Small apes adjust rhythms to facilitate song coordination

Song coordination is a universal characteristic of human music. Many animals also produce well-coordinated duets or choruses that resemble human music. However, the mechanism and evolution of song coordination have only recently been studied in animals. Here, we studied the mechanism of song coordination in three closely related species of wild Nomascus gibbons that live in polygynous groups. In each species, song bouts were dominated by male solo sequences (referred to hereafter as male sequence), and females contributed stereotyped great calls to coordinate with males. Considering the function of rhythm in facilitating song coordination in human music and animal vocalizations, we predicted that adult males adjust their song rhythm to facilitate song coordination with females. In support of this prediction, we found that adult males produced significantly more isochronous rhythms with a faster tempo in male sequences that were followed by successful female great calls (a complete sequence with "introductory" and "wa" notes). The difference in isochrony and tempos between successful great call sequences and male sequences was smaller in N. concolor compared with the other two species, which may make it difficult for females to predict a male's precise temporal pattern. Consequently, adult females of N. concolor produced more failed great call (an incomplete sequence with only introductory notes) sequences. We propose that the high degree of rhythm change functions as an unambiguous signal that can be easily perceived by receivers. In this regard, gibbon vocalizations offer an instructive model to understand the origins and evolution of human music.

An urgent call-to-action to protect the nonhuman primates and Indigenous Peoples of the Brazilian Amazon

Primates are facing an impending extinction crisis. Here, we examine the set of conservation challenges faced by the 100 primate species that inhabit the Brazilian Amazon, the largest remaining area of primary tropical rainforest in the world. The vast majority (86%) of Brazil's Amazonian primate species have declining populations. Primate population decline in Amazonia has been driven principally by deforestation related to the production of forest-risk commodities including soy and cattle ranching, the illegal logging and setting of fires, dam building, road and rail construction, hunting, mining, and the confiscation and conversion of Indigenous Peoples' traditional lands. In a spatial analysis of the Brazilian Amazon, we found that 75% of Indigenous Peoples' lands (IPLs) remained forested compared with 64% of Conservation Units (CUs) and 56% of other lands (OLs). In addition, primate species richness was significantly higher on IPLs than on CUs and OLs. Thus, safeguarding Indigenous Peoples' land rights, systems of knowledge, and human rights is one of the most effective ways to protect Amazonian primates and the conservation value of the ecosystems they inhabit. Intense public and political pressure is required and a global call-to-action is needed to encourage all Amazonian countries, especially Brazil, as well as citizens of consumer nations, to actively commit to changing business as usual, living more sustainably, and doing all they can to protect the Amazon. We end with a set of actions one can take to promote primate conservation in the Brazilian Amazon.

Scientific activism to protect the world's primates and their environments from extinction: Introduction to the special issue

Nonhuman primates and their habitats are facing an impending extinction crisis. Approximately 69% of primate species are listed by the International Union for Conservation of Nature as threatened and 93% have declining populations. Human population growth (expected to reach 10.9 billion by the year 2100), the unsustainable demands of a small number of consumer nations for forest-risk commodities, deforestation and habitat conversion, the expansion of roads and rail networks, cattle ranching, the hunting and trapping of wild primate populations, and the potential spread of infectious diseases are among the primary drivers of primate population decline. Climate change will only exacerbate the current situation. The time to act to protect primate populations is now! In this special issue of the American Journal of Primatology, we present a series of commentaries, formulated as "Action Letters." These are designed to educate and inform primatologists, conservation biologists, wildlife ecologists, political leaders, and global citizens about the conservation challenges faced by particular primate taxa and particular world regions, and present examples of specific actions that one can take, individually and collectively, to promote the persistence of wild primate populations and environmental justice for local human populations and impacted ecological communities. As scientists, researchers, and educators, primatologists are in a unique position to lead local, national, and international efforts to protect biodiversity. In this special issue, we focus on primates of the Brazilian Amazon, lemurs of northeast Madagascar, Temminck's red colobus monkey (Piliocolobus badius temminckii), night monkeys (Aotus spp.), long-tailed macaques (Macaca fascicularis), the primate pet trade, and professional capacity building to foster conservation awareness and action. We encourage primatologists, regardless of their research focus, to engage in both advocacy and activism to protect wild primate populations worldwide.

Human activity and climate change accelerate the extinction risk to non-human primates in China

Human activity and climate change affect biodiversity and cause species range shifts, contractions, and expansions. Globally, human activities and climate change have emerged as persistent threats to biodiversity, leading to approximately 68% of the ~522 primate species being threatened with extinction. Here, we used habitat suitability models and integrated data on human population density, gross domestic product (GDP), road construction, the normalized difference vegetation index (NDVI), the location of protected areas (PAs), and climate change to predict potential changes in the distributional range and richness of 26 China's primate species. Our results indicate that both PAs and NDVI have a positive impact on primate distributions. With increasing anthropogenic pressure, species' ranges were restricted to areas of high vegetation cover and in PAs surrounded by buffer zones of 2.7-4.5 km and a core area of PAs at least 0.1-0.5 km from the closest edge of the PA. Areas with a GDP below the Chinese national average of 100,000 yuan were found to be ecologically vulnerable, and this had a negative impact on primate distributions. Changes in temperature and precipitation were also significant contributors to a reduction in the range of primate species. Under the expected influence of climate change over the next 30-50 years, we found that highly suitable habitat for primates will continue to decrease and species will be restricted to smaller and more peripheral parts of their current range. Areas of high primate diversity are expected to lose from 3 to 7 species. We recommend that immediate action be taken, including expanding China's National Park Program, the Ecological Conservation Redline Program, and the Natural Forest Protection Program, along with a stronger national policy promoting alternative/sustainable livelihoods for people in the local communities adjacent to primate ranges, to offset the detrimental effects of anthropogenic activities and climate change on primate survivorship.

Effects of provisioning on the activity budget and foraging strategies of black-and-white snub-nosed monkeys (Rhinopithecus bieti) in the Baima Snow Mountain Nature Reserve, Yunnan, China

Provisioning can significantly affect the ranging patterns, foraging strategies, and time budget of wild primates. In this study, we document for the first time, the effects of provisioning on the activity budget and foraging effort in an Asian colobine. Over 3-years, we used an instantaneous scanning method at 10-min intervals to collect data on the activity budget of a semiprovisioned breeding band (SPB) of black-and-white snub-nosed monkeys (Rhinopithecus bieti) (42-70 individuals) at Xiangguqing (Tacheng), Yunnan, China. We then compared the effects of provisioning in our study band with published data on a sympatric wild nonprovisioned breeding band (NPB) of R. bieti (ca. 360 monkeys) at the same field site. The SPB spent 25.6% of their daytime feeding, 17.1% traveling, 46.9% resting, and 10.3% socializing. In comparison, the NPB devoted more time to feeding (34.9%) and socializing (14.1%), less time to resting (31.3%), and was characterized by a greater foraging effort (1.74 versus 0.96, foraging effort = (feeding + traveling)/resting; see Methods). There was no difference between bands in the proportion of their activity budget devoted to traveling (15.7% vs. 17.1%). In addition, the SPB exhibited a more consistent activity budget and foraging effort across all seasons of the year compared to the NPB. These findings suggest that the distribution, availability, and productivity of naturally occurring feeding sites is a major determinant of the behavioral strategies and activity budget of R. bieti. Finally, a comparison of our results with data on six nonprovisioned R. bieti bands indicates that caution must be raised in meta-analyses or intraspecific comparisons of primate behavioral ecology that contain data generated from both provisioned and nonprovisioned groups.

A conceptual framework for assessing behavioral flexibility of species in response to extreme climatic events

Inherent differences in the adaptive capacity of species to flexibly respond to extreme climatic events (ECEs) represent a key factor in their survivorship. We introduce and apply a conceptual framework linking knowledge about species' current ecology and biology with variation in behavioral flexibility to ECEs. We applied it to 199 non-human primate species currently exposed to cyclones across the global tropics. Our findings suggest that species characterized by an increased ability to exploit a broad range of food types, social systems that permit subgrouping, and habitat types that span a range of environmental conditions may have greater success in coping with cyclones than more narrowly constrained or less adaptable primates. Overall, 15% of species, predominantly of the families Atelidae and Cercopithecidae, were assessed as having high or very high flexibility. In contrast, ~ 60% of primates were assessed with low or very low flexibility. These were species mainly belonging to the Cheirogaleidae, Lemuridae, Lepilemuridae, and Indriidae. While much work remains to better understand mechanisms driving differences in behavioral flexibility of species exposed to extreme climate across vertebrate lineages, our framework provides a workable approach that can improve estimates of current vulnerability to these phenomena and better inform conservation and management strategies.

