The Importance of Egg Size and Social Effects for Behaviour of Arctic Charr Juveniles

Early behaviour can determine food intake and growth rate with important consequences for life history and survival in fishes. Egg size is known to affect growth rate of young Arctic charr but its influence on the development of behaviour is poorly documented. It is believed that egg size influence on growth and potentially on the behaviour of young fish decreases over time, minimized by the effects of social factors. Shortly after first feeding, we examined differences in mobility and foraging of Arctic charr in relation to egg size and social environment. The behaviour of juveniles from small and large eggs was compared five times over the course of development and in three different experimental settings: long‐term isolation (isolation before hatching), short‐term isolation vs. group rearing and mixed size group vs. homogeneous size groups. Egg size affected foraging behaviour and mobility of fish: fish coming from large eggs were more mobile and foraged more than fish coming from small eggs. Social environment affected foraging behaviour, mobility and space use: fish in a group were more mobile, foraged more and responded faster to food delivery than isolated fish. The interaction of egg size and social effects was seen primarily in foraging activities but did not affect mobility or space use. Large fish in groups foraged more than the three other groups: large fish in isolation, small fish in groups and small fish in isolation. Agonistic behaviour was rarely observed and there was no significant effect of group composition on agonistic behaviour. We discuss the importance of egg size and social effects at early stages of development with a focus on the evolutionary ecology of Arctic charr.     

Social learning and life skills training for hatchery reared fish

With the stress placed on our natural resources, many fisheries increasingly rely on restocking from hatchery-reared sources in an attempt to maintain commercially viable populations. However, the mortality rates of hatchery-reared fishes during the period directly following release are very high. The successful development of restocking programs is consequently dependent upon production and release strategies that lead to improved migratory, antipredator and feeding behaviour in hatchery fish. While relevant individual experience prior to release might improve performance, social learning potentially provides a process whereby fish can acquire locally adaptive behaviour rapidly and efficiently. It is now well over a decade since Suboski & Templeton (1989) raised the possibility of using social learning processes to improve the post-release survival of hatchery-reared fishes. This period has witnessed considerable progress in the understanding of how social learning operates in fish populations. We review new methods and recent findings that suggest how social learning protocols could realistically be applied on a large scale to enhance the viability of hatchery fish prior to their release into the wild. We also suggest a practical pre-release training protocol that may be applied at the hatchery level.     

Similarities in feeding behaviour between some marine and freshwater fishes in two tropical communities

The feeding behaviour and diets of fishes in two tropical habitats, a marine reef and a freshwater pond, were studied comparatively in Brazil. Similarities were found in the tactics employed to obtain food, the social patterns during foraging, and the general diet, notwithstanding lower-level taxonomic differences between the food items. The feeding behaviours of about one-third of the fish fauna from each community were approximately equivalent. The feeding categories of these fishes are briefly described. The similarities in the feeding modes probably reflect structural and functional properties shared by the two communities. Additional behavioural similarities of fishes in both habitats are presented and the lack of some particular foraging modes in each community is noted. The picture emerged that different, unrelated fish assemblages have the ability to evolve towards a similar behavioural and structural organization in response to comparable situations and constraints. The value of underwater observations and naturalistic studies on tropical freshwater fish assemblages is indicated.     

The integration of sociality,monoamines and stress neuroendocrinology in fish models: applications in the neurosciences

