Juggling options: Manipulation ease determines primate optimal fruit‐size choice

Fruit Choice by Two Sympatric Primate Species: Determining Nutritional Composition Using Visual and Tactile Cues

In forested environments it is challenging for fruit-eating animals to select fruits that meet their nutritional needs. Primates base their food choices on fruit phenotypic traits such as color and tactile cues to determine nutrient content to improve foraging efficiency. However, are fruit phenotypic traits reliable indicators of nutrient content? To answer this question, we integrated observations of feeding behavior with the nutritional and physical characteristics of the fruits in the diet of two sympatric primates (Nomascus concolor and Trachypithecus crepusculus) in a subtropical forest in Southwestern China. Gibbons chose fruits with high total non-structural carbohydrate content that have high chromatic contrast against a predominantly green background, while langurs chose fruits with high crude protein content and high hardness. The chromatic contrast exhibited a significant positive correlation with the carbohydrate content, and the fruit hardness demonstrated a significant positive correlation with the protein content. Chromatic conspicuousness and hardness may serve as important fruit foraging cues for gibbons and langurs. This study adds to our growing understanding of how Old World primates use color vision and tactile cues while foraging and provides new insights to the evolution of diverse animal sensory systems.

The neurobiological effects of senescence on dopaminergic system: A comprehensive review

Over time, the body undergoes a natural, multifactorial, and ongoing process named senescence, which induces changes at the molecular, cellular, and micro-anatomical levels in many body systems. The brain, being a highly complex organ, is particularly affected by this process, potentially impairing its numerous functions. The brain relies on chemical messengers known as neurotransmitters to function properly, with dopamine being one of the most crucial. This catecholamine is responsible for a broad range of critical roles in the central nervous system, including movement, learning, cognition, motivation, emotion, reward, hormonal release, memory consolidation, visual performance, sexual drive, modulation of circadian rhythms, and brain development. In the present review, we thoroughly examine the impact of senescence on the dopaminergic system, with a primary focus on the classic delimitations of the dopaminergic nuclei from A8 to A17. We provide in-depth information about their anatomy and function, particularly addressing how senescence affects each of these nuclei.

Activity budget and seasonal activity shifts in sympatric lemurs: Increased lean season effort in a cathemeral frugivore contrasts with energy conservation in a diurnal folivore

One of the most fundamental aspects of a species' behavioral strategy is its activity budget; for primates this generally involves the allocation of available time among resting, feeding, traveling, and social behavior. Comparisons between species, populations, or individuals can reveal divergences in adaptive strategies and current stressors, and reflect responses to such diverse pressures as predation, thermoregulation, nutrition, and social needs. Further, variation across seasons is an important part of behavioral strategies to survive food scarcity; this can involve increasing or decreasing effort. We documented activity over the 24-h cycle for the cathemeral, frugivorous Eulemur fulvus and the diurnal, folivorous Propithecus diadema across 13-18 months at Tsinjoarivo, Madagascar. Their activity budgets were dominated by resting (E. fulvus: 74.1%; P. diadema: 85.2%), followed by feeding (15.8%, 12.4%), traveling (9.31%, 1.74%) and social activities (0.76%, 0.70%), respectively. The lower feeding and higher resting in P. diadema likely reflect slower gastrointestinal transit and higher reliance on microbial fermentation to extract energy from fibrous food. The two species showed opposite lean season strategies. E. fulvus increased activity, with more feeding but less travel time, consistent with a shift to less-profitable fruits, and some leaves and flowers, while increasing feeding effort to compensate ("energy maximizing"). P. diadema showed less variation across months, but the lean season still evoked reduced effort across the board (feeding, travel, and social behavior), consistent with a "time minimizing" strategy prioritizing energy conservation and microbe-assisted digestion. Understanding these divergent shifts is key to understanding natural behavior and the extent of behavioral flexibility under stressful conditions. Finally, the complex patterns of fruit availability (intra- and interannually) and the species' behavioral responses across months underscore the need to move beyond simplistic "lean/abundant season" and "fruit/leaf" dichotomies in understanding underlying energetic strategies, and species' vulnerability to habitat change.