Wild common marmosets (Callithrix jacchus) employ spatial cognitive abilities to improve their food search and consumption: an experimental approach in small-scale space

Common marmosets (Callithrix jacchus) excel in a one-trial spatial memory test, yet perform poorly in a classical memory task

When quantifying animal cognition, memory represents one of the most tested domains and is key to understanding cognitive evolution. Memory tests thus play an important role in comparative cognitive research, yet slight variations in the experimental settings can substantially change the outcome, questioning whether different memory tests tap into different memory systems or whether they test memory at all. Here, we first assessed memory performance of 16 common marmosets (Callithrix jacchus) in two distinct paradigms varying in their format and delay. First, we examined marmoset memory in a 24-h delay memory test (24 h-DMT) in which they could freely explore an environment with three novel objects of which one contained food. We examined their retention the day after, and the procedure was iterated cumulatively with previous objects remaining in the enclosure until the marmosets had to choose the correct out of 30 objects. Second, we administered a classical delayed response test (DRT) in the same animals with three objects and a maximum delay of 30 s. In the DRT, marmoset performance was poor and not better than chance after 15 s already. However, individuals excelled in the 24 h-DMT, performing above chance level after 24 h even with tenfold the number of objects to choose from compared to the DRT. Moreover, individual performances in the two tests were not correlated, and typical age effects on memory could not be detected in both experiments. Together, these results suggest that the two tests explore different domains, and that the 24 h-DMT examines long-term memory. The outcome of the DRT is more difficult to assign to memory since individuals performed only moderately even in the 0-s delay condition. This puts into question whether this task design indeed tests memory or other cognitive processes.

Feeding Platforms as an Effective Strategy to Prevent the Consumption of Refuse by Urban Populations of Capuchin Monkeys (Sapajus libidinosus)

The availability of manmade foodstuffs in the environment may significantly alter the diets, behavior and health of wild animals and the ecosystems ecology. One of the principal problems faced by urban populations of capuchin monkeys is their contact with household refuse, which may provoke a number of impacts on the health of these animals. The present study tested the use of feeding platforms as a strategy to reduce the consumption of unhealthy foodstuffs by these animals and analyzed the influence of this measure on the activity patterns and social interactions of the study groups. For this, we verified the patterns of use of a feeding platform by a capuchin group in an urban park in Goiânia, central Brazil, and compared this study population with those of other parks where alternative feeding protocols are implemented, ranging from continuous provisioning to no intervention whatsoever. Behavioral data were collected using scan sampling. The data analysis was divided into two steps: (i) comparison of the different conditions found in the populations with varying types of feeding platform usage and (ii) comparison of the time budget among sites in the context of seasonal variation. The presence of feeding platforms effectively reduced the consumption of refuse in the study groups, although it did also cause an increase in agonism in the animals and altered their activity patterns, leading to a greater dependence on provisioned resources. The results of this study highlight the complex interaction between human activities and the local wildlife in the urban setting, and the need for more detailed studies, to develop more effective management strategies.

Choosing the best way: how wild common marmosets travel to efficiently exploit resources

While foraging, animals have to find potential food sites, remember these sites, and plan the best navigation route. To deal with problems associated with foraging for multiple and patchy resources, primates may employ heuristic strategies to improve foraging success. Until now, no study has attempted to investigate experimentally the use of such strategies by a primate in a context involving foraging in large-scale space. Thus, we carried out an experimental field study that aimed to test if wild common marmosets (Callithrix jacchus) employ heuristic strategies to efficiently navigate through multiple feeding sites distributed in a large-scale space. In our experiment, we arranged four feeding platforms in a trapezoid configuration with up to 60 possible routes and observe marmosets' decisions under two experimental conditions. In experimental condition I, all platforms contained the same amount of food; in experimental condition II, the platforms had different amounts of food. According to the number and arrangement of the platforms, we tested two heuristic strategies: the Nearest Neighbor Rule and the Gravity Rule. Our results revealed that wild common marmosets prefer to use routes consistent with a heuristic strategy more than expected by chance, regardless of food distribution. The findings also demonstrate that common marmosets seem to integrate different factors such as distance and quantity of food across multiple sites distributed over a large-scale space, employing a combination of heuristic strategies to select the most efficient routes available. In summary, our findings confirm our expectations and provide important insights into the spatial cognition of these small neotropical primates.

