Primate Research Research Articles

Visualizing advances in the future of primate neuroscience research.

Future neuroscience and biomedical projects involving non-human primates (NHPs) remain essential in our endeavors to understand the complexities and functioning of the mammalian central nervous system. In so doing, the NHP neuroscience researcher must be allowed to incorporate state-of-the-art technologies, including the use of novel viral vectors, gene therapy and transgenic approaches to answer continuing and emerging research questions that can only be addressed in NHP research models. This perspective piece captures these emerging technologies and some specific research questions they can address. At the same time, we highlight some current caveats to global NHP research and collaborations including the lack of common ethical and regulatory frameworks for NHP research, the limitations involving animal transportation and exports, and the ongoing influence of activist groups opposed to NHP research.

Population genetics of marmosets in Asian primate research centers and loci associated with epileptic risk revealed by whole-genome sequencing.

The common marmoset ( Callithrix jacchus) has emerged as a valuable nonhuman primate model in biomedical research with the recent release of high-quality reference genome assemblies. Epileptic marmosets have been independently reported in two Asian primate research centers. Nevertheless, the population genetics within these primate centers and the specific genetic variants associated with epilepsy in marmosets have not yet been elucidated. Here, we characterized the genetic relationships and risk variants for epilepsy in 41 samples from two epileptic marmoset pedigrees using whole-genome sequencing. We identified 14 558 184 single nucleotide polymorphisms (SNPs) from the 41 samples and found higher chimerism levels in blood samples than in fingernail samples. Genetic analysis showed fourth-degree of relatedness among marmosets at the primate centers. In addition, SNP and copy number variation (CNV) analyses suggested that the WW domain-containing oxidoreductase ( WWOX) and Tyrosine-protein phosphatase nonreceptor type 21 ( PTPN21) genes may be associated with epilepsy in marmosets. Notably, KCTD18-like gene deletion was more common in epileptic marmosets than control marmosets. This study provides valuable population genomic resources for marmosets in two Asian primate centers. Genetic analyses identified a reasonable breeding strategy for genetic diversity maintenance in the two centers, while the case-control study revealed potential risk genes/variants associated with epilepsy in marmosets.

Pedigree Data from Six Rhesus Macaque (Macaca mulatta) Matrilines at the California National Primate Research Center Indicate Inbreeding and Loss of Genetic Variation.

Relatedness and kinship structure in matrilines are a potential source of social stability. The current study aimed to analyze the extant pedigrees of 6 living matrilines in different field cages to assess rates of cross-generational inbreeding and loss of genetic variation over time. All 6 matrilines showed increasing levels of inbreeding over generation time, although the rates of increase were different. The female-to-male-adult sex ratio was correlated with average matriline inbreeding levels, while the number of adult males was positively correlated with average matriline genetic diversity. Over five times more paternal half-sibs than maternal half-sibs were present because paternity had been restricted to a few males yearly. Therefore, the relatedness through the paternal lines was over five times greater than that of the maternal lines. Overall, each matriline lost low to moderate levels of genetic variation with time. The current rates of gene flow between field cages by cross-fostered infants have not stopped inbreeding within these matrilines or loss of diversity due to genetic drift. This situation probably developed because translocated animals, especially males, may not breed successfully. Only 4 of the 22 translocated individuals, all females, eventually reproduced, resulting in 13 offspring and generating an overall breeding success of 0.59 across all 6 study matrilines. However, even this low rate of reproduction by the translocated animals reduced inbreeding and kinship among matrilines and increased genetic heterogeneity in the matrilines. Based on this study, we propose several colony management strategies, including equalizing adult sex ratios to increase the effective population size in the field cages, increasing the number of cross-fostered infants, and relying more on multigenerational pedigree data to aid the alignment of genetic and behavioral management techniques.

Species identity and behavior of cave-dwelling tree hyraxes of the Kenyan coast.

