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In the present study, relations between same-sex sexual behavior (SSB), age-class, and coalitional behavior in male rhesus macaques were examined in a re-analysis of data first analyzed and reported by Clive et al. (2023). Age-class as a focal variable was indicated in an extensive literature review, which showed that male non-adult (juvenile, adolescent) participation in SSB is extensive in this and related primate species and associated with various benefits. Clive et al. (2023) excluded juveniles from their analysis. In the re-analysis (n = 995 mounting events), it was found that non-adult involvement was substantial (51%). Most dyads contained at least one non-adult (76%). Young and prime adult mounters most often selected non-adults to mount. Mounters were often sexually motivated: most for adolescents (72%); equally for juveniles (57%) and adults (56%). Finally, the highest rate of SSB with coalitional context appeared in adolescent–adult dyads involved in multiple repeated mounts. SSB, age-class, special friendships, bonding, and coalitions were linked, as reported in some other primate species and human societies cross-culturally. Employing age-class in male SSB analysis improved description and explanation. [ABSTRACT FROM AUTHOR]

In primates, many species exhibit same-sex sexual behaviors (SSB), defined as "genital contact or genital manipulation between same-sex individuals." Several sociosexual functions have been proposed, including proceptivity enhancement, receptivity reduction, dominance assertion, practice for heterosexual copulation, tension regulation, reconciliation, and alliance formation. Capuchin monkeys are known for their rich and flexible sexual behavioral repertoire and elaborated courtships. At present, the few reports of SSB in capuchin monkeys (genera Sapajus and Cebus) focused on mounting. Here, we describe the case observed in a population of wild yellow-breasted capuchin monkeys (Sapajusxanthosternos) in which two young males, aged 5–6 years and 19 months, performed a 15-min uninterrupted sequence of courtship behaviors and mounting. Comparing with a previously established ethogram of 20 behaviors typical for heterosexual behavior of tufted capuchins, we show that these males performed 16 of them. Thus, SSBs are already present in the repertoire of young individuals and the practice may serve to create or strengthen bonds. Although same-sex mounting and genital inspection are common in capuchins' play and other social interactions, the almost entire array of courtship behaviors has never been observed in youngsters. Additionally, this example supports the notion that primate (homo)sexual behavior is not limited to genitalia and copulation, since the observed courtship included diverse behaviors different from genital contact. Thus, we propose a broader definition of sexual behavior. [ABSTRACT FROM AUTHOR]

Rare behaviors are often missing from published papers, hampering phylogenetic analyses. Here, we report, for the first time, masturbation and same-sex sexual behavior (SSB) in both male and female black-and-white colobus monkeys. We recorded these behaviors during 32 months of observation (1573 h of focal animal sampling) on Colobus vellerosus collected at the Boabeng–Fiema Monkey Sanctuary in Ghana. Males were observed masturbating and involved in SSB more than females. Subadult males were the age-sex class that engaged in both of these behaviors most often and a third of all SSB observed in young males occurred when they were forming an all-male band (AMB), which are temporally transient social groups in this species. Our data support that masturbation in males may be a sexual outlet for individuals that do not have a current sexual partner, while in females it may function in mate attraction by advertising receptivity. SSB may occur as an evolutionary byproduct but given the temporal clustering of observed events in males prior to AMB formation, our data best support the hypothesis that these behaviors facilitate male-male bonding (i.e., act as social glue). Within AMB's, males engage in coalitionary behavior to take over social groups containing females and strong bonds are important for success and later access to females, which could have selected for SSB in C. vellerosus. [ABSTRACT FROM AUTHOR]

Emergence of new technology has broadened our understanding of species behaviour, even those that are common and well studied. We report the use of a thermal camera (TC) on a diurnal Neotropical primate, the brown howler monkey (Alouatta guariba). We describe the undocumented nocturnal activity, and present other contributions of the TC for the routine activities applied in the field. We were able to quickly locate groups and observe rare behaviours, such as interspecific interactions and the process of immigration. The TC allowed the location of fresh stool on the ground, ideal for non-invasive hormone measurements and seed dispersal studies. This device can be used to address many questions, particularly those combining behaviour and hormonal measurements, but may be unhelpful for surveys. We endorse its employment as it can be an invaluable tool for studying the behaviour of Neotropical primate species, even diurnal ones. [ABSTRACT FROM AUTHOR]

In neurophysiology, nonhuman primates represent an important model for studying the brain. Typically, monkeys are moved from their home cage to an experimental room daily, where they sit in a primate chair and interact with electronic devices. Refining this procedure would make the researchers' work easier and improve the animals' welfare. To address this issue, we used home-cage training to train two macaque monkeys in a non-match-to-goal task, where each trial required a switch from the choice made in the previous trial to obtain a reward. The monkeys were tested in two versions of the task, one in which they acted as the agent in every trial and one in which some trials were completed by a "ghost agent". We evaluated their involvement in terms of their performance and their interaction with the apparatus. Both monkeys were able to maintain a constant involvement in the task with good, stable performance within sessions in both versions of the task. Our study confirms the feasibility of home-cage training and demonstrates that even with challenging tasks, monkeys can complete a large number of trials at a high performance level, which is a prerequisite for electrophysiological studies of monkey behavior. [ABSTRACT FROM AUTHOR]