Animal‐focused research has been crucial for scientific advancement, but rodents are still taking a starring role. Starting as merely supporting evidence found in rodents, the use of fish models has slowly taken a more central role and expanded its overall contributions in areas such as social sciences, evolution, physiology and recently in translational medical research. In the neurosciences, zebrafish Danio rerio have been widely adopted, contributing to our understanding of the genetic control of brain processes and the effects of pharmacological manipulations. However, discussion continues regarding the paradox of function versus structure, when fishes and mammals are compared and on the potentially evolutionarily conserved nature of behaviour across fish species. From a behavioural standpoint, we explore aversive–stress and social behaviour in selected fish models and refer to the extensive contributions of stress and monoaminergic systems. We suggest that, in spite of marked neuroanatomical differences between fishes and mammals, stress and sociality are conserved at the behavioural and molecular levels. We also suggest that stress and sociality are mediated by monoamines in predictable and non‐trivial ways and that monoamines could bridge the relationship between stress and social behaviour. To reconcile the level of divergence with the level of similarity, we need neuroanatomical, pharmacological, behavioural and ecological studies conducted in the laboratory and in nature. These areas need to add to each other to enhance our understanding of fish behaviour and ultimately how this all may lead to better model systems for translational studies.     

The relationship between dominance behaviour and growth as a function of habitat stability and community complexity: a test using salmon and trout

Predation shortly after release is the main source of mortality among hatchery‐reared fish used to restore or enhance endangered salmonid populations. We found, that hatchery‐reared salmonid young originating from endangered stocks have weak innate responses to their natural fish predators. The ability to avoid predation in fish can be improved through social learning from experienced to naïve individuals. Huge benefits would be achieved, if social learning processes could be successfully applied on a large scale to enhance viability of hatchery fish prior to release into the wild. By using model predators together with chemical cues from real predators we tested if social learning could be used to train hatchery‐reared salmonid young to avoid fish predators. As there are clear differences in social behaviour among the salmonid species, we first examined whether these differences affect the probability and efficiency of learning anti‐predator skills from trained demonstrators. We compared anti‐predator responses of observers (fish trained by using experienced fish as demonstrators) with those of control fish, which had been 'trained' by untrained naïve conspecifics. We also examined how the efficiency of social learning depends on the ratio of experienced to naïve fish involved in social transmission trials. The results of these experiments will give guidelines how social learning could be utilized in developing hatchery scale training protocols.     

Improving anti‐predator responses of hatchery reared salmonids by social learning

Predation shortly after release is the main source of mortality among hatchery‐reared fish used to restore or enhance endangered salmonid populations. We found, that hatchery‐reared salmonid young originating from endangered stocks have weak innate responses to their natural fish predators. The ability to avoid predation in fish can be improved through social learning from experienced to naïve individuals. Huge benefits would be achieved, if social learning processes could be successfully applied on a large scale to enhance viability of hatchery fish prior to release into the wild. By using model predators together with chemical cues from real predators we tested if social learning could be used to train hatchery‐reared salmonid young to avoid fish predators. As there are clear differences in social behaviour among the salmonid species, we first examined whether these differences affect the probability and efficiency of learning anti‐predator skills from trained demonstrators. We compared anti‐predator responses of observers (fish trained by using experienced fish as demonstrators) with those of control fish, which had been ‘trained’ by untrained naïve conspecifics. We also examined how the efficiency of social learning depends on the ratio of experienced to naïve fish involved in social transmission trials. The results of these experiments will give guidelines how social learning could be utilized in developing hatchery scale training protocols.     

The effects of suspensoids on fish

High suspensoid loads are a common feature of many Southern Hemisphere inland waters. Case studies on a natural lake (Chilwa), a man-made lake (Le Roux) and S.W. Indian Ocean estuaries reveal that the effects of turbidity on fish in these systems differ widely. In Lake Le Roux, high suspensoid loads influence fish by causing a reduced growth rate, a decrease in size at first maturity and maximum size, and a movement inshore by large fishes to feed on phytobenthos. High turbidities in Lake Chilwa sharply reduce food availability in benthic offshore zones, and restrict fishes to pelagic and inshore food resources. The resuspension of sediments by wind action may cause fish mortalities through deoxygenation of the water column. Moderate turbidity levels appear to be beneficial to fish in estuaries by affording protection from predators in shallow, food-rich areas. Turbidity gradients may also provide a navigational aid to fish entering estuaries.While ecological studies on Southern Hemisphere inland waters are fairly advanced, experimental work is restricted. Such research in the Northern Hemisphere has revealed that high suspensoid loads may influence breeding success, egg and larval survival, population structure and size, as well as food availability and feeding efficiency. The effect of suspensoids on the breeding success and feeding efficiency of Southern Hemisphere fish needs further investigation.Moderate suspensoid loads are a natural feature of many inland waters, but sustained high levels reduce the photic zone, blanket the benthos and interfere with the feeding efficiency of fish. The curtailment of soil erosion should therefore be regarded as a priority in the management of inland fisheries, especially in Third World countries where poor land-use practises have resulted in a marked deterioration of water quality. The need to study and manage river catchments holistically is emphasized.     

