Darting Primates: Steps Toward Procedural and Reporting Standards

Inbreeding avoidance, competition and natal dispersal in a pair-living, genetically monogamous mammal, Azara's owl monkey (Aotus azarae)

Natal dispersal is an important life-history stage influencing individual fitness, social dynamics of groups and population structure. Understanding factors influencing dispersal is essential for evaluating explanations for the evolution and maintenance of social organization, including parental care and mating systems. The social and mating systems of Azara's owl monkeys (Aotus azarae) are infrequent among mammals; these primates are pair-living, serially and genetically monogamous and both sexes directly care for offspring. To evaluate the role that competition and inbreeding avoidance play in shaping dispersal patterns, we used 25 years of demographic and genetic data to examine how variation in timing of natal dispersal is related to social (adult replacements, step-parents, births and group size) and ecological factors (seasonal abundance of resources) in a wild population of A. azarae in Formosa, Argentina. We found that all males and females dispersed from their natal groups, but subadults delayed dispersal when a step-parent of the opposite sex joined the group, indicating that they may perceive these step-parents as potential mates. Dispersal was more probable when resource conditions were better, regardless of age. Overall, agonistic conflict over food and potential mates with adults in the natal group, as well as inbreeding avoidance, contribute to regulating dispersal.

Primate landscape genetics: A review and practical guide

Landscape genetics is an emerging field that integrates population genetics, landscape ecology, and spatial statistics to investigate how geographical and environmental features and evolutionary processes such as gene flow, genetic drift, and selection structure genetic variation at both the population and individual levels, with implications for ecology, evolution, and conservation biology. Despite being particularly well suited for primatologists, this method is currently underutilized. Here, we synthesize the current state of research on landscape genetics in primates. We begin by outlining how landscape genetics has been used to disentangle the drivers of diversity, followed by a review of how landscape genetic methods have been applied to primates. This is followed by a section highlighting special considerations when applying the methods to primates, and a practical guide to facilitate further landscape genetics studies using both existing and de novo datasets. We conclude by exploring future avenues of inquiry that could be facilitated by recent developments as well as underdeveloped applications of landscape genetics to primates.

Ranging behavior and the potential for territoriality in pair-living titi monkeys (Plecturocebus discolor)

Patterns of ranging behavior and space use are key for evaluating current ideas about the evolution and maintenance of pair-living and sexual monogamy as they provide insights into the dispersion of females, the potential for territoriality, and whether males are limited to defending an area that can support only one female and her offspring. We examined ranging behavior and space use to evaluate the potential for territoriality in five groups of red titi monkeys (Plecturocebus discolor) during a 10-year study in Ecuadorian Amazonia. Mean home range size, calculated using a time-sensitive local convex hull estimation procedure, was 4.0 ± 1.4 ha. Annual home ranges of neighboring groups overlapped, on average, 0%-7%. Mean daily path length was 670 ± 194 m, resulting in defendability indices of 2.2-3.6 across groups. Groups visited, on average, 4 of 12 sections of their home range border area per day, but that was not more often than would be expected by chance, and intergroup encounters were infrequent. We did not find evidence of active monitoring for intruders in border areas, in that groups did not travel either faster or slower when at the border than when in central areas of their range. The absence of overt monitoring might be compensated for by engaging in loud calls, which the study groups did throughout their home ranges; these calls may serve as an advertisement of occupancy and a deterrent to intruding conspecifics. Our finding that red titis have a high potential for territoriality is consistent with several of the main hypotheses proposed to explain pair-living in mammals.

Automatic Identification of Individual Primates with Deep Learning Techniques

The difficulty of obtaining reliable individual identification of animals has limited researcher's ability to obtain quantitative data to address important ecological, behavioral, and conservation questions. Traditional marking methods placed animals at undue risk. Machine learning approaches for identifying species through analysis of animal images has been proved to be successful. But for many questions, there needs a tool to identify not only species but also individuals. Here, we introduce a system developed specifically for automated face detection and individual identification with deep learning methods using both videos and still-framed images that can be reliably used for multiple species. The system was trained and tested with a dataset containing 102,399 images of 1,040 individuals across 41 primate species whose individual identity was known and 6,562 images of 91 individuals across four carnivore species. For primates, the system correctly identified individuals 94.1% of the time and could process 31 facial images per second.

The evolution of pair-living, sexual monogamy, and cooperative infant care: Insights from research on wild owl monkeys, titis, sakis, and tamarins

"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.

Sexual dimorphism in the loud calls of Azara's owl monkeys (Aotus azarae): evidence of sexual selection?

Primates use different types of vocalizations in a variety of contexts. Some of the most studied types have been the long distance or loud calls. These vocalizations have been associated with mate defense, mate attraction, and resource defense, and it is plausible that sexual selection has played an important role in their evolution. Focusing on identified individuals of known sex and age, we evaluated the sexual dimorphism in a type of loud calls (hoots) in a population of wild owl monkeys (Aotus azarae) in Argentina. We found evidence of sexual dimorphism in call structure, with females and males only emitting one type of call, each differing in dominant frequency and Shannon entropy. In addition, both age-related and sex-specific differences in call usage were also apparent in response to the removal of one group member. Future acoustic data will allow us to assess if there are individual characteristics and if the structure of hoot calls presents differences in relation to the social condition of owl monkeys or specific sex responses to variants of hoot calls' traits. This will provide deeper insights into the evolution of vocal mechanisms regulating pair bonding and mate choice strategies in this and other primate species.

Morphometric signals of population decline in diademed sifakas occupying degraded rainforest habitat in Madagascar

Anthropogenic habitat change can have varied impacts on primates, including both negative and positive outcomes. Even when behavioural shifts are seen, they may reflect decreased health, or simply behavioural flexibility; understanding this distinction is important for conservation efforts. This study examines habitat-related variation in adult and immature morphometrics among diademed sifakas (Propithecus diadema). We collected morphometric data from sifakas at Tsinjoarivo, Madagascar (19 years, 188 captures, 113 individuals). Captures spanned 12 groups, five within continuous forest ("CONT"), and seven in degraded fragments ("FRAG") where sifakas have lower nutritional intakes. Few consistent differences were found between CONT and FRAG groups. However, using home range quality as a covariate rather than a CONT/FRAG dichotomy revealed a threshold: the two FRAG groups in the lowest-quality habitat showed low adult mass and condition (wasting), and low immature mass and length (stunting). Though less-disturbed fragments apparently provide viable habitat, we suggest the sifakas in the most challenging habitats cannot evolve fast enough to keep up with such rapid habitat change. We suggest other long-lived organisms will show similar morphometric "warning signs" (wasting in adults, stunting in immatures); selected morphometric variables can thus be useful at gauging vulnerability of populations in the face of anthropogenic change.

Ethics of Primate Fieldwork: Toward an Ethically Engaged Primatology

Field primatologists have ethical responsibilities that extend beyond study subjects to the local human communities living near primate populations and their surrounding ecosystems. In this review, we explore the history of ethical discussions within anthropological primatology and examine the best practices for an ethically engaged primatology that should be followed and role-modeled by primatologists. An increasing number of primates are showing reduced population sizes and are in imminent danger of extinction; thus, we need to carefully consider the ethics of intervening to ensure the survival of remaining populations, the impact of anthropogenic factors (e.g., climate change), and whether long-term field research results in conservation outcomes that consider local human communities. Because best practices change over time as theoretical frameworks and methodological tools advance and scientific goals change, field primatologists must continually reflect on what constitutes ethical practice and consider how research influences the overlapping dimensions of fieldwork: primates, people, and ecosystems.