Hylobates Lar Research Articles

Taxonomic and genetic assessment of captive White-Handed Gibbons (Hylobateslar) in Peninsular Malaysia with implications towards conservation translocation and reintroduction programmes.

Conservation translocation and reintroduction for the purpose of repopulating and reinforcing extirpated or depleted populations has been recognised as an important conservation tool, particularly for gibbon conservation in the immediate future. Feasibility assessments involving multiple factors, including taxonomic and genetic assessment of rescued and captive gibbons, are imperative prior to translocation and reintroduction programmes. In this study, we attempt to determine the subspecies and origin of captive Hylobateslar, White-handed gibbons, from Peninsular Malaysia to assist in future translocation and reintroduction programmes. A total of 12 captive and rescued H.lar samples were analysed using the control region segment of mitochondrial DNA. Sequence analyses and phylogenetic trees constructed using neighbour-joining, maximum likelihood, Bayesian inference, and network methods congruently differentiate all 12 captive individuals used in this study from other H.lar subspecies suggesting that these individuals belong to the H.larlar subspecies. In addition, two populations of H.l.lar were observed: (1) a southern population consisting of all 12 individuals from Peninsular Malaysia, and (2) a possible northern population represented by three individuals (from previous studies), which might have originated from the region between the Isthmus of Kra, Surat Thani-Krabi depression, and Kangar-Pattani. Our findings suggest that the complete control region segment can be used to determine the subspecies and origin of captive H.lar.

Distribution of cholinergic neurons in the brains of a lar gibbon and a chimpanzee.

Using choline acetyltransferase immunohistochemistry, we describe the nuclear parcellation of the cholinergic system in the brains of two apes, a lar gibbon (Hylobates lar) and a chimpanzee (Pan troglodytes). The cholinergic nuclei observed in both apes studied are virtually identical to that observed in humans and show very strong similarity to the cholinergic nuclei observed in other primates and mammals more generally. One specific difference between humans and the two apes studied is that, with the specific choline acetyltransferase antibody used, the cholinergic pyramidal neurons observed in human cerebral cortex were not labeled. When comparing the two apes studied and humans to other primates, the presence of a greatly expanded cholinergic medullary tegmental field, and the presence of cholinergic neurons in the intermediate and dorsal horns of the cervical spinal cord are notable variations of the distribution of cholinergic neurons in apes compared to other primates. These neurons may play an important role in the modulation of ascending and descending neural transmissions through the spinal cord and caudal medulla, potentially related to the differing modes of locomotion in apes compared to other primates. Our observations also indicate that the average soma volume of the neurons forming the laterodorsal tegmental nucleus (LDT) is larger than those of the pedunculopontine nucleus (PPT) in both the lar gibbon and chimpanzee. This variability in soma volume appears to be related to the size of the adult derivatives of the alar and basal plate across mammalian species.

Genetic analysis of hybridization between white-handed (Hylobates lar) and pileated (Hylobates pileatus) gibbons in a contact zone in Khao Yai National Park, Thailand.

Natural hybridization has played various roles in the evolutionary history of primates. Its consequences range from genetic introgression between taxa, formation of hybrid zones, and formation of new lineages. Hylobates lar, the white-handed gibbon, and Hylobates pileatus, the pileated gibbon, are largely allopatric species in Southeast Asia with a narrow contact zone in Khao Yai National Park, Thailand, which contains both parental types and hybrids. Hybrid individuals in the zone are recognizable by their intermediate pelage and vocal patterns, but have not been analyzed genetically. We analyzed mitochondrial and microsatellite DNA of 52 individuals to estimate the relative genetic contributions of the parental species to each individual, and the amount of introgression into the parental species. We obtained fecal samples from 33 H. lar, 15 H. pileatus and four phenotypically intermediate individuals in the contact zone. Both mitochondrial and microsatellite markers confirmed distinct differences between these taxa. Both H. lar and H. pileatus contributed to the maternal lineages of the hybrids based on mitochondrial analysis; hybrids were viable and present in socially normal reproductive pairs. The microsatellite analysis identified ten admixed individuals, four F1 hybrids, which corresponded to phenotypic hybrids, and six H. lar-like backcrosses. All 15 H. pileatus samples were identified as originating from genetically H. pileatus individuals with no H. lar admixture; hence, backcrossing is biased toward H. lar. A relatively low number of phenotypic hybrids and backcrossed individuals along with a high number of parental types indicates a bimodal hybrid zone, which suggests relatively strong bias in mate selection between the species.

