American Journal of Primatology最新文献

The high energy costs of brains suggest that a species' current brain size is adaptive. However, although the comparative data for mammals suggest a positive effect on fitness in larger-brained species because of higher adult survival and thus longer lifespan, it also reveals two negative effects, namely later age at first reproduction owing to slower development and a tendency towards reduced reproductive allocation owing to larger newborns. Here we suggest that what is missing is the positive impact of brain size on immature survival, causally linked to greater parental investment in larger-brained species. Using long-term demographic data on natural populations of 18 primate species, we find a strong positive brain size effect on immature survival, which is already apparent during the first year. We suggest this effect is caused by parental protection and provisioning, allowing young to survive better and mature slowly but surely. This survival effect may well be the strongest adaptive benefit of increased brain size. It remains unknown to what extent this effect generalizes to non-primates.

In stark contrast to our own highly plastic communicative abilities, nonhuman primate vocalizations were historically considered fixed and innate, with very little ability to learn or modify vocal signals. However, recent studies indicate that primate vocalizations do show evidence of developmental plasticity, most notably in their context and usage. We build on these studies by investigating developmental changes in one of the most common calls of white-faced capuchins (Cebus imitator), the twitter. Specifically, we examined the behavioral context around twitter vocalizations in a wild population of white-faced capuchins in the Taboga Forest Reserve, Costa Rica. We analyzed the use of twitters in relation to behavioral state (social, foraging, travel, or resting), immediate context (approaching and leaving others), and specific social behaviors (grooming and aggression). Immatures (infants and juveniles) twitter primarily in a social state, while adults twitter primarily in a foraging state. The twitters produced by immatures were more closely associated with approaching other group members within 1 m, compared to adults. This contextual shift with development from social to foraging prompted us to also look for corresponding acoustic changes. However, the acoustic properties of twitters were not related to context or age, with the one exception that adult twitters were longer than those from immatures. Overall, our results suggest that the twitter is a call with multiple functions, with a shift in usage from social to foraging contexts across development. This adds to the growing evidence of flexibility and learning in primate vocal communication.

The common marmoset (Callithrix jacchus) is a valuable model for studying aging due to its physiological and social similarities to humans, including shared susceptibilities to age-related diseases. However, the effects of healthy aging on marmoset mastication and swallowing are poorly understood, despite their importance for modeling human aging and understanding marmoset ecology and longevity (efficient food processing impacts foraging success and predation risk). Given their specialized diet, dental adaptations, and relatively long lifespan compared with other biomedical models commonly used, like rodents, understanding how elderly marmosets maintain feeding efficiency is particularly important, yet lifespan research on their feeding physiology is scarce. Using cineradiography (with a microfocal X-ray source and beryllium image intensifier), we examined masticatory and swallowing physiology across the marmoset lifespan (1 month to 19 years) in 26 healthy individuals, analyzing 45 recordings (80 feeding events, 784 swallows). Our study revealed a developmental trajectory in marmoset chewing and swallowing, from infancy to old age, characterized by progressively refined handling of larger food portions and boluses. We identified distinct anatomical, functional, and behavioral differences in feeding physiology among age groups. Elderly marmosets exhibited significantly faster feeding rates than infants and adults, consuming larger portions and forming larger boluses, requiring fewer mastications and swallows, likely reflecting age-related adaptations. Notably, old and very old marmosets showed comparable feeding efficiency, suggesting compensatory mechanisms to maintain function despite age-related challenges (e.g., tooth loss or muscle weakness) and may contribute to longevity. The consistent pattern of esophageal retention across age groups indicates this pattern is likely typical for the species. This study establishes baseline feeding characteristics for marmosets, reinforcing their value as a translational aging model and enhancing their utility for investigating age-related changes in human chewing and swallowing, including dysphagia. Future research should explore the underlying mechanisms and functional implications of these changes.

In mammals, estrogens and progestogens are crucial for gestation, fetal development, and maternal preparation for parturition and lactation. Measuring these hormones allows for the diagnosis of pregnancy, estimation of pregnancy failures, and potentially prenatal sex determination. We evaluated urinary estrogen and progestogen metabolites as biomarkers for gestation detection and for their utility for fetal sex determination in wild Assamese macaques (Macaca assamensis) using 586 samples from 19 females, including 19 successful pregnancies. Four enzyme-immunoassays were tested for suitability in measuring urinary sex steroids using serial dilution: three assays targeting progestogen and one targeting estrogen metabolites (estrone conjugates, E1C). We performed a biological validation by measuring urinary hormone metabolites in one female across pre-, early-, late-, and post-gestation. None of the progestogen measurements reflected gestational status, while E1C levels showed the expected increases during gestation. Next, we measured urinary E1C across gestation in all females and investigated fetal sex effects on maternal E1C levels, expecting differences between females carrying male versus female fetuses. Urinary E1C levels increased as early as 9 days postconception and declined sharply at parturition, mirroring patterns in other primates. During late gestation, females carrying male fetuses had significantly higher E1C levels than those carrying female fetuses, yet overlapping values limit precision for prenatal sex determination. Urinary E1C offers a noninvasive marker for gestation monitoring in Assamese macaques, with application in ecological and conservation research. Additionally, results indicate intra- and inter-species-specific differences in steroid hormone metabolism and excretion, which need to be considered when selecting markers for reproductive monitoring.