Air pollution is a global environmental problem, and its effects on human behavior, psychology, and health have been well studied. However, very few studies were done on if and how air pollution affects animal behavior, for example, social conflict. Many physiological and psychological evidences suggest a possible positive relationship between air pollution and animal social conflict, thus we established a multiple linear regression model using a captive monkey group to explore if monkeys behave more aggressively in polluted air. Our results confirmed that daily social fighting behaviors occurred more when air is polluted. Temperature has a nonlinear effect on monkey social conflict, with a fighting peak at 25–29 °C. To our knowledge, this is the first report that animal social conflict, like humans, is also affected by air pollution and temperature. [ABSTRACT FROM AUTHOR]

With their large body size and "slow" life histories, atelin primates are thought to follow a risk‐averse breeding strategy, similar to capital breeders, in which they accumulate energy reserves in anticipation of future reproductive events such as gestation and lactation. However, given the paucity of longitudinal data from wild populations, few studies to date have been able to compare the timing of reproductive events (e.g., copulations, conceptions, and births) in relation to shifting resource availability over multiple years. We examined the reproductive patterns of two atelin species—white‐bellied spider monkeys (Ateles belzebuth) and lowland woolly monkeys (Lagothrix lagotricha poeppigii)—in relation to habitat‐wide estimates of fruit availability at the Tiputini Biodiversity Station (TBS) in Amazonian Ecuador. Our sample included 4 years of data on births (N = 36) and copulations (N = 170) for Lagothrix, 10 years of data on births (N = 35) and copulations (N = 74) for Ateles, and 7 years of data on ripe fruit availability. Reproductive events were distinctly seasonal. For both species, births were concentrated between May and September, a time period in which ripe fruit was relatively scarce, while inferred conceptions occurred between September and January, when ripe fruit availability was increasing and maintained at high‐levels throughout the forest. Interannual variation in births was relatively stable, except for in 2016 when twice as many infants were born following a strong El Niño event that may have led to unusually high levels of fruit productivity during the 2015 breeding season. Although copulations were observed year‐round, an overwhelming majority (>90% for Lagothrix and >80% for Ateles) took place between August and February when females were most likely to conceive. Collectively, these data follow the reproductive patterns observed in other atelin primates, and, as proposed by others, suggest that atelins may follow a risk‐averse breeding strategy. Highlights: Both spider monkeys and woolly monkeys display reproductive seasonality in the patterns of copulations, conceptions, and births.While births are more common during periods of low fruit availability, spider monkeys and woolly monkeys copulate and conceive at higher frequencies when fruit availability is increasing or maintained at high levels.Consistent with capital breeding, both species had low infant mortality; interannual variation in births was influenced by fruit availability; and early months of gestation coincided with fruit abundance peaks, when females could store energy reserves. [ABSTRACT FROM AUTHOR]

The dopamine D2 receptor (DRD2) and dopamine transporter (DAT) play a regulatory role in dopaminergic neurotransmission and thus play an important role in drug addiction. The prefrontal cortex (PFC), a critical part of the mesencephalic dopaminergic system, is thought to be involved in the development and maintenance of drug addiction. The addiction to ketamine is thought to induce behavioral effects primarily through actions on the central nervous system. However, the neural mechanism underlying the effects of ketamine addiction remains unclear. In this study, we investigate the involvement of PFC DRD2 and DAT in ketamine addiction effects after ketamine administration for 10 weeks in nonhuman primates. To this end, after administering ketamine to rhesus monkeys for 10 weeks, we assessed changes in body weight and behavior. Additionally, neuronal changes in the PFC were examined by hematoxylin and eosin (HE) staining; the DRD2 and DAT mRNA and protein expression levels in the PFC were determined by real-time PCR and Western blot analysis, respectively. After 10-week ketamine administration, the assessment of the manifestations of toxicity in rhesus monkeys revealed significant changes in body weight and behavior, decreased DRD2 and DAT mRNA and protein expression in the PFC, and histological abnormalities including neuronal eosinophilia, pyknosis and disorderly arrangement of neurons in the PFC. These results suggest that the reduced expression of DRD2 and DAT in PFC could be involved in the behavioral and the neurological changes induced by ketamine administration, which may play an important role in the molecular mechanisms of ketamine addiction. • Ketamine addiction led to significant changes in the body weight and behaviors in rhesus monkeys. • Ketamine addiction led to decreased DRD2 and DAT expression in rhesus monkey PFC. • The downregulation of DRD2 and DAT in PFC may be involved in the behavioral changes induced by ketamine in rhesus monkeys. [ABSTRACT FROM AUTHOR]

Relaxed open-mouth display serves important social functions in relation to submission, reconciliation, affiliation and reassurance among non-human primate societies; however, quantitative evidence on this behavior remains insufficient among multi-level social groups. From July to November 2016, we examined four potential functions of the relaxed open-mouth display during pairwise, intra-unit social interactions among 18 free-ranging adult and sub-adult golden snub-nosed monkeys (Rhinopithecus roxellana) who belonged to three one-male, multi-female units (OMU) at Dalongtan, Shennongjia National Park, China. Results showed that: compared with no relaxed open-mouth display, (1) the occurrence of displacement by a dominant individual approaching a subordinate was lower and the distance of the subordinate to the approaching dominant was shorter when the subordinate showed open-mouth display; (2) relaxed open-mouth display reduced the probability of continued attack for victims of aggression and allowed victims to achieve closer proximity to the aggressor during post-conflict periods; (3) relaxed open-mouth display by dominant individuals allowed them to achieve closer proximity to subordinates; and (4) the exchange of relaxed open-mouth display had a greater impact on the outcome of interactions than one individual alone giving this signal. These findings suggest that relaxed open-mouth display serves important functions regarding submission, reconciliation, affiliation and reassurance in coordinating social interactions within OMUs in golden snub-nosed monkeys. [ABSTRACT FROM AUTHOR]