We surveyed tree hyrax populations living in forests, limestone rocky formations, and caves in coastal Kenya to identify the species and estimate the threat-level populations are in. Tree hyrax vocalizations were recorded in three different habitats with passive acoustic monitoring (PAM) for a total of 84 h in January and February 2022. We also observed tree hyrax behavior with thermal imaging camera and photographed individuals. Tree hyraxes in coastal Kenya are vocally active throughout the night, with most calls emitted between 23.00 and 04.00. We identified four different calls: snort, hac, hac ping-pong, and wheeze. Their calling range is between 220 and 15,000 Hz. Calls of tree hyraxes from the coast of Kenya were compared with calls stored by the Oxford Brookes University's Nocturnal Primate Research Group and identified as eastern tree hyrax, previously recorded from Tanzania. Here, we present what are, to our knowledge, the first photographs of live D. validus from Kenya. These tree hyraxes live in social groups. Due to strong pressure from humans, conservation measures are necessary to prevent the extinction of these isolated D. validus populations in Kenya.

Complex pattern of facial remapping in somatosensory cortex following congenital but not acquired hand loss.

Cortical remapping after hand loss in the primary somatosensory cortex (S1) is thought to be predominantly dictated by cortical proximity, with adjacent body parts remapping into the deprived area. Traditionally, this remapping has been characterised by changes in the lip representation, which is assumed to be the immediate neighbour of the hand based on electrophysiological research in non-human primates. However, the orientation of facial somatotopy in humans is debated, with contrasting work reporting both an inverted and upright topography. We aimed to fill this gap in the S1 homunculus by investigating the topographic organisation of the face. Using both univariate and multivariate approaches we examined the extent of face-to-hand remapping in individuals with a congenital and acquired missing hand (hereafter one-handers and amputees, respectively), relative to two-handed controls. Participants were asked to move different facial parts (forehead, nose, lips, tongue) during functional MRI (fMRI) scanning. We first confirmed an upright face organisation in all three groups, with the upper-face and not the lips bordering the hand area. We further found little evidence for remapping of both forehead and lips in amputees, with no significant relationship to the chronicity of their phantom limb pain (PLP). In contrast, we found converging evidence for a complex pattern of face remapping in congenital one-handers across multiple facial parts, where relative to controls, the location of the cortical neighbour - the forehead - is shown to shift away from the deprived hand area, which is subsequently more activated by the lips and the tongue. Together, our findings demonstrate that the face representation in humans is highly plastic, but that this plasticity is restricted by the developmental stage of input deprivation, rather than cortical proximity.

Of mice and Mike—An underappreciated Ebola virus disease model may have paved the road for future filovirology

In 1998, Mike Bray and colleagues published the first immunocompetent laboratory mouse model of Ebola virus disease. Often labeled by peer reviewers as inferior to large nonhuman primate efforts, this model initially laid the foundation for the recent establishment of panel-derived cross-bred and humanized mouse models and a golden hamster model. Nonhuman primate research has always been associated with ethical concerns and is sometimes deemed scientifically questionable due to the necessarily low animal numbers in individual studies. Independent of these concerns, the now-global severe shortage of commercially available large nonhuman primates may pragmatically push research toward increased and improved rodent modeling that may altogether replace nonhuman primate studies in the short term as well as in an optimal future.

The Benefits and Challenges of Conducting Primate Research in Different Settings.

Internationally, primate research takes place in laboratories, zoos, sanctuaries, and the wild. All of these settings present unique advantages and challenges in terms of methodology, translatability, animal welfare, and ethics. In this novel commentary, we explore the scientific and ethical benefits and drawbacks of conducting non-invasive psychological research with primates in each setting. We also suggest ways to overcome some of the barriers. We argue that while there may be greater experimental control in laboratory-based research, settings that more closely mirror primates' natural habitats are generally better suited to meet their specialized needs. More naturalistic research settings, including field studies, may also circumvent some ethical concerns associated with research in captivity, and yield more ecologically valid data.

