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Characterizing genetically distinct populations of primates is important for protecting biodiversity and effectively allocating conservation resources. Skywalker gibbons (Hoolock tianxing) were first described in 2017, with the only confirmed population consisting of 150 individuals in Mt. Gaoligong, Yunnan Province, China. Based on river geography, the distribution of the skywalker gibbon has been hypothesized to extend into Myanmar between the N'Mai Kha and Ayeyarwaddy Rivers to the west, and the Salween River (named the Thanlwin River in Myanmar and Nujiang River in China) to the east. We conducted acoustic point-count sampling surveys, collected noninvasive samples for molecular mitochondrial cytochrome b gene identification, and took photographs for morphological identification at six sites in Kachin State and three sites in Shan State to determine the presence of skywalker gibbons in predicted suitable forest areas in Myanmar. We also conducted 50 semistructured interviews with members of communities surrounding gibbon range forests to understand potential threats. In Kachin State, we audio-recorded 23 gibbon groups with group densities ranging between 0.57 and 3.6 group/km2. In Shan State, we audio-recorded 21 gibbon groups with group densities ranging between 0.134 and 1.0 group/km2. Based on genetic data obtained from skin and saliva samples, the gibbons were identified as skywalker gibbons (99.54–100% identity). Although these findings increase the species' known population size and confirmed distribution, skywalker gibbons in Myanmar are threatened by local habitat loss, degradation, and fragmentation. Most of the skywalker gibbon population in Myanmar exists outside protected areas. Therefore, the IUCN Red List status of the skywalker gibbon should remain as Endangered. [ABSTRACT FROM AUTHOR]

Primate communities in the Genting Highlands consist of a single species of Hylobatidae and four species of Cercopithecidae, which are known to exhibit social interaction behaviour. Thus, a study on the diets of Symphalangus syndactylus (siamang; family Hylobatidae) and Macaca nemestrina (pig-tailed macaque; family Cercopithecidae) was carried out at Genting Highlands, in order to compare the dietary preferences and interspecific competition between the two primate families. A DNA metabarcoding approach was used to analyse diet intake using non-invasive samples based on the trnL region. Based on the 140 amplicon sequence variants (ASVs) generated, 26 plant orders, 46 different families, 60 genera and 49 species were identified from 23 different plant classes. Fabaceae and Moraceae were classified as the most preferred plants at the family level for S. syndactylus; meanwhile, Piperaceae and Arecaceae were classified as the most preferred for M. nemestrina. Only six out of the 60 different plant genera classified in this study, were found to be consumed by both species. Therefore, the low similarity of preferred plants in the diets between the two families suggests that there is little interspecific competition. These findings are important for future conservation management of highland primates, especially in the Genting Highlands. [ABSTRACT FROM AUTHOR]

Nonhuman primate vocalizations have been traditionally described as stereotyped and most likely genetically determined. However, there is increasing evidence of flexibility with a wide variety of species demonstrating the ability to change aspects of their calls, such as note order and phrase duration. We assess patterns of variation in note order and temporal features in wild siamang (Symphalangus syndactylus) phrases. We used three types of analyses on 1,015 ululating scream phrases (US-II), containing 21,609 notes, produced by ten siamang groups at three field sites. First, to assess similarity or differences in the organization of notes in the US-II phrase, we calculated the Levenshtein distance (LD), which quantifies the similarity of sequences of strings through the number of insertions, deletions, and substitutions required to transform one into the other. Second, we used a supervised classification approach to see how well we could assign US-II phrases to their groups and sites. Third, we compared five unsupervised clustering algorithms to investigate the tendency to cluster in US-II phrase types. The note order of the US-II phrase was variable shown by relatively large LD values; there also were significant mean differences between groups. Supervised classification using support vector machine and leave-one-out cross-validation returned 89.5% accuracy for site and 53.1% for group. For unsupervised clustering, the most stable solution based on the Silhouette coefficient returned four unique clusters or classes of the US-II phrase in our dataset. Our findings indicate high levels of intragroup variation in the US-II phrase and are consistent with previous reports on siamang vocalizations being flexible. Quantifying variation in the siamang US-II phrase provides a crucial first step in understanding the evolutionary forces that shaped these signals and the potential information they convey. [ABSTRACT FROM AUTHOR]