Evidence of social learning in black-and-white ruffed lemurs (Varecia variegata)

Although many studies have examined social learning capabilities in apes and monkeys, experiments involving prosimians remain largely absent. We investigated the potential for social learning in black-and-white ruffed lemurs using a two-action foraging task. Eight individuals were divided into two experimental groups and exposed to conspecifics using one of two techniques to access food. Subjects were then given access to the apparatus and their retrieval techniques were recorded and compared. All subjects made their first retrieval using the technique they observed being demonstrated, and there were significant differences between the two groups in their overall response patterns. These results suggest that prosimians are capable of social learning and that additional long-term field studies may reveal the presence of behavioural traditions similar to those found in other primates.     

The role of learning in fish behaviour

Summary The behavioural patterns of fish are the result of innate (built-in) patterns of maturation (developmental changes) and of learning processes (imprinting and trial-and-error learning). Innate behavioural patterns are considered to be hard-wired and inflexible. However, through learning, fish can adapt to environmental change. For instance, the homing behaviour of fish may be partly the result of the development of specific parts of the brain and partly because of changes in behaviour with experience. Similarly, one can assume that the feeding mode of fish involving snap-responses is innate, but learning enables fish to modify their foraging behaviour in response to a fluctuating environment. By reviewing these and other examples, such as the role of recognition learning and socially transmitted behaviour, one can illustrate the importance of learning in the everyday life of fishes. Although learning plays a large role in the behaviour of fishes, the learning capacity of fishes may also be useful to fisheries research and hatchery operations.     

Convergent, parallel and correlated evolution of trophic morphologies in the subfamily schizothoracinae from the Qinghai-Tibetan plateau

Schizothoracine fishes distributed in the water system of the Qinghai-Tibetan plateau (QTP) and adjacent areas are characterized by being highly adaptive to the cold and hypoxic environment of the plateau, as well as by a high degree of diversity in trophic morphology due to resource polymorphisms. Although convergent and parallel evolution are prevalent in the organisms of the QTP, it remains unknown whether similar evolutionary patterns have occurred in the schizothoracine fishes. Here, we constructed for the first time a tentative molecular phylogeny of the schizothoracine fishes based on the complete sequences of the cytochrome b gene. We employed this molecular phylogenetic framework to examine the evolution of trophic morphologies. We used Pagel's maximum likelihood method to estimate the evolutionary associations of trophic morphologies and food resource use. Our results showed that the molecular and published morphological phylogenies of Schizothoracinae are partially incongruent with respect to some intergeneric relationships. The phylogenetic results revealed that four character states of five trophic morphologies and of food resource use evolved at least twice during the diversification of the subfamily. State transitions are the result of evolutionary patterns including either convergence or parallelism or both. Furthermore, our analyses indicate that some characters of trophic morphologies in the Schizothoracinae have undergone correlated evolution, which are somewhat correlated with different food resource uses. Collectively, our results reveal new examples of convergent and parallel evolution in the organisms of the QTP. The adaptation to different trophic niches through the modification of trophic morphologies and feeding behaviour as found in the schizothoracine fishes may account for the formation and maintenance of the high degree of diversity and radiations in fish communities endemic to QTP.     