Primate gastrulation and early organogenesis at single-cell resolution

Our understanding of human early development is severely hampered by limited access to embryonic tissues. Due to their close evolutionary relationship with humans, nonhuman primates are often used as surrogates to understand human development but currently suffer from a lack of in vivo datasets, especially from gastrulation to early organogenesis during which the major embryonic cell types are dynamically specified. To fill this gap, we collected six Carnegie stage 8–11 cynomolgus monkey (Macaca fascicularis) embryos and performed in-depth transcriptomic analyses of 56,636 single cells. Our analyses show transcriptomic features of major perigastrulation cell types, which help shed light on morphogenetic events including primitive streak development, somitogenesis, gut tube formation, neural tube patterning and neural crest differentiation in primates. In addition, comparative analyses with mouse embryos and human embryoids uncovered conserved and divergent features of perigastrulation development across species—for example, species-specific dependency on Hippo signalling during presomitic mesoderm differentiation—and provide an initial assessment of relevant stem cell models of human early organogenesis. This comprehensive single-cell transcriptome atlas not only fills the knowledge gap in the nonhuman primate research field but also serves as an invaluable resource for understanding human embryogenesis and developmental disorders.

The challenges of primate research and conservation in Paraguay


 
 
 The primate fauna of Paraguay consists of just five species (Sapajus cay, Alouatta caraya, Aotus azarae, Plecturocebus pallescens and Mico melanurus) and has been largely overlooked by the international primatological community. Not-withstanding, Paraguay currently has the second highest deforestation rate in Latin America and the threats facing Paraguayan primates are as severe as anywhere else on the continent. Primate conservation in Paraguay is complicated by the complete absence of a homegrown primatological research community and the country lacks the solid biological research foundation required for the development of robust management strategies. Only one university degree in biology is available in the country (with the Universidad Nacional de Asunción), and opportunities for postgraduate education in biological sciences require studying abroad, whilst the limited number of career opportunities upon graduation mean that those receiving such training frequently prefer to pursue their career elsewhere rather than return to the country to practice. No higher education courses in primatology are currently available in Paraguay. Fundación Para La Tierra (PLT) is a Paraguayan conservation and education NGO (80086144-2), founded in 2010. PLT focuses on conservation of Paraguay’s natural habitats through scientific research, community engagement and education, and implements Paraguay’s only long-term primatology research projects: the “Hooded Capuchin Project” conserving Sapajus cay in what little remains of the Upper Paraná Atlantic Forest and the “Urban Howler Monkey Project” researching the behavioural ecology of Alouatta caraya inhabiting the city of Pilar. The PLT primate projects adopt a multi-faceted approach: long-term scientific research, training and supporting local people with an interest in primates, supervision of international students and environmental education in schools. In this article we will discuss the challenges of develop- ing such a project, and a vision for the future of primatology in Paraguay.
 
 

Astemizole-Methylene Blue Combination Therapy Reduces Monotherapy Adverse Effects in Balb/C Mice

Aims: To determine the toxicity of astemizole-methylene blue combination therapy as effective candidates for therapeutic repurposing against malaria.
 Study Design: Randomized block study design.
 Place and Duration of Study: Department of Tropical and Infectious Diseases, Institute of Primate Research, between July and December, 2019.
 Methodology: The Lorke’s technique was used to evaluate the toxicity of the drug combinations in
 Balb/c mice (N=25). The mice were monitored for clinical signs at 2-hour intervals. After 48 hours, the mice were euthanized, and their tissues collected, weighed and grossly examined. Biochemistry and hematological tests were performed after blood samples were collected. Analysis of Variance and the t-test were used for statistical analysis; differences were considered significant if P values were less than 0.05 (p˂ 0.05).
 Results: The findings revealed that mice treated with methylene blue alone experienced a decrease of appetite, while mice treated with astemizole alone experienced slight tremors, which were not observed in the medication combined groups. When compared to the negative controls, the astemizole-methylene blue 3:1 combination group exhibited reduced heart (p=0.007) and liver (p=0.0001) mean weights. Platelet levels in the astemizole-methylene blue 3:1 group were lower in comparison to the other groups (p=0.005), according to the hematological data collected.
 Conclusion: When delivered in ratios with less astamizole, astemizole-methylene blue combination therapy showed better results in terms of safety than monotherapy with either drug alone.