Assessing body weight is common practice for monitoring health in common marmosets (Callithrix jacchus). Body composition analysis via quantitative magnetic resonance (QMR) is a more in-depth assessment allowing measurements of lean and fat mass, but it is expensive and remains unavailable to most. Alternatively, body condition scoring (BCS) is an instrument-free method for visually inspecting and palpating lean and fat tissue. Animals are rated for lean and fat mass abundance, using an ordinal scale with species-specific descriptions as reference. However, modified BCS systems developed for other species are being used, because no BCS system has been fully validated for marmosets. The accuracy of BCS in identifying marmosets with poor body condition or obesity remains unknown. We assessed an adapted BCS for marmosets (n = 68, 2–16 years). Objectives were to (1) determine whether BCS predicts body weight and body composition, and (2) evaluate the performance of BCS as a screening test for low body condition and obesity in marmosets, in comparison to QMR body composition analysis. BCS predicted body weight and body composition (F(15, 166) = 7.51, Wilks' Λ = 0.240, p < 0.001), and was better at predicting low lean mass and obesity, than at predicting low adiposity. Marmosets with low BCS had higher odds of low lean mass (B = 3.37, (95% CI, 0.95–5.78), OR = 29.0, p = 0.006). Marmosets with excessively high BCS had higher odds of obesity (B = 2.72, (95% CI, 1.07–4.38), OR = 15.23, p = 0.001). The accuracy rates of BCS in identifying low body condition (79.4%–91.2%) and obesity (77.9%) suggest that it can serve as an instrument-free screening method in marmosets.

Climate change is one of the main drivers of shifts in species distributions. Ecological niche models (ENMs) are valuable tools for assessing these effects and informing conservation efforts. This study employed ENMs to assess the impact of climate change on the present (from 1970 to 2000) and future (up to 2100) climate suitability patterns of the black-and-gold howler monkey (Alouatta caraya [A. caraya]), which is facing serious threats due to habitat changes and disease, especially in the southernmost part of its range. We also evaluated the effectiveness of current protected sites for the species' conservation in the future. For each 20-year interval, we used seven different algorithms and reconstructed a consensus map using ensemble techniques. We then reevaluated the geographical patterns of habitat suitability, accounting for dispersal restrictions and fragmentation history. Our results suggest that areas of high habitat suitability for A. caraya may be much smaller than the geographic distribution reported by the IUCN, with future projections predicting a continuous decrease in suitable areas from 2021 to 2100. Furthermore, most sites with high suitability for A. caraya are located outside protected areas, with < 11% of its potential distribution range currently under protection. The extent of protected areas further drops by nearly 50% when only areas that remain suitable for A. caraya over the next 80 years (refuges) are considered. Moreover, areas with higher suitability indices are clustered within the Chaco and Pampa regions, which have been subjected to significant habitat conversion during the last 35 years. Therefore, climate change and habitat conversion pose a significant threat to A. caraya's effective conservation, warranting a review of its conservation status.

Infant survival is an important component of parental fitness in iteroparous species with slow life histories. From the infant's perspective, survival can be more or less directly influenced by the social environment, with group members potentially representing either a threat or a buffer against external stressors. Therefore, studying social relationship patterns during early development may provide insights into the effect of social factors on infant survival. To understand how group members interact with infants, and whether social relationships change due to the presence of infants, we conducted focal behavioral observations on four groups of wild redfronted lemurs (Eulemur rufifrons) during the birth season. Infant handling consisted mostly of grooming, while aggressive infant handling behaviors and allomaternal care occurred very rarely. Infants were groomed by individuals of all age-sex classes at similar rates except for a trend of higher infant handling rates in juvenile females. After giving birth, mothers received more approaches and were closer in proximity to other group members than before birth, but there were no changes in grooming rates of mothers and other group members. Mothers also initiated more aggressive interactions towards other group members after giving birth. Therefore, other redfronted lemurs were clearly attracted to infants, which caused changes in affinitive relationships of mothers. At the same time, the increase in maternal aggression indicates that group members also represent some threat to infants. Our study provides a starting point for future studies, exploring how these early infant handling interactions and the mother's relationships impact an infant's subsequent survival, development and future relationships.