| Description |
Genetic load is a relative measure of the quantity of harmful mutations within a genome, and a population's demographic history can affect this measure. Small populations that have undergone a severe bottleneck have increased inbreeding. These factors can decrease genetic diversity and fix deleterious mutations in the population, increasing the realized genetic load. In this study, we analyzed whole genome sequencing data for 17 individuals from Sumatran, Bornean, and Tapanuli orangutans. The Tapanuli orangutan is the most endangered great ape species and has the smallest population size of the three species of orangutans. We hypothesized that the Tapanuli orangutan would have both the largest relative genetic load and the greatest realized load. To compare the genetic load among these three species, we focused on three types of variants: loss of function indels, loss of function SNPs, and missense SNPs. We found that the Sumatran orangutans have the largest genetic load followed by the Tapanuli, then the Bornean. However, when examining realized load, the Bornean orangutan had the largest. These findings did not support our hypothesis but add to the growing pool of research contradicting the longstanding theory that larger effective population sizes should be associated with smaller genetic load. In the specific case of the Tapanuli orangutan, very recent population declines might not have had the chance to shape genetic load yet. Future research should include more individual genomes to further explore the connections between genetic diversity, realized genetic load, and inbreeding. |