We observed behavioural activity patterns, daily movements and reproductive ecology (birth rate, death rate, breeding seasons, mating) of urban rhesus macaques (Macaca mulatta) in man-made environment after their reintroduction in Asola-Bhatti Wildlife Sanctuary, Delhi, India using instantaneous sampling or scan sampling method. The daily activity patterns of rhesus macaques inhabiting in the sanctuary were observed from 6:00 h to 18:00 hrs per day from March 2016 to June 2017. The percentage of each activity was estimated quantitatively and birth rate per female per troop in a year was calculated in total 21 troops of rhesus macaques. Macaques adopted different time slot for maximum utilization of food and space available and we estimated the percent time spent of each activity pattern and their variations in a particular geographic area. Daily average distance travelled was 1.89 km/day and it was restricted to the feeding platforms. Mortality was incredibly low (0.17) and high reproductive success was in females per troop. Number of females per troop was 4.48 on average, mean birth rate was calculated 2.20 per female per troop in a year, gestation length 160 days on average. Breeding seasons were April to June and late August to October, although there was no seasonal variation in daily activity pattern and movement ranges throughout the year in the sanctuary. Our study recommendation will help in reducing human-macaque conflicts in urban areas and will serve as a potential source of information of ecology, behaviour of urban rhesus macaques and their management. [ABSTRACT FROM AUTHOR]

Highlights • Coding of common behaviours represents reliable method of personality assessment. • Behaviour coding is not necessarily time-consuming personality assessment method. • Five observational hours per individual were sufficient for personality evaluation. • Two personality components were described for cotton-top tamarins. Abstract Individual variation in behaviour has been shown to have important ecological and evolutionary consequences. Research on animal personality has therefore received considerable attention, yet some methodological issues remain unresolved. We tested whether assessing personality by coding common behaviours is as time-consuming method as some researchers believe it to be. Altogether, 300 hours of observation were collected on 20 captive cotton-top tamarins (Saguinus oedipus). We first examined the repeatability of behavioural indices that represented the behavioural repertoire of cotton-top tamarins. We then compared the personality structures, based on different lengths of observation time, of these behavioural indices. The minimum observational time necessary to obtain a stable personality structure was 5 to 7 hours per individual. This stable structure included two components: Extraversion and Confidence, which were similar to those described in great apes, Old World monkeys, and other New World monkeys. Our findings suggest that, at least in the case of cotton-top tamarins, behavioural coding over relatively short periods of time can be used to assess personality and that longer observation periods may yield diminishing returns. [ABSTRACT FROM AUTHOR]

Highlights • A multiple stimulus assessment identified food preferences in rhesus macaques. • The consistency of food preferences across subjects and time was variable. • Using preferred foods increased engagement during husbandry training sessions. • Using preferred foods increased performance in a progressive ratio task. Abstract The use of systematic preference assessments can enhance positive reinforcement training with captive animals. We found that the multiple stimulus without replacement (MSWO) technique identified food preferences in laboratory housed rhesus macaques, with raisins and grapes being ranked higher on average than dried apricot, pasta, and green beans (Friedman Test, χ2 (4) = 35.52, p <.001). Agreement between individuals (N = 21) was moderate (Kendall's W = 0.42), and consistency across time varied among individuals (W =.03–.90). Highly preferred items identified by the MSWO assessment were subsequently found to increase subjects' engagement in a husbandry task on which they were being trained (Mann-Whitney U = 6.00, p =.002) and to improve performance on a progressive ratio schedule (Wilcoxon signed-rank test, Z = −2.17, p =.03) when compared with low preference items. The progressive ratio technique supplements other preference assessment techniques by measuring the amount of work a subject will do to gain access to an item. The use of more effective reinforcers identified through systematic assessment has the potential to increase animal performance on husbandry and research tasks and to improve animal welfare in the laboratory setting. [ABSTRACT FROM AUTHOR]

Male reproductive strategies have been well studied in primate species where the ability of males to monopolize reproductive access is high. Less is known about species where males cannot monopolize mating access. Vervet monkeys (Chlorocebus pygerythrus) are interesting in this regard as female codominance reduces the potential for male monopolization. Under this condition, we assessed whether male dominance rank still influences male mating and reproductive success, by assigning paternities to infants in a population of wild vervets in the Eastern Cape, South Africa. To determine paternity, we established microsatellite markers from noninvasive fecal samples via cross-species amplification. In addition, we evaluated male mating and reproductive success for 3 groups over 4 mating seasons. We identified 21 highly polymorphic microsatellites (number of alleles = 7.5 ± 3.1 [mean ± SD], observed heterozygosity = 0.691 ± 0.138 [mean ± SD]) and assigned paternity to 94 of 97 sampled infants (96.9%) with high confidence. Matings pooled over 4 seasons were significantly skewed across 3 groups, although skew indices were low (B index = 0.023–0.030) and mating success did not correlate with male dominance. Paternities pooled over 4 seasons were not consistently significantly skewed (B index = 0.005–0.062), with high-ranking males siring more offspring than subordinates only in some seasons. We detected 6 cases of extra-group paternity (6.4%) and 4 cases of natal breeding (4.3%). Our results suggest that alternative reproductive strategies besides priority of access for dominant males are likely to affect paternity success, warranting further investigation into the determinants of paternity among species with limited male monopolization potential. [ABSTRACT FROM AUTHOR]