One-Trial Appetitive Learning Tasks for Drug Targeting

One-trial appetitive learning developed from one-trial passive avoidance learning as a standard test of retrograde amnesia. It consists of one learning trial followed by a retention test, in which physiological manipulations are presented. As in passive avoidance learning, food- or waterdeprived rats or mice finding food or water inside an enclosure are vulnerable to the retrograde amnesia produced by electroconvulsive shock treatment or the injection of various drugs. In one-trial taste or odor learning conducted in rats, birds, snails, bees, and fruit flies, there is an association between a food item or odorant and contextual stimuli or the unconditioned stimulus of Pavlovian conditioning. The odor-related task in bees was sensitive to protein synthesis inhibition as well as cholinergic receptor blockade, both analogous to results found on the passive avoidance response in rodents, while the task in fruit flies was sensitive to genetic modifications and aging, as seen in the passive avoidance response of genetically modified and aged rodents. These results provide converging evidence of interspecies similarities underlying the neurochemical basis of learning.

A single brief stressful event time-dependently affects object recognition memory and promotes familiarity preference in marmoset monkeys

A stressful experience can enhance information storage and impair memory retrieval in the rodent novel object recognition (NOR) task. However, recent conflicting results underscore the need for further investigation. Nonhuman primates may provide a unique, underexplored and more translational means to investigate stress-mediated changes in memory. Therefore, we assessed whether a single brief extrinsic stress event affects information encoding, storage and/or retrieval in adult marmoset monkeys submitted to the NOR task. This consisted of an initial 10 min familiarization period with two identical neutral objects. After a 6 h delay, a 10 min test trial was held where a new and familiar object could be explored. Stress was induced by a 15 min restraint event held before or after the encoding phase, or prior to retrieval. Pre-encoding stress had no effect on task performance, as this group displayed above-chance novelty preference similar to non-stressed controls. Post-encoding stress induced memory deficits, with both objects being explored equally. Interestingly, pre-retrieval stress induced an above-chance familiarity preference. A single brief stressful event thus affects recognition memory in a time-dependent manner. Also, negative discrimination ratios can be used as a measure of memory in the NOR task and a change in strategy may not mean memory failure in spontaneous learning paradigms.

An Introduction to the Callithrix Genus and Overview of Recent Advances in Marmoset Research

We provide here a current overview of marmoset (Callithrix) evolution, hybridization, species biology, basic/biomedical research, and conservation initiatives. Composed of 2 subgroups, the aurita group (C aurita and C flaviceps) and the jacchus group (C geoffroyi, C jacchus, C kuhlii, and C penicillata), this relatively young primate radiation is endemic to the Brazilian Cerrado, Caatinga, and Atlantic Forest biomes. Significant impacts on Callithrix within these biomes resulting from anthropogenic activity include (1) population declines, particularly for the aurita group; (2) widespread geographic displacement, biological invasions, and range expansions of C jacchus and C penicillata; (3) anthropogenic hybridization; and (4) epizootic Yellow Fever and Zika viral outbreaks. A number of Brazilian legal and conservation initiatives are now in place to protect the threatened aurita group and increase research about them. Due to their small size and rapid life history, marmosets are prized biomedical models. As a result, there are increasingly sophisticated genomic Callithrix resources available and burgeoning marmoset functional, immuno-, and epigenomic research. In both the laboratory and the wild, marmosets have given us insight into cognition, social group dynamics, human disease, and pregnancy. Callithrix jacchus and C penicillata are emerging neotropical primate models for arbovirus disease, including Dengue and Zika. Wild marmoset populations are helping us understand sylvatic transmission and human spillover of Zika and Yellow Fever viruses. All of these factors are positioning marmosets as preeminent models to facilitate understanding of facets of evolution, hybridization, conservation, human disease, and emerging infectious diseases.

Navigating in a challenging semiarid environment: the use of a route-based mental map by a small-bodied neotropical primate

To increase efficiency in the search for resources, many animals rely on their spatial abilities. Specifically, primates have been reported to use mostly topological and rarely Euclidean maps when navigating in large-scale space. Here, we aimed to investigate if the navigation of wild common marmosets inhabiting a semiarid environment is consistent with a topological representation and how environmental factors affect navigation. We collected 497 h of direct behavioral and GPS information on a group of marmosets using a 2-min instantaneous focal animal sampling technique. We found that our study group reused not only long-route segments (mean of 1007 m) but entire daily routes, a pattern that is not commonly seen in primates. The most frequently reused route segments were the ones closer to feeding sites, distant to resting sites, and in areas sparse in tree vegetation. We also identified a total of 56 clustered direction change points indicating that the group modified their direction of travel. These changes in direction were influenced by their close proximity to resting and feeding sites. Despite our small sample size, the obtained results are important and consistent with the contention that common marmosets navigate using a topological map that seems to benefit these animals in response to the exploitation of clustered exudate trees. Based on our findings, we hypothesize that the Caatinga landscape imposes physical restrictions in our group's navigation such as gaps in vegetation, small trees and xerophytic plants. This study, based on preliminary evidence, raises the question of whether navigation patterns are an intrinsic characteristic of a species or are ecologically dependent and change according to the environment.