Learning From Mistakes: Decision-making Biases Within the Primate Lineage

Humans and animals alike make thousands of decisions each day, and good decision-making is crucial to survive and thrive in a competitive world. Much research has focused on how to make ‘rational’ decisions based on stable and absolute preferences. In reality, however, human and animal decisions are extremely context dependent. We show and act on relative rather than absolute preferences (e.g., relative to irrelevant options, previous choices, or what others receive), and these tendencies can lead to consistently ‘irrational’ behavior. Studying the flaws in our cognitive system can help us learn how it works. This dissertation explored the extent to which we share several such decision-making biases with other primates. In a series of manual and computerized tasks, capuchin monkeys’ and rhesus macaques’ choices shifted in response to theoretically irrelevant factors like the presence of unattainable options, inferior options, or social partners; how much work they had previously invested; and how frequently different stimuli were encountered. These findings suggest that evolutionary ancient mechanisms can underlie similar biases in humans, highlighting the need to evaluate the potential function of decision-making strategies in a species’ physical and social environment. However, seemingly minor aspects of the experimental paradigms, like monkeys’ baseline preferences or whether information about the reward contingencies was signaled, affected the magnitude of these biases. Such methodological details may contribute to mixed evidence for decision-making biases in animals and need to be assessed systematically for comparative research to make valid inferences. In doing so, studying whether species other than humans make similar mistakes allows us to better understand the underlying cognitive mechanisms and the evolutionary forces that shape them

Rational Fools: (Ir)rational Choices of Humans, Rhesus Macaques, and Capuchin Monkeys in Dynamic Stochastic Environments

Human and animal decision-making is known to violate rational expectations in a variety of contexts. Statistical structures of real-world environments may account for such seemingly irrational behavior. In a computerized experiment, 16 capuchins, 7 rhesus monkeys, and 30 humans chose between up to three options of different value. The options disappeared and became available again with different probabilities. Subjects overwhelmingly chose transitively (A\u3eB, B\u3eC, and A\u3eC) in the control condition, where doing so maximized overall gain. However, most subjects also adhered to transitivity in the test condition, where it was suboptimal but led to negligible losses compared to the optimal strategy. Only a few of the capuchins were able to maximize long-term gain by violating transitivity. Adhering to rational choice principles may facilitate the formation of near-optimal decision rules when short- and long-term goals align. Such cognitive shortcuts may have evolved to preserve mental resources

Climatic, social and reproductive influences on behavioural thermoregulation in a female-dominated lemur

It is well-established that social rank in a large group confers a higher adaptive value to a dominant individual relative to others, though there is scant evidence that members of small social groups either have similar social standing or maintain strict dominance. We aimed to determine whether members of small social groups, using the southern bamboo lemur (Hapalemur meridionalis) as a model, gain rank-related benefits. We first established a dominance hierarchy through a network-based analysis of win-loss interactions, which showed that adult females maintained social dominance within their groups, similar to many strepsirrhine species. To address whether dominant individuals gained rank-related benefits, we then explored how social dynamics may permit access to resting huddles, which provide a physiological benefit. Social thermoregulation, i.e. huddling, is a behavioural energy conservation mechanism, and among many mammals is a direct response to decreasing ambient temperatures. As such, huddling behaviour may have evolved among social animals because of its potential direct and indirect benefits. To examine the effect of dominance rank within small social groups on huddling inclusion, we used generalized linear mixed-effects models to predict the likelihood of huddling to occur during resting bouts from climatic (e.g., temperature, precipitation), social (e.g., affiliation, dominance rank, grooming) and reproductive (e.g., access, infant protection) variables. We found that colder temperatures, especially during shorter resting bouts, increased the likelihood of huddling. Grooming between partners with a high discrepancy in rank increased huddling. Additionally, huddling increased during the reproductive season, potentially offering greater opportunity for males to gain favour with sexually receptive females, and also when new-borns were present, providing essential thermal maintenance and potential anti-predator protection to infants. Taken as a whole, our results suggest that even in small social groups, females gain rank-related benefits by controlling access to huddles, i.e., the intrinsic benefits of social thermoregulation