Studies of nonhuman primate cognition have traditionally employed subjects from the monkey (Cercopithecoidea) and ape (Hominidae) lineages, with relatively much less examination of the phylogenetically intermediate gibbons (Hylobatidae). To begin to rectify this gap in our understanding of primate cognition, we used a short-term training and testing method to preliminarily evaluate siamang gibbon (Symphalangus syndactylus) performance on a battery of standardized cognitive tasks, using Monkey CANTAB cognition testing software (Lafayette-Campden Neuroscience) and a computer touchscreen apparatus. Five different operant tasks examining distinct perceptual and cognitive functions were used to train and test each subject over a period of five weeks. Over 1900 cognitive testing trials were completed with three subjects. Despite limited training and testing opportunity, all siamangs achieved proficiency scores well above chance (> 65%) in both Concurrent Discrimination and Spatial Working Memory tasks. Over the limited training opportunities available, our subjects did not achieve proficiency in Delayed Match-to-Sample, Paired Associates Learning, or Conditional Visual Discrimination tasks; however, subjects did exhibit (to varying degrees) improved performance in these tasks, suggesting that additional training may lead to higher proficiency and that siamangs demonstrate effective, task-based learning capabilities. We present one of the first successful tests of a hylobatid ape using touchscreen cognitive testing methods and demonstrate that hylobatids can be evaluated using the same methods now commonly employed in tests of other nonhuman primates. Further, our testing regime proved to be behaviorally rewarding for our subjects, suggesting that hylobatids may benefit from advanced forms of interactive cognitive enrichment.

Background: The gut morphology of Symphalangus syndactylus exhibits an intermediate structure that aligns with its consumption of fruit and ability to supplement its diet with leaves. The Siamang relies on its gut microbiome for energy extraction, immune system development, and the synthesis of micronutrients. Gut microbiome composition may be structured based on several factors such as age, sex, and habitat. No study has yet been carried out on the gut microbiota of the Hylobatidae members in Malaysia especially S. syndactylus., Methods: This study aims to resolve the gut microbiome composition of S. syndactylus by using a fecal sample as DNA source, adapting high-throughput sequencing, and 16S rRNA as the targeted region., Results: A total of 1 272 903 operational taxonomic units (OTUs) reads were assigned to 22 phyla, 139 families, and 210 genera of microbes. The {Unknown Phylum} Bacteria-2 is the dominant phyla found across all samples. Meanwhile, {Unknown Phylum} Bacteria-2 and Firmicutes are genera that have the highest relative abundance found in the Siamang gut., Conclusions: This study yields nonsignificance relationship between Siamang gut microbiome composition with these three factors: group, sex, and age., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Primate communities in the Genting Highlands consist of a single species of Hylobatidae and four species of Cercopithecidae, which are known to exhibit social interaction behaviour. Thus, a study on the diets of Symphalangussyndactylus (siamang; family Hylobatidae) and Macacanemestrina (pig-tailed macaque; family Cercopithecidae) was carried out at Genting Highlands, in order to compare the dietary preferences and interspecific competition between the two primate families. A DNA metabarcoding approach was used to analyse diet intake using non-invasive samples based on the trnL region. Based on the 140 amplicon sequence variants (ASVs) generated, 26 plant orders, 46 different families, 60 genera and 49 species were identified from 23 different plant classes. Fabaceae and Moraceae were classified as the most preferred plants at the family level for S.syndactylus ; meanwhile, Piperaceae and Arecaceae were classified as the most preferred for M.nemestrina . Only six out of the 60 different plant genera classified in this study, were found to be consumed by both species. Therefore, the low similarity of preferred plants in the diets between the two families suggests that there is little interspecific competition. These findings are important for future conservation management of highland primates, especially in the Genting Highlands., Competing Interests: No conflict of interest to declare Disclaimer: This article is (co-)authored by any of the Editors-in-Chief, Managing Editors or their deputies in this journal., (Roberta Chaya Tawie Tingga, Millawati Gani, Nur Azimah Osman, Nor Rahman Aifat, Eddie Chan, Shamsul Khamis, Emelda Rosseleena Rohani, Norlinda Mohd-Daut, Abd Rahman Mohd-Ridwan, Badrul Munir Md-Zain.)

