Due to an extreme asymmetry in parental investment, raising the potential for sexual conflict, orangutans provide unique insights into the role of sexual conflict in male and female reproductive strategies. Sexual selection acts on reproductive strategies, selecting for strategies that increase an individual's reproductive success. Sexual conflict results when the reproductive strategies of one sex impose costs on the other. Three forms of sexual selection have been documented in orangutans—male-male competition, female choice, and sexual coercion. This dissertation asks (1) how males employ reproductive strategies to increase their likelihood of reproductive success in the face of multi-male mating by females and (2) how females employ reproductive strategies to enact female choice and increase infant survival in the face of male-male competition and sexual coercion. I investigate these two questions using genetic paternity, long-term association data, and a year of behavioral data from orangutans (Pongo pygmaeus wurmbii) in Gunung Palung National Park, West Kalimantan, Indonesia. Brown-modified Hinde Indices, initiation and termination of associations, and following data reveal that female participation is necessary to sustain longer male-female associations and females use facultative associations to employ mate choice. Genetic paternity determination found low reproductive skew, with flanged males siring more offspring than unflanged males. Investigation of female infanticide avoidance strategies showed that females with dependent offspring under age six associate with males less often than other categories of females do, and mothers decrease the distance with their offspring during associations with males. These results highlight the importance of both female choice and male-male competition in reproductive outcomes, and illustrate how facultative associations play a key role in the reproductive strategies of both male and female orangutans. Both sexes’ strategies are studied, demonstrating the dynamic co-evolution of strategies and counterstrategies. I also consider the implications of these findings for the evolution of male bimaturism. Examining orangutan mating and reproductive behaviors deepens our understanding of how sexual conflict and sexual selection have shaped their unusual mating system and broadens our understanding of sexual conflict in reproductive strategies in a species with an extreme disparity between maternal and paternal investment. / 2025-08-31T00:00:00Z