African papionins are a highly successful subtribe of Old World monkeys with an extensive fossil record. On the basis of both molecular and morphological data, crown African papionins are divided into two clades: Cercocebus/Mandrillus and Papio/Lophocebus/Rungwecebus/Theropithecus (P/L/R/T), though phylogenetic relationships in the latter clade, among both fossil and extant taxa, remain difficult to resolve. While previous phylogenetic studies have focused on either molecular or morphological data, here African papionin molecular and morphological data were combined using both supermatrix and molecular backbone approaches. Theropithecus is supported as the sister taxon to Papio/Lophocebus/Rungwecebus , and while supermatrix analyses using Bayesian methods are largely unresolved, analyses using parsimony are broadly similar to earlier studies. Thus, the position of Rungwecebus relative to Papio and Lophocebus remains equivocal, possibly due to complex patterns of reticulation. Parapapio is likely a paraphyletic grouping of primitive African papionins or possibly a collection of stem P/L/R/T taxa, and a similar phylogenetic position is also hypothesized for Pliopapio . ?Papio izodi is either a stem or crown P/L/R/T taxon, but does not group with other Papio taxa. Dinopithecus and Gorgopithecus are also stem or crown P/L/R/T taxa, but their phylogenetic positions remain unstable. Finally, T. baringensis is likely the most basal Theropithecus taxon, with T. gelada and T. oswaldi sister taxa to the exclusion of T. brumpti . By integrating large amounts of molecular and morphological data, combined with the application of updated parsimony and Bayesian methods, this study represents the most comprehensive analysis of African papionin phylogenetic history to date. [ABSTRACT FROM AUTHOR]

The specific contribution of core auditory cortex to auditory perception –such as categorization– remains controversial. To identify a contribution of the primary auditory cortex (A1) to perception, we recorded A1 activity while monkeys reported whether a temporal sequence of tone bursts was heard as having a “small” or “large” frequency difference. We found that A1 had frequency-tuned responses that habituated, independent of frequency content, as this auditory sequence unfolded over time. We also found that A1 firing rate was modulated by the monkeys’ reports of “small” and “large” frequency differences; this modulation correlated with their behavioral performance. These findings are consistent with the hypothesis that A1 contributes to the processes underlying auditory categorization. [ABSTRACT FROM AUTHOR]

Humans and animals must evaluate the costs and expected benefits of their actions to make adaptive choices. Prior studies have demonstrated the involvement of the basal ganglia in this evaluation. However, little is known about the role of the external part of the globus pallidus (GPe), which is well positioned to integrate motor and reward-related information, in this process. To investigate this role, the activity of 126 neurons was recorded in the associative and limbic parts of the GPe of two monkeys performing a behavioral task in which different levels of force were required to obtain different amounts of liquid reward. The results first revealed that the activity of associative and limbic GPe neurons could be modulated not only by cognitive and limbic but also motor information at the same time, both during a single period or during different periods throughout the trial, mainly in an independent way. Moreover, as a population, GPe neurons encoded these types of information dynamically throughout the trial, when each piece of information was the most relevant for the achievement of the action. Taken together, these results suggest that GPe neurons could be dedicated to the parallel monitoring of task parameters essential to adjusting and maintaining goal-directed behavior. [ABSTRACT FROM AUTHOR]

Finding a sought visual target object requires combining visual information about a scene with a remembered representation of the target to create a “target match” signal that indicates when a target is in view. Target match signals have been reported to exist within high-level visual brain areas including inferotemporal cortex (IT), where they are mixed with representations of image and object identity. However, these signals are not well understood, particularly in the context of the real-world challenge that the objects we search for typically appear at different positions, sizes, and within different background contexts. To investigate these signals, we recorded neural responses in IT as two rhesus monkeys performed a delayed-match-to-sample object search task in which target objects could appear at a variety of identity-preserving transformations. Consistent with the existence of behaviorally-relevant target match signals in IT, we found that IT contained a linearly separable target match representation that reflected behavioral confusions on trials in which the monkeys made errors. Additionally, target match signals were highly distributed across the IT population, and while a small fraction of units reflected target match signals as target match suppression, most units reflected target match signals as target match enhancement. Finally, we found that the potentially detrimental impact of target match signals on visual representations was mitigated by target match modulation that was approximately (albeit imperfectly) multiplicative. Together, these results support the existence of a robust, behaviorally-relevant target match representation in IT that is configured to minimally interfere with IT visual representations. [ABSTRACT FROM AUTHOR]

Nonhuman primates constitute an indispensable model system for studying higher brain functions at the neurophysiological level. Studies involving these animals elucidated the neuronal mechanisms of various cognitive and executive functions, such as visual attention, working memory, and decision-making. Positive reinforcement training (PRT) constitutes the gold standard for training animals on the cognitive tasks employed in these studies. In the laboratory, PRT is usually based on application of a liquid reward as the reinforcer to strengthen the desired behavior and absence of the reward if the animal's response is wrong. By trial and error, the monkey may adapt its behavior and successfully reduce the number of error trials, and eventually learn even very sophisticated tasks. However, progress and success of the training strongly depend on reasonable error rates. If errors get too frequent, they may cause a drop in the animal's motivation to cooperate or its adaptation to high error rates and poor overall performance. We introduce in this report an alternative training regime to minimize errors and base the critical information for learning on graded rewarding. For every new task rule, the feedback to the animal is provided by different amounts of reward to distinguish the desired, optimal behavior from less optimal behavior. We applied this regime in different situations during training of visual attention tasks and analyzed behavioral performance and reaction times to evaluate its effectiveness. For both simple and complex behaviors, graded rewarding was found to constitute a powerful technique allowing for effective training without trade-off in accessible task difficulty or task performance. [ABSTRACT FROM AUTHOR]