The body proportions of extant animals help inform inferences about the behaviors of their extinct relatives, but relationships between body proportions, behavior, and phylogeny in extant primates remain unclear. Advances in behavioral data, molecular phylogenies, and multivariate analytical tools make it an opportune time to perform comprehensive comparative analyses of primate traditional limb length proportions (e.g., intermembral, humerofemoral, brachial, and crural indices), body size-adjusted long bone proportions, and principal components. In this study we used a mix of newly-collected and published data to investigate whether and how the limb length proportions of a diverse sample of primates, including monkeys, apes, and modern humans, are influenced by behavior and phylogeny. We reconfirm that the intermembral index, followed by the first principal component of traditional limb length proportions, is the single most effective variable distinguishing hominoids and other anthropoids. Combined limb length proportions and positional behaviors are strongly correlated in extant anthropoid groups, but phylogeny is a better predictor of limb length proportion variation than of behavior. We confirm convergences between members of the Atelidae and extant apes (especially Pan), members of the Hylobatidae and Pongo, and a potential divergence of Presbytis limb proportions from some other cercopithecoids, which correlate with adaptations for forelimb-dominated behaviors in some colobines. Collectively, these results substantiate hypotheses indicating that extinct hominins and other hominoid taxa can be distinguished by analyzing combinations of their limb length proportions at different taxonomic levels. From these results, we hypothesize that fossil skeletons characterized by notably disparate limb length proportions are unlikely to have exhibited similar behavioral patterns., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Establishing protected areas (PAs) is an essential strategy to reduce biodiversity loss. However, many PAs do not provide adequate protection due to poor funding, inadequate staffing and equipment, and ineffective management. As part of China's recent economic growth, the Chinese government has significantly increased investment in nature reserves over the past 20 years, providing a unique opportunity to evaluate whether PAs can protect threatened species effectively. We compiled data from published literature on populations of gibbons (Hylobatidae), a threatened taxon with cultural significance, that occurred in Chinese reserves after 1980. We evaluated the ability of these PAs to maintain gibbon habitat and populations by comparing forest cover and human disturbance between reserves and their surrounding areas and modeling the impact of reserve characteristics on gibbon population trends. We also assessed the perspective of reserve staff concerning PA management effectiveness through an online survey. Reserves effectively protected gibbon habitat by reducing forest loss and human disturbance; however, half the reserves lost their gibbon populations since being established. Gibbons were more likely to survive in reserves established more recently, at higher elevation, with less forest loss and lower human impact, and that have been relatively well studied. A larger initial population size in the 1980s was positively associated with gibbon persistence. Although staff of all reserves reported increased investment and improved management over the past 20–30 years, no relationship was found between management effectiveness and gibbon population trends. We suggest early and emphatic intervention is critical to stop population decline and prevent extinction. Article impact statement: Protected areas in China effectively protect gibbon habitat but not gibbon populations, even with increased investment in recent decades. [ABSTRACT FROM AUTHOR]

Information about the taxonomy and geographical distribution of a species is essential to understand its evolution and for conservation efforts. The phylogeny of the Hylobatidae remains unclear. India is reported to have one species of Hoolock gibbon (Hoolock hoolock) but a recent study based on pelage colour suggested that another species, H. leuconedys, occurs in the Mishmi Hills between the Dibang and Nao Dehing rivers in Arunachal Pradesh. We examined whether H. leuconedys occurs in India and its evolutionary relationships with other Hylobatidae species. We collected blood, tissue, and fecal samples from various populations of H. hoolock (N = 17) and the Mishmi Hills gibbons (N = 14) from their distribution in Northeast India, zoos, and rescues centers. We isolated DNA from these samples and constructed phylogenetic trees using partial D-loop and COI markers. We also performed whole mitochondrial analysis to study the phylogenetics of the Hylobatidae family. Our genetic analysis showed that none of the samples from India were H. leuconedys, and that all samples from the Mishmi Hills could be assigned to H. hoolock. Our mitogenome analysis supported this conclusion. We estimate that gibbon divergence from a common ancestor occurred 8.38 mya and that the split between H. hoolock and H. leuconedys occurred 1.49 mya. These findings will facilitate exchange of individuals from different zoos for captive breeding programs and conservation and management of wild populations of these gibbons. [ABSTRACT FROM AUTHOR]

Sleeping tree selection and related behaviours of a family group and a solitary female siamang (Symphalangus syndactylus) were investigated over a 5-month period in northern Sumatra, Indonesia. We performed all day follows, sleeping tree surveys and forest plot enumerations in the field. We tested whether: (1) physical characteristics of sleeping trees and the surrounding trees, together with siamang behaviours, supported selection based on predation risk and access requirements; (2) the preferences of a solitary siamang were similar to those of a family group; and (3) sleeping site locations within home ranges were indicative of home range defence, scramble competition with other groups or other species, or food requirements. Our data showed that (1) sleeping trees were tall, emergent trees with some, albeit low, connectivity to the neighbouring canopy, and that they were surrounded by other tall trees. Siamangs showed early entry into and departure from sleeping trees, and slept at the ends of branches. These results indicate that the siamangs' choice of sleeping trees and related behaviours were strongly driven by predator avoidance. The observed regular reuse of sleeping sites, however, did not support anti-predation theory. (2) The solitary female displayed selection criteria for sleeping trees that were similar to those of the family group, but she slept more frequently in smaller trees than the latter. (3) Siamangs selected sleeping trees to avoid neighbouring groups, monopolise resources (competition), and to be near their last feeding tree. Our findings indicate selectivity in the siamangs' use of sleeping trees, with only a few trees in the study site being used for this purpose. Any reduction in the availability of such trees might make otherwise suitable habitat unsuitable for these highly arboreal small apes. [ABSTRACT FROM AUTHOR]