Participatory action research for primate conservation: A critical analysis of a nonformal education program in Southern Mexico.

Historically, Mexico has had an important role in primate conservation research, however, studies have rarely included the human dimensions of primatology. Inclusion of these disciplines should be a priority, considering that human activities are responsible for the current socio-ecological crisis. Mexico is habitat for three primate species, and all are threatened. This urgency demands new approaches and broader perspectives. First, we propose three main research frameworks relevant for conducting PCEPs in Latin America: Participatory Action Research, Arts-based education in PCEPs and Knowledge Coproduction. Furthermore, we aimed to (1) describe a case study about primate conservation education in Southern Mexico based on participatory visual methods under the umbrella of Participatory Action Research (PAR), and (2) to conduct a self-reflective, critical, straightforward, and constructive analysis of the experience. We discuss the various challenges faced during the process (e.g., traditional teaching prevalence at schools, teachers that are not school-based, time and academic constraints). Additionally, we highlight some PAR aspects applicable for researchers and practitioners interested to go further than knowledge transmission (e.g., codesign, arts-based education, placed-based education, critical thinking, and capacity building). To collectively progress in primate conservation education in Mexico and other Latin American countries, projects could greatly benefit from context-specific, people-centered approaches, such as PAR. We encourage researchers to share more of their personal research experiences including both their successes and failures.

OpenMonkeyChallenge: Dataset and Benchmark Challenges for Pose Estimation of Non-human Primates.

The ability to automatically estimate the pose of non-human primates as they move through the world is important for several subfields in biology and biomedicine. Inspired by the recent success of computer vision models enabled by benchmark challenges (e.g., object detection), we propose a new benchmark challenge called OpenMonkeyChallenge that facilitates collective community efforts through an annual competition to build generalizable non-human primate pose estimation models. To host the benchmark challenge, we provide a new public dataset consisting of 111,529 annotated (17 body landmarks) photographs of non-human primates in naturalistic contexts obtained from various sources including the Internet, three National Primate Research Centers, and the Minnesota Zoo. Such annotated datasets will be used for the training and testing datasets to develop generalizable models with standardized evaluation metrics. We demonstrate the effectiveness of our dataset quantitatively by comparing it with existing datasets based on seven state-of-the-art pose estimation models.

Does behaviour predict weight gain during adulthood in captive group-living rhesus macaques?

Many non-human primates (NHPs) in captivity become overweight. Individual variation in adiposity may result from differences in behaviour related to energy intake, energy expenditure and dominance rank. Understanding how behaviour contributes to becoming overweight may provide opportunities to improve housing and husbandry of captive group-living NHPs. This study therefore investigated whether behaviour predicts weight gain during adulthood in captive female rhesus macaques (Macaca mulatta) housed in three social groups at the Biomedical Primate Research Centre in Rijswijk, the Netherlands. Relative adiposity was quantified with a species-specific weight-for-height index (WHI) during three consecutive annual health checks. Behavioural data were collected at baseline on food intake, activity budgets and dominance rank. We examined which factors were associated with WHI at baseline and whether behaviour predicted the subsequent change in WHI over time, while controlling for individual characteristics. At baseline, a high WHI was associated with low activity levels, but not related to food intake, age or dominance rank. WHI did not differ from baseline after one year but had significantly increased after the second year. This increase in WHI was independent of food intake and activity budgets, while higher-ranking females had a higher increase in WHI compared to lower-ranking monkeys. This suggests that captive NHPs with a high dominance rank are more prone to becoming overweight, whereas differences in activity budgets are merely a consequence and not a cause. Thus, dominance rank, but not behaviour, likely predicts weight gain during adulthood in captive group-living NHPs.