Predator avoidance and dietary fibre predict diurnality in the cathemeral folivore Hapalemur meridionalis

Though numerous mammalian taxa exhibit cathemerality (i.e. activity distributed across the 24-h cycle), this includes very few primates, exceptions being species from Aotinae and Lemuridae. Four non-mutually exclusive hypotheses have been proposed to explain the ultimate determinants for cathemeral activity in lemurs: thermoregulatory benefits, anti-predator strategy, competition avoidance and metabolic dietary-related needs. However, these have only been explored in the frugivorous genus Eulemur, with some species increasing nocturnality as a possible response to avoid diurnal raptors and to increase their ability to digest fibre during resource-scarce periods. Since Eulemur lack specializations for digesting bulk food, this strategy would allow for processing fibres over the full 24-h. The folivorous lemurids, i.e. genus Hapalemur, provide a divergent model to explore these hypotheses due to gastrointestinal adaptations for digesting dietary fibre and small body size compared to Eulemur. We linked continuous activity data collected from archival tags with observational behaviour and feeding data from three groups of adult Hapalemur meridionalis from January to December 2013. We tested the effects of thermoregulation, predator avoidance and the weighted proportion of digestible dietary fibre on the daily diurnal/nocturnal activity ratio using a Linear Mixed-Model. Our best-fit model revealed that increased canopy exposure and dietary fibre predicted greater diurnality. Our findings partly contrast with previous predictions for frugivorous lemurids. We propose a divergent adaptive explanation for folivorous lemurids. We suggest that the need to avoid terrestrial predators, as well as longer digestive bouts during bulk food periods, may override cathemerality in favour of diurnality in these bamboo lemurs

Huddling is more important than rest site selection for thermoregulation in southern bamboo lemurs

Resting site selection can have important effects on the behaviour and fitness of organisms. The maintenance of optimal body temperatures (Tb) when faced with environmental variables has often been attributed to either specific microhabitat rest site characteristics or to behavioural strategies. Among many small group living endotherms, social thermoregulation (i.e., huddling) is utilised as a behavioural energy conservation mechanism at low ambient temperatures (Ta), thus decreasing the metabolic cost of maintaining Tb. Though unusual among primates, lemurs are hypometabolic and exhibit a diversity of thermoregulatory strategies; however, objective Tb measurements have thus far been limited to small-bodied lemurs (e.g., Cheirogaleids). As such, we sought to determine whether a medium-sized lemur model, the southern bamboo lemur (Hapalemur meridionalis), would maintain thermoregulation through microhabitat rest site selection, huddling behaviour, or potentially both strategies. Within a degraded littoral forest fragment in southeast Madagascar, we conducted full-day focal observations on three groups of H. meridionalis between January and December 2013. Adult individuals were collared with data-loggers that collected instantaneous skin temperature Tsk (°C). We calculated the mean Tsk of the focal individual during each resting bout, and the proportional rate of huddling between the focal and conspecifics. In addition, we recorded all resting sites utilised ≥15 min and collected standard tree characteristics. We fitted Linear Mixed-Effects Models to determine the thermoregulatory combined effect of specific resting site characteristics, huddling behaviour, and environmental variables on Tsk. Our results showed that lemurs selected tree sites with larger diameter at breast height; however, huddling was most predictive of increasing Tsk whereas resting site characteristics were not included in the best-fit model. It is possible that microhabitat rest site selection is not significant in a degraded forest as the potential environmental buffering is limited, thus thermoregulatory mechanisms are likely best served by behavioural strategies, i.e., social huddling. Key-words: huddling; skin temperature; Hapalemur meridionalis; energy conservation; thermal ecology; southern bamboo lemur; Madagascar; strepsirrhine

The Evolution of Primate Short-Term Memory.