Siamangs ( Symphalangussyndactylus ) are native to Peninsular Malaysia, Sumatra and southern Thailand and their taxonomical classification at subspecies level remains unclear. Morphologically, two subspecies were proposed as early as 1908 by Thomas namely Symphalangus s.syndactylus and Symphalanguss.continentis. Thus, this study aims to clarify the Siamang subspecies status, based on mtDNA D -loop sequences. Faecal samples were collected from wild Siamang populations at different localities in Peninsular Malaysia. A 600-bp sequence of the mitochondrial D -loop region was amplified from faecal DNA extracts and analysed along with GenBank sequences representing Symphalangus sp., Nomascus sp., Hylobates sp., Hoolock sp. and outgroups ( Pongopygmaeus , Macacafascicularis and Papiopapio ). The molecular phylogenetic analysis in this study revealed two distinct clades formed by S.s.syndactylus and S.s.continentis which supports the previous morphological delineation of the existence of two subspecies. Biogeographical analysis indicated that the Sumatran population lineage was split from the Peninsular Malaysian population lineage and a diversification occurrred in the Pliocene era (~ 3.12 MYA) through southward expansion. This postulation was supported by the molecular clock, which illustrated that the Peninsular Malaysian population (~ 1.92 MYA) diverged earlier than the Sumatran population (~ 1.85 MYA). This is the first study to use a molecular approach to validate the subspecies statuses of S.s.syndactylus and S.s.continentis . This finding will be useful for conservation management, for example, during Siamang translocation and investigations into illegal pet trade and forensics involving Malayan and Sumatran Siamangs., Competing Interests: No conflict of interest to declare Disclaimer: This article is (co-)authored by any of the Editors-in-Chief, Managing Editors or their deputies in this journal., (Nur Hartini Sariyati, Muhammad Abu Bakar Abdul-Latiff, Nor Rahman Aifat, Abd Rahman Mohd-Ridwan, Nur Azimah Osman, Kayal Vizi Karuppannan, Eddie Chan, Badrul Munir Md-Zain.)

It has been extensively studied that the gut microbiome provides animals flexibility to adapt to food variability. Yet, how gut phageome responds to diet variation of wild animals remains unexplored. Here, we analyze the eco-evolutionary dynamics of gut phageome in six wild gibbons (Hoolock tianxing) by collecting individually-resolved fresh fecal samples and parallel feeding behavior data for 15 consecutive months. Application of complementary viral and microbial metagenomics recovers 39,198 virulent and temperate phage genomes from the feces. Hierarchical cluster analyses show remarkable seasonal diet variations in gibbons. From high-fruit to high-leaf feeding period, the abundances of phage populations are seasonally fluctuated, especially driven by the increased abundance of virulent phages that kill the Lachnospiraceae hosts, and a decreased abundance of temperate phages that piggyback the Bacteroidaceae hosts. Functional profiling reveals an enrichment through horizontal gene transfers of toxin-antitoxin genes on temperate phage genomes in high-leaf season, potentially conferring benefits to their prokaryotic hosts. The phage-host ecological dynamics are driven by the coevolutionary processes which select for tail fiber and DNA primase genes on virulent and temperate phage genomes, respectively. Our results highlight complex phageome-microbiome interactions as a key feature of the gibbon gut microbial ecosystem responding to the seasonal diet., (© 2024. The Author(s).)

Gibbons (family Hylobatidae) are renowned for their melodious territorial songs but other aspects of their acoustic communication have received little research attention. Here we describe an apparently novel idiosyncratic non-song vocalization in an adult captive Southern white-cheeked gibbon (Nomascus siki), which we suggest acts specifically in attracting a human's attention. For this preliminary report we analysed 25 individual calls recorded over a period of 6 months. Typically, calling is accompanied by clapping and feet-slapping, behaviours not reported from gibbons in comparable situations so far. The utilization of both innovative vocalizations and other acoustic displays as human-directed attention getters, reminiscent of our white-cheeked gibbon subject, is known from great apes, which further suggests a concordant behavioural function. However, the gibbon's displays, despite their unequivocal novelty, could also represent unintentional behavioural responses related to frustration. Eventually, experimental approaches are required to clarify what underlies this unusual behaviour. [ABSTRACT FROM AUTHOR]