Effects of group size on the responsiveness of zebrafish, Brachydanio rerio (Hamilton Buchanan), to alanine, a chemical attractant

Previous studies have examined the effects of grouping on the locating (search) phase of foraging and feeding behaviour in fishes. Few studies have examined whether schooling in fishes may facilitate individual foraging by enhancing a group's responsiveness to food odours. The purpose of the current study was to assess the effect of increasing group size on the responsiveness of zebrafish, Brachydanio rerio (Hamilton Buchanan), to L-alanine, an amino acid which is an important constituent of prey odours for many fishes. Based on the results of previous studies, either an increasing or decreasing linear relationship or a unimodal (convex or concave) relationship between responsiveness and group size was expected; the results, however, were bimodal. Groups of four fish were most responsive to alanine, as determined by the mean percentage of occurrences of fish in the area of a behavioural arena (an octagonal fluviarium) into which alanine was infused (at 10⁻³, 10⁻⁴, or 10⁻⁵ M). Groups of two, six and eight fish were significantly less responsive ( P < 0.05) than either groups of four fish or individual fish. The responses of groups of two, six and eight fish were not significantly different from each other.     

Physiological effects of dominance hierarchies: laboratory artefacts or natural phenomena?

Studies of fish behaviour have demonstrated the existence of social interactions that result in dominance hierarchies. In environments in which resources, such as food, shelter and mates, are limited, social competition results in some fish becoming dominant and occupying the most profitable positions. This behaviour has been observed in natural environments and also in many laboratory‐based experiments. When two fish have been confined in a small tank, one of them usually has exhibited behaviour that suggests it is dominant over the other submissive animal. Physiological consequences of social interaction can be seen in both dominants and subordinates but are more extreme in the subordinate. However, this scenario is without doubt an artificial situation. Fewer experiments have been conducted using laboratory experiments that are more socially and physically complex than those experienced by dyads in tanks. In simple fluvial tanks, through which water is recirculated, the physiological responses of fish to social competition have generally been qualitatively similar to those recorded among dyads. However, when environmental disturbances, complex resource distributions, increase in water flushing, presence of predators and competing species of fish have been included in experimen‐tal designs, there have been fewer, diminished or no physiological dierences between dominant and subordinate fish. There have been very few studies of physiology in relation to dominance in natural habitats, and those that have been conducted suggest that under some circumstances hierarchies may cause less intense physiological responses than have been suggested based on results of laboratory studies in simple environments. Possible reasons for these variations are discussed. The need is identified for a well structured experimental approach to the investi‐gation of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes. It is also suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important.     

Amphibious fish: why do they leave water?

Summary Amphibious behaviour in fish has evolved separately many times since the first amphibious fishes, the rhipidistian crossopterygians, ventured onto land about 350 million years ago. This behaviour has resulted in the colonization and eventual domination by vertebrates of the terrestrial habitat. It is generally proposed that aquatic hypoxia, owing to metabolic oxygen consumption and organic decay, was the most important selective force in the evolution of air-breathing vertebrates (e.g. Randall et al., 1981). Modern amphibious fish species give an insight into the reasons for leaving and eventually abandoning the aquatic habitat. Amphibious fishes today leave the water for a variety of reasons associated with degradation of their aquatic habitat, or biotic factors within it.The possible causal factors which may elicit an emergence response are summarized in Fig. 1(a) and (b). Amphibious fish inhabiting closed systems, as typified by freshwater or intertidal pools, may leave water for any of the reasons detailed in Fig. 1(a). The relative importance of any one stimulus is likely to vary between different species. However, it is possible that in closed systems, adverse fluctuations in physico-chemical parameters will have a more important effect in eliciting amphibious behaviour than will biotic factors. In open systems, such as coastal waters or large freshwater bodies, effectively two routes of escape from adverse aquatic conditions are available to amphibious fish. They may move onto land, or alternatively they may move underwater to find better conditions. In such a system, where physico-chemical parameters remain relatively constant, abiotic factors are unlikely to have a significant influence on amphibious behaviour. The dominant stimulus in open systems is possibly the three-way interaction between predation, competition, and short-or long-term food availability (Fig. 1(b)).It is unlikely that any one of the factors discussed in this review will act alone in causing amphibious behaviour, and in this respect the available literature on fish leaving water is lacking. Much of it is fragmentary and partly anecdotal, and the limited amount of experimental work tends to concentrate on individual causal factors. There is evidently scope for detailed examination of emersion in a number of amphibious fishes, testing a matrix of environmental and biotic stimuli, in an attempt to determine in more detail the reasons for such behaviour.     