Adaptations to a cold climate promoted social evolution in Asian colobine primates

The biological mechanisms that underpin primate social evolution remain poorly understood. Asian colobines display a range of social organizations, which makes them good models for investigating social evolution. By integrating ecological, geological, fossil, behavioral, and genomic analyses, we found that colobine primates that inhabit colder environments tend to live in larger, more complex groups. Specifically, glacial periods during the past 6 million years promoted the selection of genes involved in cold-related energy metabolism and neurohormonal regulation. More-efficient dopamine and oxytocin pathways developed in odd-nosed monkeys, which may have favored the prolongation of maternal care and lactation, increasing infant survival in cold environments. These adaptive changes appear to have strengthened interindividual affiliation, increased male-male tolerance, and facilitated the stepwise aggregation from independent one-male groups to large multilevel societies.

Wild gibbons plan their travel pattern according to food types of breakfast

Planning for the future is a complex skill that is often considered uniquely human. This cognitive ability has never been investigated in wild gibbons (Hylobatidae). Here we evaluated the movement patterns from sleeping trees to out-of-sight breakfast trees in two groups of endangered skywalker gibbons (Hoolock tianxing). These Asian apes inhabit a cold seasonal montane forest in southwestern China. After controlling for possible confounding variables including group size, sleeping pattern (sleep alone or huddle together), rainfall and temperature, we found that food type (fruits or leaves) of the breakfast tree was the most important factor affecting gibbon movement patterns. Fruit breakfast trees were more distant from sleeping trees compared with leaf trees. Gibbons left sleeping trees and arrived at breakfast trees earlier when they fed on fruits compared with leaves. They travelled fast when breakfast trees were located further away from the sleeping trees. Our study suggests that gibbons had foraging goals in mind and plan their departure times accordingly. This ability may reflect a capacity for route-planning, which would enable them to effectively exploit highly dispersed fruit resources in high-altitude montane forests.

Effects of food availability and climate on the activity budget of Shortridge's langur (Trachypithecus shortridgei) in the Drung Valley, Gaoligong Mountains, China

Food availability and climate represent environmental factors that affect species' social behavior, ranging patterns, diet, and activity budget. From August 2012 to September 2013, we examined the effects of seasonal changes in food availability, temperature, and rainfall on the diet and behavioral ecology of Shortridge's langur (Trachypithecus shortridgei) an Endangered primate species inhabiting moist evergreen broadleaf forests in the Eastern Himalayas. Our field site represents the northernmost latitudinal distribution of this species. Data were collected using scan sampling at 10 min intervals, and analyzed based on generalized linear models. The results indicate that the langurs experienced two feeding peaks (9:00 and 17:00) and two traveling peaks (10:00 and 19:00) during each day. Periods of rest, mainly occurred between 10:00 and 13:00, and overnight. Feeding accounted for 38.5% of the daily activity budget, followed by resting (35%), traveling (24.5%), and socializing (2%). During periods when young leaves were most available, the langurs increased feeding time on young leaves (35% vs. 4%). During periods of maximum fruit availability, the langurs decreased total time spent feeding (36.6% vs. 40.4%), devoted more time to traveling (28.1% vs. 21%), and increased time spent consuming fruit (49.1% vs. 11.8%). During the winter, the langurs increased their consumption of mature leaves (44.5%) and reduced time spent traveling (20.2% vs. 25.4%). Overall, time spent resting was greatest in the spring (47.5%), time spent feeding was greatest during the summer (51.1%), and time spent in traveling was greatest in the autumn (33.2%). The frequency of social interactions remained relatively constant throughout the year. Foraging effort was greatest in the summer, when fruits dominated the diet. Like other species of temperate langurs, T. shortridgei devoted less time to resting, more time to feeding, and was characterized by a greater year-round foraging effort than tropical/subtropical langurs.

Comparative susceptibility of SARS-CoV-2, SARS-CoV, and MERS-CoV across mammals

Exploring wild reservoirs of pathogenic viruses is critical for their long-term control and for predicting future pandemic scenarios. Here, a comparative in vitro infection analysis was first performed on 83 cell cultures derived from 55 mammalian species using pseudotyped viruses bearing S proteins from SARS-CoV-2, SARS-CoV, and MERS-CoV. Cell cultures from Thomas's horseshoe bats, king horseshoe bats, green monkeys, and ferrets were found to be highly susceptible to SARS-CoV-2, SARS-CoV, and MERS-CoV pseudotyped viruses. Moreover, five variants (del69-70, D80Y, S98F, T572I, and Q675H), that beside spike receptor-binding domain can significantly alter the host tropism of SARS-CoV-2. An examination of phylogenetic signals of transduction rates revealed that closely related taxa generally have similar susceptibility to MERS-CoV but not to SARS-CoV and SARS-CoV-2 pseudotyped viruses. Additionally, we discovered that the expression of 95 genes, e.g., PZDK1 and APOBEC3, were commonly associated with the transduction rates of SARS-CoV, MERS-CoV, and SARS-CoV-2 pseudotyped viruses. This study provides basic documentation of the susceptibility, variants, and molecules that underlie the cross-species transmission of these coronaviruses.

Habitat restoration is the greatest challenge for population recovery of Hainan gibbons (Nomascus hainanus)

Hainan gibbons are among the world's most critically endangered primates, with a remaining population of only 35 individuals distributed across 5 social groups in the Bawangling Branch of the Hainan Tropical Rainforest National Park, China. Habitat conversion and forest fragmentation over the past 40 years have reduced their geographical distribution by 95%. In the absence of a quantitative assessment of the availability of remaining suitable habitat, it is unclear whether this species can survive to the end of this century. We used behavioral observations, ArcGIS, remote sensing, stereo optical imagery, and MaxEnt modeling to identify patterns of Hainan gibbon range use and compare changes in the distribution of suitable forest types and areas of forest fragmentation over the past 20 years (2000-2020). The results indicate that the combined range of the 5 extant Hainan gibbon groups totaled 14.89 km² . The home range of the smallest group (Group E, 3 individuals) was 1.51 km² , which likely represents the minimum home range size for this species. The remaining area of highly suitable and moderately suitable habitat totals 26.9 km² . However, habitat connectivity across the gibbon range is very low (less than 0.5), limiting the ability of Hainan gibbons to move between forest patches. The results of this study indicate that the availability of suitable habitat in Bawangling is insufficient to allow for future Hainan gibbon population growth. Therefore, immediate action must be taken to restore, reforest, and establish ecological corridors to reconnect areas of suitable habitat for these critically endangered gibbons.

Identifying the environmental and anthropogenic causes, distribution, and intensity of human rhesus macaque conflict in Nepal

Reducing conflict between humans and wildlife is considered a top conservation priority. However, increasingly human-induced disturbances across natural landscapes have escalated encounters between humans and wildlife. In Nepal, forests have been destroyed, fragmented, and developed for human settlements, agricultural production, and urban centers for decades. As a result, human-wildlife conflict, in the form of crop-raiding, livestock predation, and injuries to humans and wildlife, is common throughout the country. In particular, crop-raiding by macaques is an increasingly common form of human-wildlife conflict. Rhesus macaques (Macaca mulatta) have been identified as a top ten crop-raiding wildlife species in Nepal. In order to better understand the nationwide distribution and intensity of human-rhesus macaque conflict (HRMC), we conducted an extensive literature review of reported incidences of HRMC during the period 2000 to 2021 in Nepal. We also created an online survey to obtain nationwide data on the location and severity of HRMC, and modeled the set of ecological factors that affect habitat suitability for rhesus macaques. An ensemble of three different species distribution model (SDM) algorithms were used to analyze these data. We found that almost 44% of Nepal's land area contains suitable habitat for rhesus macaques, with less than 8% of all suitable habitat located in protected national parks. As humans continue to alter and fragment natural landscapes, HRMC in Nepal has intensified. At present, nearly 15% of the country's land area in which human settlements are permitted, is characterized by moderate or high rates of HRMC. We argue that prioritizing programs of forest restoration, strategic management plans designed to connect isolated forest fragments with high rhesus macaque population densities, creating government programs that compensate farmers for income lost due to crop-raiding, and educational outreach that informs local villagers of the importance of conservation and protecting biodiversity, offer the most effective solutions to reduce HRMC in Nepal.

