International Journal of Primatology最新文献

Interspecific hybridization occurs almost in all major primate radiations. Intermediate phenotypes, sometimes seen in mixed-species groups, are often the first indications of hybridization. Beyond natural hybridization, human activities, such as habitat fragmentation or population depletion, can be important drivers for initiating or intensifying the formation of mixed-species groups and hybridization. As hybridization can lead to the cyto-nuclear extinction of species, it may pose additional threats to threatened primates. To assess the frequency of mixed-species groups and intermediate phenotypes between threatened Phayre’s (Trachypithecus phayrei) and capped langurs (T. pileatus), we conducted population surveys in six forests of northeast Bangladesh between 2018 and 2023. We also tested the hybrid status of one individual with intermediate phenotype genetically, by sequencing the maternally-inherited mitochondrial cytochrome b gene and fragments of two biparentally-inherited loci. During our surveys, we encountered 98 groups of langurs of which 41 were Phayre’s langur groups, 49 capped langur groups, and eight mixed-species groups (8%). In three mixed-species groups, we detected three individuals of intermediate phenotype, among them one adult female whose nipples were elongated indicating that she had an infant, and thus was likely to be fertile. Genetic analyses confirmed the hybrid status (most likely F1) of one individual with intermediate phenotype. To our knowledge, there are no reports of mixed-species groups and hybridization from other parts of the range where the species occur sympatrically. Hence, it seems likely that such groups occur mainly in the northern part of their common range where natural habitats are deteriorating fast. Therefore, we suggest monitoring of the populations, to find out whether the frequency of mixed-species groups increases, and a large-scale population genetic study to investigate whether hybridization is a recent phenomenon or occurred historically in the zone of range overlap in Bangladesh.

Humans can retain memories for months to decades. In contrast, relatively few studies have examined such very long-term memory in nonhuman animals. We, therefore, investigated whether chimpanzees (Pan troglodytes) who had learned arbitrary relations between stimuli remembered these relations over a long period. In Experiment 1, we tested four chimpanzees, one of whom (Chloe) had learned a “symbolic” matching task between colors and geometric forms at age 9–10 years, and three who had not been previously trained, on their memory for these relations 19 years later. Chloe showed perfect accuracy in the test trials; the three other chimpanzees did not perform better than chance level. In Experiment 2, we tested Popo and Reo, who had learned the same set at the same time as Chloe, on their memory 27 years later. Although they relearned the identity-matching task very quickly (savings effect), they did not retain the stimulus relations learned 27 years ago. In Experiment 3, we tested Chloe’s retention of a different set of stimulus relations, which she had learned at the same time as those tested in Experiment 1 but with less intensive training than with the first set. She did not perform better than the chance level. Finally, in Experiment 4, we tested the memory retention of another chimpanzee, Ai, who had learned to “label” objects with lexigrams more than 20 years earlier by using the matching task. She did not perform significantly better than chance on test trials. Thus, our results were not consistent across the experiments, providing only limited evidence that chimpanzees retain associative stimulus relations over the long term. Several factors, such as the effect of cognitive environments, the levels of processing, and the context-dependent nature of memory retrieval, could have affected our results, but none of these factors can account for all the results from the four experiments.

In response to environmental and social challenges, animals mount physiological “stress responses” involving elevated glucocorticoid (GC) levels, which may have long-term consequences for health and survival. However, the degree to which social factors drive these physiological responses is likely modulated by a species’ social system, including social organisation, dispersal patterns, and the steepness of the dominance hierarchy, which influence the costs and benefits of social interactions. We examined the relationship between dominance rank, unit size, and faecal GC metabolite (fGC) levels in wild female Guinea baboons (Papio papio). Guinea baboons live in multilevel societies with female-biased dispersal and shallow rank relationships. Units consisting of one primary male and associated females form the core of these societies. We hypothesised that females experience higher competition for male protection or access to food in larger units and that lower-ranking females would bear the costs of this competition. We predicted that membership in a larger unit and lower rank would be associated with higher fGC levels. We collected 251 faecal hormone samples from 14 individuals. A capture event during the sampling period allowed us to validate our method's sensitivity to stress responses. However, we found no evidence of a link between unit size or rank and fGC levels, suggesting that neither incurs a significant physiological cost in this species. These results extend our insights into the physiological correlates of behavioural variation in female primates, expanding our understanding of their adaptability and resilience to social stressors in relatively egalitarian multilevel societies with female-biased dispersal.

