Strategic rejection of newborns is associated with substantially extended lifespan in parents and increased lifespan in well-reared offspring in owl monkeys
Parental rejection of apparently healthy newborns is widely classified as a behavioural abnormality in captive primate colonies, yet its biological significance remains unclear. In owl monkeys (Aotus nancymaae), parental rejection, defined here as cessation of nursing leading to rescue nursery rearing, is typically lethal for offspring and is transmitted across generations despite reducing offspring survival. Here, we tested whether parental rejection is associated with lifespan and reproductive differences in parents and their surviving offspring. We analysed long-term demographic records from a captive colony of 962 individuals and compared survival and reproductive outcomes between rejector and non-rejector parents using survival analyses and regression-based models. Parents who rejected offspring lived significantly longer than non-rejectors, with an average lifespan advantage of approximately 4-4.5 years in both males and females. This survival difference was concentrated during the prime reproductive period (6-20 years). Well-reared offspring of rejector parents also lived longer than offspring of non-rejectors, with a mean lifespan difference of 1.26 years. Rejector parents produced more offspring overall, but this difference was explained by extended lifespan rather than higher reproductive output per year. Analyses stratified by rejection timing showed no longevity advantage in first-birth rejectors, whereas parents rejecting later-born offspring exhibited longer survival. Together, these findings show that parental rejection is associated with longer lifespan in parents and in their well-reared offspring under captive conditions. These patterns are consistent with altered allocation of parental investment under energetic or environmental stress.