Macrotidal estuaries: a region of collision between migratory marine animals and tidal power development

Macrotidal estuaries of the inner Bay of Fundy are utilized by large numbers of migratory fishes, particularly dogfish, sturgeon, herring, shad, Atlantic salmon and striped bass as well as by other migratory marine animals, many of which have large body sizes (squid, Lamnid sharks, seals and whales). Tagging experiments indicate the fishes originate from stocks derived over the entire North American Atlantic coast from Florida to Labrador. Population estimates suggest up to 2.0 times 10⁶adult American shad (Alosa sapidissima) migrate through an individual embayment each year. These migrations are an integral part of the life history of the respective species and appear to be controlled in part by the near shore movements of ocean currents. In other regions of the world similar macrotidal estuaries exist (Cook Inlet, Alaska; Severn Estuary, U.K.) and they, like the Bay of Fundy, are linked in continuum to the local ocean currents. We propose that marine animals utilize all these regions in a manner similar to the Bay of Fundy estuaries and properly designed surveys will reveal their presence. Fish passage studies utilizing the Annapolis estuary low-head, tidal turbine on the Bay of Fundy have shown that turbine related mortality of 20–80% per passage occurs depending on fish species, fish size and the efficiency of turbine operation. We suggest that introduction of tidal turbines into open ocean current systems will cause widespread impact on marine populations resulting in significant declines in abundance.     

Intraguild indirect effects through trophic cascades between stream-dwelling fishes

1. To examine the strength and role of indirect effects through trophic cascades by omnivorous fish on algal biomass in streams, we introduced one of four fish species (ayu Plecoglossus altivelis altivelis, pike gudgeon Pseudogobio esocinus esocinus, Japanese dace Tribolodon hakonensis and pale chub Zacco platypus) in experimental pools. We also investigated the indirect effects of gudgeon, dace and chub on the growth of ayu. 2. We chose the four fish species across a continuum of omnivory. Ayu fed mainly on benthic algae, and gudgeon predominantly on invertebrates. Dace and chub fed on both algae and invertebrates, but dace preyed on invertebrates more than chub. 3. The presence of gudgeon, dace and chub reduced the number of algal-feeding invertebrates and increased the algal biomass through trophic cascades. Consequently, ayu growth rate over the experimental period in pools with one of the three fish species was 25.9-44.1 times greater than the growth rate in pools with only ayu. 4. The positive indirect effect on ayu growth was large for gudgeon and dace and small for chub, whereas the addition of ayu reduced ayu growth considerably due to intraspecific competition. 5. The relative intensity of indirect effects on ayu growth through trophic cascades was predictable from the food overlap between ayu and the other fishes. However, the similar strength of indirect effects by gudgeon and dace that fed differently on algae and invertebrates suggests that feeding behaviour, prey preference and trait-mediated indirect interactions were also important in the prediction.     

