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Abstract ObjectivesWe quantified variation in fecal cortisol across reproductive periods in Azara's owl monkeys (Aotus azarae) to examine physiological mechanisms that may facilitate biparental care. Specifically, we evaluated evidence for the explanation that owl monkeys have hormonal mechanisms to mobilize energy during periods when each sex is investing heavily in reproduction, that is, the gestation period for females and the infant care period for males. Materials and methodsBetween 2011 and 2015, we monitored 10 groups of Azara's owl monkeys from a wild population in Formosa, Argentina and collected fecal samples from 26 adults (13 males, 13 females). Using enzyme‐linked immunosorbent assays, we quantified fecal cortisol as a proxy for evaluating stress responses, including energetic demands, on both sexes during periods of reproduction and parental care. ResultsMale cortisol was lowest during periods when they were caring for young infants (<3 months) compared with periods with older infants or no infant. Female cortisol was elevated during gestation compared with other periods. Mean fecal cortisol in both males and females was lower when an infant was present compared with when females were gestating. DiscussionOur results do not support the hypothesis that owl monkey males have elevated fecal cortisol during periods when they need to mobilize energy to provide intensive infant care. Our findings are also inconsistent with the Maternal Relief hypothesis. However, results from studies measuring fecal cortisol must be interpreted with care and alternative explanations, such as seasonal fluctuations in diet and thermoenergic demands, should be considered when drawing conclusions. 

Abstract Loud calls play an important function in regulating the use of space and structuring social groups and mating systems in a wide range of taxa. In pair‐living territorial animals, where encounters with neighbors and solitary conspecifics are common, these calls are mainly associated with resource defense or mate guarding behaviors. Owl monkeys (Aotus azarae) live in groups of one pair of reproducing adults and 1–4 younger, non‐reproducing individuals. Both sexes disperse when they are around 3 years of age; they become solitary floaters who compete to replace same‐sex adults from other groups. Here, we examined the behavioral responses of Azara's owl monkey pairs toward calls of unpaired and unfamiliar males and females to better understand if the competition between floaters and groups is in relationship to the defense of their territory, their mates, or both. We collected behavioral data from six groups, before, during, and after the playing back of unfamiliar male and female loud calls and of a control stimulus at the center and border of their home ranges. Overall, our results showed that the playback location did not elicit differential responses in the monkeys and that both sexes were more reactive to male than female unfamiliar calls, as evidenced by higher rates of sociosexual and vocal responses, movement toward the playback, and intergroup encounters during and after the experiments. Our study indicates that paired male and female owl monkeys mainly defend their partners toward intruders and emphasizes the need of including the role of sexual competition on both sexes in models about the evolution of pair‐living social organizations and sexual monogamy mating systems. 

Abstract “Monogamy” and pair bonding have long been of interest to anthropologists and primatologists. Their study contributes to our knowledge of human evolutionary biology and social evolution without the cultural trappings associated with studying human societies directly. Here, we first provide an overview of theoretical considerations, followed by an evaluation of recent comparative studies of the evolution of “social monogamy”; we are left with serious doubts about the conclusions of these studies that stem from the often poor quality of the data used and an overreliance on secondary sources without vetting the data therein. We then describe our field research program on four “monogamous” platyrrhines (owl monkeys, titis, sakis, and tamarins), evaluate how well our data support various hypotheses proposed to explain “monogamy,” and compare our data to those reported on the same genera in comparative studies. Overall, we found a distressing lack of agreement between the data used in comparative studies and data from the literature for the taxa that we work with. In the final section, we propose areas of research that deserve more attention. We stress the need for more high‐quality natural history data, and we urge researchers to be cautious about the uncritical use of variables of uncertain internal validity. Overall, it is imperative that biological anthropologists establish and follow clear criteria for comparing and combining results from published studies and that researchers, reviewers, and editors alike comply with these standards to improve the transparency, reproducibility, and interpretability of causal inferences made in comparative studies. 

Argentina lies within the southernmost distributional range of five neotropical primates, the brown howler monkey Alouatta guariba, the black-and-gold howler monkey Alouatta caraya, the black-horned capuchin Sapajus nigritus, the Azara’s capuchin Sapajus cay, and the Azara’s owl monkey Aotus azarae; the first three of which are globally threatened. These species occupy different ecoregions: the Alto Paraná Atlantic forest, the Araucaria moist forest, the humid Chaco, the Southern Cone Mesopotamian savanna, the Paraná Ffooded savanna, and the Southern Andean Yungas. The recently approved National Primate Conservation Plan of Argentina calls for identifying priority areas to focus conservation actions for these species. We used species distribution models to estimate species ranges and then used the Zonation software to perform a spatial conservation prioritization analysis based on primate habitat quality and connectivity to identify potential areas of importance at national and ecoregional levels. Only 7.2% (19,500 km2) of the area inhabited by primates in Argentina is under protection. Outside the current protected areas, the top-ranked 1% and 5% priority areas identified in our analysis covered 1894 and 7574 km2, respectively. The top 1% areas were in the Atlantic forest of Misiones province, where S. nigritus, A. guariba, and A. caraya are distributed, and in the humid portion of eastern Chaco and Formosa provinces, where A. azarae and A. caraya are present. The top 5% areas included portions of the Yungas, where S. cay is the only primate present. Priority areas in Chaco and Formosa provinces are particularly relevant because of the paucity of protected areas and the high deforestation rate. The endangered A. guariba population will benefit from the better protection of the priority areas of Misiones. The potential priority areas proposed herein, considered within a context of a broad participatory process involving relevant stakeholders and local people, will help guide new and innovative conservation policies and practices while supporting management objectives.