Nuclear organization of catecholaminergic neurons in the brains of a lar gibbon and a chimpanzee.

Using tyrosine hydroxylase immunohistochemistry, we describe the nuclear parcellation of the catecholaminergic system in the brains of a lar gibbon (Hylobates lar) and a chimpanzee (Pan troglodytes). The parcellation of catecholaminergic nuclei in the brains of both apes is virtually identical to that observed in humans and shows very strong similarities to that observed in mammals more generally, particularly other primates. Specific variations of this system in the apes studied include an unusual high-density cluster of A10dc neurons, an enlarged retrorubral nucleus (A8), and an expanded distribution of the neurons forming the dorsolateral division of the locus coeruleus (A4). The additional A10dc neurons may improve dopaminergic modulation of the extended amygdala, the enlarged A8 nucleus may be related to the increased use of communicative facial expressions in the hominoids compared to other primates, while the expansion of the A4 nucleus appears to be related to accelerated evolution of the cerebellum in the hominoids compared to other primates. In addition, we report the presence of a compact division of the locus coeruleus proper (A6c), as seen in other primates, that is not present in other mammals apart from megachiropteran bats. The presence of this nucleus in primates and megachiropteran bats may reflect homology or homoplasy, depending on the evolutionary scenario adopted. The fact that the complement of homologous catecholaminergic nuclei is mostly consistent across mammals, including primates, is advantageous for the selection of model animals for the study of specific dysfunctions of the catecholaminergic system in humans.

Comparative anatomy of the subscapularis, teres major and latissimus dorsi muscles from salamanders to mammals with special reference to their innervations from the brachial plexus.

It has been reported that the ramification pattern of spinal motor nerves reflected the spatial orientation of motoneuron pools in the ventral horn of spinal cord and this topography of spinal motor nuclei was very similar in different vertebrates. Therefore, the ramification pattern of spinal nerves was an important criterion for discussing the phylogenetic homology of muscles. It has been reported that the human subscapularis muscle was innervated by several branches, the proximal branch of them was from the ventral layer of the dorsal cord and the distal one from the dorsal layer of the dorsal cord of the brachial plexus. This fact suggested the human subscapularis had different phylogenetic origins. In this study, I unveil the phylogenetic origin of the mammalian subscapularis. The animals observed were a chimpanzee, a lar gibbon, a cat, a fetal pig, a koala, a possum (mammals), a lizard, an iguana (reptiles) and salamanders (amphibians). The branches to the mammalian subscapularis were divided into proximal and distal groups based on the origin from the brachial plexus, just like the human subscapularis. In salamanders and lizards, the homologous branch with the mammalian proximal branch to the subscapularis was observed and the segmentally higher branch innervating the latissimus dorsi was homologous with the distal branch to the mammalian subscapularis. Conclusively, I suppose that the dorsal-most portion of the reptilian latissimus dorsi muscle differentiates to the mammalian teres major, and the segmentally higher portion of the reptilian latissimus dorsi contributes to the formation of the mammalian subscapularis.

Nuclear organization of serotonergic neurons in the brainstems of a lar gibbon and a chimpanzee.

In the current study, we detail, through the analysis of immunohistochemically stained sections, the morphology and nuclear parcellation of the serotonergic neurons present in the brainstem of a lar gibbon and a chimpanzee. In general, the neuronal morphology and nuclear organization of the serotonergic system in the brains of these two species of apes follow that observed in a range of Eutherian mammals and are specifically very similar to that observed in other species of primates. In both of the apes studied, the serotonergic nuclei could be readily divided into two distinct groups, a rostral and a caudal cluster, which are found from the level of the decussation of the superior cerebellar peduncle to the spinomedullary junction. The rostral cluster is comprised of the caudal linear, supralemniscal, and median raphe nuclei, as well as the six divisions of the dorsal raphe nuclear complex. The caudal cluster contains several distinct nuclei and nuclear subdivisions, including the raphe magnus nucleus and associated rostral and caudal ventrolateral (CVL) serotonergic groups, the raphe pallidus, and raphe obscurus nuclei. The one deviation in organization observed in comparison to other primate species is an expansion of both the number and distribution of neurons belonging to the lateral division of the dorsal raphe nucleus in the chimpanzee. It is unclear whether this expansion occurs in humans, thus at present, this expansion sets the chimpanzee apart from other primates studied to date.