Global importance of Indigenous Peoples, their lands, and knowledge systems for saving the world's primates from extinction

Primates, represented by 521 species, are distributed across 91 countries primarily in the Neotropic, Afrotropic, and Indo-Malayan realms. Primates inhabit a wide range of habitats and play critical roles in sustaining healthy ecosystems that benefit human and nonhuman communities. Approximately 68% of primate species are threatened with extinction because of global pressures to convert their habitats for agricultural production and the extraction of natural resources. Here, we review the scientific literature and conduct a spatial analysis to assess the significance of Indigenous Peoples' lands in safeguarding primate biodiversity. We found that Indigenous Peoples' lands account for 30% of the primate range, and 71% of primate species inhabit these lands. As their range on these lands increases, primate species are less likely to be classified as threatened or have declining populations. Safeguarding Indigenous Peoples' lands, languages, and cultures represents our greatest chance to prevent the extinction of the world's primates.

The fecal metabolome of black howler monkeys (Alouatta pigra) varies in response to seasonal dietary changes

Mammals rely on the metabolic functions of their gut microbiota to meet their energetic needs and digest potentially toxic components in their diet. The gut microbiome plastically responds to shifts in host diet and may buffer variation in energy and nutrient availability. However, it is unclear how seasonal differences in the gut microbiome influence microbial metabolism and nutrients available to hosts. In this study, we examine seasonal variation in the gut metabolome of black howler monkeys (Alouatta pigra) to determine whether those variations are associated with differences in gut microbiome composition and nutrient intake, and if plasticity in the gut microbiome buffers shortfalls in energy or nutrient intake. We integrated data on the metabolome of 81 faecal samples from 16 individuals collected across three distinct seasons with gut microbiome, nutrient intake and plant metabolite consumption data from the same period. Faecal metabolite profiles differed significantly between seasons and were strongly associated with changes in plant metabolite consumption. However, microbial community composition and faecal metabolite composition were not strongly associated. Additionally, the connectivity and stability of faecal metabolome networks varied seasonally, with network connectivity being highest during the dry, fruit‐dominated season when black howler monkey diets were calorically and nutritionally constrained. Network stability was highest during the dry, leaf‐dominated season when most nutrients were being consumed at intermediate rates. Our results suggest that the gut microbiome buffers seasonal variation in dietary intake, and that the buffering effect is most limited when host diet becomes calorically or nutritionally restricted.

Disassociation of social and sexual partner relationships in a gibbon population with stable one-male two-female groups

Adult males living in a one-male multi-female social group are expected to try to monopolize copulations with resident females to increase reproductive fitness. Gibbons have traditionally been described as living in monogamous groups, with the sole resident adult male assumed to sire all of the group's offspring. Here, we used microsatellite analyses and behavioral observations to examine rates of extra-group paternity (EGP) over 16 years in a population of crested gibbons (Nomascus concolor) that form stable and long-term one-male two-female social units. Forty percent of offspring (N = 14) were sired by extra-group males. To understand this high level of EGP, we tested whether inbreeding avoidance was related to EGP. Females who engaged in EGP did not show larger pairwise relatedness with their resident male compared to females who did not engage in EGP. Nevertheless, the standardized heterozygosity of EGP offspring was significantly higher than for offspring sired by the group's resident male. These results provide partial support for the inbreeding avoidance hypothesis. It appears that resident male crested gibbons are unable to monopolize resident females' matings. Our results indicate that long-term social partners are often distinct from sexual partners in this population. Clearly, the breeding system of crested gibbons is more flexible than previously thought, indicating a need for integrating long-term behavioral data and genetic research to re-evaluate gibbon social and sexual relationships derived from concepts of monogamy and pair-bonding.

Diverse grouping and mating strategies in the Critically Endangered Hainan gibbon (Nomascus hainanus)

Understanding flexibility in the social structure and mating strategies of the world's last remaining population (35 individuals) of wild Hainan gibbons (Nomascus hainanus) is critical for developing effective management plans to aid in their population recovery. Three of the five remaining Hainan gibbon groups (A, B, and C) currently live in a social unit characterized by two or three adult males, two reproducing adult females, and offspring. A fourth group (D) contains one adult male, two adult females, and offspring, and Group E contains a single adult male-adult female pair with a young infant. In this study, we describe observations of copulations between multiple resident males and one of the two resident females in Group C. Group C is best described as a small multi-male/multi-female group. We found that this breeding female (F2) solicited copulations from two resident adult males (M1 and M2) on the same day, and also mated with each of these two males on different days. Resident males were not observed to interrupt the mating pair. Although factors such as a biased adult sex ratio, severe population disruption, and habitat degradation can help explain variation in group composition and mating strategies in Hainan gibbons, we argue that there exists considerable mating system variability across gibbon species, and that this variability offers important insights into male and female Hainan gibbon group structure and reproductive strategies.

The 10th anniversary of the scientific description of the black snub-nosed monkey (Rhinopithecus strykeri): It is time to initiate a set of new management strategies to save this critically endangered primate from extinction

Traditionally, the genus Rhinopithecus (Milne-Edwards, 1872, Primates, Colobinae) included four allopatric species, restricted in their distributions to China and Vietnam. In 2010, a fifth species, the black snub-nosed monkey (Rhinopithecus strykeri) was discovered in the Gaoligong Mountains located on the border between China and Myanmar. Despite the remoteness, complex mountainous terrain, dense fog, and armed conflict that characterizes this region, over this past decade Chinese and Myanmar scientists have begun to collect quantitative data on the ecology, behavior and conservation requirements of R. strykeri. In this article, we review the existing data and present new information on the life history, ecology, and population size of R. strykeri. We discuss these data in the context of past and current conservation challenges faced by R. strykeri, and propose a series of both short-term and long-term management actions to ensure the survival of this Critically Endangered primate species. Specifically, we recommend that the governments and stakeholders in China and Myanmar formulate a transboundary conservation agreement that includes a consensus on bilateral exchange mechanisms, scientific research and monitoring goals, local community development, cooperation to prevent the hunting of endangered species and cross-border forest fires. These actions will contribute to the long-term conservation and survival of this Critically Endangered species.

Factors affecting the crop raiding behavior of wild rhesus macaques in Nepal: Implications for wildlife management

In many areas of South Asia and Southeast Asia, macaques inhabiting agricultural landscapes are considered serious crop pests by local farmers. In Nepal, for example, the expansion of monocultures, increased forest fragmentation, the degradation of natural habitats, and changing agricultural practices have led to a significant increase in the frequency of human-macaque conflict. In order to more fully understand the set of factors that contribute to macaque crop raiding, and the set of preventive measures that can be put in place to avoid human-macaque conflict, we examined patterns of crop raiding by a group of 52 rhesus macaques (Macaca mulatta) in the Kavrepalanchok district, Nepal. We present data on macaque inflicted crop damage in 172 agricultural plots (each plot measuring 380 m²) from August to October 2019. Our results indicate that farmland invasions by macaques were principally affected by crop type (maize was preferred over rice), nearness of farmland to both the forest edge and the major travel route used by the macaques, and the mitigation efforts applied by farmers to discourage crop raiding. We found that as the proportion of maize farmland in the most direct path from the macaque's main travel route to nearby crop raiding sites increased, the amount of maize damage decreased. This is likely explained by the fact that macaques traveling across several adjacent maize fields encounter multiple farmers protecting their crops. We estimated that the financial cost to individual farmer households of macaque maize and rice raiding was on average US$ 14.9 or 4.2% of their annual income from cultivating those two crops. As human-macaque conflict is one of the most critical challenges faced by wildlife managers in South Asia and Southeast Asia, studies of macaque crop raiding behavior provide an important starting point for developing effective strategies to manage human-macaque conflict while promoting both primate conservation and the economic well-being of the local community.