How much nonhuman animals understand about seeing has been the focus of comparative cognition research for decades. Many social primates (and other species) are sensitive to cues about what others can and cannot see. Whether this sensitivity evolved in primates through shared descent or convergent evolution remains unclear. The current study tested gibbons—the apes that are least studied yet most distantly related to humans and one of the less social primates—in two food-competition tasks. Specifically, we presented eastern hoolock gibbons, Hoolock leuconedys, and silvery gibbons, Hylobates moloch, with a choice between a contested piece of food visible to both themselves and a human competitor and an uncontested piece visible only to themselves. Subjects successfully stole the uncontested food when the competitor turned away his body (N = 10, experiment 1) and his head (N = 9, experiment 2). However, when the head of the experimenter was oriented towards the contested piece of food, whether the competitor opened or closed his eyes made no difference. Subjects' sensitivity to body- and head-orientation cues was comparable to that of chimpanzees, rhesus macaques, and ring-tailed lemurs—species living in much larger groups than gibbons. These findings support the continuity hypothesis that sensitivity to body- and head-orientation cues is a product of shared descent among primates. [ABSTRACT FROM AUTHOR]

Citizen science‐based research has been used effectively to estimate animal abundance and breeding patterns, to monitor animal movement, and for biodiversity conservation and education. Here, we evaluate the feasibility of using social media observations to assess the distribution of small apes in Peninsular Malaysia. We searched for reports of small ape observations in Peninsular Malaysia on social media (e.g., blogs, Facebook, Instagram, Twitter, YouTube, iNaturalist, etc.), and also used online, radio, print messaging, and word of mouth to invite citizen scientists such as birders, amateur naturalists, hikers, and other members of the public to provide information about small ape observations made during their activities. These reports provided new information about the occurrence of all three species of small apes (Hylobates agilis, Hylobates lar, and Symphalangus syndactylus) in Peninsular Malaysia. Social media users reported observations of small apes in almost every state. Despite the fact that small apes are believed to occur primarily in the interior of large forested areas, most observations were from fairly small (<100 km2) forests near areas of high traffic and high human population (roads and urban areas). This suggests that most outdoor enthusiasts primarily visit well‐traveled and easily accessible areas, which results in biased sampling if only incidental observations reported on social media are used. A more targeted approach specifically soliciting reports from citizen scientists visiting large, less‐accessible forests may result in better sampling in these habitats. Social media reports indicated the presence of small apes in at least six habitats where they had not been previously reported. We verified the reported data based on whether reports included a date, location, and uploaded photographs, videos and/or audio recordings. Well‐publicized citizen science programs may also build awareness and enthusiasm about the conservation of vulnerable wildlife species. Research Highlights: Citizen scientists reported >100 observations of small apes, including all three species in Peninsular Malaysia, on social media or directly to the authors.Social media and direct citizen scientist reports provided new information about the distribution and persistence of small apes in Peninsular Malaysia.Reports of small ape sightings were concentrated in forests near roads and urban areas, with significant gaps in larger protected areas likely due to inaccessibility of remote forests.Citizen science reports and social media surveys provide useful supplements to formal surveys for small apes in Malaysia, especially in at‐risk forests near roads and urban areas. [ABSTRACT FROM AUTHOR]

The cao vit gibbon (Nomascus nasutus) is one of the rarest primates on Earth and now only survives in a single forest patch of less than 5000 ha on the Vietnam-China border. Accurate monitoring of the last remaining population is critical to inform ongoing conservation interventions and track conservation success over time. However, traditional methods for monitoring gibbons, involving triangulation of groups from their songs, are inherently subjective and likely subject to considerable measurement errors. To overcome this, we aimed to use 'vocal fingerprinting' to distinguish the different singing males in the population. During the 2021 population survey, we complemented the traditional observations made by survey teams with a concurrent passive acoustic monitoring array. Counts of gibbon group sizes were also assisted with a UAV-mounted thermal camera. After identifying eight family groups in the acoustic data and incorporating long-term data, we estimate that the population was comprised of 74 individuals in 11 family groups, which is 38% smaller than previously thought. We have no evidence that the population has declined-indeed it appears to be growing, with new groups having formed in recent years-and the difference is instead due to double-counting of groups in previous surveys employing the triangulation method. Indeed, using spatially explicit capture-recapture modelling, we uncovered substantial measurement error in the bearings and distances from field teams. We also applied semi- and fully-automatic approaches to clustering the male calls into groups, finding no evidence that we had missed any males with the manual approach. Given the very small size of the population, conservation actions are now even more urgent, in particular habitat restoration to allow the population to expand. Our new population estimate now serves as a more robust basis for informing management actions and tracking conservation success over time., (© 2024. The Author(s).)