Nuclear organization of orexinergic neurons in the hypothalamus of a lar gibbon and a chimpanzee.

Employing orexin-A immunohistochemical staining we describe the nuclear parcellation of orexinergic neurons in the hypothalami of a lar gibbon and a chimpanzee. The clustering of orexinergic neurons within the hypothalamus and the terminal networks follow the patterns generally observed in other mammals, including laboratory rodents, strepsirrhine primates and humans. The orexinergic neurons were found within three distinct clusters in the ape hypothalamus, which include the main cluster, zona incerta cluster and optic tract cluster. In addition, the orexinergic neurons of the optic tract cluster appear to extend to a more rostral and medial location than observed in other species, being observed in the tuberal region in the anterior ventromedial aspect of the hypothalamus. While orexinergic terminal networks were observed throughout the brain, high density terminal networks were observed within the hypothalamus, medial and intralaminar nuclei of the dorsal thalamus, and within the serotonergic and noradrenergic regions of the midbrain and pons, which is typical for mammals. The expanded distribution of orexinergic neurons into the tuberal region of the ape hypothalamus, is a feature that needs to be investigated in other primate species, but appears to correlate with orexin gene expression in the same region of the human hypothalamus, but these neurons are not revealed with immunohistochemical staining in humans. Thus, it appears that apes have a broader distribution of orexinergic neurons compared to other primate species, but that the neurons within this extension of the optic tract cluster in humans, while expressing the orexin gene, do not produce the neuropeptide.

Influences of Forest Structure on the Density and Habitat Preference of Two Sympatric Gibbons (Symphalangus syndactylus and Hylobates lar)

Forest structure, defined as the three-dimensional vertical and horizontal distribution of canopy vegetation, has a great influence on the distribution patterns and abundance of forest primates. The complexity of this structural canopy produces a diverse range of microhabitats and distinct ecological niches, allowing ecologically similar species to coexist. Degradation of forests through anthropogenic factors significantly alters forest structure, and arboreal species such as gibbons are particularly vulnerable to these changes because of their reliance on canopy for survival. We investigated how forest structural variables influenced the density of two sympatric gibbon species (siamangs, Symphalangus syndactylus and lar gibbons, Hylobates lar) in Sikundur, a historically disturbed tropical lowland forest in north Sumatra. We used auditory sampling to establish group density in 10 locations and assessed structural characteristics of forest within 4–6 vegetation plots in each location. Lar gibbon group densities were 0.53–3.10 groups/km2 and siamang group densities were lower, with 0.0–1.0 groups/km2. The densities of both species were positively influenced by median height of first bole and the percentage of canopy connectivity. Lar gibbon group density was positively related to large (diameter at breast height 30–100 cm), tall (20–25 m) trees with a large crown area (100–300 m2), while siamang group density showed no significant relationships with these variables. These findings show canopy connectivity and height to first bole are significant structural variables for the continued presence of both gibbon species although, ecologically similar species can be influenced by different levels of structural disturbance. This canopy structural variation between sympatric species existing in the same ecosystem allows for home range overlap, low interspecific competition, and coexistence.

Effects of scent enrichment on behavioral and physiological indicators of stress in zoo primates.

