American Journal of Primatology最新文献

Variation in animal perception provides excellent opportunities for studying adaptation. Unusually, primates exhibit a great deal of inter- and intra-specific visual system variation. Here, we discuss what is known about the retinal cone mosaic, and the sources of variation in primate cone types and their relative expression. We focus on catarrhines (African and Asian monkeys and apes and humans), which have evolved uniform trichromacy, exhibiting short- (S), medium- (M), and long-wave (L) cones. Catarrhines generally exhibit high inter-specific consistency in the peak sensitivities of their L and M sensitive cones. One under-explored component of variation is the relative expression of those cones, that is, the L:M ratio. Across catarrhines, the mean L:M ratio is 1:1, with some limited intraspecific variation. Intriguingly, humans show two big differences compared to other catarrhines. Firstly, their mean L:M ratio is shifted to 2:1. Secondly, they show vast (75-fold) intraspecific L:M ratio variation. We discuss evidence as to whether this difference in the mean ratio, and this high intraspecific variation, are likely to have functional consequences, concluding that indeed this variation likely impacts color perception. We finish by suggesting possible explanations for the higher mean ratio of L:M cones in humans, highlighting similarities with other aspects of our color vision that differ from other catarrhines. We hope that the suggestions and questions we raise will inspire future research on primate cone ratios.

Lion-tailed macaques (Macaca silenus), endemic to the Western Ghats of India, are increasingly threatened by habitat loss and degradation, and are vulnerable to environmental change. Insights into their spatial ecology can reveal the strategies that enable these macaques to navigate and use spatially complex heterogeneous spaces. This is crucial for conservation, given the increasing human disturbance in and around the Western Ghats. This study, conducted in Silent Valley National Park between January and June of 2019, 2022, and 2023, focused on two macaque troops occupying habitats with varying human presence—in the park's core (Sairandhri) and in the buffer (Keeripara). The observed group sizes of the Sairandhri and Keeripara troops were 51 and 21, respectively. We examined differences in the spatial ecology of these troops by assessing their vertical space use, two-dimensional (2D) and three-dimensional (3D) home ranges, and using an integrated step-selection function to understand movement-based habitat selection. We observed similarities in movement patterns across the two troops, with notable differences mainly in their vertical use of the forest. The Keeripara troop, resident in a more disturbed area, utilized a smaller home range (1.80 km²). They spent 94.2% of their time in mid-level canopy (6–20 m), descending rarely (1.1%) into lower strata (≤ 5 m), likely due to perceived high risk from predators and humans, and proximity to roads. The Sairandhri troop, resident in the less disturbed area, had a larger home range (3.05 km²) and exhibited greater terrestriality (11.3%), with 84.2% observed time in mid-canopies. Both troops preferred areas with canopy cover and fruiting trees, displaying similar slow movements (indicated through small step lengths and large turning angles) near these resources. Our findings suggest that lion-tailed macaques may be less strictly arboreal than previously believed, displaying more terrestriality in less disturbed habitats. Strategic use of 3D space based on local ecological and anthropogenic conditions highlights the need for conservation efforts that maintain canopy connectivity to support the ecological flexibility of this vulnerable species.

Parasite infection is one key risk inherent in group living and is considered to influence the formation and evolution of animal societies. Previous studies investigating the relationship between sociability (a measure of an individual's level of social engagement) and parasite infection have yielded mixed results, with some observing positive relationships between social network centrality and infection and others observing negative or no sociability-infection links. Here, we aggregated behavioral and parasitological data from three groups of rhesus macaques (Macaca mulatta brevicaudus) in China and two groups of Japanese macaques (Macaca fuscata and Macaca fuscata yakui) to test whether sociability generally predicts geohelminth infection in macaques with similar social structure. We discovered variability in the relationship between sociability and geohelminth infection across these different groups of macaques, and results did not support a general pattern linking sociability to geohelminth infection. Among the five groups, we found a significant positive relationship between sociability and infection in only one group. These results call into question how generally useful an indicator social network centrality metrics are in predicting geohelminth parasite infection across individuals, at least relative to other factors that influence infection dynamics. We discuss potential confounds when examining relationships between sociability and infection across populations and groups, and encourage future studies that can account for these while focusing on the mechanisms that might link social factors and parasite infection to fully understand this relationship.