Call combinations allow animals to expand the communicative power of small repertoires with acoustically inflexible elements. In Campbell's monkeys, Cercopithecus campbelli , males possess a small repertoire of calls that can be merged to an acoustically invariable suffix and which are concatenated into various sequences, mainly in response to external disturbances. The vocal repertoire of adult females has been less well studied although it is much richer, containing both alarm and various social calls. In particular, females possess a low-pitched contact call, produced either alone or merged with a high-pitched, arched unit. Combined contact calls are identity-richer and easier to detect than simple calls. Here, we investigated the socioecological factors that determined the production of single and combined utterances and found that combined utterances were more common when identity was relevant such as in mixed-species associations and during socially important vocal exchanges. In contrast, single calls were used mainly when predation risk was high, as part of this species' generally cryptic antipredator strategy. We discuss these finding in the light of current theories regarding the evolution of combinatorial signalling. [ABSTRACT FROM AUTHOR]

In numerous social species, males direct aggression towards female group members during intergroup fights, and this behaviour is commonly thought to function as mate guarding, even though males often target non-receptive females. In studying intergroup fights in a wild population of vervet monkeys, we found that male intragroup aggression was primarily directed towards individuals who had either just finished exhibiting, orwere currently attempting to instigate intergroup aggression. Targeted females were less likely to instigate intergroup aggression in the future, indicating that male intragroup aggression functioned as coercion (when directed towards those who were currently trying to instigate a fight) and punishment (when directed towards those who had recently fought). These manipulative tactics effectively prevented intergroup encounters from escalating into fights and often deescalated ongoing conflicts. Males who were likely sires were those most likely to use punishment/coercion, particularly when they were wounded, and, therefore, less able to protect vulnerable offspring should a risky intergroup fight erupt. This work, along with our previous finding that females use punishment and rewards to recruit males into participating in intergroup fights, highlights the inherent conflict of interest that exists between the sexes, as well as the role that social incentives can play in resolving this conflict. Furthermore, unlike other studies which have found punishment to be used asymmetrically between partners, these works represent a novel example of reciprocal punishment in a non-human animal. [ABSTRACT FROM AUTHOR]

Monkeys and other animals appear to share with humans two risk attitudes predicted by prospect theory: an inverse-S-shaped probability-weighting (PW) function and a steeper utility curve for losses than for gains. These findings suggest that such preferences are stable traits with common neural substrates. We hypothesized instead that animals tailor their preferences to subtle changes in task contexts, making risk attitudes flexible. Previous studies used a limited number of outcomes, trial types, and contexts. To gain a broader perspective, we examined two large datasets of male macaques' risky choices: one from a task with real (juice) gains and another from a token task with gains and losses. In contrast to previous findings, monkeys were risk seeking for both gains and losses (i.e., lacked a reflection effect) and showed steeper gain than loss curves (loss seeking). Utility curves for gains were substantially different in the two tasks. Monkeys showed nearly linear PWs in one task and S-shaped ones in the other; neither task produced a consistent inverse-S-shaped curve. To account for these observations, we developed and tested various computational models of the processes involved in the construction of reward value. We found that adaptive differential weighting of prospective gamble outcomes could partially account for the observed differences in the utility functions across the two experiments and thus provide a plausible mechanism underlying flexible risk attitudes. Together, our results support the idea that risky choices are constructed flexibly at the time of elicitation and place important constraints on neural models of economic choice. [ABSTRACT FROM AUTHOR]

Studies of the effects of habitat fragmentation and degradation on primate positional behavior, strata use, and substrate utilization offer valuable insights into the behavioral and ecological flexibility of primates whose habitats have undergone extensive anthropogenic disturbance. In this study, we evaluated how positional behavior, strata use, and substrate utilization differed between Bale monkeys (Chlorocebus djamdjamensis)-bamboo-eating cercopithecids endemic to the southern Ethiopian Highlands-occupying continuous versus fragmented forests. Bale monkeys in forest fragments (where bamboo had been degraded or eradicated) spent significantly more time on the ground and in understory strata whereas those in continuous forest spent significantly more time in the middle and upper strata. Bale monkeys in forest fragments also spent significantly more time walking and galloping and significantly less time climbing than those in continuous forest. Our results suggest that, unlike the primarily arboreal Bale monkeys in continuous forest, Bale monkeys in forest fragments should be characterized as semi-terrestrial. In response to habitat disturbance in fragments, we observed a greater emphasis on terrestrial foraging and travel among Bale monkeys in these human altered habitats, which may put them at greater risk of predation and conflict with nearby human populations. Bale monkeys in fragments exhibit flexibility in their positional behavioral repertoire and their degree of terrestriality is more similar to their sister taxa in Chlorocebus than to Bale monkeys in continuous forest. These findings suggest that habitat alteration may compel Bale monkeys to exhibit semi-terrestrial behaviors crucial for their persistence in human-modified habitats. Our results contribute to a growing body of literature on primate behavioral responses to anthropogenic modification of their habitats and provide information that can contribute to the design of appropriate conservation management plans. [ABSTRACT FROM AUTHOR]