Reports of primate violence frequently note wounds to the genital region, raising the possibility that attackers target genitals to eliminate the reproductive capacity of rivals. Alternatively, in chimpanzees (Pan troglodytes) and other species with prominent genitals, injuries may occur simply because large size makes genitals easy targets. To test these hypotheses, we compiled records of wounds suffered by chimpanzees in four communities at three long-term study sites (Gombe, Tanzania; Kibale, Uganda; Fongoli, Senegal), including both nonlethal (N = 1,268 wounds; N = 891 male wounds; N = 377 female wounds) and lethal attacks (N = 258 wounds), to determine whether genital wounding occurred more frequently than expected by chance. In nonfatal cases, wounds occurred in the genital region more often than expected for females (Kasekela: N = 9/80 wounds, Mitumba: N = 8/61 wounds, Fongoli: N = 11/84 wounds, Kanyawara: N = 31/152 wounds), but only in Kasekela did males suffer genital wounds more often than expected by chance (Kasekela: N = 3/80 wounds, Mitumba: N = 2/48 wounds, Fongoli: N = 6/413 wounds, Kanyawara: N = 4/350 wounds). In contrast, killings of males involved genital wounds more often than expected (N = 12/258 wounds). Increased genital wounding may occur when genitals are more accessible, such as when females flee from male aggression, exposing their hindquarters, or when victims are immobilized during fatal attacks.

Genetic diversity allows species to survive in a dynamic environment where selective criteria are ever-changing. As a result, the long-term survival of a species can be affected by its levels of genetic diversity. The Kashmir gray langur, Semnopithecus ajax, is an Endangered primate species endemic to the northwestern Himalaya. It has a fragmented distribution, is exposed to severe anthropogenic and climatic pressures, and has received little scientific attention. We investigated patterns of genetic diversity, population structure, and demographic history in wild populations of the Kashmir gray langur in the Kashmir Himalaya. We sampled 15 langur groups by using noninvasive sampling for scat collection and also obtained a tissue sample from a dead langur for whole-genome sequencing. We sequenced a mt-DNA fragment encompassing part of the noncoding D-loop region (728 bp) for 63 samples and protein-coding Cytochrome b (775 bp) for 37 samples. We generated whole-genome data by using PCR-free shotgun sequencing. We also reconstructed the demographic history of the Kashmir gray langur through coalescent analysis using MSMC2. We observed (± SD) lower haplotype (Hd = 0.207 ± 0.088) and nucleotide (π = 0.00126 ± 0.00077) diversity in Cytochrome b (693 bp) gene sequences than in noncoding partial D-loop (625 bp) gene sequences (Hd = 0.878 ± 0.026 and π = 0.00735 ± 0.002). Concatenated alignment (Cytochrome b and D-loop, 1318 bp) defined 21 unique haplotypes with haplotype diversity of 0.935 ± 0.024 and nucleotide diversity of 0.00532 ± 0.00193. The haplotype network and maximum likelihood phylogenetic tree revealed strong signatures of genetic differentiation among geographic populations, with the Jhelum River appearing to be a prominent barrier to gene flow between these populations. We found no evidence of isolation-by-distance. Mean genome-wide heterozygosity was very low (0.00034). We estimated the long-term effective population size to be 8,702 individuals; however, the most recent estimate indicated a lower value of 1,844 individuals. Our study emphasizes the need for habitat connectivity to mitigate the negative impacts of habitat loss and fragmentation on the genetic diversity of terrestrial and arboreal animals inhabiting the Himalayan ecosystems, particularly habitat specialist species.