Shigella fl exneri is a nonmotile gram-negative bacillus that affects humans and nonhuman primates. In August 2021, 15 primates at the ABQ BioPark demonstrated clinical signs of Shigella infection: 3 out of 4 Sumatran and hybrid orangutans ( Pongo abelii ), 6 out of 8 gorillas ( Gorilla gorilla ), 2 out of 9 chimpanzees ( Pan troglodytes ), and 4 out of 4 siamangs ( Hylobates syndactylus ). Three siamangs and one gorilla succumbed to complications of shigellosis during the initial outbreak and a chimpanzee died 10 mon later. Although it is well documented that Shigella may cause morbidity and mortality in nonhuman primates, the rapid and devastating nature of the outbreak, the difference from previous reports in zoological collections (enzootic vs outbreak), and the chronological overlap with the increase in human cases in the region makes discussion of this Shigella outbreak of significance. The cases presented here are significantly different than previous reports, because these were part of an outbreak that arose and subsided, versus other reports where the authors describe an enzootic disease with persistently infected animals. Close communication with the New Mexico Department of Health allowed for the investigation into possible sources of the outbreak, recommendations regarding biosecurity protocols, and staff education.

White-cheeked macaque Macaca leucogenys is a recently described primate species discovered by camera-trap surveys in the Medog region in 2015. The species was thought to be narrowly distributed in southeastern Tibet. However, knowledge on the distribution and conservation of the species is quite limited. Based on a systematic camera-trapping survey, we report the occurrence of the species in the Gaoligong Mountains, over 350 km southeast of the nearest known population. We recorded 3025 photographs of white-cheeked macaques representing 481 independent records from 59 camera-trap stations with total trapping efforts of 18,437 camera days. Notably, part of the newly discovered locations of the white-cheeked macaque are outside of nature reserves without any formal protection and management. Our survey also confirms the occurrence of ten primate species in the Gaoligong Mountains, accounting for 35.7% of China's primates, including the Skywalker hoolock gibbon Hoolock tianxing and the Myanmar snub-nosed monkey Rhinopithecus strykeri etc. These findings reveal a new distribution record for the white-cheeked macaque and further highlight the conservation values of Gaoligong Mountains for globally threatened primate species. We also provide a preliminary report on the daily activity patterns of this endangered species, which enriches the bio-ecological data of the poorly studied species. We believe the report has significant implications for understanding the ecology of the species and improving conservation planning., (© 2023. The Author(s), under exclusive licence to Japan Monkey Centre.)

Investigations on manual laterality in non-human primates can help clarify human evolutionary origins of hand preference and cerebral cognition. Although body posture can influence primate hand preference, investigations on how posture affects hylobatid manual laterality are still in their infancy. This study focused on how spontaneous bipedal behavioral tasks affect hand preference in Hylobatidae. Ten captive northern white-cheeked gibbons (Nomascus leucogenys) were chosen as focal subjects. Unimanual grooming during sitting posture and supported bipedal posture were applied as behavioral tasks. The gibbons displayed a modest tendency on left-hand preference during sitting posture and right-hand preference during supported bipedal posture, although no group-level hand preference was detected for either posture. From the sitting to supported bipedal posture, 70% of individuals displayed different degrees of right-side deviation trends. The strength of manual laterality in the supported bipedal posture was higher than that in the sitting posture. We found significant sex differences in manual laterality during supported bipedal posture but not during sitting posture. Thus, to a certain degree, bipedal posture in N. leucogenys facilitates stronger hand preference, elicits a rightward trend in manual laterality, and produces sex-specific hand preference. [ABSTRACT FROM AUTHOR]

Elective health checks form an important part of the preventative healthcare of many zoo-housed animals. These procedures are not without risk or financial expenditure, meaning careful cost–benefit analysis is required when determining the frequency and intensity with which they are implemented. This study evaluated the value of elective health checks (n = 74) carried out on 33 gibbons at a single UK zoological collection from 2011 to 2018. Data were categorised by health check type, animal age, clinical findings and outcome. Univariable binary logistic regression and multivariable modelling were used to identify factors associated with the likelihood of actionable (clinically significant) outcomes. In total, 51.35% of all elective health checks resulted in an actionable outcome. Elderly heath checks had 13.64 times greater odds of an actionable outcome and 34 times greater odds of a significant radiographic finding, when compared to routine (non-elderly) health checks. Our findings suggest that 75% wild longevity is a suitable threshold for identifying elderly captive gibbons and increasing health check frequency. Whilst further work is needed to ascertain whether these findings can be extrapolated to other collections and/or species, this study demonstrates how the analysis of clinical data can aid in the implementation of an effective and evidence-based preventative healthcare plan.