We often orient to where we are about to reach. Spatial and temporal correlations in eye and arm movements may depend on the posterior parietal cortex (PPC). Spatial representations of saccade and reach goals preferentially activate cells in the lateral intraparietal area (LIP) and the parietal reach region (PRR), respectively. With unimanual reaches' eye and arm movement patterns are highly stereotyped. This makes it difficult to study the neural circuits involved in coordination. Here, we employ bimanual reaching to two different targets. Animals naturally make a saccade first to one target and then the other, resulting in different patterns of limb-gaze coordination on different trials. Remarkably, neither LIP nor PRR cells code which target the eyes will move to first. These results suggest that the parietal cortex plays at best only a permissive role in some aspects of eye-hand coordination and makes the role of LIP in saccade generation unclear. [ABSTRACT FROM AUTHOR]

When animal behavior is studied in a laboratory environment, the animals are often extensively trained to shape their behavior. A crucial question is whether the behavior observed after training is part of the natural repertoire of the animal or represents an outlier in the animal's natural capabilities. This can be investigated by assessing the extent to which the target behavior is manifested during the initial stages of training and the time course of learning. We explored this issue by examining smooth pursuit eye movements in monkeys naïve to smooth pursuit tasks. We recorded the eye movements of monkeys from the 1st days of training on a step-ramp paradigm. We used bright spots, monkey pictures and scrambled versions of the pictures as moving targets. We found that during the initial stages of training, the pursuit initiation was largest for the monkey pictures and in some direction conditions close to target velocity. When the pursuit initiation was large, the monkeys mostly continued to track the target with smooth pursuit movements while correcting for displacement errors with small saccades. Two weeks of training increased the pursuit eye velocity in all stimulus conditions, whereas further extensive training enhanced pursuit slightly more. The training decreased the coefficient of variation of the eye velocity. Anisotropies that grade pursuit across directions were observed from the 1st day of training and mostly persisted across training. Thus, smooth pursuit in the step-ramp paradigm appears to be part of the natural repertoire of monkeys' behavior and training adjusts monkeys' natural predisposed behavior. [ABSTRACT FROM AUTHOR]

The article focuses on a study regarding the limitation of parental interaction during vocal development as it affects acoustic call structure in marmoset monkeys. Topics discussed include social interaction has a direct impact not only on the maturation of the vocal behavior but also on acoustic call structures during vocal development, systematic differences in call entropy and social interaction in proper primate vocal development.

Abnormal behavior occurs in a number of captive nonhuman primate species and is often used as an indicator of welfare. However, reported levels of abnormal behavior often vary across species, making general welfare judgments difficult. The purpose of this study was to assess differences in levels of abnormal behavior and associated risk factors across three species of Old World monkeys in order to identify similarities and differences across species. The subjects were 415 (109 females) cynomolgus macaques ( Macaca fascicularis ), 365 (181 females) rhesus macaques ( Macaca mulatta ), and 331 (187 females) baboons ( Papio hamadryas ) that had been singly-housed for 30–120 days. A 5-min observation using one-zero sampling recorded the presence or absence of abnormal behavior for each animal. Macaques exhibited higher levels of abnormal behavior than baboons (29% vs. 14%; χ 2 (1) = 24.849, p < 0.001), but there was no difference between macaque species (30% vs. 28%; χ 2 (1) = 0.263, p = 0.608). Risk factors also varied. Overall, males exhibited greater levels of motor stereotypies ( b = 0.425, p < 0.05), females greater levels of abnormal appetitive behavior ( b = 1.703, p < 0.05), and older animals greater levels of self-directed behavior ( b = 0.065, p < 0.05). However, macaques exhibited greater levels of motor stereotypy ( b = 2.527, p < 0.001) and self-directed behavior ( b = 2.968, p < 0.005) than did baboons. There was also a genus x sex interaction for abnormal appetitive behavior ( b = −2.379, p < 0.01) and a genus x age interaction for motor stereotypy ( b = −0.167, p < 0.05). These results demonstrate that differences in abnormal behavior exist across closely-related primate species. Therefore, a single species cannot be used generally as a model for abnormal behavior or animal welfare. [ABSTRACT FROM AUTHOR]

Cooperative breeders live in social groups in which individuals in an age-sex class vary in reproductive development due to reproductive dominance by a few individuals in each group. Among callitrichids, adult males have been implicated in driving group reproductive output, but uneven sampling efforts, the underlying effects of group size, and pseudoreplication at the group and species levels are confounding variables in these analyses. We examined the drivers of group reproductive output in callitrichids by 1) conducting a meta-analysis of published studies of callitrichid group composition; 2) assigning developmental class based on reproductive morphology; and 3) using multivariate modeling to test whether the proportion of individuals of each developmental class predicts the presence and the number of surviving offspring among free-ranging Weddell's saddleback tamarins ( Leontocebus weddelli) and emperor tamarins ( Saguinus imperator) in Peru. The meta-analysis revealed that the number of adult females and group size, but not the number of adult males, are significantly correlated with group reproductive output. Statistical models of the new dataset revealed that the proportion of primary breeding males, primary breeding females, and group size predicted whether groups had surviving infants, and that only the proportion of primary breeding females and group size predicted the number of surviving infants. Thus, primary breeding males appear to be necessary for groups to raise any infants, but a higher proportion of primary breeding females and a larger group size increase group reproductive output overall. [ABSTRACT FROM AUTHOR]

