A composite menstrual cycle of captive orangutans, with associated hormonal and behavioral variability

Alternative reproductive tactics of unflanged and flanged male orangutans revisited

In many slowly developing mammal species, males reach sexual maturity well before they develop secondary sexual characteristics. Sexually mature male orangutans have exceptionally long periods of developmental arrest. The two male morphs have been associated with behavioral alternative reproductive tactics, but this interpretation is based on cross-sectional analyses predominantly of Northwest Sumatran populations. Here we present the first longitudinal analyses of behavioral changes of 10 adult males that have been observed in both unflanged and flanged morph. We also analyzed long-term behavioral data on an additional 143 individually identified males from two study sites, Suaq (Sumatra, Pongo abelii) and Tuanan (Borneo, Pongo pygmaeus wurmbii), to assess male mating tactics cross-sectionally in relation to population, male morph (unflanged and flanged), and other socio-ecological factors. Both our longitudinal and cross-sectional results confirm and refine previous cross-sectional accounts of the differences in mating tactics between the unflanged and the flanged male morphs. In the unflanged morph, males exhibit higher sociability, particularly with females, and higher rates of both copulation and sexual coercion than in the flanged morph. Based on our results and those of previous studies showing that females prefer flanged males, and that flanged males have higher reproductive success, we conclude that unflanged males face a trade-off between avoiding male-male contest competition and gaining mating access to females, and thus follow a "best-of-a-bad-job" mating strategy.

Zoo studies in primate physiology, health, and welfare

Researchers have been studying primates in zoos for more than half a century. There are numerous benefits to conducting research with zoo collections, such as access to a variety of species, ease of sample collection, and the potential to manipulate some research variables. While much of the primate research conducted in zoos is behavioral, there also is a tradition of research focused on reproduction and endocrinology, especially in North America. The contributions to this special issue exemplify how this tradition continues today through a collection of articles on basic and applied research on reproduction and using physiological measures of health and welfare that could be beneficial across primate taxa. As is the case for primatological research in zoos more broadly, the articles in this special issue reflect a taxonomic bias for great apes despite the high species diversity found across zoo collections. Given this bias as well as the threat of extinction faced by many species, there remains a pressing need to increase primatology in zoos through research dedicated to both conservation in the wild and wellbeing in human care.