Foraging networks and social tolerance in a cooperatively breeding primate (Callithrix jacchus)

Within-group competition over food resources can be a major cost of social living. In the wild, foragers are confronted with social (e.g. hierarchical rank) and ecological (e.g. food availability and distribution) challenges that affect their foraging decisions and feeding success. Exhibiting prosocial behaviours, such as tolerance at feeding sites, can benefit group members by developing affiliative social relationships, enhancing access to resources and maximizing fitness. We examined social tolerance at feeding sites in Callithrix jacchus, a cooperatively breeding primate species. We investigated the set of social (rank, age and sex) and ecological (food availability) factors that influence the structure and dynamics of within-group foraging association networks. We designed and conducted an experimental field study of four wild groups of common marmosets in which we controlled food distribution (concentrated or scattered) and productivity (high, medium or low food rewards). Then, we used social network analyses to assess the number and strength of foraging associations among group members, their effects on individual food consumption, and whether recent experiences with conspecifics during foraging affected subsequent associations. Overall, common marmoset foraging association networks were cohesive, as group members jointly occupied feeding sites. The number and strength of associations varied depending on the ecological context. Associations were stronger during conditions in which food was concentrated at a single site. Individuals obtained greater access to food resources when sharing a feeding site with conspecifics, but once a food item was obtained, the forager moved to a nearby tree and consumed it away from others. Additionally, the strength of previous foraging associations and subsequent levels of social tolerance at feeding sites were positively related, a relationship compatible with the ability of memorizing associations over time and recalling the information in future decision-making. In sum, marmosets adjusted their partner choices and the strength of foraging associations in response to food availability. They exhibited increased social tolerance at feeding sites during conditions in which opportunities for contest competition were expected to be greatest. These cooperative breeding primates appear to mutually benefit by maintaining cohesive and strong affiliative relationships, and by increasing opportunities for coordinated behaviour and offspring survival.

Assessing the Influence of Environmental Sources on the Gut Mycobiome of Tibetan Macaques

The distribution and availability of microbes in the environment has an important effect on the composition of the gut microbiome of wild vertebrates. However, our current knowledge of gut-environmental interactions is based principally on data from the host bacterial microbiome, rather than on links that establish how and where hosts acquire their gut mycobiome. This complex interaction needs to be clarified. Here, we explored the relationship between the gut fungal communities of Tibetan macaques (Macaca thibetana) and the presence of environmental (plant and soil) fungi at two study sites using the fungal internal transcribed spacer (ITS) and next generation sequencing. Our findings demonstrate that the gut, plant and soil fungal communities in their natural habitat were distinct. We found that at both study sites, the core abundant taxa and ASVs (Amplicon Sequence Variants) of Tibetan macaques’ gut mycobiome were present in environmental samples (plant, soil or both). However, the majority of these fungi were characterized by a relatively low abundance in the environment. This pattern implies that the ecology of the gut may select for diverse but rare environmental fungi. Moreover, our data indicates that the gut mycobiome of Tibetan macaques was more similar to the mycobiome of their plant diet than that present in the soil. For example, we found three abundant ASVs (Didymella rosea, Cercospora, and Cladosporium) that were present in the gut and on plants, but not in the soil. Our results highlight a relationship between the gut mycobiome of wild primates and environmental fungi, with plants diets possibly contributing more to seeding the macaque’s gut mycobiome than soil fungi.

Social strategies used by dispersing males to integrate into a new group in Tibetan macaques (Macaca thibetana)

In group-living mammals, an individual's fitness depends, in part, on the quality of social relationships it has with others. Among species of nonhuman primates in which one sex is philopatric, individuals of that sex often develop strong social bonds and alliances with closely related kin. Less is known regarding the social processes used by dispersing adults to form stable bonds with nonkin in their new group. From May to December 2009, April to August 2010, September to December 2011, and February to May 2012, we collected data on grooming interactions in wild Tibetan macaques (Macaca thibetana), a female philopatric species, at Mt. Huangshan, China. Our goal was to compare social interactions and bond formation between resident males, recent immigrant males, and resident females. Our results indicate that recent immigrant males formed stable partner relationships with a small number of resident females and groomed these females more frequently or for longer than they received grooming. In contrast, resident males switched female grooming partners more frequently, received more grooming than they gave, and formed relationships with a greater number of female partners. We argue that the ability of recent immigrant male Tibetan macaques to maintain strong and persistent social bonds with a small set of resident adult females is a primary factor that enables them to establish residence in a new multimale-multifemale group. The present study provides new and important insights into the integrated social strategies used by dispersing males and resident females to maintain group stability.

Investment in science can mitigate the negative impacts of land use on declining primate populations

Changes in land use and the conversion of natural forests to agricultural fields and cattle pastures are threatening the survival of many species of wild animals, including nonhuman primates. Given its almost 1.4 billion people, China faces a difficult challenge in balancing economic development, human well-being, environmental protection, and animal conservation. We examined the effects of poverty, anthropogenic land use (cropland and pasture/grazing), human population growth, government investment in science and public attention to primates during the period from the 1980s to 2015 on primate population persistence in China. We analyzed these data using generalized mixed-effects models, structural equation models (SEM) and random forests (a machine learning technique). We found that 16 of 21 (76%) primate species in China, for which data are available, have experienced a population decline over the past 35 years. Factors contributing most to primate population decline included human poverty and the conversion of natural habitat to cropland. In contrast, the five species of primates that were characterized by recent population increases were the subjects of substantial government research funding and their remaining distribution occurs principally in protected areas (PAs). We argue that increased funding for research, the establishment and expansion of PAs, a national policy focused on reducing poverty, and educational programs designed to inform and encourage local people to participate in scientific investigation and wildlife protection, can mitigate the negative impacts of historical patterns of land conversion on primate population survival in China.

Captivity Is Associated With Gut Mycobiome Composition in Tibetan Macaques (Macaca thibetana)

Although recent studies have revealed that gut fungi may play an important functional role in animal biology and health, little is known concerning the effects of anthropogenic pressures on the gut mycobiome. Here, we examined differences of the gut mycobiome in wild and captive populations of Tibetan macaques (Macaca thibetana) targeting the fungal internal transcribed spacer (ITS) and using next generation sequencing. Our findings demonstrate that the diversity, composition, and functional guild of the Tibetan macaque gut mycobiome differ across populations living in different habitats. We found that Tibetan macaques translocated from the wild into a captive setting for a period of 1 year, were characterized by a reduction in fungal diversity and an increase in the abundance of potential gut fungal pathogens compared to wild individuals. Furthermore, we found that the relative abundance of two main fungal guilds of plant pathogens and ectomycorrhizal fungi was significantly lower in captive individuals compared to those living in the wild. Our results highlight that, in addition to bacteria, gut fungi vary significantly among individuals living in captive and wild settings. However, given limited data on the functional role that fungi play in the host’s gut, as well as the degree to which a host’s mycobiome is seeded from fungi in the soil or ingested during the consumption of plant and animal foods, controlled studies are needed to better understand the role of the local environment in seeding the mycobiome.

Mitochondrial DNA control region sequencing of the critically endangered Hainan gibbon (Nomascus hainanus) reveals two female origins and extremely low genetic diversity

The Hainan gibbon (Nomascus hainanus) is endemic to China and is the world's rarest ape. The remaining wild population totals only 33 individuals. In the current study, we sequenced the Mitochondrial DNA control region of 12 wild Hainan gibbons representing three social groups of the five remaining groups. By conducting population genetic analyses, we found that the proportion of four nucleotides (T, C, A and G) were 29.0%, 27.2%, 31.9% and 11.9%, respectively. Hypervariable segments of the mtDNA D-loop region (1005 bp in length), indicated five variable sites (a point mutation), with only two haplotypes present among the 12 samples. We observed that the genetic diversity of Hainan gibbons is lower than that reported in any other wild primate population, and that the two haplotypes detected, represent two ancestral lineages. These findings have important implications for proposing effective conservation strategies to protect this Critically Endangered ape species.

