Transfer of the Nonmatch-to-Goal rule in Monkeys across Cognitive Domains

To solve novel problems, it is advantageous to abstract relevant information from past experience to transfer on related problems. To study whether macaque monkeys were able to transfer an abstract rule across cognitive domains, we trained two monkeys on a nonmatch-to-goal (NMTG) task. In the object version of the task (O-NMTG), the monkeys were required to choose between two object-like stimuli, which differed either only in shape or in shape and color. For each choice, they were required to switch from their previously chosen object-goal to a different one. After they reached a performance level of over 90% correct on the O-NMTG task, the monkeys were tested for rule transfer on a spatial version of the task (S-NMTG). To receive a reward, the monkeys had to switch from their previously chosen location to a different one. In both the O-NMTG and S-NMTG tasks, there were four potential choices, presented in pairs from trial-to-trial. We found that both monkeys transferred successfully the NMTG rule within the first testing session, showing effective transfer of the learned rule between two cognitive domains.     

Adult Cleaner Wrasse Outperform Capuchin Monkeys,Chimpanzees and Orang-utans in a Complex Foraging Task Derived from Cleaner – Client Reef Fish Cooperation

The insight that animals'' cognitive abilities are linked to their evolutionary history, and hence their ecology, provides the framework for the comparative approach. Despite primates renowned dietary complexity and social cognition, including cooperative abilities, we here demonstrate that cleaner wrasse outperform three primate species, capuchin monkeys, chimpanzees and orang-utans, in a foraging task involving a choice between two actions, both of which yield identical immediate rewards, but only one of which yields an additional delayed reward. The foraging task decisions involve partner choice in cleaners: they must service visiting client reef fish before resident clients to access both; otherwise the former switch to a different cleaner. Wild caught adult, but not juvenile, cleaners learned to solve the task quickly and relearned the task when it was reversed. The majority of primates failed to perform above chance after 100 trials, which is in sharp contrast to previous studies showing that primates easily learn to choose an action that yields immediate double rewards compared to an alternative action. In conclusion, the adult cleaners'' ability to choose a superior action with initially neutral consequences is likely due to repeated exposure in nature, which leads to specific learned optimal foraging decision rules.     

Vicarious learning from human models in monkeys

We examined whether monkeys can learn by observing a human model, through vicarious learning. Two monkeys observed a human model demonstrating an object-reward association and consuming food found underneath an object. The monkeys observed human models as they solved more than 30 learning problems. For each problem, the human models made a choice between two objects, one of which concealed a piece of apple. In the test phase afterwards, the monkeys made a choice of their own. Learning was apparent from the first trial of the test phase, confirming the ability of monkeys to learn by vicarious observation of human models.     

Capuchins do cooperate: the advantage of an intuitive task

We used a cooperative pulling task to examine proximate aspects of cooperation in captive brown capuchin monkeys, Cebus apella. Specifically, our goal was to determine whether capuchins can learn the contingency between their partner's participation in a task and its successful completion. We examined whether the monkeys visually monitored their partners and adjusted pulling behaviour according to their partner's presence. Results on five same-sex pairs of adults indicate that (1) elimination of visual contact between partners significantly decreased success, (2) subjects glanced at their partners significantly more in cooperative tests than in control tests in which no partner-assistance was needed, and (3) they pulled at significantly higher rates when their partner was present rather than absent. Therefore, in contrast to a previous report by Chalmeau et al. (1997, Animal Behaviour, 54, 1215-1225), cooperating capuchins do seem able to take the role of their partner into account. However, the type of task used may be an important factor affecting the level of coordination achieved. Copyright 2000 The Association for the Study of Animal Behaviour.     

Can Monkeys Make Investments Based on Maximized Pay-off?