Pierolapithecus catalaunicus (~12 million years ago, northeastern Spain) is key to understanding the mosaic nature of hominid (great ape and human) evolution. Notably, its skeleton indicates that an orthograde (upright) body plan preceded suspensory adaptations in hominid evolution. However, there is ongoing debate about this species, partly because the sole known cranium, preserving a nearly complete face, suffers from taphonomic damage. We 1) carried out a micro computerized tomography (CT) based virtual reconstruction of the Pierolapithecus cranium, 2) assessed its morphological affinities using a series of two-dimensional (2D) and three-dimensional (3D) morphometric analyses, and 3) modeled the evolution of key aspects of ape face form. The reconstruction clarifies many aspects of the facial morphology of Pierolapithecus . Our results indicate that it is most similar to great apes (fossil and extant) in overall face shape and size and is morphologically distinct from other Middle Miocene apes. Crown great apes can be distinguished from other taxa in several facial metrics (e.g., low midfacial prognathism, relatively tall faces) and only some of these features are found in Pierolapithecus , which is most consistent with a stem (basal) hominid position. The inferred morphology at all ancestral nodes within the hominoid (ape and human) tree is closer to great apes than to hylobatids (gibbons and siamangs), which are convergent with other smaller anthropoids. Our analyses support a hominid ancestor that was distinct from all extant and fossil hominids in overall facial shape and shared many features with Pierolapithecus . This reconstructed ancestral morphotype represents a testable hypothesis that can be reevaluated as new fossils are discovered.

Flexor digitorum superficialis (FDS) shows diverse muscle-tendon arrangements among primates. The intramuscular nerve distribution pattern is a criterion for discussing the homology of FDS. In this study, the muscle-tendon arrangement and intramuscular nerve distribution of FDS were examined in the siamang, western lowland gorilla, western chimpanzee, and Japanese macaques. The FDS had muscle bellies to digits II-V. FDS had proximal belly and intermediate tendon except for siamang. Distal belly to digit II (in the western lowland gorilla and western chimpanzees) or distal bellies to digits II and V (in Japanese macaque) originated from the intermediate tendon. In all specimens, nerve branches within digit III belly extended into digit IV belly, and nerve branch(es) within digit IV belly extended into digit V belly. This consistent pattern suggested that each muscle belly to digits III-V is interspecifically homologous. The digit II belly in the siamang and the distal belly to digit II in the western lowland gorilla, western chimpanzees, and Japanese macaques could be homologous based on their similar innervating patterns. The proximal belly was innervated by branches from the communicating nerve between median and ulnar nerves in the western lowland gorilla or branches from median and ulnar nerves in western chimpanzees. In the siamang and Japanese macaque, the whole FDS was innervated by median nerve. The proximal belly in the western lowland gorilla, western chimpanzees, and Japanese macaques could be classified into different groups from the other part of the FDS., (© 2023. The Author(s), under exclusive licence to Japanese Association of Anatomists.)

Estimating the population size of primate species is very important in identifying appropriate conservation actions and measuring their effectiveness. All 17 species of gibbons recognized by the IUCN are considered threatened with extinction. Thus, there is a great need to determine and monitor their status, to conduct effective conservation interventions. Gibbons can be detected by their loud and long song bouts, and surveys usually rely on auditory point count methods. However, gibbon groups do not call daily, so we need a correction factor based on the daily calling probability to estimate gibbon population size accurately. Several studies have estimated such correction factors, but these estimates might be negatively biased if gibbon groups move beyond the maximum hearing distance or are far from the listening post and their calls are faint. We aimed to address this issue and estimate the calling probability and correction factor accurately. We collected data on southern yellow-cheeked crested gibbon (Nomascus gabriellae) in Cat Tien National Park, Vietnam, from July to October 2016, using an auditory point count method. We explored the influence of the maximum distance between the listening post and the gibbons on estimates of the calling probability, correction factor, and population size. We detected 44 gibbon groups during the survey. The calling probability and correction factor decreased with the maximum distance from the listening post to the gibbon groups. If we used all the gibbon groups to estimate the correction factor, population estimates were 15% and 18% higher than those estimated using only gibbon groups detected within 700 m and 500 m, respectively. Based on these findings, we recommend that researchers calculate the calling probability and correction factor for several maximum distances and determine the percentage overestimation of the gibbon population. They should then choose the correction factor so as to balance sample size and the risk of overestimation of gibbon population size. [ABSTRACT FROM AUTHOR]