Advocacy and Activism as Essential Tools in Primate Conservation

Primates are facing a global extinction crisis driven by an expanding human population, environmental degradation, the conversion of tropical forests into monocultures for industrial agriculture and cattle ranching, unsustainable resource extraction, hunting, climate change, and the threat of emerging zoonotic diseases. And, although many primate scientists have dedicated their careers to conservation, 65% of primate species are listed as Vulnerable, Endangered, or Critically Endangered, and >75% are experiencing a population decline. Projections indicate that by the end of the century, an additional 75% of the area currently occupied by wild primates will be lost to agriculture. Clearly, we are losing the battle and must change business-as-usual if we are to protect wild primates and their habitats. This article is a call to action. Primate societies and their membership need to expand their engagement in scientific advocacy and scientific activism designed to educate, inspire, organize, and mobilize global citizens to join together, lobby business leaders and politicians in both primate habitat countries and in consumer nations, boycott forest-risk products, participate in demonstrations and letter writing campaigns, and use social media to effect transformational change. We are the experts, and the more we and our professional organizations drive the public policy debate on wildlife conservation and environmental justice, the more successful we will be in protecting the world's primates from extinction. The time to act is now!

Effects of Hierarchical Steepness on Grooming Patterns in Female Tibetan Macaques (Macaca thibetana)

Hierarchical steepness, defined as status asymmetries among conspecifics living in the same group, is not only used as a main characteristic of animal social relationships, but also represents the degree of discrepancy between supply and demand within the framework of biological market theory. During September and December 2011, we studied hierarchical steepness by comparing variation in grooming patterns in two groups of Tibetan macaques (Macaca thibetana), a primate species characterized by a linear dominance hierarchy. Using a focal sampling method, we collected behavioral data from two provisioned, free-ranging groups (YA1 and YA2) at Mt. Huangshan, China. We found that female dominance hierarchies were steeper in the YA1 group (0.81 based on the proportion of wins-losses and 0.66 based on dyadic dominance indices) than among members of the YA2 group (0.76 based on the proportion of wins-losses and 0.56 based on dyadic dominance indices). Females in the YA1 group groomed more frequently and for longer duration than females in YA2. Further analysis showed that grooming patterns of high- and low-ranking females did not differ between the two groups. However, middle-ranking females in YA1 groomed conspecifics more frequently and for longer duration than middle-ranking females in YA2. Our results suggest that the steepness of a dominance hierarchy plays an important role in the set of social strategies used by middle-ranking females to avoid a reduction in rank, as well as to increase their rank (the dilemma of middle class hypothesis). We suggest that future studies focus on individuals of middle-rank in order to better understand how the dynamics of rank stability and rank changes influence social relationships, and affiliative and competitive interactions in non-human primates.

Navigating in a challenging semiarid environment: the use of a route-based mental map by a small-bodied neotropical primate

To increase efficiency in the search for resources, many animals rely on their spatial abilities. Specifically, primates have been reported to use mostly topological and rarely Euclidean maps when navigating in large-scale space. Here, we aimed to investigate if the navigation of wild common marmosets inhabiting a semiarid environment is consistent with a topological representation and how environmental factors affect navigation. We collected 497 h of direct behavioral and GPS information on a group of marmosets using a 2-min instantaneous focal animal sampling technique. We found that our study group reused not only long-route segments (mean of 1007 m) but entire daily routes, a pattern that is not commonly seen in primates. The most frequently reused route segments were the ones closer to feeding sites, distant to resting sites, and in areas sparse in tree vegetation. We also identified a total of 56 clustered direction change points indicating that the group modified their direction of travel. These changes in direction were influenced by their close proximity to resting and feeding sites. Despite our small sample size, the obtained results are important and consistent with the contention that common marmosets navigate using a topological map that seems to benefit these animals in response to the exploitation of clustered exudate trees. Based on our findings, we hypothesize that the Caatinga landscape imposes physical restrictions in our group's navigation such as gaps in vegetation, small trees and xerophytic plants. This study, based on preliminary evidence, raises the question of whether navigation patterns are an intrinsic characteristic of a species or are ecologically dependent and change according to the environment.

The Genetic Status of the Critically Endangered Hainan Gibbon (Nomascus hainanus): A Species Moving Toward Extinction

The Hainan gibbon (Nomascus hainanus), once widespread across Hainan, China, is now found only in the Bawangling National Nature Reserve. With a remaining population size of 33 individuals, it is the world's rarest primate. Habitat loss and fragmentation are the primary drivers of Hainan gibbon population decline. In this study, we integrated data based on field investigations and genotype analyses of 10 microsatellite loci (from fecal samples) to assess genetic diversity in this Critically Endangered primate species. We found that the genetic diversity of the Hainan gibbon is extremely low, with 7 of 8 microsatellite loci exhibiting decreased diversity. Additional molecular analyses are consistent with field observations indicating that individuals in groups A, B, and C are closely related, the female-male sex ratios of the offspring deviates significantly from 1:1, and the world's remaining Hainan gibbon population is expected to experience continued high levels of inbreeding in the future. Given extensive habitat loss (99.9% of its natural range has been deforested) and fragmentation, this rarest ape species faces impending extinction unless corrective measures are implemented immediately.

Comprehensive Knowledge of Reservoir Hosts is Key to Mitigating Future Pandemics

Coronavirus disease 2019 (COVID-19) and other epidemics (such as severe acute respiratory syndrome [SARS], Ebola, and H1N1) are stark reminders that knowledge of animal behavior and ecosystem health are key to controlling the spread of zoonotic diseases early in their onset. However, we have very limited information about the set of behavioral and ecological factors that promote viral spillover and the effects that has on ecosystem health and disease transmission. Thus, expanding our current knowledge of reservoir hosts and pandemics represents an urgent and critical tool in ecological epidemiology. We also propose to create an integrative database that ranks animal species in terms of their likelihood as hosts for specific infectious diseases. We call for a global and cooperative effort of field and laboratory scientists to create, maintain, and update this information in order to reduce the severity of future pandemics.

Neonatal nipple preference and maternal cradling laterality in wild Taihangshan macaques (Macaca mulatta tcheliensis)

Lateralized behavior is considered an observable phenotype of cerebral functional asymmetry and has been documented in many mammalian species. In the present study, we examined evidence of lateralization in neonatal nipple contact, maternal cradling, and the relationship between these two behaviors during the first 12 weeks of life in wild Taihangshan macaques (Macaca mulatta tcheliensis). The results showed that across our sample of nine mother-infant dyads: (1) Seven of nine neonates exhibited a significant left-side nipple preference during the first 12 weeks of life, whereas eight of nine mothers displayed a significant right-side cradling preference; (2) at the population level, there was a significant preference for left nipple contact by neonatal Taihangshan macaques and a significant right-hand maternal cradling preference; (3) at the population level, there was a nonsignificant negative correlation between neonatal nipple preference and maternal cradling bias; and (4) the strength of individual neonatal nipple preference and maternal cradling laterality were not correlated. We conclude that asymmetry in nipple contact of Taihangshan macaques occurs early in behavioral development. Given that infant Taihangshan macaques are able to nurse and cling unassisted to their mothers within a few days after birth, it appears that the infant rather than its mother is responsible for determining a nipple-side preference. Our results indicating a left-side nipple bias in 78% of wild neonatal Taihangshan macaques are most consistent with the heartbeat hypothesis.

Male and female birth attendance and assistance in a species of non-human primate (Rhinopithecus bieti)

Birth attendance, or midwifery service, is an important characteristic in human evolution, and has been argued to separate our lineage from other taxa in the animal kingdom. Recent studies, however, indicate that similar or analogous behaviors also may occur in a small number of nonhuman primate species. Here, we report the first case of both male and female attendance and female birth assistance in a wild species of nonhuman primate, the black-and-white snub-nosed monkey (Rhinopithecus bieti). At our field site in Yunnan, China we observed a diurnal birth event in which the leader male of a one-male unit (OMU) remained in close- proximity (0-2 m) to the parturient, groomed her, and remained vigilant over a five hour pre- and postpartum period. In addition, a multiparous female member of the OMU also remained in close proximity to the soon-to-be mother, helped to pull the neonate from the birth canal, took the neonate from the new mother within 15 s of the birth, held the infant for 20 min, and then severed the umbilical cord. For the next several days the leader male traveled in close-proximity to the new mother and four days after the birth event, we observed him to share food with her. Given that diurnal births are extremely rare in this primate species; it remains unclear the degree to which the events we observed commonly occur during nighttime births. We argue that adult male and female black-and-white snub-nosed monkeys are highly attracted to young infants, and birth attendance and birth assistance in this, and certain other primate species, may play a critical role in maternal and infant survivorship.