Knowledge of the geographic distributions of species is fundamental for conservation management. Ateles fusciceps rufiventris is currently listed as Vulnerable. It is found in Colombia and Panamá and may be present in Ecuador. It has been subject to very few studies and its true current conservation status is unknown. We used 3 years of interviews and field observations to determine its current distribution in Colombia, complemented with searches of the literature and databases for the entire range. We evaluated the quality of available habitat using a publicly available data layer of forest integrity information and niche modeling. We estimated the original and current extent of occurrence (EOO) of the taxon based on an ecological niche model (ENM) using MaxEnt and calculated the area of occupancy (AOO) for Colombia, where we conducted field sampling. We also identified the main threats to the subspecies during our interviews and field observations. Of the 39 sites we visited, we confirmed the presence of A. f. rufiventris by direct observation or secondary information at 15 (38%), although all sites had potential habitat for the subspecies. We estimated that the EOO of A. f. rufiventris in Colombia covers 118,730 km² and that forests in the potential habitat have reduced by ~ 60% in the last 30 years, leaving an estimated current AOO in Colombia of ~ 17,800 km² to ~ 47,000 km², with just 11% in state-protected areas. Interviews and field observations showed that clearcutting for agriculture and cattle ranching were the most frequent threats at sites where we found no evidence of the subspecies. Illegal crops, hunting for subsistence and trade, including as pets, were the most frequent threats at sites where we found the subspecies. We found a dramatic reduction in suitable habitat and a high incidence of forest degradation, deforestation, and hunting affecting the subspecies. Conservation efforts should focus on restoration in strategic areas, and on reducing deforestation and hunting pressure. Community-based conservation could be employed to increase areas of protected habitat on communal lands and decrease hunting pressure, to ensure the long-term survival of this highly threatened primate.

Diet and home range use patterns provide information on the needs of species faced with changing forest quality. Many primates have diets and foraging strategies that maximize nutrient uptake and minimize energy expenditure, resulting in well-defined home ranges. Primates use their home range in varying ways depending on the spatial distribution of resources. The western hoolock gibbon (Hoolock hoolock) is a small, frugivorous ape that maintains a home range in closed-canopy forests. The species is globally Endangered and lives Bangladesh, India and Myanmar in shrinking forest patches. We studied a group of gibbons, consisting of two adult males, an adult female, an immature male, and an infant in Lawachara National Park in northeastern Bangladesh. We used scan sampling to determine their diet, home range size and daily path lengths from April 2019 to March 2020. We also mapped fruiting trees and sleeping sites within their home range from April 2019 to March 2020. The gibbons’ diet varied seasonally, but fruits (mostly figs) dominated throughout the year (fruits: 51%; leaves: 35%; flowers: 5%; buds: 6%), peaking in the monsoons. Home range size was 50.79 ha (90% Kernel Density Estimate) or 47.72 ha (Grid Cell Method). The mean daily path length was 1057.2 m (range 451–1938; n = 33). The home range was smaller during the monsoons and larger in winter. Daily path lengths decreased in the monsoon likely because of abundance of fruits, and also decreased in winter, possibly owing to low temperatures. Gibbons used multiple sites for foraging and slept in large trees with a dense canopy. They slept at a mean of 22.82 m (range 16–30 m) above ground in trees with lianas, possibly as an antipredator strategy. Continued monitoring of ecological factors that influence gibbon foraging and habitat use can help to formulate targeted conservation plans for this Endangered small ape.

The vocal structure of gibbons has long been believed to be under strong genetic control and consistent with phylogeny. Gibbon vocalizations show hierarchical structures and song coordination behaviors, which may have different functions and convey distinct information compared to basic notes. However, previous studies have not compared vocalizations at multiple levels across species. We compared the vocal structures of three Nomascus species in the wild in South China, namely the western black gibbon (Nomascus concolor), Cao vit gibbon (N. nasutus), and Hainan gibbon (N. hainanus) at the levels of note (six features of four types of notes), male sequence (eight features), and song coordination (four features of the overlap pattern between male and female songs). We selected 15 recordings for each species: N. concolor (six groups, 2006 to 2021), N. nasutus (seven groups, 2008 to 2021), and N. hainanus (six groups, 2020 to 2021). We used permuted random forest analysis to test for species differences in vocal structure and the contribution of acoustic features to species differences at each level. We used acoustic features to construct a hierarchical clustering tree, and compared it with phylogenetic relationships. We found significant differences at all levels except the boom note. Acoustic similarity did not match genetic similarity in boom and pre-modulated notes, suggesting that genetic differences are not the only factor leading to species differences in vocal structures. We also found different contributions of acoustic features to differentiation in vocal structure at different levels. Our study suggests that we need to compare gibbon vocalizations at different levels to understand their differentiation and evolution.