Cortical activity changes continuously during the course of the day. At a global scale, population activity varies between the ‘synchronized’ state during sleep and ‘desynchronized’ state during waking. However, whether local fluctuations in population synchrony during wakefulness modulate the accuracy of sensory encoding and behavioral performance is poorly understood. Here, we show that populations of cells in monkey visual cortex exhibit rapid fluctuations in synchrony ranging from desynchronized responses, indicative of high alertness, to highly synchronized responses. These fluctuations are local and control the trial variability in population coding accuracy and behavioral performance in a discrimination task. When local population activity is desynchronized, the correlated variability between neurons is reduced, and network and behavioral performance are enhanced. These findings demonstrate that the structure of variability in local cortical populations is not noise but rather controls how sensory information is optimally integrated with ongoing processes to guide network coding and behavior. [ABSTRACT FROM AUTHOR]

The vocalizations of primates contain information about speaker individuality. Many primates, including humans, are able to distinguish conspecifics based solely on vocalizations. The purpose of this study was to investigate the acoustic characteristics used by Japanese macaques in individual vocal discrimination. Furthermore, we tested human subjects using monkey vocalizations to evaluate species specificity with respect to such discriminations. Two monkeys and five humans were trained to discriminate the coo calls of two unfamiliar monkeys. We created a stimulus continuum between the vocalizations of the two monkeys as a set of probe stimuli (whole morph). We also created two sets of continua in which only one acoustic parameter, fundamental frequency (f0) or vocal tract characteristic (VTC), was changed from the coo call of one monkey to that of another while the other acoustic feature remained the same (f0 morph and VTC morph, respectively). According to the results, the reaction times both of monkeys and humans were correlated with the morph proportion under the whole morph and f0 morph conditions. The reaction time to the VTC morph was correlated with the morph proportion in both monkeys, whereas the reaction time in humans, on average, was not correlated with morph proportion. Japanese monkeys relied more consistently on VTC than did humans for discriminating monkey vocalizations. Our results support the idea that the auditory system of primates is specialized for processing conspecific vocalizations and suggest that VTC is a significant acoustic feature used by Japanese macaques to discriminate conspecific vocalizations. [ABSTRACT FROM AUTHOR]

The open field test is commonly used to measure anxiety-related behavior and exploration in rodents. Here, we used it as a standardized novel environment in which to evaluate the behavioral response of infant titi monkeys ( Callicebus cupreus), to determine the effect of presence of individual family members, and to assess how adverse early experience alters infant behavior. Infants were tested in the open field for 5 days at ages 4 and 6 months in four successive 5 min trials on each day. A transport cage, which was situated on one side of the open field, was either empty (non-social control) or contained the father, mother, or sibling. Infant locomotor, vocalization, and exploratory behavior were quantified. Results indicated that age, sex, social condition, and early experience all had significant effects on infant behavior. Specifically, infants were generally more exploratory at 6 months and male infants were more exploratory than females. Infants distinguished between social and non-social conditions but made few behavioral distinctions between the attachment figure and other individuals. Infants which had adverse early life experience demonstrated greater emotional and physical independence, suggesting that early adversity led to resiliency in the novel environment. [ABSTRACT FROM AUTHOR]

To test the hypothesis that the premotor cortex in and behind the caudal bank of the arcuate sulcus can generate saccades, we stimulated electrically the periarcuate region of alert rhesus monkeys. We were able to produce saccades from sites of the premotor cortex that were contiguous with the frontal eye fields and extended up to 2 mm behind the smooth pursuit area. However, premotor sites often elicited saccades with ipsiversive characteristic vectors, lower peak velocities, and flatter velocity profiles when compared to saccades evoked from the frontal eye field. [ABSTRACT FROM AUTHOR]

Hormones have a key role in energy allocation, so their study allows understanding individual metabolic strategies. Because different hormones convey different information on the responses of individuals to energetic demands, a simultaneous analysis of variation in multiple hormones may offer a more reliable picture of metabolic strategies than single hormone assessments. In this study we focused on determining which factors were related to variation in fecal glucocorticoid and thyroid hormone metabolites in wild mantled howler monkeys ( Alouatta palliata ). Over 12 months, we determined fecal glucocorticoid and thyroid hormone metabolite levels of 11 adults belonging to two groups, and examined the relationship between hormone metabolites and a variety of behavioral, physiological, and ecological factors (e.g., food intake, sex/reproductive state, activity, participation in agonistic interactions). We found that glucocorticoids were elevated in gestating and lactating females compared to males and cycling females, and were also higher when individuals were more active and participated in agonistic interactions. Thyroid hormone levels were also related to sex/reproductive state and activity, but were additionally positively related to fruit intake and negatively related to young leaf intake. Our study demonstrates that the non-invasive measurement of glucocorticoid and thyroid hormones of howler monkeys allows assessing different underlying physiological processes. By combining different biomarkers, which has seldom been done with wildlife, we could also parse the influence of psychological vs. metabolic challenges for individual energetic condition, which may be instrumental for deciding which factors should be accounted for when studying different hormone-behavior interactions. [ABSTRACT FROM AUTHOR]