Effects of parasites on fish behaviour: a review and evolutionary perspective

Fish serve as hosts to a range of parasites that are taxonomically diverse and that exhibit a wide variety of life cycle strategies. Whereas many of these parasites are passed directly between ultimate hosts, others need to navigate through a series of intermediate hosts before reaching a host in (or on) which they can attain sexual maturity. The realisation that parasites need not have evolved to minimise their impact on hosts to be successful, and in many cases may even have a requirement for their hosts to be eaten by specific predators to ensure transmission, has renewed interest in the evolutionary basis of infection-associated host behaviour. Fishes have proved popular models for the experimental examination of such hypotheses, and parasitic infections have been demonstrated to have consequences for almost every aspect of fish behaviour. Despite a scarcity of knowledge regarding the mechanistic basis of such behaviour changes in most cases, and an even lower understanding of their ecological consequences, there can be little doubt that infection-associated behaviour changes have the potential to impact severely on the ecology of infected fishes. Changes in foraging efficiency, time budget, habitat selection, competitive ability, predator-prey relationships, swimming performance and sexual behaviour and mate choice have all been associated with – and in some cases been shown to be a result of – parasite infections, and are reviewed here in some detail. Since the behavioural consequences of infections are exposed to evolutionary selection pressures in the same way as are other phenotypic traits, few behavioural changes will be evolutionarily neutral and host behaviour changes that facilitate transmission should be expected. Despite this expectation, we have found little conclusive evidence for the Parasite Increased Trophic Transmission (PITT) hypothesis in fishes, though recent studies suggest it is likely to be an important mechanism. Additionally, since the fitness consequences of the many behavioural changes described have rarely been quantified, their evolutionary and ecological significance is effectively unknown.Potential hosts may also change their behaviour in the presence of infective parasite stages, if they adopt tactics to reduce exposure risk. Such `behavioural resistance', which may take the form of habitat avoidance, prey selectivity or avoidance of infected individuals, can be viewed as behavioural change associated with the threat of being parasitised, and so is included here. Actually harbouring infections may also stimulate fishes to perform certain types of simple or complex behaviours aimed at removing parasites, such as substrate scraping or the visitation of cleaning stations, although the efficacy of the latter as a parasite removal strategy is currently subject to a good deal of debate.The effects parasites have on shoaling behaviour of host fish have attracted a good deal of attention from researchers, and we have provided a case study to summarise the current state of knowledge. Parasites have been shown to affect most of the antipredator effects of shoaling (such as vigilance, co-ordinated evasion and predator confusion) and can also impair an individual's foraging ability. It therefore seems unsurprising that, in a number of species avoidance of parasitised individuals has evolved which may explain the occurrence of parasite-assorted shoals in the field. Parasitised fish are found more often in peripheral shoal positions and show a reduced tendency for shoaling in some fish species. Given the array of host behaviours that may be changed, the fitness consequences of shoal membership for parasitised hosts and their parasites are not always easy to predict, yet an understanding of these is important before we can make predictions regarding the ecological impact of infections on host fish populations.Clearly, there remain many gaps in our knowledge regarding the effects of parasites on the behaviour of host fish. We believe that a much greater understanding of the importance of infection-associated behaviour changes in fish could be gained from high quality research in comparatively few areas. We have completed our review by highlighting the key research topics that we believe should attract new research in this field.     

Size,sex and social experience: Experimental tests of multiple factors mediating contest behaviour in a rockpool fish

Aggressive contests amongst conspecifics are important to understand from an ecological and evolutionary perspective as contest dynamics can directly influence individual fitness. For some species, individual attributes such as relative body size closely predict the outcome, intensity and duration of contests, whereas for others, prior social experiences play a key role. However, disentangling the relative effects of individual attributes and social experiences is challenging from an experimental perspective, and because of this, few studies have investigated relative effects of multiple factors. Rockpool fishes have been well studied in terms of factors governing abundance, distribution and community structure, but much less so in terms of contest behaviour. This is surprising because contest dynamics are likely to directly affect the distribution of fishes along the rocky shore, and hence indirectly govern population and community composition. Here, we explored multiple factors potentially influencing contest behaviour in a numerically dominant, resident intertidal fish species, Bathygobius cocosensis (Gobiidae). Using a series of staged pairwise contest trials, we investigated the effect of size, sex and social experiences (namely prior residency and winner–loser experiences) on contest dynamics. We found no evidence that prior residency influenced contest outcome, suggesting social experiences play a minor role in contest dynamics. Previous winner/loser experience also did not influence contest outcome, although this is likely a product of low sample size. In addition, the likelihood of winning was unrelated to contestant sex, and the combination of sexes in paired contests did not influence contest intensity or duration. Instead, body size was related to contest outcome, intensity and duration in the majority of experimental trials. These results suggest that body size rather than sex or social experiences is the key determinant of contest dynamics in this species. We suggest that the dynamic biotic and abiotic environment inhabited by intertidal fish may reduce the influence of prior social experiences in modulating contest dynamics.     

