Reproductive physiology with emphasis on endometrial cycles of woolly and uakari monkeys-A literature review

The ability of a species to withstand human impact depends on its life history characteristics, including social, ranging, and reproductive activity. The genera Lagothrix and Cacajao are more susceptible to anthropic action than small-sized primates due to their slower life histories, more restricted geographical ranges, and lower population densities. This narrative literature review aimed to gather scientific information available from the last 60 years on the reproductive biology of females of the genera Lagothrix and Cacajao. Most studies on the genus Lagothrix, mainly focused on L. lagothricha and L. l. poeppigii, present important advances on reproductive strategies, reproductive productivity, functional morphology and physiology, including seasonality, sexual cycle, gestation and fetal development in captive and free-living populations. Contrary, there is much less known about the reproductive biology of the genus Cacajao, with studies on free-living C. calvus and C. melanocephalus highlighting reproductive behavior, and basic description of the sexual cycle, gestation, and lactation. Unfortunately, the morphology of the female genital organs is only described in C. calvus, and there is still scarce information about the menstrual activity and the placenta. This literature review encourages primatologists, morphophysiologists, reproductive specialists, and ecologists to conduct comprehensive studies of these species to better understand the gaps in knowledge about reproduction, their relationship with their environment, including climatic and social variables. Understanding the integrative reproductive biology of these species will be a clue for improving the assessment of the resilience capacity of free-living populations and, consequently, establishing more appropriate management programs, and for the development of ex situ management techniques for the conservation of the species. Woolly monkeys and uakaries are vulnerable to the anthropic impacts due to their slower reproductive activity compared to other Neotropical primates. There is limited information available on the female reproductive physiology of these species. Although blood clots and endometrial desquamation were not observed, the presence of a menstrual cycle is not excluded. This highlights the importance of conducting further research on the reproduction of these primates.image This review systematizes scientific literature published in the last 60 years (1963-2023).Both genera present low reproductive performance in captivity systems.Slow reproducers and low productivity compared to small and medium-sized Neotropical primates.Limited morphophysiological knowledge for the application of reproductive biotechnology.