Though competition and cooperation are often considered opposing forces in an arms race driving natural selection, many animals, including humans, cooperate in order to mitigate competition with others. Understanding others' psychological states, such as seeing and knowing, others' goals and intentions, and coordinating actions are all important for complex cooperation-as well as for predicting behavior in order to take advantage of others through tactical deception, a form of competition. We outline evidence of primates' understanding of how others perceive the world, and then consider how the evidence from both deception and cooperation fits this framework to give us a more complete understanding of the evolution of complex social cognition in primates. In experimental food competitions, primates flexibly manipulate group-mates' behavior to tactically deceive them. Deception can infiltrate cooperative interactions, such as when one takes an unfair share of meat after a coordinated hunt. In order to counter competition of this sort, primates maintain cooperation through partner choice, partner control, and third party punishment. Yet humans appear to stand alone in their ability to understand others' beliefs, which allows us not only to deceive others with the explicit intent to create a false belief, but it also allows us to put ourselves in others' shoes to determine when cheaters need to be punished, even if we are not directly disadvantaged by the cheater. [ABSTRACT FROM AUTHOR]

Culture extends biology in that the setting of development shapes the traditions that individuals learn, and over time, traditions evolve as occasional variations are learned by others. In humans, interactions with others impact the development of cognitive processes, such as sustained attention, that shape how individuals learn as well as what they learn. Thus, learning itself is impacted by culture. Here, we explore how social partners might shape the development of psychological processes impacting learning a tradition. We studied bearded capuchin monkeys learning a traditional tool-using skill, cracking nuts using stone hammers. Young monkeys practice components of cracking nuts with stones for years before achieving proficiency. We examined the time course of young monkeys' activity with nuts before, during, and following others' cracking nuts. Results demonstrate that the onset of others' cracking nuts immediately prompts young monkeys to start handling and percussing nuts, and they continue these activities while others are cracking. When others stop cracking nuts, young monkeys sustain the uncommon actions of percussing and striking nuts for shorter periods than the more common actions of handling nuts. We conclude that nut-cracking by adults can promote the development of sustained attention for the critical but less common actions that young monkeys must practice to learn this traditional skill. This work suggests that in nonhuman species, as in humans, socially specified settings of development impact learning processes as well as learning outcomes. Nonhumans, like humans, may be culturally variable learners. [ABSTRACT FROM AUTHOR]

It has been hypothesized that same-sex mounts can reflect the hierarchical relationship in a mounting dyad and it is widely deemed that mounting and being mounted are demonstrations of dominant and subordinate status, respectively. In this research, we aimed to test whether same-sex mounts function as dominance assertion in male golden snub-nosed monkeys ( Rhinopithecus roxellana). We investigated this behavior in eight-individuals, captive all-male unit (AMU) in Shanghai wild animal park, China. Behavioral observations were conducted with a total of 1,855 mounts recorded from November, 2014 to June, 2015, during which the alpha male was replaced in the beginning of April. In support to the dominance assertion hypothesis, we found that during the entire study period the higher-ranking male was more likely to be the mounter than the lower-ranking one, except the mounts that happened among juveniles in peaceful and playful social contexts. Our study indicates that the hierarchical relationship of a mounting dyad can be influenced by the age-class of the participants and the social context where mounting occurs. We suggest that same-sex mounts might have different functions in different age groups and be multifunctional in a species. [ABSTRACT FROM AUTHOR]

How nonhuman primates deal with birth, at the moment of delivery, and during the following days, remains poorly explored because of the unpredictability of this event, particularly for forest-dwelling arboreal species. Available studies highlight intra- and interspecific variation which suggest flexibility of the timing of delivery, of behavior associated with labor contractions and parturition, and the social context and ambient noise surrounding delivery. Here, we present the findings of a two-decade survey of reproduction in a population of captive Campbell's monkeys. Analysis of 34 births (with a female-biased sex ratio) showed that deliveries occurred systematically at night and more frequently during week-ends and in fall (September-November). This suggests the existence of both circadian and infradian biological rhythms. We present the first detailed description of a birth for this species and its short-term social consequences. In line with previous findings for other monkeys and apes, labor (estimated by unusual stretching postures) and parturition were rapid, and delivery occurred in a clear social and vocal context. During the following days, the new mother became the center of attention of for young (kin and non-kin) females and rose through the hierarchy. We discuss socio-ecological factors, notably captivity conditions and the high degree of tolerance in the species' social system, and confirm the existence of both 'rigidity' and 'flexibility' in the primates' adaptive reproductive strategies. [ABSTRACT FROM AUTHOR]

Understanding individual differences in captive squirrel monkeys is a topic of importance both for improving welfare by catering to individual needs, and for better understanding the results and implications of behavioral research. In this study, 23 squirrel monkeys ( Saimiri sciureus), housed in an environment that is both a zoo enclosure and research facility, were assessed for (i) the time they spent by an observation window under three visitor conditions: no visitors, small groups, and large groups; (ii) their likelihood of participating in voluntary research; and (iii) zookeepers, ratings of personality. A Friedman's ANOVA and Wilcoxon post-hoc tests comparing mean times found that the monkeys spent more time by the window when there were large groups present than when there were small groups or no visitors. Thus, visitors do not seem to have a negative effect and may be enriching for certain individuals. Through GLMM and correlational analyses, it was found that high scores on the personality trait of playfulness and low scores on cautiousness, depression, and solitude were significant predictors of increased window approach behavior when visitors were present. The GLMM and correlational analyses assessing the links between personality traits and research participation found that low scores of cautiousness and high scores of playfulness, gentleness, affection, and friendliness, were significant predictors. The implications of these results are discussed in relation to selection bias and its potential confounding effect on cognitive studies with voluntary participation. [ABSTRACT FROM AUTHOR]