Animals can maximize benefits but it is not known if they adjust their investment according to expected pay-offs. We investigated whether monkeys can use different investment strategies in an exchange task. We tested eight capuchin monkeys (Cebus apella) and thirteen macaques (Macaca fascicularis, Macaca tonkeana) in an experiment where they could adapt their investment to the food amounts proposed by two different experimenters. One, the doubling partner, returned a reward that was twice the amount given by the subject, whereas the other, the fixed partner, always returned a constant amount regardless of the amount given. To maximize pay-offs, subjects should invest a maximal amount with the first partner and a minimal amount with the second. When tested with the fixed partner only, one third of monkeys learned to remove a maximal amount of food for immediate consumption before investing a minimal one. With both partners, most subjects failed to maximize pay-offs by using different decision rules with each partner' quality. A single Tonkean macaque succeeded in investing a maximal amount to one experimenter and a minimal amount to the other. The fact that only one of over 21 subjects learned to maximize benefits in adapting investment according to experimenters' quality indicates that such a task is difficult for monkeys, albeit not impossible.     

Brown Lemurs (Eulemur fulvus) Can Master the Qualitative Version of the Reverse-Reward Contingency

Behavioral flexibility that requires behavioral inhibition has important fitness consequences. One task commonly used to assess behavioral inhibition is the reverse-reward task in which the subject is rewarded by the non selected items. Lemurs were tested for their ability to solve the qualitative version of the reverse-reward task with the choice between identical quantities of different food items instead of different quantities of the same food. Two of four subjects mastered the task without a correction procedure and were able to generalize the acquired rule to novel combinations of food. One of the two subjects competent on the quality version of the task could transfer this ability to different quantities of the same food. Our results are compared to lemurs’ performances when tested under the quantitative version in a previous study and those of capuchin monkeys tested under a similar paradigm. The whole results suggest that the qualitative version of the reverse-reward task may be easier to master than its quantitative counterpart and that lemurs perform better than capuchin monkeys as they were able to later transfer the learning rule to the quantitative version of the task.     

Top-down control-signal dynamics in anterior cingulate and prefrontal cortex neurons following task switching

The prefrontal cortex (PFC) and anterior cingulate cortex (ACC) have both been implicated in cognitive control, but their relative roles remain unclear. Here we recorded the activity of single neurons in both areas while monkeys performed a task that required them to switch between trials in which they had to look toward a flashed stimulus (prosaccades) and trials in which they had to look away from the stimulus (antisaccades). We found that ACC neurons had a higher level of task selectivity than PFC neurons during the preparatory period on trials immediately following a task switch. In ACC neurons, task selectivity was strongest after the task switch and declined throughout the task block, whereas task selectivity remained constant in the PFC. These results demonstrate that the ACC is recruited when cognitive demands increase and suggest a role for both areas in task maintenance and the implementation of top-down control.     

Lack of prosociality in great apes,capuchin monkeys and spider monkeys: convergent evidence from two different food distribution tasks

Prosociality can be defined as any behaviour performed to alleviate the needs of others or to improve their welfare. Prosociality has probably played an essential role in the evolution of cooperative behaviour and several studies have already investigated it in primates to understand the evolutionary origins of human prosociality. Two main tasks have been used to test prosociality in a food context. In the Platforms task, subjects can prosocially provide food to a partner by selecting a prosocial platform over a selfish one. In the Tokens task, subjects can prosocially provide food to a partner by selecting a prosocial token over a selfish one. As these tasks have provided mixed results, we used both tasks to test prosociality in great apes, capuchin monkeys and spider monkeys. Our results provided no compelling evidence of prosociality in a food context in any of the species tested. Additionally, our study revealed serious limitations of the Tokens task as it has been previously used. These results highlight the importance of controlling for confounding variables and of using multiple tasks to address inconsistencies present in the literature.     

Working memory of action: a comparative study of ability to selecting response based on previous action in New World monkeys (Saimiri sciureus and Callithrix jacchus)

Working memory of the outcome of one's own action is important for organizing and learning appropriate behaviors in a given condition. To examine whether non-human primates with different neocortical sizes show different abilities regarding working memory for action, the performance of squirrel monkeys (Saimiri sciureus) and common marmosets (Callithrix jacchus) in a kind of delayed-response task was compared. In this task, subjects were required to select a response based on short-term memory of the outcome of their own prior action, which requires working memory of action. These monkeys have a similar phylogenetic status (i.e. Ceboidea), but the size of the neocortex relative to the rest of the brain (relative size of the neocortex) is quite different. We found that both two species could attend to and remember their own actions and could select a response based on that memory. However, the performance level was higher for squirrel monkeys than for marmosets. These results suggest that non-human primates with differentially developed neocortices have different abilities regarding working memory of action.     