Current and future trends in socio-economic, demographic and governance factors affecting global primate conservation

Currently, ~65% of extant primate species (ca 512 species) distributed in 91 countries in the Neotropics, mainland Africa, Madagascar, South Asia and Southeast Asia are threatened with extinction and 75% have declining populations as a result of deforestation and habitat loss resulting from increasing global market demands, and land conversion for industrial agriculture, cattle production and natural resource extraction. Other pressures that negatively impact primates are unsustainable bushmeat hunting, the illegal trade of primates as pets and as body parts, expanding road networks in previously isolated areas, zoonotic disease transmission and climate change. Here we examine current and future trends in several socio-economic factors directly or indirectly affecting primates to further our understanding of the interdependent relationship between human well-being, sustainable development, and primate population persistence. We found that between 2001 and 2018 ca 191 Mha of tropical forest (30% canopy cover) were lost as a result of human activities in the five primate range regions. Forty-six percent of this loss was in the Neotropics (Mexico, Central and South America), 30% in Southeast Asia, 21% in mainland Africa, 2% in Madagascar and 1% in South Asia. Countries with the greatest losses (ca 57% of total tree cover loss) were Brazil, Indonesia, DRC, China, and Malaysia. Together these countries harbor almost 50% of all extant primate species. In 2018, the world human population was estimated at ca 8bn people, ca 60% of which were found in primate range countries. Projections to 2050 and to 2100 indicate continued rapid growth of the human populations in these five primate range regions, with Africa surpassing all the other regions and totaling ca 4bn people by the year 2100. Socioeconomic indicators show that, compared to developed nations, most primate range countries are characterized by high levels of poverty and income inequality, low human development, low food security, high levels of corruption and weak governance. Models of Shared Socioeconomic Pathway scenarios (SSPs) projected to 2050 and 2100 showed that whereas practices of increasing inequality (SSP4) or unconstrained growth in economic output and energy use (SSP5) are projected to have dire consequences for human well-being and primate survivorship, practices of sustainability-focused growth and equality (SSP1) are expected to have a positive effect on maintaining biodiversity, protecting environments, and improving the human condition. These results stress that improving the well-being, health, and security of the current and future human populations in primate range countries are of paramount importance if we are to move forward with effective policies to protect the world's primate species and promote biodiversity conservation.

Life in a harsh environment: the effects of age, sex, reproductive condition, and season on hair cortisol concentration in a wild non-human primate

Hair cortisol concentration (HCC) provides a long-term retrospective measure of hypothalamic–pituitary–adrenal axis activity, and is increasingly used to assess the life history, health and ecology of wild mammals. Given that sex, age, season and pregnancy influence HCC, and that it may indicate ongoing stress, we examined HCC in common marmosets (Callithrix jacchus) naturally inhabiting a hot and dry semi-desert like habitat, Caatinga, in northeastern Brazil. We trapped, measured, weighed, marked and collected shaved hair from the back of the neck of 61 wild marmosets during the wet and dry seasons. Using enzyme immunoassay, we found that HCC was higher in the dry season compared with the wet season among all age/sex classes. Females had significantly higher HCC than males, juveniles had higher HCC than adults, and reproductively active adult females and non-pregnant/non lactating adult females did not differ in HCC. There were no interaction effects of sex, age, group, or season on HCC. The magnitude of the effect of this extremely hot and dry environment (average yearly rainfall was only 271 mm) on HCC in common marmosets is difficult to ascertain as these animals are also experiencing a variety of other stressors. However, the elevated HCC seen in common marmosets during the 5–8 month dry season, suggests these primates face an extended period of heat, water and possibly nutritional stress, which appears to result in a high rate of juvenile mortality.

Infant attraction: why social bridging matters for female leadership in Tibetan macaques

Leadership is a key issue in the study of collective behavior in social animals. Affiliation–leadership models predict that dyadic partner preferences based on grooming relationships or alliance formation positively affect an individual’s decision to follow or support a conspecific. In the case of many primate species, females without young infants are attracted to mother–infant dyads. However, the effects of mother–infant–female associations on affiliation–leadership models remain less clear. In free-ranging Tibetan macaques Macaca thibetana, we used social network analysis to examine the importance of “mother-infant-adult female” social bridging events as a predictor of who leads and who follows during group movement. Social bridging is a common behavior in Tibetan macaques and occurs when 2 adults, generally females, engage in coordinated infant handling. Using eigenvector centrality coefficients of social bridging as a measure of social affiliation, we found that among lactating females, initiating bridging behavior with another female played a significant role in leadership success, with the assisting female following the mother during group movement. Among nonlactating females, this was not the case. Our results indicate that infant attraction can be a strong trigger in collective action and directing group movement in Tibetan macaques and provides benefits to mothers who require helpers and social support in order to ensure the safety of their infants. Our study provides new insights into the importance of the third-party effect in rethinking affiliation–leadership models in group-living animals.

Cafeteria-style feeding trials provide new insights into the diet and nutritional strategies of the black snub-nosed monkey (Rhinopithecus strykeri): Implications for conservation

Anthropogenic changes and fragmentation of natural habitats often exert a negative effect on resource availability and distribution, and the nutritional ecology and feeding behavior of nonhuman primates. The goals of this study are to examine food choice and to identify the nutritional profile of foods consumed by the Critically Endangered black snub-nosed monkey (Rhinopithecus strykeri). To accomplish our study goals, we presented cafeteria-style feeding trials of fresh food items collected in the home range of wild black snub-nosed monkeys to the only two captive R. strykeri, and compared the nutritional profiles of the leafy foods (buds, young, and mature leaves, 100 i23tems from 70 plant species) selected with those avoided (54 items from 48 plant species). Overall, the results indicate that captive R. strykeri selected foods that were higher in moisture (Mo; 77.7%), crude protein (CP; 21.2%), total nonstructural carbohydrates (TNC; 34.9%), and phosphorus (P; 0.37%) while tending to avoid foods with a neutral detergent fiber (NDF) content of greater than 46.8%. Leaves collected in autumn and selected by the monkeys were characterized by a slightly higher amount of metabolizable energy (ME) than those rejected (1,350 kJ/100 g vs. 1,268 kJ/100 g). In contrast, the protein content of foods collected and consumed during the spring was greater (22.9%) than in autumn (16.4%). Random Forests modeling, an ensemble learning method, indicated that the proportion of Mo, NDF, ME, CP, P, and TNC were among the most important factors in predicting which items were consumed by the captive R. strykeri during spring and autumn. On the basis of the nutritional profile of foods consumed across the two seasons, we identified 18 nutrient-rich native plant species that we recommend for use in ex- and in-situ conservation management and reforestation programs to provide long-term access to a nutritionally adequate diet.

Bachelor groups in primate multilevel society facilitate gene flow across fragmented habitats

In the face of ongoing habitat fragmentation, many primate species have experienced reduced gene flow resulting in a reduction of genetic diversity, population bottlenecks, and inbreeding depression, including golden snub-nosed monkeys Rhinopithecus roxellana. Golden snub-nosed monkeys live in a multilevel society composed of several 1 male harem units that aggregate to form a cohesive breeding band, which is followed by one or more bachelor groups composed of juvenile, subadult, and adult male members. In this research, we examine the continuous landscape resistance surface, the genetic diversity and patterns of gene flow among 4 isolated breeding bands and 1 all-male band in the Qinling Mountains, China. Landscape surface modeling suggested that human activities and ecological factors severely limit the movement of individuals among breeding bands. Although these conditions are expected to result in reduced gene flow, reduced genetic diversity, and an increased opportunity for a genetic bottleneck, based on population genetic analyses of 13 microsatellite loci from 188 individuals inhabiting 4 isolated breeding bands and 1 all-male band, we found high levels of genetic diversity but low levels of genetic divergence, as well as high rates of gene flow between males residing in the all-male band and each of the 4 breeding bands. Our results indicate that the movement of bachelor males across the landscape, along with their association with several different breeding bands, appears to provide a mechanism for promoting gene flows and maintaining genetic diversity that may counteract the otherwise isolating effects of habitat fragmentation.