Captive breeding is vital for primate conservation, with modern zoos serving a crucial role in breeding populations of threatened species and educating the general public. However, captive populations can experience welfare issues that may also undermine their reproductive success. To enhance the wellbeing of endangered zoo primates, we conducted a study to assess the effects of a new scent enrichment program on captive red-ruffed lemurs (Varecia rubra), black howler monkeys (Alouatta caraya), siamangs (Symphalangus syndactylus), lar gibbons (Hylobates lar) and orangutans (Pongo pygmaeus pygmaeus). We combined behavioral observations and fecal endocrinology analyses to evaluate the effects of a series of essential oils (benzoin, lavender, lemongrass) on five captive troops (N = 19) housed at Dudley Zoo & Castle and Twycross Zoo (UK). We recorded observations of natural species-specific and abnormal stress-related behaviors for 480 h using instantaneous scan sampling. We collected 189 fecal samples and measured the fecal cortisol concentrations using radioimmunoassay. We found a significant effect of the scent enrichment on behaviors, with red-ruffed lemurs and black howler monkeys reducing their social interactions, as well as red-ruffed lemurs and lar gibbons decreasing their stress-related behaviors after they were exposed to the series of essential oils. We also found that red-ruffed lemurs displayed a significant increase in fecal glucocorticoids following exposure to essential oils. Our contradictory findings suggest that the effects of this series of essential oils may change depending on the species-specific social lives and olfactory repertoires of primates. In conclusion, we cannot recommend using these essential oils widely with zoo primates without additional evaluation.

White-handed gibbons (Hylobates lar) alter ranging patterns in response to habitat type.

Small apes are often characterized as inhabiting small home ranges and being dependent on evergreen forest due to their dietary specialization on ripe fruits. Yet few primate studies, particularly those with gibbons, have considered intraspecific variations in ranging behaviors in response to local ecological conditions. This study examines Endangered white-handed gibbon (Hylobates lar) ranging patterns in a heterogeneous landscape. We conducted 13months of behavioral observations on four white-handed gibbon groups living in Huai Kha Khaeng Wildlife Sanctuary in western Thailand, and combine these data with group location and transect-based productivity data. We compare home range area, site fidelity, and microhabitat preferences. Home range (HR) area varied considerably among the four groups (17-61 hectares). Site fidelity was higher in one of the groups with more evergreen forest in the HR (0.72 ± 0.1) than one of the groups with very little evergreen forest in the habitat (0.47 ± 0.07). While groups with more evergreen forest in the HR preferred evergreen forest areas, groups with very little evergreen forest within the HR demonstrated less preference for evergreen forest areas. We conclude that gibbons at this site exhibit a considerable degree of behavioral variation in response to local ecological conditions. These findings suggest that while gibbons exhibit significant ecological flexibility, this flexibility may be limited by habitat type and key food resources.

White-handed gibbons discriminate context-specific song compositions

White-handed gibbons produce loud and acoustically complex songs when interacting with their neighbours or when encountering predators. In both contexts, songs are assembled from a small number of units although their composition differs in context-specific ways. Here, we investigated whether wild gibbons could infer the ‘meaning’ when hearing exemplars recorded in both contexts (i.e. ‘duet songs’ vs. ‘predator songs’). We carried out a playback experiment by which we simulated the presence of a neighbouring group producing either its duet or a predator song in order to compare subjects’ vocal and locomotor responses. When hearing a recording of a duet song, subjects reliably responded with their own duet song, which sometimes elicited further duet songs in adjacent groups. When hearing a recording of a predator song, however, subjects typically remained silent, apart from one of six groups which replied with its own predator song. Moreover, in two of six trials, playbacks of predator songs elicited predator song replies in non-adjacent groups. Finally, all groups showed strong anti-predator behaviour to predator songs but never to duet songs. We concluded that white-handed gibbons discriminated between the two song types and were able to infer meaning from them. We discuss the implications of these findings in light of the current debate on the evolutionary origins of syntax.

