Excretory deposits surrounding food sites facilitate social learning of food preferences in Norway rats

Competition and generalization impede cultural formation in wild jackdaws

Animal cultures have now been demonstrated experimentally in diverse taxa from flies to great apes. However, experiments commonly use tasks with unrestricted access to equal pay-offs and innovations seeded by demonstrators who are trained to exhibit strong preferences. Such conditions may not reflect those typically found in nature. For example, the learned preferences of natural innovators may be weaker, while competition for depleting resources can favour switching between strategies and generalizing from past experience. Here we show that in experiments where wild jackdaws (Corvus monedula) can freely discover depleting supplies of novel foods, generalization has a powerful effect on learning, allowing individuals to exploit multiple new opportunities through both social and individual learning. Further, in contrast to studies with trained demonstrators, individuals that were first to innovate showed weak preferences. As a consequence, many individuals ate all available novel foods, displaying no strong preference and no group-level culture emerged. Individuals followed a 'learn from adults' strategy, but other demographic factors played a minimal role in shaping social transmission. These results demonstrate the importance of generalization in allowing animals to exploit new opportunities and highlight how natural competitive dynamics may impede the formation of culture.

A Good Life for Laboratory Rodents?

Most would agree that animals in research should be spared "unnecessary" harm, pain, or distress, and there is also growing interest in providing animals with some form of environmental enrichment. But is this the standard of care that we should aspire to? We argue that we need to work towards a higher standard-specifically, that providing research animals with a "good life" should be a prerequisite for their use. The aims of this paper are to illustrate our vision of a "good life" for laboratory rats and mice and to provide a roadmap for achieving this vision. We recognize that several research procedures are clearly incompatible with a good life but describe here what we consider to be the minimum day-to-day living conditions to be met when using rodents in research. A good life requires that animals can express a rich behavioral repertoire, use their abilities, and fulfill their potential through active engagement with their environment. In the first section, we describe how animals could be housed for these requirements to be fulfilled, from simple modifications to standard housing through to better cage designs and free-ranging options. In the second section, we review the types of interactions with laboratory rodents that are compatible with a good life. In the third section, we address the potential for the animals to have a life outside of research, including the use of pets in clinical trials (the animal-as-patient model) and the adoption of research animals to new homes when they are no longer needed in research. We conclude with a few suggestions for achieving our vision.

Impacts of invasive plants on animal behaviour

The spread of invasive species is a threat to ecosystems worldwide. However, we know relatively little about how invasive species affect the behaviour of native animals, even though behaviour plays a vital role in the biotic interactions which are key to understanding the causes and impacts of biological invasions. Here, we explore how invasive plants - one of the most pervasive invasive taxa - impact the behaviour of native animals. To promote a mechanistic understanding of these behavioural impacts, we begin by introducing a mechanistic framework which explicitly considers the drivers and ecological consequences of behavioural change, as well as the moderating role of environmental context. We then synthesise the existing literature within this framework. We find that while some behavioural impacts of invasive plants are relatively well-covered in the literature, others are supported by only a handful of studies and should be explored further in the future. We conclude by identifying priority topics for future research, which will benefit from an interdisciplinary approach uniting invasion ecology with the study of animal behaviour and cognition.

On evolutionary causes and evolutionary processes

In this essay I consider how biologists understand 'causation' and 'evolutionary process', drawing attention to some idiosyncrasies in the use of these terms. I suggest that research within the evolutionary sciences has been channeled in certain directions and not others by scientific conventions, many of which have now become counterproductive. These include the views (i) that evolutionary processes are restricted to those phenomena that directly change gene frequencies, (ii) that understanding the causes of both ecological change and ontogeny is beyond the remit of evolutionary biology, and (iii) that biological causation can be understood by a dichotomous proximate-ultimate distinction, with developmental processes perceived as solely relevant to proximate causation. I argue that the notion of evolutionary process needs to be broadened to accommodate phenomena such as developmental bias and niche construction that bias the course of evolution, but do not directly change gene frequencies, and that causation in biological systems is fundamentally reciprocal in nature. This article is part of a Special Issue entitled: In Honor of Jerry Hogan.

Further experimental analysis of the social learning and transmission of foraging information amongst Norway rats