Distinguished primatologist address-moving from advocacy to activism: Changing views of primate field research and conservation over the past 40 years

Field studies of wild nonhuman primates have grown exponentially over the past 40 years and our knowledge of primate behavior, ecology, and social, and mating systems has expanded greatly. However, we are facing a major extinction crisis with some 60% of all primate species listed as threatened and more than 75% of species with declining populations. The primary factor driving primate population decline is human population increase, which over the past 50 years has resulted in the unsustainable conversion and degradation of natural landscapes for industrial agriculture, the production of nonagricultural commodities for international trade, pastureland for cattle, dam construction, fossil fuel exploration, mining, and the construction of road networks and infrastructure to support large urban centers. Recent ecological modeling predicts that by the end of the century, the four primate-richest countries in the world will lose 32-78% of their existing primate habitat to agricultural expansion, and nine of the top 15 primate-richest countries are expected to have 80-100% of their primate species extinct or threatened with extinction. If we are going to save the world's primates, the time to act is now! Not only should all primate field research include a strong conservation component, but in addition we must actively join with our professional societies, zoos and research facilities, universities, conservation organizations, concerned business leaders, global citizens, like-minded political leaders, and grassroots organizations to inform, demand and direct governments, multinational corporations, and international organizations to engage in transformational change to protect biodiversity and seek environmental justice against those entities that actively destroy our planet. As the chief academic discipline dedicated to the study of primates, we must organize and collectively move from being advocates for primate conservation to becoming activists for primate conservation. This is a call to action.

Plasticity in the Human Gut Microbiome Defies Evolutionary Constraints

The gut microbiome of primates, including humans, is reported to closely follow host evolutionary history, with gut microbiome composition being specific to the genetic background of its primate host. However, the comparative models used to date have mainly included a limited set of closely related primates. To further understand the forces that shape the primate gut microbiome, with reference to human populations, we expanded the comparative analysis of variation among gut microbiome compositions and their primate hosts, including 9 different primate species and 4 human groups characterized by a diverse set of subsistence patterns (n = 448 samples). The results show that the taxonomic composition of the human gut microbiome, at the genus level, exhibits increased compositional plasticity. Specifically, we show unexpected similarities between African Old World monkeys that rely on eclectic foraging and human populations engaging in nonindustrial subsistence patterns; these similarities transcend host phylogenetic constraints. Thus, instead of following evolutionary trends that would make their microbiomes more similar to that of conspecifics or more phylogenetically similar apes, gut microbiome composition in humans from nonindustrial populations resembles that of generalist cercopithecine monkeys. We also document that wild cercopithecine monkeys with eclectic diets and humans following nonindustrial subsistence patterns harbor high gut microbiome diversity that is not only higher than that seen in humans engaging in industrialized lifestyles but also higher compared to wild primates that typically consume fiber-rich diets.IMPORTANCE The results of this study indicate a discordance between gut microbiome composition and evolutionary history in primates, calling into question previous notions about host genetic control of the primate gut microbiome. Microbiome similarities between humans consuming nonindustrialized diets and monkeys characterized by subsisting on eclectic, omnivorous diets also raise questions about the ecological and nutritional drivers shaping the human gut microbiome. Moreover, a more detailed understanding of the factors associated with gut microbiome plasticity in primates offers a framework to understand why humans following industrialized lifestyles have deviated from states thought to reflect human evolutionary history. The results also provide perspectives for developing therapeutic dietary manipulations that can reset configurations of the gut microbiome to potentially improve human health.

Expanding global commodities trade and consumption place the world’s primates at risk of extinction

As a consequence of recent human activities. populations of approximately 75% of the world’s primates are in decline, and more than 60% of species (n = 512) are threatened with extinction. Major anthropogenic pressures on primate persistence include the widespread loss and degradation of natural habitats caused by the expansion of industrial agriculture, pastureland for cattle, logging, mining, and fossil fuel extraction. This is the result of growing global market demands for agricultural and nonagricultural commodities. Here, we profile the effects of international trade of forest-risk agricultural and nonagricultural commodities, namely soybean, oil palm, natural rubber, beef, forestry products, fossil fuels, metals, minerals, and gemstones on habitat conversion in the Neotropics, Africa, and South and Southeast Asia. Total estimated forest loss for these regions between 2001 and 2017 was ca 179 million ha. The average percent of commodity-driven permanent deforestation for the period 2001–2015 was highest in Southeast Asia (47%) followed by the Neotropics (26%), South Asia (26%), and Africa (7%). Commodities exports increased significantly between 2000 and 2016 in all primate range regions leading to the widespread conversion of forested land to agricultural fields and an increase in natural resource extraction. In 2016, US $1.1 trillion of natural-resource commodities were traded by countries in primate range regions. The Neotropics accounted for 41% of the total value of these exports, Southeast Asia for 27%, Africa 21%, and South Asia 11%. Major commodity exporters in 2016 were Brazil, India, Indonesia, Malaysia and South Africa, countries of high primate diversity and endemism. Among the top 10 importers were China, the US, Japan, and Switzerland. Primate range countries lag far behind importer nations in food security and gross domestic product per capita, suggesting that trade and commodity-driven land-use have done little to generate wealth and well-being in primate habitat countries. Modeling of land-use and projected extinction of primate species by 2050 and 2100 under a business as usual scenario for 61 primate range countries indicate that each country is expected to see a significant increase in the number of species threatened with extinction. To mitigate this impending crisis, we advocate the “greening” of trade, a global shift toward a low-meat diet, reduced consumption of oil seed, diminished use of tropical timber, fossil fuels, metals, minerals, and gemstones from the tropics, accompanied by a stronger and sustained global resolve to regulate and reverse the negative impacts of growing unsustainable global demands and commodity trade on income inequality, and the destruction of primates and their habitats.

The gut microbiome and metabolome of saddleback tamarins (Leontocebus weddelli): Insights into the foraging ecology of a small-bodied primate

Body mass is a strong predictor of diet and nutritional requirements across a wide range of mammalian taxa. In the case of small-bodied primates, because of their limited gut volume, rapid food passage rate, and high metabolic rate, they are hypothesized to maintain high digestive efficiency by exploiting foods rich in protein, fats, and readily available energy. However, our understanding of the dietary requirements of wild primates is limited because little is known concerning the contributions of their gut microbiome to the breakdown and assimilation of macronutrients and energy. To study how the gut microbiome contributes to the feeding ecology of a small-bodied primate, we analyzed the fecal microbiome composition and metabolome of 22 wild saddleback tamarins (adult body mass 360-390 g) in Northern Bolivia. Samples were analyzed using high-throughput Illumina sequencing of the 16 S rRNA gene V3-V5 regions, coupled with GC-MS metabolomic profiling. Our analysis revealed that the distal microbiome of Leontocebus weddelli is largely dominated by two main bacterial genera: Xylanibacter and Hallella (34.7 ± 14.7 and 22.6 ± 12.4%, respectively). A predictive analysis of functions likely carried out by bacteria in the tamarin gut demonstrated the dominance of membrane transport systems and carbohydrate metabolism as the predominant metabolic pathways. Moreover, given a fecal metabolome composed mainly of glucose, fructose, and lactic acid (21.7 ± 15.9%, 16.5 ± 10.7%, and 6.8 ± 5.5%, respectively), the processing of highly fermentable carbohydrates appears to play a central role in the nutritional ecology of these small-bodied primates. Finally, the results also show a potential influence of environmentally-derived bacteria in colonizing the tamarin gut. These results indicate high energetic turnover in the distal gut of Weddell's saddleback tamarin, likely influenced by dominant bacterial taxa that facilitate dietary dependence on highly digestible carbohydrates present in nectar, plant exudates, and ripe fruits.