Composition of frugivores of Baccaurea ramiflora (Phyllanthaceae) and effects of environmental factors on frugivory in two tropical forests of China and Thailand

Frugivory and seed dispersal are key processes that shape both plant and animal communities, they are important in the maintenance and regeneration of forest ecosystems while threatened by environmental changes. This study investigated the frugivores and environmental factors affecting animal visitation and fruit consumption of the evergreen tree Baccaurea ramiflora (Lour.) in Chinese (Xishuangbanna) and Thai (Mo Singto) tropical forest plots. The two plots differ in their mammal faunas, with more large species (Asian elephant, white-handed gibbon, bears) surviving on the Mo Singto plot. We asked whether these differences could resulted in different seed dispersal patterns on the two plots. Nine individual trees were selected in each plot to record arboreal and ground frugivores of B. ramiflora using camera traps. A total of 27 frugivore species were captured from both forest plots, 15 species in Xishuangbanna and 22 in Mo Singto, with ten species shared in both plots. The major frugivores of B. ramiflora in Xishuangbanna were all pre-dispersal seed predators with little contribution to seed dispersal, including Palla’s squirrel (Callosciurus erythraeus), red-cheeked squirrel (Dremomys rufigenis) and black giant squirrel (Ratufa bicolor). Meanwhile, the major frugivores in Mo Singto were two effective seed dispersers pig-tailed macaque (Macaca leonina) and white-handed gibbon (Hylobates lar), and seed predator black giant squirrel (Ratufa bicolor). The diversity and body size of frugivores in the Xishuangbanna plot were relatively small compared with those in Mo Singto plot. Small-bodied frugivores showed higher activity in Xishuangbanna plot whereas relatively larger frugivores were most active in the Mo Singto plot. The environmental factor that consistently influenced frugivore activity (visitation and consumption of B. ramiflora fruits) was fruit abundance. Ground cover was also a predictor for average visit length and fruit consumption of frugivores. Frugivores visitation rate was higher in Xishuangbanna while average visit length and consumption rates were higher in Mo Singto. The defaunation of large body-size frugivores in Xishuangbanna could have been a result of habitat loss and higher hunting pressure. This may lead to shorter dispersal distances for large-seeded plants, restricting their ability to move across changing landscapes, and threatening their chances of survival over the long term.

二足歩行時の前額面における体幹姿勢調節：ヒト、シロテテナガザル、ニホンザルの比較

二足歩行時の前額面における体幹姿勢調節：ヒト、シロテテナガザル、ニホンザルの比較

Distribution, number, and certain neurochemical identities of infracortical white matter neurons in the brains of three megachiropteran bat species.

A large population of infracortical white matter neurons, or white matter interstitial cells (WMICs), are found within the subcortical white matter of the mammalian telencephalon. We examined WMICs in three species of megachiropterans, Megaloglossus woermanni, Casinycteris argynnis, and Rousettus aegyptiacus, using immunohistochemical and stereological techniques. Immunostaining for neuronal nuclear marker (NeuN) revealed substantial numbers of WMICs in each species-M. woermanni 124,496 WMICs, C. argynnis 138,458 WMICs, and the larger brained R. aegyptiacus having an estimated WMIC population of 360,503. To examine the range of inhibitory neurochemical types we used antibodies against parvalbumin, calbindin, calretinin, and neural nitric oxide synthase (nNOS). The calbindin and nNOS immunostained neurons were the most commonly observed, while those immunoreactive for calretinin and parvalbumin were sparse. The proportion of WMICs exhibiting inhibitory neurochemical profiles was ~26%, similar to that observed in previously studied primates. While for the most part the WMIC population in the megachiropterans studied was similar to that observed in other mammals, the one feature that differed was the high proportion of WMICs immunoreactive to calbindin, whereas in primates (macaque monkey, lar gibbon and human) the highest proportion of inhibitory WMICs contain calretinin. Interestingly, there appears to be an allometric scaling of WMIC numbers with brain mass. Further quantitative comparative work across more mammalian species will reveal the developmental and evolutionary trends associated with this infrequently studied neuronal population.

Are social media reports useful for assessing small ape occurrence? A pilot study from Peninsular Malaysia.

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.

Infant loss during and after male replacement in gibbons.