Ethical considerations in fish research

Fishes are used in a wide range of scientific studies, from conservation research with potential benefits to the species used to biomedical research with potential human benefits. Fish research can take place in both laboratories and field environments and methods used represent a continuum from non-invasive observations, handling, through to experimental manipulation. While some countries have legislation or guidance regarding the use of fish in research, many do not and there exists a diversity of scientific opinions on the sentience of fish and how we determine welfare. Nevertheless, there is a growing pressure on the scientific community to take more responsibility for the animals they work with through maximising the benefits of their research to humans or animals while minimising welfare or survival costs to their study animals. In this review, we focus primarily on the refinement of common methods used in fish research based on emerging knowledge with the aim of improving the welfare of fish used in scientific studies. We consider the use of anaesthetics and analgesics and how we mark individuals for identification purposes. We highlight the main ethical concerns facing researchers in both laboratory and field environments and identify areas that need urgent future research. We hope that this review will help inform those who wish to refine their ethical practices and stimulate thought among fish researchers for further avenues of refinement. Improved ethics and welfare of fishes will inevitably lead to increased scientific rigour and is in the best interests of both fishes and scientists.     

Identifying Social Learning in Animal Populations: A New ‘Option-Bias’ Method

Background

Studies of natural animal populations reveal widespread evidence for the diffusion of novel behaviour patterns, and for intra- and inter-population variation in behaviour. However, claims that these are manifestations of animal ‘culture’ remain controversial because alternative explanations to social learning remain difficult to refute. This inability to identify social learning in social settings has also contributed to the failure to test evolutionary hypotheses concerning the social learning strategies that animals deploy.

Methodology/Principal Findings

We present a solution to this problem, in the form of a new means of identifying social learning in animal populations. The method is based on the well-established premise of social learning research, that - when ecological and genetic differences are accounted for - social learning will generate greater homogeneity in behaviour between animals than expected in its absence. Our procedure compares the observed level of homogeneity to a sampling distribution generated utilizing randomization and other procedures, allowing claims of social learning to be evaluated according to consensual standards. We illustrate the method on data from groups of monkeys provided with novel two-option extractive foraging tasks, demonstrating that social learning can indeed be distinguished from unlearned processes and asocial learning, and revealing that the monkeys only employed social learning for the more difficult tasks. The method is further validated against published datasets and through simulation, and exhibits higher statistical power than conventional inferential statistics.

Conclusions/Significance

The method is potentially a significant technological development, which could prove of considerable value in assessing the validity of claims for culturally transmitted behaviour in animal groups. It will also be of value in enabling investigation of the social learning strategies deployed in captive and natural animal populations.     

Evaluation of a behavioural response of Mediterranean coastal fishes to novel recreational feeding situation

Fish may learn to associate food with human presence through recreational hand-feeding, a popular tourist activity. The conditional learning—e.g. when an organism learns by continuous exposure to one stimulus—of different coastal fish species exposed to novel feeding situations was evaluated. The latencies of learning response to the initiation of supplementary feeding were rapid and species-specific. However differences in the learning response between different fishes decreased over time, demonstrating that associating with others might incur costs especially for small-sized species, likely due to increased competition for food. Nevertheless some other fish species did not acquire any specific human oriented behavior, being naturally timid or avoiding humans.