Non-human primates (NHPs) exhibit sensory systems remarkably similar to humans, including vision, hearing, touch, and smell. NHPs process and respond to external stimuli through their mature sensory systems, playing a crucial role in intra- and inter-group communication. Understanding their sensory systems and communication signals is essential for better management of NHPs used in experimental research.
In the wild, diverse sensory signals among monkey groups convey clear information within and between groups, establishing cooperative relationships to defend against intruders and reinforce hierarchical orders within the group. Therefore, understanding NHPs' behavior is crucial for experimental research. It's important to note that when analyzing animal behavior, the context in which the behavior occurs must also be considered. For example, mutual grooming behavior in NHPs can occur both in tense and relaxed situations, representing different internal states of the animals. Additionally, analyzing multiple behaviors comprehensively is essential. For instance, screaming accompanied by baring teeth indicates fear.
1. Vision
Humans derive around 80-90% of external information through vision. Similarly, vision is a primary sensory source for NHPs. Their binocular vision overlaps, allowing convergence on targets, resulting in a singular visual experience that aids in precise visual perception. This binocular convergence pattern enables them to quickly locate predators and adeptly navigate through jungles to hunt various prey.
Monkey body language and facial expressions are highly diverse. Common facial expressions include "grinning," yawning, and staring. It's noteworthy that "grinning" does not necessarily signify happiness; rather, when monkeys bare their teeth and tighten their lips slightly, it indicates fear or tension. Adult male monkeys yawn to display their canines, demonstrating dominance. While humans may stare out of interest, NHPs' gaze signifies vigilance and threat display. Therefore, it's advisable to avoid direct eye contact with NHPs to prevent them from feeling threatened. Both males and females, regardless of rank, will raise their tails to exhibit their genitals to higher-ranking individuals, a behavior that helps alleviate tension between parties. Conversely, a typical posture of monkeys during threat displays involves erecting all body hair, crouching on all fours, and staring at the intruder.
Monkeys have sensitive color vision, allowing them to discern fruit ripeness and tender green shoots. Male monkeys can also discern the varying degrees of redness in female genital swellings, determining mating receptivity.
While humans and narrow-nosed NHPs share trichromatic color vision, some broad-nosed NHP species exhibit varying color discrimination abilities. Diurnal broad-nosed monkeys like macaques and squirrel monkeys, and nocturnal broad-nosed monkeys like owl monkeys, possess different color vision capabilities. For instance, diurnal broad-nosed monkeys, such as macaques and squirrel monkeys, along with some females, are red-green colorblind, distinguishing only between blue and green. Owl monkeys, being nocturnal, can only discern black and white and different shades of gray. Although biological experiments often utilize diurnal NHPs, owl monkeys, with their specialized and advanced visual systems, are also commonly used in visual research.
2. Olfaction and Taste
NHPs rely on keen olfaction for foraging and social interactions, particularly evident in broad-nosed monkeys, which possess scent glands used for odor marking. These glands, located on the perineum, chest, or face, secrete oily substances used to mark various information such as identity, territory occupation, path marking, or reproductive status of resources or mating partners. Dominant male monkeys emit odor signals to suppress the estrus of subordinate females. Monkeys like macaques, squirrel monkeys, and owl monkeys moisten their bodies and limbs with urine to mark their passage routes. Understanding this information helps establish rational hygiene standards for experimental NHPs. It's noteworthy that monkeys mark their living environment with their scent, so thorough cleaning by technicians should be avoided to prevent stress to the animals.
NHPs have a preference for sweet-tasting food. Therefore, providing them with fully ripe fruits and vegetables aligns with this taste preference and serves as enrichment.
3. Hearing
Research indicates that humans perceive sound frequencies in the range of 20 Hz to 20 kHz, while NHPs have a wider hearing range. The lower limit of NHPs' hearing frequency is 125 Hz, with different species having varying upper limits. For instance, the upper hearing frequencies for macaques, squirrel monkeys, and owl monkeys are 30k, 43k, and 49k Hz, respectively. Narrow-nosed monkeys like macaques and crab-eating monkeys also have upper hearing limits of up to 42 kHz. As humans cannot perceive ultrasound above 20 kHz, experimenters should monitor ultrasound in the NHPs' experimental environment to minimize disturbance to the animals.
While humans use flexible vocal cords and throat vibrations to convey intricate language information, NHPs have limited control over this and can only produce sounds with different rhythms and syllables. When a juvenile monkey is separated from its mother, it emits "phee phee" or "whoo whoo" sounds to call for her. In the wild, NHPs also use vocal signals to communicate food discoveries, with langur monkeys emitting low "coo coo" sounds when finding low-quality food and rhythmic sounds when discovering high-quality food.
4. Touch
NHPs possess rich sensors internally and externally to perceive temperature, pain, pressure, etc. Mutual grooming is the most common form of tactile communication within monkey groups. Mutual grooming helps maintain social structure and group hygiene among NHPs. Grooming induces the release of more endorphins in NHPs, reducing heart rate and relieving tension, ultimately leading to relaxation for both groomer and groomed. Mutual grooming behaviors also occur during NHPs' reproductive processes. However, not all NHPs exhibit grooming behavior; it's less common in owl monkeys and is typically performed only by mothers for infants in squirrel monkey groups.
About Prisys
Prisys is located in the Fengxian Lingang Nanqiao Science and Technology Park in Shanghai, with an investment exceeding 100 million yuan and an area of approximately 4,000 square meters, the center integrating NHPs model development, clinical-level research activities, industrial-scale research capabilities, and high-standard animal welfare. It provides customers with pharmacokinetics and pharmacology research, drug metabolism and toxicology evaluation, disease models and disease target validation, drug and pharmaceutical technology concept validation, disease clinical indicators and biomarkers, parallel clinical experiments, and medical device validation services.
Prisys continually develops various new models for diseases, covering over 40 NHPs models in areas such as respiratory diseases, metabolic syndrome, hematologic diseases, inflammation and immunological diseases, ophthalmic diseases, central nervous system disorders, and behavioral analysis. It holds 57 intellectual property rights, most of which are innovative models, opening up new avenues for disease research, new drug target discovery, biomarker validation, drug therapy evaluation, vaccine evaluation, intervention therapy technology development, and pre-clinical trials, gradually becoming a distinctive part of the global biopharmaceutical industry chain with Chinese characteristics and transitioning from research to industrial application support platform.