Estimating the population variance, standard deviation, and coefficient of variation: Sample size and accuracy

Small sample sizes are often used in human and primate evolutionary research to estimate population parameters such as the mean, variance, and standard deviation, as well as statistical measures such as the coefficient of variation. Determining how well sample estimates represent population parameters is essential for establishing confidence in the inferences made using those samples. We present methods for determining a priori the probability, based on Cochran's theorem, that the sample variance and sample standard deviation are within a specified fraction of the population parameters. We validate these methods using random resampling with replacement of a single variable from a commonly used large craniometric data set comprising modern human population samples from around the world. Results based on Cochran's theorem, which we validate, indicate that large random samples comprising hundreds of observations, rather than tens of observations, are needed to be confident that the sample estimate is a reasonably accurate approximation of the true population variance. Smaller sample sizes on the order of tens of observations, however, are sufficient for estimating the population standard deviation. We extend our method of validation to show that the coefficient of variation mirrors closely the results for the standard deviation.

Little Evidence to Support the Risk–Disturbance Hypothesis as an Explanation for Responses to Anthropogenic Noise by Pygmy Marmosets (Cebuella niveiventris) at a Tourism site in the Peruvian Amazon

The risk–disturbance hypothesis states that animals react to human stressors in the same way as they do to natural predators. Given increasing human–wildlife contact, understanding whether animals perceive anthropogenic sounds as a threat is important for assessing the long-term sustainability of wildlife tourism and proposing appropriate mitigation strategies. A study of pygmy marmoset (Cebuella niveiventris) responses to human speech found marmosets fled, decreased feeding and resting, and increased alert behaviors in response to human speech. Following this study, we investigated pygmy marmoset reactions to playbacks of different acoustic stimuli: controls (no playback, white noise and cicadas), anthropogenic noise (human speech and motorboats), and avian predators. For each playback condition, we recorded the behavior of a marmoset and looked at how the behaviors changed during and after the playback relative to behaviors before. We repeated this on ten different marmoset groups, playing each condition once to each group. The results did not replicate a previous study on the same species, at the same site, demonstrating the importance of replication in primate research, particularly when results are used to inform conservation policy. The results showed increased scanning during playbacks of the cicadas and predators compared with before the playback, and an increase in resting after playbacks of avian predators, but no evidence of behavior change in response to playbacks of human speech. There was no effect of ambient sound levels or distance between the playback source and focal animals on their behavior for all playback conditions. Although we find that noise can change the behavior of pygmy marmosets, we did not find evidence to support the risk–disturbance hypothesis.

Functional Insulinomas in a Rhesus Macaque (Macaca mulatta)

We report a rare case of functional insulinomas in a 16.7-year-old female Rhesus macaque (Macaca mulatta) that was presented with neuroglycopenic signs to the breeding colony hospital at the Tulane National Primate Research Center. At initial and follow-up examinations, the animal was consistently hypoglycaemic and was clinically maintained with additional fruits, other high-sugar food items and dextrose supplementation. Occasional episodes of seizure and collapse resolved quickly on administration of high-sugar food items. At necropsy, the uncinate process of the pancreas had a 2.2cm diameter, red, round, firm neoplastic mass, and another neoplasm was identified on histological examination of the head of pancreas. Histologically, neoplastic cells exhibited neuroendocrine packeting, resembled pancreatic islet cells and immunolabelled for chromogranin A, synaptophysin and insulin but not for somatostatin, gastrin or pancreatic polypeptide. A few cells immunolabelled for glucagon. The clinical signs and gross and histological findings were consistent with functional insulinomas.

Chimpanzee and pig-tailed macaque iPSCs: Improved culture and generation of primate cross-species embryos.

As our closest living relatives, non-human primates uniquely enable explorations of human health, disease, development, and evolution. Considerable effort has thus been devoted to generating induced pluripotent stem cells (iPSCs) from multiple non-human primate species. Here, we establish improved culture methods for chimpanzee (Pan troglodytes) and pig-tailed macaque (Macaca nemestrina) iPSCs. Such iPSCs spontaneously differentiate in conventional culture conditions, but can be readily propagated by inhibiting endogenous WNT signaling. As a unique functional test of these iPSCs, we injected them into the pre-implantation embryos of another non-human species, rhesus macaques (Macaca mulatta). Ectopic expression of gene BCL2 enhances the survival and proliferation of chimpanzee and pig-tailed macaque iPSCs within the pre-implantation embryo, although the identity and long-term contribution of the transplanted cells warrants further investigation. In summary, we disclose transcriptomic and proteomic data, cell lines, and cell culture resources that may be broadly enabling for non-human primate iPSCs research.

