: 10.1126/science.adz1430