Short-term memory is implicated in a range of cognitive abilities and is critical for understanding primate cognitive evolution. To investigate the effects of phylogeny, ecology and sociality on short-term memory, we tested the largest and most diverse primate sample to date (421 non-human primates across 41 species) in an experimental delayed-response task. Our results confirm previous findings that longer delays decrease memory performance across species and taxa. Our analyses demonstrate a considerable contribution of phylogeny over ecological and social factors on the distribution of short-term memory performance in primates; closely related species had more similar short-term memory abilities. Overall, individuals in the branch of Hominoidea performed better compared to Cercopithecoidea, who in turn performed above Platyrrhini and Strepsirrhini. Interdependencies between phylogeny and socioecology of a given species presented an obstacle to disentangling the effects of each of these factors on the evolution of short-term memory capacity. However, this study offers an important step forward in understanding the interspecies and individual variation in short-term memory ability by providing the first phylogenetic reconstruction of this trait’s evolutionary history. The dataset constitutes a unique resource for studying the evolution of primate cognition and the role of short-term memory in other cognitive abilities.info:eu-repo/semantics/publishedVersio

Establishing an infrastructure for collaboration in primate cognition research

Inferring the evolutionary history of cognitive abilities requires large and diverse samples. However, such samples are often beyond the reach of individual researchers or institutions, and studies are often limited to small numbers of species. Consequently, methodological and site-specific-differences across studies can limit comparisons between species. Here we introduce the ManyPrimates project, which addresses these challenges by providing a large-scale collaborative framework for comparative studies in primate cognition. To demonstrate the viability of the project we conducted a case study of short-term memory. In this initial study, we were able to include 176 individuals from 12 primate species housed at 11 sites across Africa, Asia, North America and Europe. All subjects were tested in a delayed-response task using consistent methodology across sites. Individuals could access food rewards by remembering the position of the hidden reward after a 0, 15, or 30-second delay. Overall, individuals performed better with shorter delays, as predicted by previous studies. Phylogenetic analysis revealed a strong phylogenetic signal for short-term memory. Although, with only 12 species, the validity of this analysis is limited, our initial results demonstrate the feasibility of a large, collaborative open-science project. We present the ManyPrimates project as an exciting opportunity to address open questions in primate cognition and behaviour with large, diverse datasets

Establishing an infrastructure for collaboration in primate cognition research

Inferring the evolutionary history of cognitive abilities requires large and diverse samples. However, such samples are often beyond the reach of individual researchers or institutions, and studies are often limited to small numbers of species. Consequently, methodological and site-specific-differences across studies can limit comparisons between species. Here we introduce the ManyPrimates project, which addresses these challenges by providing a large-scale collaborative framework for comparative studies in primate cognition. To demonstrate the viability of the project we conducted a case study of short-term memory. In this initial study, we were able to include 176 individuals from 12 primate species housed at 11 sites across Africa, Asia, North America and Europe. All subjects were tested in a delayed-response task using consistent methodology across sites. Individuals could access food rewards by remembering the position of the hidden reward after a 0, 15, or 30-second delay. Overall, individuals performed better with shorter delays, as predicted by previous studies. Phylogenetic analysis revealed a strong phylogenetic signal for short-term memory. Although, with only 12 species, the validity of this analysis is limited, our initial results demonstrate the feasibility of a large, collaborative open-science project. We present the ManyPrimates project as an exciting opportunity to address open questions in primate cognition and behaviour with large, diverse datasets

The Evolution of Primate Short-Term Memory

Short-term memory is implicated in a range of cognitive abilities and is critical for understanding primate cognitive evolution. To investigate the effects of phylogeny, ecology and sociality on short-term memory, we tested the largest and most diverse primate sample to date (421 non-human primates across 41 species) in an experimental delayed-response task. Our results confirm previous findings that longer delays decrease memory performance across species and taxa. Our analyses demonstrate a considerable contribution of phylogeny over ecological and social factors on the distribution of short-term memory performance in primates; closely related species had more similar short-term memory abilities. Overall, individuals in the branch of Hominoidea performed better compared to Cercopithecoidea, who in turn performed above Platyrrhini and Strepsirrhini. Interdependencies between phylogeny and socioecology of a given species presented an obstacle to disentangling the effects of each of these factors on the evolution of short-term memory capacity. However, this study offers an important step forward in understanding the interspecies and individual variation in short-term memory ability by providing the first phylogenetic reconstruction of this trait’s evolutionary history. The dataset constitutes a unique resource for studying the evolution of primate cognition and the role of short-term memory in other cognitive abilities