Cooperative problem solving in a cooperatively breeding primate (Saguinus oedipus)

We investigated cooperative problem solving in unrelated pairs of the cooperatively breeding cottontop tamarin, Saguinus oedipus, to assess the cognitive basis of cooperative behaviour in this species and to compare abilities with other apes and monkeys. A transparent apparatus was used that required extension of two handles at opposite ends of the apparatus for access to rewards. Resistance was applied to both handles so that two tamarins had to act simultaneously in order to receive rewards. In contrast to several previous studies of cooperation, both tamarins received rewards as a result of simultaneous pulling. The results from two experiments indicated that the cottontop tamarins (1) had a much higher success rate and efficiency of pulling than many of the other species previously studied, (2) adjusted pulling behaviour to the presence or absence of a partner, and (3) spontaneously developed sustained pulling techniques to solve the task. These findings suggest that cottontop tamarins understand the role of the partner in this cooperative task, a cognitive ability widely ascribed only to great apes. The cooperative social system of tamarins, the intuitive design of the apparatus, and the provision of rewards to both participants may explain the performance of the tamarins.     

Does the Macaque Monkey Provide a Good Model for Studying Human Executive Control? A Comparative Behavioral Study of Task Switching

The ability to swiftly and smoothly switch from one task set to another is central to intelligent behavior, because it allows an organism to flexibly adapt to ever changing environmental conditions and internal needs. For this reason, researchers interested in executive control processes have often relied on task-switching paradigms as powerful tools to uncover the underlying cognitive and brain architecture. In order to gather fundamental information at the single-cell level, it would be greatly helpful to demonstrate that non-human primates, especially the macaque monkey, share with us similar behavioral manifestations of task-switching and therefore, in all likelihood, similar underlying brain mechanisms. Unfortunately, prior attempts have provided negative results (e.g., Stoet & Snyder, 2003b), in that it was reported that macaques do not show the typical signature of task-switching operations at the behavioral level, represented by switch costs. If confirmed, this would indicate that the macaque cannot be used as a model approach to explore human executive control mechanisms by means of task-switching paradigms. We have therefore decided to re-explore this issue, by conducting a comparative experiment on a group of human participants and two macaque monkeys, whereby we measured and compared performance costs linked to task switching and resistance to interference across the two species. Contrary to what previously reported, we found that both species display robust task switching costs, thus supporting the claim that macaque monkeys provide an exquisitely suitable model to study the brain mechanisms responsible for maintaining and switching task sets.     

Men’s Sexual Faithfulness Judgments May Contain a Kernel of Truth

Mechanisms enabling men to identify women likely to engage in extra-pair copulations (EPCs) would be advantageous in avoiding cuckoldry. Men’s judgments of female sexual faithfulness often show high consensus, but accuracy appears poor. We examined whether accuracy of these judgments made to images of women could be improved through i) employing a forced choice task, in which men were asked to select the more faithful of two women and/or ii) providing men with full person images. In Experiment 1, men rated 34 women, for whom we had self-reported EPC behavior, on faithfulness, trustworthiness or attractiveness from either face or full person photographs. They then completed a forced choice task, selecting the more faithful of two woman from 17 pairs of images, each containing one woman who had reported no EPCs and one who had reported two or more EPCs. Men were unable to rate faithfulness with any accuracy, replicating previous findings. However, when asked to choose the more faithful of two women, they performed significantly above chance, although the ability to judge faithfulness at above-chance levels did not generalize to all pairs of women. Although there was no significant difference in accuracy for face and full person image pairs, only judgments from faces were significantly above chance. In Experiment 2, we showed that this accuracy for faces was repeatable in a new sample of men. We also showed that individual variation in accuracy was unrelated to variation in preferences for faithfulness in a long-term partner. Overall, these results show that men’s judgments of faithfulness made from faces of unfamiliar women may contain a kernel of truth.     