The use of tools to drink water is well-documented in wild chimpanzees, but the specific function of this behavior is unclear. Here we use a large data set of drinking behaviors spanning 14 years of observation from the Kanyawara community of chimpanzees living in Kibale National Park, Uganda, to test two possible functions of leaf-sponges and other drinking tools. On the one hand, chimpanzees may use tools to access water that is hard to reach, which predicts that chimpanzees will preferentially use tools to drink at tree holes and crevices compared to all other locations. Conversely, chimpanzees may use these tools to filter stagnant water, in which case they would use tools more often at holes and puddles compared to running water sources (e.g., streams). We compared both likelihood of using a tool to drink at different locations, as well as overall rates of drinking, and found chimpanzees in this community most often drink from streams without tools. However, when they do use tools, they preferentially do so to drink at tree holes. Given known age and sex effects on tool use in chimpanzees, we also examined demographic variation in drinking tool use to understand the emergence of this behavior. While females use tools more often than males overall—in part driven by differences in drinking rates at different locations—both males and females use tools more frequently at tree holes than other locations when they do drink there. Finally, comparisons by age indicate that this selectivity strengthens over development with older chimpanzees showing a more pronounced effect of using tools more often at tree holes, suggesting that younger chimpanzees may exhibit exploratory tool use behavior. These results pinpoint the specific function of tool use during drinking and further suggest that even simple tools may require learning for use in appropriate contexts.

Rhesus and pigtail macaques are closely related and have similar social structures, yet differences in their behavior, socio-ecology, and personality have been observed, although not systematically documented. Given these differences, it is important to assess pigtail macaque cognition independently, rather than relying on rhesus macaque findings as a proxy. To gain a better understanding of pigtail macaque cognition, we used a battery of three cognitive tasks. Rhesus macaques were tested on the same tasks to validate our methods and to allow for comparison. Across just three tasks, we found significant differences between the two closely related species. In the three cups task, which tests short-term memory, both pigtail and rhesus macaques performed significantly better when they had to recall the location of a hidden food reward after a 0 s delay compared to a 15 s delay. However, in the 15 s delay condition, only rhesus macaques performed above chance levels, whereas pigtail macaques did not. In the reversal learning task, which tested rule learning and cognitive flexibility, we found species differences in learning performance. For the quantity discrimination task, which tests numerosity, we found that both rhesus and pigtail macaques were more accurate at discriminating "easy" ratios of foods (e.g., 1 vs. 5 or 2 vs. 6) than the "hard" ratios (e.g., 2 vs. 3 or 4 vs. 5). However, pigtail macaques were more accurate than rhesus macaques in the hard ratio trials. These contribute to a novel understanding of cognition in pigtail macaques while also increasing research rigor in translational research.

Pyrocognition has been part of the hominin behavioral repertoire for at least one million years. Here, we report evidence of naturally occurring pyrocognitive behavior in wild bonnet macaques (Macaca radiata) inhabiting a temple site in India. We recorded 2704 instances of macaques attempting to extinguish the fire in offering lamps that contained a food reward (sesame seeds, rice flour, or coconut). Overall, we found significant variation associated with age, with adults experiencing higher foraging success (males 81.1% and females 75.3%) than subadults (males 30.1% and females 18.8%). In addition, there was a positive correlation between the number of lamp manipulations and foraging success among adults, but not among subadults. It appears that despite extensive exposure to burning lamps, subadult bonnet macaques failed to fully understand how their actions in attempting to extinguish the fire resulted in obtaining the food reward. In contrast, over time several adult bonnet macaques appeared to understand how their actions in extinguishing the fire resulted in successfully obtaining a food reward (i.e., causal knowledge). Our results indicate that pyrocognitive behavior develops slowly in bonnet macaques, differs between adults and subadults, is not sex-based, and provides an instructive model for pyrocognition in early hominins.

The Gaoligong Mountains, located in the southeastern Tibetan Plateau, is one of the world's biodiversity hotspots and provides a refugium for many endangered endemic animals. In this study, we reported a population genetic study on black snub-nosed monkey (Rhinopithecus strykeri), a critically endangered primate endemic to the Gaoligong Mountains, yet their large-scale population genetic study remains underexplored. Here, we performed population genetic analyses from two geographical populations (Pianma and Luoma) based on targeted genomic single-nucleotide polymorphism (SNP) data (37.7 K) and mitochondrial DNA (mtDNA) control region (842 bp). Both nuclear SNP data and mtDNA revealed relatively low levels of genetic variation in both populations compared to other reported primates, which is most likely to be explained by loss of historical genetic diversity due to inbreeding and long-term small effective population size, thus potentially aggravating the effects of inbreeding and genetic depression. Phylogenetic and population structure analyses for mtDNA revealed two deep lineages (approximately 0.69 million years ago), but limited genetic differentiation in nuclear data, which might have been caused by the Late Cenozoic uplift of the Tibetan Plateau and glacial refuge, and subsequent secondary contact as a result of historically high and bidirectional gene flow between populations. Ecological niche modeling and landscape connectivity analyses also showed historical and recent connectivity between two geographical populations. The demographic history inferred from both mtDNA and nuclear data revealed at least two continuous declines in the effective population size occurring around 43 Kya and 8–10 Kya, respectively, probably due to Pleistocene glaciations and subsequent human activities. Our results provide the first detailed and comprehensive genetic insights into the genetic diversity, population structure, and demographic history of a critically endangered species, and provide essential baseline information to guide conservation efforts.