According to the sexual selection hypothesis, infanticide during resident male replacement is an adaptive strategy that has evolved because the killing of unweaned offspring sired by previous males shortens the inter-birth intervals of the mothers whose infants are targeted and thereby increases the reproductive fitness of the perpetrator. To test this hypothesis, we describe previously unreported cases of primary male replacement for two gibbon species (Hylobates lar and Nomascus nasutus), and review all other reported cases of primary male replacement in gibbons. Overall, infants were present in nearly half of all cases (16/33, 48%) and of the 18 infants present during replacement, 50% (N = 9) disappeared within 2 months of the event. In four of the five cases where there was sufficient demographic information to identify the likely sire of the subsequent offspring of females that lost infants, the new male was believed to be the sire. Infants were also less likely to die or disappear if the new male and original resident male were possible kin. However, there was no significant difference in the age of infants between those that died or disappeared following replacement and those that survived to weaning (p = .630). Our review of takeover-related infant loss in gibbons confirms that periods of male instability are risky for unweaned infants and that replacing males benefit from infant loss. Nevertheless, variability in the context of infant loss and difficulties related to data collection in the field make it difficult to test competing hypotheses concerning the mechanisms and functions of infanticide in the small apes.

Intestinal Parasites and the Occurrence of Zoonotic Giardia duodenalis Genotype in Captive Gibbons at Krabokkoo Wildlife Breeding Center, Thailand.

Intestinal parasitic infections can have an impact on health and growth of wildlife. The current study aims were to determine the prevalence of intestinal parasites and to molecular characterize Giardia duodenalis and Cryptosporidium spp. in captive gibbons at Krabokkoo Wildlife Breeding Center, Thailand. Fifty-five gibbons, 2 agile- (Hylobates agilis), 38 lar- (Hylobates lar) and 15 pileated gibbons (Hylobates pileatus) were included in this study. Fecal samples were collected individually at Krabokkoo Wildlife Breeding Center, Chachoengsao province, eastern Thailand, in November 2013. Intestinal parasitic infections were examined by zinc sulfate centrifugation flotation and by a commercially available immunofluorescent assay (IFA) for detection of G. duodenalis and Cryptosporidium spp.. Polymerase chain reaction targeting the Giardia glutamate dehydrogenase (gdh), beta- giardin (bg), triose phosphate isomerase (tpi) genes, and the Cryptosporidium small subunit-rRNA and heat-shock protein (hsp70) following by DNA sequencing were performed on the IFA positive samples. The overall prevalence of intestinal parasitic infection in gibbons at Krabokkoo Wildlife Breeding Center was 12.7% (95%CI: 5.3–24.5), Strongyloides spp. eggs or larvae were present in all positive samples. Co-infections with G. duodenalis were detected in 1.8% (95%CI: 0.1–9.7) of the samples. Based on the sequencing results of the three genes, the IFA Giardia positive isolate typed as the zoonotic genotype B. Since the data reveals the occurrence of zoonotic Giardia genotype, good hygiene management is suggested to prevent the transmission of this pathogen from gibbon to human, and vice versa.

The body center of mass in primates: Is it more caudal than in other quadrupedal mammals?

Whole body center of mass (BCoM) position values are lacking for a comparative sample of primates. Therefore, it still remains unknown whether the BCoM in primates is more posteriorly located than in other mammals. The aim of the present report is to provide data for a large sample of primate species and to compare the position of the BCoM in primates to non-primate mammals. We collected morphometrics on eight primate species belonging to various families: Hylobatidae (Nomascus grabriellae, Nomascus Siki), Cercopithecidae (Cercopithecus roloway, Cercopithecus lhoesti, Colobus guereza, Trachypithecus francoisi), Cebidae (Sapajus xanthosternos), and Atelidae (Ateles fusciceps). Using a geometric model, we assessed the position of the BCoM in a natural quadrupedal posture and in a control posture. To complete our comparative sample with a wider range of morphotypes, we added the data available in the literature for hominoids (Pan paniscus, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus, Hylobates lar) and another cercopithecoid species (Papio anubis). We also evaluated the phylogenetic signal of the position of the BCoM in primates. The variation in the position of the BCoM in primates is very large, ranging from 40% of the distance between the hip and the shoulder in Ateles fusciceps to 63% in Hylobates lar. We observed a strong phylogenetic signal for this trait: hominoid species, as well as the baboon, have a cranial BCoM relative to the midline between the hip and the shoulder, arboreal cercopithecoids and the spider monkey have a caudal BCoM, and the capuchin monkey has a BCoM positioned at mid-trunk. The variation observed in non-primate quadrupedal mammals lies inside the variation range of primates, from 51% in Felis catus to 63% in Canis familiaris. The BCoM of primates is not more posteriorly located than in other quadrupedal mammals; however, there is a substantial range of variation in primates, from caudal (in arboreal quadrupeds) to cranial (in hominoids and terrestrial quadrupeds) positions. This variation is related to a phylogenetic model that suggests stabilizing selection for this trait. It seems that the BCoM position mostly depends of the size of the appendicular system (i.e., limbs) and the tail. Therefore, it may also reflect a general trend in quadrupedal mammals with arboreal species exhibiting a caudal BCoM and terrestrial species exhibiting a cranial BCoM. These results are discussed in the context of the locomotor evolution of primates including locomotor habits and gait mechanics. We also propose a new "passive" mechanism for the explanation of the particular weight support pattern observed in primates with tails.

