148 Genomic Analysis of Male Reproductive Skew in Bornean and Sumatran Orangutans

Faculty Mentor: Timothy Webster (Anthropology, University of Utah)

Bornean and Sumatran orangutans exhibit pronounced differences in their social behavior, which impacts the extent to which males in these species can monopolize reproductive success. This male reproductive skew has different effects on genetic diversity on the X chromosome compared to the autosomes, providing us with a genomic record documenting how variation in sociality across orangutans has shaped patterns of sexual selection. We analyzed sixteen publicly published genomes from Bornean and Sumatran orangutans to compare ratios of genetic diversity between the species. After removing sites impacted by selection and correcting for male mutation bias, we found that Sumatran orangutans (autosomal mean: 0.0059; X/A ratio: 0.767) and Bornean orangutans (autosomal mean: 0.006; X/A ratio: 0.794) had comparable autosomal diversity and comparable ratios of X chromosome to autosomal diversity. While these results do not support our hypothesis of greater reproductive skew in Sumatran orangutans, they could be affected by other demographic phenomena. We are therefore currently working on modeling X/A diversity ratios in the context of the complete demographic history of both species. Our results inform our understanding of both male reproductive skew in orangutans and how variation in environmental productivity and sociality shape male reproductive strategies across primates more generally.