Trait variation and trait stability in common marmosets (Callithrix jacchus) inhabiting ecologically distinct habitats in northeastern Brazil

Understanding the set of factors that promote and constrain a species' ability to exploit ecologically distinct habitats is central for addressing questions of intraspecific variability in behavior and morphology. In this study, we compared newly collected data with published data on body measurements, group size and composition, daily path length, home range, and reproductive output in wild common marmosets naturally inhabiting two contrasting environments in northeastern Brazil: the Atlantic Forest (AF), which is characterized by high biodiversity and reduced seasonality in food availability and the Caatinga (CAT), which is characterized by a severe hot and dry season lasting from 5 to 11 months, drought-resistant plant species, and reduced primary productivity. Despite marked differences in ecological conditions, CAT marmosets and AF marmosets differed minimally in daily path length, home range, reproductive output, and infant survivorship. CAT marmosets were found to live in smaller groups containing fewer adult females than AF marmosets, and also were characterized by a greater surface area to body mass ratio, a trait that may represent an adaptation to the hot and dry conditions of the Caatinga. We propose that in conjunction with body mass reduction, minor adjustments in behavior, the exploitation of cacti as a source of water and nutrients, and access to exudates as a dependable year-round food resource, common marmosets successfully used the same adaptive pattern to maintain high reproductive output and infant survivorship in exploiting these two ecologically distinct environments.

Genome-wide characterization of endogenous retroviruses in snub-nosed monkeys

Background

Endogenous retroviruses (ERV) are remnants of former exogenous retroviruses that had previously invaded the germ line of the host that can be vertically transmitted across generations. While the majority of ERVs lack infectious capacity due to the accumulation of deleterious mutations, some ERVs remain active and produce potentially infectious viral particles. ERV sequences have been reported in all mammals; however, the distribution and diversity of ERVs in several primate taxa remains unclear. The aim of this study was to identify and classify the ERV sequences in the genomes of the golden snub-nosed monkey (Rhinopithecus roxellana) and the black and white snub-nosed monkey (Rhinopithecus bieti), two endangered primate species that exploit high altitude (2,500–4,500 m) temperate forests in southern and central China.

Methods

We used a TBLASTN program to search the ERV sequences of golden snub-nosed monkey genome and the black and white snub-nosed monkey genome. We retrieved all complete accession sequences from the homology search and then used the program, RetroTector, to check and identify the ERV sequences.

Results

We identified 284 and 263 endogenous retrovirus sequences in R. roxellana and R. bieti respectively. The proportion of full-length sequences of all ERV was 30% in R. roxellana and 21% in R. bieti and they were described as class I and class II or gamma-retrovirus and beta-retrovirus genera. The truncation pattern distribution in the two species was virtually identical. By analyzing and comparing ERV orthologues among 6 primate species, we identified the co-evolution of ERVs with their host. We also examined ERV-like sequences and found 48 such genes in R. roxellana and 63 in R. bieti. Some of those genes are associated with diseases, suggesting that ERVs might have involved the abnormal expression of certain genes that have contributed to deleterious consequences for the host.

Conclusions

Our results indicate that ERV sequences are widely distributed in snub-nosed monkeys, and their phylogenetic history can mirror that of their hosts over long evolutionary time scales. In addition, ERV sequences appear to have an important influence on the evolution of host pathology.

Effects of habitat fragmentation and human disturbance on the population dynamics of the Yunnan snub-nosed monkey from 1994 to 2016

In this study, we integrate data from field investigations, spatial analysis, genetic analysis, and Generalized Linear Models (GLMs) to evaluate the effects of habitat fragmentation on the population dynamics, genetic diversity, and range shifts in the endangered Yunnan snub-nosed monkey (Rhinopithecus bieti). The results indicate that from 1994 to 2016, R. bieti population size increased from less than 2,000 to approximately 3,000 individuals. A primary factor promoting population recovery was the establishment of protected nature reserves. We also found that subpopulation growth rates were uneven, with the groups in some areas, and the formation of new groups. Both the fragmentation index, defined as the ratio of the number of forest patches to the total area of forest patches (e.g., increased fragmentation), and increasing human population size had a negative effect on population growth in R. bieti. We recommend that government conservation plans prioritize the protection of particular R. bieti populations, such as the Baimei and Jisichang populations, which have uncommon haplotypes. In addition, effective conservation strategies need to include an expansion of migration corridors to enable individuals from larger populations such as Guyoulong (Guilong) to serve as a source population to increase the genetic diversity of smaller R. bieti subpopulations. We argue that policies designed to protect endangered primates should not focus solely on total population size but also need to determine the amount of genetic diversity present across different subpopulations and use this information as a measure of the effectiveness of current conservation policies and the basis for new conservation policies.

Balancing contest competition, scramble competition, and social tolerance at feeding sites in wild common marmosets (Callithrix jacchus)

Models of primate sociality focus on the costs and benefits of group living and how factors such as rank, feeding competition, alliance formation, and cooperative behavior shape within-group social relationships. We conducted a series of controlled field experiments designed to investigate how resource distribution (one or three of four reward platforms) and amount of food on a reward platform affected foraging strategies and individual feeding success in four groups of wild common marmosets (Callithrix jacchus) living in the Caatinga of northeastern Brazil. At our field site, common marmoset groups are characterized by a single breeding female who can produce twin litters twice per year, strong social cohesion, and cooperative infant care provided principally by several adult male helpers. We found that except for the dominant breeding female, rank (based on aggression) was not a strong predictor of feeding success. Although the breeding female in each group occupied the highest rank position and obtained the greatest daily feeding success, all other group members, including adults and juveniles experienced relatively equal feeding success across most experimental conditions. This was accomplished using a balance of behavioral strategies related to contest competition, scramble competition (associated with a finder's advantage), and social tolerance (sharing the same feeding platform). Based on these results, the social structure of common marmosets is best described as "single female dominance," with the breeding female maximizing food intake needed to offset the energetic costs associated with reproductive twinning and the ability to produce two litters per year. Cooperative infant caregiving, in which the number of helpers is positively correlated with offspring survivorship, requires a set of behavioral strategies that serve to reduce contest competition and promote prosocial behaviors at feeding sites.

Routine allomaternal nursing in a free-ranging Old World monkey

While regular allomaternal nursing (suckling) has been documented in a number of rodent and carnivore species, as well as in some prosimians, New World monkeys, and humans, it is not common in Old World monkeys and apes. Here, we present a detailed field study of allomaternal nursing in golden snub-nosed monkeys (Rhinopithecus roxellana, Colobinae). We found that more than 87% of infants were nursed by females other than their mothers. Allomaternal nursing was largely confined to the first 3 months of an infant's life and occurred predominantly between related females who nursed each other's offspring in a reciprocal manner. Allomaternal nursing enhanced infant survivorship and did not have a negative impact on the future reproductive success of allonursers. Our findings expand the taxonomic distribution of allomaternal nursing and provide fresh insight into the possible factors driving evolution of allomaternal nursing behavior in primates, including humans.

Seasonal changes in social cohesion among males in a same-sex primate group

Male-male interactions in mixed-sex groups of social mammals are typically characterized by a mix of hostility and affiliation, as a result of inherent conflicts over mating opportunities, and the costs and benefits of social alliances, co-operative behaviors, and coalitionary defense. In species of nonhuman primates that form all-male groups, it is still unclear how the tradeoffs between the benefits of forming an all-male group and the cost of male-male competition in seeking mating opportunities with females in bisexual groups influence social cohesion in different seasons. Here, we used social network analysis to quantify the impact of reproductive seasonality on social cohesion and clique size of bachelor males residing in an all-male unit (AMU) in wild black-and-white snub-nosed monkeys (Rhinopithecus bieti). These primates are strict seasonal breeders and live in a modular social system composed of a number of one-male units (OMUs) and an associated peripheral AMU. We found that the AMU social network had a significantly lower density, centralization, clustering coefficient, and smaller clique size during the mating season compared to the non-mating period. However, aggression among AMU males during both mating and non-mating periods was low. Our results suggest that network structure topology in male same-sex social units is modulated by seasonal changes. Bachelor males engage in two types of competition to gain reproductive success: first, which is analogous to contest competition, in which bachelor males act aggressively and challenge OMU leader males in an attempt to take over an OMU; and second, which is more analogous to scramble competition, in which bachelor males avoid aggressive interactions and instead engage in sneaky copulations with fertile females. Our work adds to an understanding of the maintenance of all-male groups in species that form a multilevel society.