The distribution, number, and certain neurochemical identities of infracortical white matter neurons in a lar gibbon (Hylobates lar) brain.

We examined the number, distribution, and immunoreactivity of the infracortical white matter neuronal population, also termed white matter interstitial cells (WMICs), in the brain of a lesser ape, the lar gibbon. Staining for neuronal nuclear marker (NeuN) revealed WMICs throughout the infracortical white matter, these cells being most numerous and dense close to cortical layer VI, decreasing significantly in density with depth in the white matter. Stereological analysis of NeuN-immunopositive cells revealed a global estimate of ~67.5 million WMICs within the infracortical white matter of the gibbon brain, indicating that the WMICs are a numerically significant population, ~2.5% of the total cortical gray matter neurons that would be estimated for a primate brain the mass of that of the lar gibbon. Immunostaining revealed subpopulations of WMICs containing neuronal nitric oxide synthase (nNOS, ~7 million in number, with both small and large soma volumes), calretinin (~8.6 million in number, all of similar soma volume), very few WMICs containing parvalbumin, and no calbindin-immunopositive neurons. These nNOS, calretinin, and parvalbumin immunopositive WMICs, presumably all inhibitory neurons, represent ~23.1% of the total WMIC population. As the white matter is affected in many cognitive conditions, such as schizophrenia, autism and also in neurodegenerative diseases, understanding these neurons across species is important for the translation of findings of neural dysfunction in animal models to humans. Furthermore, studies of WMICs in species such as apes provide a crucial phylogenetic context for understanding the evolution of these cell types in the human brain.

The Japan Monkey Centre Primates Brain Imaging Repository for comparative neuroscience: an archive of digital records including records for endangered species

Advances in magnetic resonance imaging (MRI) and computational analysis technology have enabled comparisons among various primate brains in a three-dimensional electronic format. Results from comparative studies provide information about common features across primates and species-specific features of neuroanatomy. Investigation of various species of non-human primates is important for understanding such features, but the majority of comparative MRI studies have been based on experimental primates, such as common marmoset, macaques, and chimpanzee. A major obstacle has been the lack of a database that includes non-experimental primates’ brain MRIs. To facilitate scientific discoveries in the field of comparative neuroanatomy and brain evolution, we launched a collaborative project to develop an open-resource repository of non-human primate brain images obtained using ex vivo MRI. As an initial open resource, here we release a collection of structural MRI and diffusion tensor images obtained from 12 species: pygmy marmoset, owl monkey, white-fronted capuchin, crab-eating macaque, Japanese macaque, bonnet macaque, toque macaque, Sykes’ monkey, red-tailed monkey, Schmidt’s guenon, de Brazza’s guenon, and lar gibbon. Sixteen postmortem brain samples from the 12 species, stored in the Japan Monkey Centre (JMC), were scanned using a 9.4-T MRI scanner and made available through the JMC collaborative research program (http://www.j-monkey.jp/BIR/index_e.html). The expected significant contributions of the JMC Primates Brain Imaging Repository include (1) resources for comparative neuroscience research, (2) preservation of various primate brains, including those of endangered species, in a permanent digital form, (3) resources with higher resolution for identifying neuroanatomical features, compared to previous MRI atlases, (4) resources for optimizing methods of scanning large fixed brains, and (5) references for veterinary neuroradiology. User-initiated research projects beyond these contributions are also anticipated.