Conservation genomics of two endangered buntings reveal genetic diversity before and after severe population declines.

Background: Museomics utilizes historical genetic data from museum specimens to inform threatened species conservation. The Yellow-breasted Bunting (Emberiza aureola) and the Jankowski's Bunting (E. jankowskii), categorized as Critically Endangered or Endangered, respectively, have experienced population declines since the 1970s-1980s. Comparing genetic diversity changes before and after declines is crucial for refining conservation strategies.

Results: We de novo assembled genomes for both species and resequenced 29 E. aureola (16 historical pre-decline specimens from the 1930s to the 1950s) and 18 E. jankowskii (4 historical pre-decline specimens from the 1950s to the 1960s), with 45 individuals from six least-concern Emberiza species for comparison. Genetic diversity remained stable in both endangered species from the pre-decline to post-decline periods, with their overall genetic diversity levels being comparable to those of their least-concern congeners. While historically, both had large effective population sizes, E. jankowskii showed a gradual decline over 1000 generations, whereas E. aureola remained stable. Both modern populations of E. aureola and E. jankowskii exhibited a higher proportion of long runs of homozygosity (ROH) compared to their historical counterparts, indicating an increased impact of inbreeding following population declines.

Conclusions: Despite severe population declines, both species retained high genetic diversity but experienced increased inbreeding. E. jankowskii faces ongoing effective population size decline. These insights guide targeted conservation strategies, highlighting the value of museomics in understanding demographic and genetic histories.