Gibbons (Hylobatidae) were widely distributed across much of China during recent centuries, but are now restricted to a few small areas of Hainan, Guangxi, and Yunnan provinces due to massive habitat loss and hunting. Six gibbon species have occurred recently in China. Two of them ( Hylobates lar and Nomascus leucogenys ) are now extinct; two others ( Nomascus nasutus and Nomascus hainanus ) each have only one small population with less than 30 individuals; Hoolock leuconedys has a small population of less than 200 individuals distributed in 17 locations; and even the most common species, Nomascus concolor , has populations containing only about 270 social groups (ca. 1200 individuals). Illegal hunting, forest fragmentation, small population size, limited habitat, and various other types of human disturbance still threaten remnant gibbon populations. Currently, all gibbon species are listed as Class One Protected Animals by Chinese law and about 85% of gibbon groups are protected within nature reserves. Several long-term monitoring and research programs have been established in order to better understand gibbon population dynamics, ecology, and behavioral adaptations to human disturbance, and habitat restoration and conservation education programs are underway. In order to ensure long-term survival of gibbons in China, expanding and establishing nature reserves, strengthening law enforcement, increasing conservation education, establishing captive breeding programs for reintroduction, recruiting new researchers and students, and international cooperation are suggested. If most of these activities can be achieved, Chinese gibbons may still have a future in the wild. [ABSTRACT FROM AUTHOR]

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 km 2 . The home range of the smallest group (Group E, 3 individuals) was 1.51 km 2 , which likely represents the minimum home range size for this species. The remaining area of highly suitable and moderately suitable habitat totals 26.9 km 2 . 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., (© 2022 The Authors. Integrative Zoology published by International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)

Summary In brachiation, two main gaits are distinguished, ricochetal brachiation and continuous contact brachiation. During ricochetal brachiation, a flight phase exists and the body centre of mass (bCOM) describes a parabolic trajectory. For continuous contact brachiation, where at least one hand is always in contact with the substrate, we showed in an earlier paper that four step-to-step transition types occur. We referred to these as a ‘point’, a ‘loop’, a ‘backward pendulum’ and a ‘parabolic’ transition. Only the first two transition types have previously been mentioned in the existing literature on gibbon brachiation. In the current study, we used three-dimensional video and force analysis to describe and characterize these four step-to-step transition types. Results show that, although individual preference occurs, the brachiation strides characterized by each transition type are mainly associated with speed. Yet, these four transitions seem to form a continuum rather than four distinct types. Energy recovery and collision fraction are used as estimators of mechanical efficiency of brachiation and, remarkably, these parameters do not differ between strides with different transition types. All strides show high energy recoveries (mean = 70±11.4%) and low collision fractions (mean = 0.2±0.13), regardless of the step-to-step transition type used. We conclude that siamangs have efficient means of modifying locomotor speed during continuous contact brachiation by choosing particular step-to-step transition types, which all minimize collision fraction and enhance energy recovery.

The southern white-cheeked gibbon Nomascus siki is endemic to Indochina and is classified as critically endangered on the International Union for Conservation of Nature (IUCN) Red List. The most updated information on the status of this species dates back to a decade ago. As hunting has tremendous impacts on wildlife in Southeast Asia, the population of N. siki might have changed a lot in the last decade. Updated information on the status and potential distribution of this species is critically important for conservation and prioritization, especially for N. siki because of its undefined distribution range. The goal of this study was to review the population status of N. siki in Vietnam and Lao People's Democratic Republic (PDR) and to model its potential distribution. In Vietnam, this species has been intensively surveyed in all major areas of occurrence from 2016 to 2021. The total number of N. siki groups recorded and estimated in Vietnam were 324 and 483, respectively. In Lao PDR, the occurrence of N. siki has been confirmed in Nam Kading, Nakai Nam Theun, Hin Nam No, and Phou Hinpoun national protected areas. However, population estimates are generally lacking. The suitable habitat of N. siki was predicted from about 105.00° to 106.80° E longitude and from about 16.60° to 17.90° N latitude located in Quang Binh and Quang Tri provinces (Vietnam), and Khammounan and Savannakhet provinces (Lao PDR). The area of the potential distribution range is about 9894.15 km 2 , both in Vietnam and Lao PDR. Particularly, the high, medium, and low suitable habitats were estimated at around 1229.58 km 2 , 3019.68 km 2 , and 5644.89 km 2 , respectively. The area of suitable habitat of N. siki in Vietnam was predicted to be 4151.25 km 2 , of which only 1257.93 km 2 (30.30%) is in the protected area network. Dong Chau-Khe Nuoc Trong and Bac Huong Hoa Nature Reserves, and Phong Nha-Ke Bang National Park should receive priority for conservation of N. siki in Vietnam. Improving conservation beyond the protected areas' boundaries or transforming the forest enterprises and watershed protection forests into protected areas should also be considered as an alternative for the conservation of N. siki. In Lao PDR, surveys of the species in its entire distribution range should be the first priority., (© 2023. The Author(s), under exclusive licence to Japan Monkey Centre.)