An assessment of ambient noise and other environmental variables in a nonhuman primate housing facility.

Acoustic noise and other environmental variables represent potential confounds for animal research. Of relevance to auditory research, sustained high levels of ambient noise may modify hearing sensitivity and decrease well-being among laboratory animals. The present study was conducted to assess environmental conditions in an animal facility that houses nonhuman primates used for auditory research at the Vanderbilt University Medical Center. Sound levels, vibration, temperature, humidity and luminance were recorded using an environmental monitoring device placed inside of an empty cage in a macaque housing room. Recordings lasted 1 week each, at three different locations within the room. Vibration, temperature, humidity and luminance all varied within recommended levels for nonhuman primates, with one exception of low luminance levels in the bottom cage location. Sound levels at each cage location were characterized by a low baseline of 58-62 dB sound pressure level, with transient peaks up to 109 dB sound pressure level. Sound levels differed significantly across locations, but only by about 1.5 dB. The transient peaks beyond recommended sound levels reflected a very low noise dose, but exceeded startle-inducing levels, which could elicit stress responses. Based on these findings, ambient noise levels in the housing rooms in this primate facility are within acceptable levels and unlikely to contribute to hearing deficits in the nonhuman primates. Our results establish normative values for environmental conditions in a primate facility, can be used to inform best practices for nonhuman primate research and care, and form a baseline for future studies of aging and chronic noise exposure.

Formulation of phage cocktails and evaluation of their interaction with antibiotics in inhibiting carbapenemase-producing Klebsiella pneumoniae in vitro in Kenya.

BackgroundThe development of alternative control measures, such as phage therapy or adjunctive therapy, is urgently needed to manage the dissemination of carbapenemase-producing Klebsiella pneumoniae.ObjectiveThis study aimed to evaluate the therapeutic potential of formulated phage cocktails and their interaction with select antibiotics in inhibiting the growth of carbapenemase-producing K. pneumoniae clinical isolate in vitro in Kenya.MethodsThe study was conducted from February 2021 to October 2021 at the Institute of Primate Research, Nairobi, Kenya. Phage cocktails were formulated based on the morphology and biological properties of precipitated Klebsiella phages. The efficacy of individual bacteriophages and phage cocktails as well as their combination with antibiotics were determined for their inhibitory activity on carbapenemase-producing K. pneumoniae (KP20).ResultsThe precipitated bacteriophages were members of Myoviridae, Siphoviridae and Podoviridae. Regarding the evaluation of the phage cocktails, the absorbances at 600 nm of the bacterial culture treated with the two-phage cocktail (2φ MA) ranged from 0.173 to 0.246 at 16 h and 20 h whereas it peaked from 2.116 to 2.190 for the positive control. Moreover, the results of the adjunctive therapy showed that the optical density at 600 nm of the bacterial culture treated with 2φ MA was 0.186 at 24 h post-incubation time while it was 0.099 with the bacterial culture treated with imipenem in combination with 2φ MA.ConclusionThis study demonstrated that the two-phage cocktail in combination with imipenem was able to synergistically delay the increase in carbapenemase-producing K. pneumoniae growth in vitro.

Why I Will Boycott Complex Family Planning Board Certification.

Corresponding author: Jeffrey T. Jensen, MD, MPH, Department of Obstetrics & Gynecology, Oregon National Primate Research Center, Oregon Health & Science University, Portland, OR; email: [email protected]. Financial Disclosure The author did not report any potential conflicts of interest. Department of Obstetrics & Gynecology and the Women's Health Research Unit, Oregon Health & Science University, and the Oregon National Primate Research Center, Portland, Oregon. Peer reviews and author correspondence are available at https://links.lww.com/AOG/C759.