Adult male Norway rats were tested to see if their foraging efficiency could be improved by social learning and to investigate whether foraging information could be socially transmitted along a chain of animals. In Experiment 1, 'observers' were placed in one of four conditions, distinguished by the nature of their experience during an observation phase, in which they either observed: (1) a trained conspecific unearthing buried carrot; (2) a trained conspecific digging; (3) carrot pieces only; or (4) an empty enclosure (the control group). When tested 24 h later it was found that subjects in group 1 alone exhibited a significantly elevated foraging ability relative to the control group, being more active, and unearthing more carrot pieces in total. The results show that perception of a trained demonstrator conspecific successfully foraging for food is necessary for social learning of foraging information to occur, probably by a local enhancement mechanism. In Experiment 2, chains of transmission were established by allowing each observer to act 24 h later as the demonstrator for the next observer. In one of two transmission groups subjects were given an extra period of individual foraging experience in the test enclosure, with no demonstrator present. Enhanced levels of foraging efficiency were maintained across eight transmission episodes for both transmission groups relative to a no-transmission control. Subjects in the group with the additional experience unearthed significantly more buried food than subjects in the other transmission group. The experiments extend our standard transmission group was upheld. The superior performance of demonstrators in this group, as reflected in their higher level of carrot digging, suggests that the extra period of experience did indeed enhance their ability to act as effective demonstrators. The elevated performance of subjects in this group is attributed to a combination of social and individual learning. This finding suggests that the stability of social transmission may, under some circumstances, be bolstered by individual reinforcement of socially learned and enhanced patterns of behaviour. It also lends support to the hypothesis, proposed to account for the findings of our earlier study, that motivational factors such as fatigue, may detract from subjects' performance as demonstrators when this demonstration follows closely after the additional period of individual experience, but that a 24 h period is sufficient to allow such motivational factors to decay. If individual experience can buttress socially learned traits then this interaction may act so as to prolong the period of time that a socially transmitted trait remains in a population. It is conceivable that an additional period of foraging longer than 10 min may further enhance subjects' subsequent performance as demonstrators. The complex relationship between individual and social learning has received little attention. It is not clear how, if at all, social learning is different from other forms of learning (Plotkin, 1988), apart from the obvious requirement that another animal somehow be involved in the social learning process. Boyd and Richerson (1985) argue that social and individual learning are, at least in humans, alternative ways of acquiring a particular behavioural variant. Most recent studies of animal social learning, on the other hand, tend to emphasize the stimulus enhancing role of the demonstrator animal (Galef, 1988a), thereby suggesting that social learning is a sub-category of individual learning. This study shows that individual learning can reinforce the acquisition and expression of socially acquired behavioural variants.

When to approach novel prey cues? Social learning strategies in frog-eating bats

Animals can use different sources of information when making decisions. Foraging animals often have access to both self-acquired and socially acquired information about prey. The fringe-lipped bat, Trachops cirrhosus, hunts frogs by approaching the calls that frogs produce to attract mates. We examined how the reliability of self-acquired prey cues affects social learning of novel prey cues. We trained bats to associate an artificial acoustic cue (mobile phone ringtone) with food rewards. Bats were assigned to treatments in which the trained cue was either an unreliable indicator of reward (rewarded 50% of the presentations) or a reliable indicator (rewarded 100% of the presentations), and they were exposed to a conspecific tutor foraging on a reliable (rewarded 100%) novel cue or to the novel cue with no tutor. Bats whose trained cue was unreliable and who had a tutor were significantly more likely to preferentially approach the novel cue when compared with bats whose trained cue was reliable, and to bats that had no tutor. Reliability of self-acquired prey cues therefore affects social learning of novel prey cues by frog-eating bats. Examining when animals use social information to learn about novel prey is key to understanding the social transmission of foraging innovations.

The receptor guanylyl cyclase type D (GC-D) ligand uroguanylin promotes the acquisition of food preferences in mice

Rodents rely on olfactory stimuli to communicate information between conspecifics that is critical for health and survival. For example, rodents that detect a food odor simultaneously with the social odor carbon disulfide (CS(2)) will acquire a preference for that food. Disruption of the chemosensory transduction cascade in CS(2-)sensitive olfactory sensory neurons (OSNs) that express the receptor guanylyl cyclase type D (GC-D; GC-D+ OSNs) will prevent mice from acquiring these preferences. GC-D+ OSNs also respond to the natriuretic peptide uroguanylin, which is excreted into urine and feces. We analyzed if uroguanylin could also act as a social stimulus to promote the acquisition of food preferences. We found that feces of mice that had eaten odored food, but not unodored food, promoted a strong preference for that food in mice exposed to the feces. Olfactory exploration of uroguanylin presented with a food odor similarly produced a preference that was absent when mice were exposed to the food odor alone. Finally, the acquisition of this preference was dependent on GC-D+ OSNs, as mice lacking GC-D (Gucy2d(-)(/-) mice) showed no preference for the demonstrated food. Together with our previous findings, these results demonstrate that the diverse activators of GC-D+ OSNs elicit a common behavioral result and suggest that this specialized olfactory subsystem acts as a labeled line for a type of associative olfactory learning.

A case study in behavioral analysis, synthesis and attention to detail: social learning of food preferences

Philip Teitelbaum's focus on detailed description of behavior, the interplay of analysis and synthesis in experimental investigations and the importance of converging lines of evidence in testing hypotheses has proven useful in fields distant from the physiological psychology that he studied throughout his career. Here we consider the social biasing of food choice in Norway rats as an instance of the application of Teitelbaum's principles of behavioral analysis and synthesis and the usefulness of convergent evidence as well as the contributions of detailed behavioral analysis of social influences on food choice to present understanding of both sensory processes and memory.