Father's physique influences mate preferences but not the actual choice of male somatotype in heterosexual women and homosexual men

Body constitution plays an important role in human mate choice. Cross-cultural research reports that women on average prefer men with muscular physique. It is still unclear, however, what mechanisms influence the inter-individual variation in mate preferences and choices of partner's physique. In this study, we tested the mechanisms of an imprinting-like effect (similarity between father and an ideal and actual partner) and of homogamy (similarity between self and an ideal and actual partner) for male physique in heterosexual women and homosexual men. To assess the variation in male physique, we employed somatotype paradigm which characterizes body constitution using three components: endomorphic (heavy-set), mesomorphic (muscular), and ectomorphic (lean). In total, 149 homosexual men and 769 heterosexual women from the Czech Republic indicated the somatotype of their father, ideal and actual partner, and in homosexual men also their own somatotype. In line with previous research, the somatotype most preferred by both men and women was the mesomorphic, followed by the ectomorphic and the endomorphic one. Women's preferences for an ideal partner somatotype weakly correlated with their fathers' somatotype, especially in women who reported a positive relationship with their fathers during childhood. Among homosexual men, we found imprinting-like preferences only for the ectomorphic somatotype component and no significant association with the quality of their relationships with their fathers. We also found no significant relationship between the fathers' and actual partners' somatotype in either heterosexual women or homosexual men. Our research indicates that fathers have a rather weak influence on mate preference for somatotypes and no influence on actual mate choice.     

Comparative performance of orangutans (Pongo spp.), gorillas (Gorilla gorilla gorilla), and drills (Mandrillus leucophaeus), in an ephemeral foraging task

A goal of the comparative approach is to test a variety of species on the same task. Here, we examined whether the factors that helped capuchin monkeys improve their performance in a dichotomous choice task would generalize to three other primate species: orangutans, gorillas, and drill monkeys. In this task, subjects have access to two options, each resulting in an identical food, but one (the ephemeral option) is only available if it is chosen first, whereas the other one (the permanent option) is always available. Therefore, the food‐maximizing solution is to choose the ephemeral option first, followed by the permanent option for an additional reward. On the original version (plate task), the options were discriminated by the color and pattern of the plates holding the food, while on two subsequent versions we used altered cues that we predicted would improve performance: (1) the color of the foods themselves (color task), which we hypothesized was relevant to primates, who choose foods rather than substrates on which foods are found when foraging, and (2) patterned cups covering the foods (cup task), which we hypothesized would help primates avoid the prepotent response associated with visible food. Like capuchins, all three species initially failed to solve the plate task. However, while orangutans improved their performance from the plate to the color task, they did not for the cup task, and only a few gorillas and no drills succeeded in either task. Unfortunately, our ability to interpret these data was obscured by differences in the subjects' level of experience with cognitive testing and practical constraints that precluded the use of completely identical procedures across species. Nonetheless, we consider what these results can tell us, and discuss the value of conducting studies across multiple sites despite unavoidable differences.     

Partner Choice Drives the Evolution of Cooperation via Indirect Reciprocity

Indirect reciprocity potentially provides an important means for generating cooperation based on helping those who help others. However, the use of ‘image scores’ to summarize individuals’ past behaviour presents a dilemma: individuals withholding help from those of low image score harm their own reputation, yet giving to defectors erodes cooperation. Explaining how indirect reciprocity could evolve has therefore remained problematic. In all previous treatments of indirect reciprocity, individuals are assigned potential recipients and decide whether to cooperate or defect based on their reputation. A second way of achieving discrimination is through partner choice, which should enable individuals to avoid defectors. Here, I develop a model in which individuals choose to donate to anyone within their group, or to none. Whereas image scoring with random pairing produces cycles of cooperation and defection, with partner choice there is almost maximal cooperation. In contrast to image scoring with random pairing, partner choice results in almost perfect contingency, producing the correlation between giving and receiving required for cooperation. In this way, partner choice facilitates much higher and more stable levels of cooperation through image scoring than previously reported and provides a simple mechanism through which systems of helping those who help others can work.     

Chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>) learn to act with other individuals in a cooperative task

We presented two chimpanzees with a task in which they were required to pull each end of a rope simultaneously to drag blocks supporting food into reach. The chimpanzees did not succeed in initial tests. They did not immediately understand the necessity for cooperation, and they did not adjust their behavior to work with the partner. However, the frequency of success gradually increased as the number of sessions increased and the task was varied. They began to look at the partner frequently, wait if the partner was not holding the rope, and pull the rope in synchrony with the partner. However, they did not use interactive behaviors or eye contact to synchronize their behavior. One chimpanzee was then paired with a human partner in the same situation. After initial failures, the chimpanzee began to solicit the human partner for cooperation: looking up at his face, vocalizing, and taking the partner’s hand. When this chimpanzee was again paired with the chimpanzee partner, no soliciting behavior was observed. Thus, the chimpanzees could learn to coordinate their behavior through trial and error. Communicative behavior emerged during the task, but the communication differed according to the identity of the partner.     

Calculated reciprocity? A comparative test with six primate species

Little evidence of calculated reciprocity has been found in non-human primates so far. In this study, we used a simple experimental set-up to test whether partners pulled a sliding table to altruistically provide food to each other in short-term interactions. We tested 46 dyads of chimpanzees, bonobos, gorillas, orangutans, brown capuchin monkeys and spider monkeys to examine whether a subject’s tendency to provide food to a partner was directly affected by the partner’s previous behaviour, by the species, by the condition (i.e., whether the partner could access the food provided by the subject) and by the social tolerance levels within each dyad. Chimpanzees and orangutans were the only species pulling significantly more when the partner could retrieve the food altruistically provided. However, no species reciprocated food exchanges, as subjects’ probability to pull was not affected by the previous number of the partner’s pulls, with the possible exception of one orangutan dyad. Although subjects clearly knew how the apparatus worked and easily obtained food for themselves, individuals did not usually take the opportunity to provide food to their partners, suggesting that calculated reciprocity is not a common behaviour and that food exchanges are usually not reciprocated in the short-term within dyads.     

Reversible frequency-dependent switches in male mate choice

Current sexual-selection theories predict that mating should occur preferentially with the highest-quality partner, and assume that for distinguishing among potential mates the choosy sex applies an internal representation of the characteristics of the desired mate, i.e. a template. Binary choice experiments were performed to test male mate choice between two different female colour morphs in the damselfly Ischnura elegans. Choice experiments were conducted before and after an habituation period, during which males were exposed to only one female colour morph. Given the choice between the two female morphs, males did exhibit a choice for the most recently experienced female morph. This is the first evidence for a reversible switch in mate choice in a frequency-dependent way. In contrast with previous studies on mate choice, template formation in male I. elegans seems not to be based on quality. Switching mate choice in a frequency-dependent manner, choosing the most common morph, probably allows males to minimize their search efforts and to maximize fitness.     

A tunable genetic switch based on RNAi and repressor proteins for regulating gene expression in mammalian cells

Here, we introduce an engineered, tunable genetic switch that couples repressor proteins and an RNAi target design to effectively turn any gene off. We used the switch to regulate the expression of EGFP in mouse and human cells and found that it offers >99% repression as well as the ability to tune gene expression. To demonstrate the system's modularity and level of gene silencing, we used the switch to tightly regulate the expression of diphtheria toxin and Cre recombinase, respectively. We also used the switch to tune the expression of a proapoptotic gene and show that a threshold expression level is required to induce apoptosis. This work establishes a system for tight, tunable control of mammalian gene expression that can be used to explore the functional role of various genes as well as to determine whether a phenotype is the result of a threshold response to changes in gene expression.     

Coordinated control of XerC and XerD catalytic activities during Holliday junction resolution

Site-specific recombinases XerC and XerD function in the segregation of circular bacterial replicons. In a recombining nucleoprotein complex containing two molecules each of XerC and XerD, coordinated reciprocal switches in recombinase activity ensure that only XerC or XerD is active at any one time. Mutated recombinases that carry sub?stitutions of a catalytic arginine residue stimulate cleavage and strand exchange mediated by the partner recombinase on DNA substrates that are normally recombined poorly by the partner. This is associated with a reciprocal impairment of the recombinase's own ability to initiate catalysis. The extent of this switch in catalysis is modulated by changes in recombination site sequence and is not a direct consequence of any catalytic defect. We propose that altered interactions between the mutated proteins and their wild-type partners lead to an increased level of an alternative Holliday junction intermediate that has a conformation appropriate for resolution by the partner recombinase. The results indicate how subtle changes in protein-DNA architecture at a Holliday junction can redirect recombination outcome.