From fish to fashion: experimental and theoretical insights into the evolution of culture

Recent years have witnessed a re-evaluation of the cognitive capabilities of fishes, including with respect to social learning. Indeed, some of the best experimental evidence for animal traditions can be found in fishes. Laboratory experimental studies reveal that many fishes acquire dietary, food site and mating preferences, predator recognition and avoidance behaviour, and learn pathways, through copying other fishes. Concentrating on foraging behaviour, we will present the findings of laboratory experiments that reveal social learning, behavioural innovation, the diffusion of novel behaviour through populations and traditional use of food sites. Further studies reveal surprisingly complex social learning strategies deployed by sticklebacks. We will go on to place these observations of fish in a phylogenetic context, describing in which respects the learning and traditionality of fish are similar to, and differ from, that observed in other animals. We end by drawing on theoretical insights to suggest processes that may have played important roles in the evolution of the human cultural capability.

The role of social context and individual experience in novel task acquisition in cottontop tamarins, Saguinus oedipus

In socially tolerant settings, naïve individuals may have opportunities to interact jointly with knowledgeable demonstrators and novel tasks. This process is expected to facilitate social learning. Individual experience may also be important for reinforcing and honing socially acquired behaviours. We examined the role of joint interaction and individual experience in the acquisition of a novel foraging task in captive cottontop tamarins. The task involved learning how to locate and access two hidden food rewards from among 10 differently cued forage sites. Tamarins were tested in three different conditions: (1) individually, (2) while interacting with a naïve mate, and (3) while interacting with a mate trained as a knowledgeable demonstrator. For tamarins tested with mates present, we interspersed social input test days with exposure to the task while alone. Tamarins were tested again 17 months after their last exposure to the task, to assess long-term memory. All tamarins tested with knowledgeable demonstrators solved the task. In contrast, tamarins tested alone or with naïve mates had similarly high levels of neophobia and low levels of task acquisition. We conclude that joint interaction occurs in mated pairs of cottontop tamarins and facilitates the spread of novel behaviour. Interspersing test days with a knowledgeable demonstrator present and test days alone with the task helped tamarins to achieve the ultimate goal of the task: obtaining food rewards. Tamarins performed similarly when tested 17 months later, regardless of their initial learning environment. Tamarins had memory deficits for the location of hidden food rewards, but retained memory of the necessary motor actions and solved the task.

Social transmission and memory of food preferences in pine voles (Microtus pinetorum)

The social transmission of food preferences is affected by factors including the length of time a preference is maintained. The authors investigated the social transmission of food preferences in pine voles (Microtus pinetorum) and whether food items had to be present for memory to persist. A demonstrator vole was fed cocoa-flavored food, a nonpreferred food. After interacting with a demonstrator vole, observer voles preferred cocoa-flavored food as compared with either naive voles that had not interacted with demonstrators or voles that had been exposed to odors. Observers retained this preference for 72 hr after interacting with an observer whether or not flavored foods were present. The ability to learn which food items are palatable and safe may benefit a generalist herbivore that has faced selection to avoid toxic baits.

Stimulus enhancement in greylag geese: socially mediated learning of an operant task

We recently observed the spreading of a novel tradition in a flock of semiferal greylag geese, Anser anser: an increasing number of individuals began to bite and chew the stems of butterbur, Petasites hybridus. Because this behaviour spread particularly fast within families, social learning seemed to be involved. We therefore designed an experiment with hand-reared goslings, which were socially imprinted on humans, to investigate whether and how the observation of an experienced tutor affects the acquisition of a novel skill. Goslings had to open the gliding lid of a box to get at a food reward. To each of seven hand-reared observers a human tutor demonstrated where and how to open the lid, whereas seven controls remained untutored. All observers learned to perform the task but only one of the controls succeeded. The observers explored more often at the position shown by the tutor than elsewhere and seemingly learned by trial and error. In contrast, control birds explored primarily at positions that did not allow them to open the box. These results indicate that in greylag goslings the observation of an experienced model facilitates the learning of an operant task. We conclude that stimulus enhancement followed by operant conditioning were the mechanisms involved, which may have accounted for the fast spread of the stem-chewing tradition between family members. Copyright 2000 The Association for the Study of Animal Behaviour.

Olfactory memory in rats, cholinergic agents and benzodiazepine receptor ligands

Drugs and their effects on olfactory learning processes in rats were tested using a modified version of the runway apparatus developed by Ades. Rats were first exposed to a conspecific urine sample and 24 h later were exposed to the same stimulus in the runway. Observations recorded the time spent investigating the urine and the number of sniffs at the site, these being considered to be indices of memory. Diazepam-treated rats (4 or 6 mg/kg) and scopolamine-treated rats (0.5 or 1 mg/kg) showed increases for both parameters. When both drugs were administered simultaneously, the impairing effect was potentiated. However, no changes in learning responses were observed in rats treated with physostigmine (0.125, 0.25, 0.5 mg/kg) or methyl beta-carboline-3-carboxylate (0.3, 0.5, 1 mg/kg), although the administration of physostigmine or methyl beta-carboline-3-carboxylate was shown to antagonize the impairing effect of diazepam or scopolamine respectively. These observations support the hypothesis of interactions existing between cholinergic agents and benzodiazepine receptor ligands and of such interactions affecting olfactory acquisition processes. The runway apparatus appears to be a valid candidate model to be used for the assessment of pharmacological influences on olfactory learning in rats.