Showing papers in "Behaviour in 2012"

Zebrafish embryos and larvae in behavioural assays

Abstract: Zebrafish embryos and early larvae are becoming increasingly important as models in biomedical research because of their low cost, high throughput and potential as a replacement for adult, higher vertebrate model species. The functional domains of drug targets, and other functionally important proteins, are often highly conserved between the zebrafish and mammals. Furthermore, the zebrafish embryo or larva shows a complex behavioural repertoire only a few days after fertilization. Here, we show how behavioural studies in mammals are being translated to the zebrafish embryo/larva model. We give emphasis to behavioural studies that may be relevant to drug screening or safety toxicology. We show how video tracking hardware and software can be used to provide an automated, high data-content readout for zebrafish behavioural responses. Published behavioural assays using zebrafish developmental stages include responses to dark challenge, acoustic stimuli, novel environments and various pharmacological compounds. Future prospects for zebrafish developmental behavioural studies include the potential to move from 96-well format studies into microfluidic-based embryo cultures. The zebrafish embryo model is already becoming a useful system for identifying molecular-genetic pathways associated with behavioural responses.

A comparison of the light/dark and novel tank tests in zebrafish

Abstract: The recent introduction of tasks to assess the behavior of zebrafish in novel and/or aversive environments has spurred great interest, prompting attempts to determine which constructs are modeled by these tasks (e.g., fear, anxiety, or some other construct). A review of the pharmacological and behavioral experiments indicates that not all behavioral testing models are equivalent. A more precise understanding of the parameters that influence task performance affords a wider selection of experimental procedures for investigating a particular construct, and also provides tools for differentiating the various constructs that may ultimately be of interest. In this review we will more closely examine two behavioral assays commonly used to measure the construct of ‘anxiety’ in adult zebrafish, with the conclusion that they do not both appear to be measuring a single underlying state.

Comparing behavioral responses across multiple assays of stress and anxiety in zebrafish (Danio rerio)

Abstract: Animals encounter stressful situations multiple times throughout their lives and often successfully cope with them. Individuals vary in the nature and intensity of their behavioral and physiological response to stressors, often representing correlated and qualitatively distinct coping styles (e.g., proactive and reactive). These alternative coping styles are ways an animal can overcome a variety of stressful situations, which ultimately can have important fitness consequences. Here we use zebrafish (Danio rerio) recently wild-derived and selectively bred for amount of stationary behavior (High and Low lines) and a classic domesticated strain (AB) to document the utility of these zebrafish strains in understanding coping mechanisms. The Low Stationary Behavior (LSB) line of zebrafish displayed significantly lower stress and anxiety-related behaviors than the High Stationary Behavior (HSB) across six stress and anxiety-related behavioral assays. In some assays, we observed strain differences in behavior within three minutes of the start of the trial. Males also showed reduced levels of anxiety-related behaviors relative to females in two assays. Comparing wild-derived and domesticated strains, the AB line displayed significantly lower levels of anxietyrelated behavior in half of the assays. This study demonstrates that our selectively bred lines from wild-caught zebrafish (HSB, LSB) exhibit consistent and divergent behavioral stress responses across multiple distinct assays. Hence these lines may prove useful in understanding the proximate and ultimate mechanisms of coping with stress and anxiety.

Is there a role for aggression in round goby invasion fronts

Abstract: The role of aggression as a factor promoting invasiveness remains hotly debated. Increased aggression or a lack of tolerance for conspecifics may promote population spread. Some previous research suggests that more aggressive or bold individuals are increasingly likely to disperse and as such these individuals may be overrepresented at the invasion front. In contrast, it has also been argued that individuals at the invasion front represent the least aggressive or least competitive individuals in the population, as these animals are excluded from established areas. Accordingly, the invasion front should be made up of shy, submissive individuals that exhibit reduced aggression. In this study we explore these alternative predictions by quantifying the levels of intra-specific aggression in the round goby (Neogobius melanostomus), an invasive fish that continues to spread rapidly through the Laurentian Great Lakes region in North America. We collected size matched male round goby from an invasion front as well as from an area with an established population, and we staged resource contests between them. Invasion front fish won 65% of the contests and tended to perform more aggressive acts overall. Invasion front fish were not more active or bold prior to the contest, and used the same types of aggressive displays as fish from established areas. Our results also showed that body size asymmetry was an overriding determinant of competitive outcomes, and that body size rather than individual variation in aggressiveness might be the most important contributing factor determining the composition of round goby invasion fronts throughout the Laurentian Great Lakes and its tributaries.

Behavioral responses of sea lamprey (Petromyzon marinus) to a putative alarm cue derived from conspecific and heterospecific sources

Abstract: The sea lamprey, Petromyzon marinus , exhibits a spectacular alarm response to the odor emitted from decayed conspecifics that may differ substantially in function from the well-characterized system in ostariophysan fishes. Here, we report a series of three laboratory experiments designed to characterize the behavioral responses of migratory-phase lampreys to a set of odors derived from conspecific and heterospecific tissues, determine whether sex or sexual maturation alters these responses, and ascertain if the putative alarm substance derives from a particular region of the body. A number of the findings were consistent with the prevailing predator-avoidance paradigm for fish alarm substances released from the skin after predator attack in that: (1) dilute odors derived from freshly ground skin were highly repellent; (2) the substance is contained in the organism early in life; (3) the odor derived from a close relative was avoided whereas those of a distant relative were not; and (4) upon sexual maturity female response to the alarm substance was attenuated. Two interesting patterns arose that differed substantially from the prevailing paradigm: (1) conspecific odors remained repellent after 96 h of aerobic decay; and (2) the cue was emitted from multiple areas of the body, not just the skin, and the repellency of the odor derived from any tissue increased in accordance with its mass. A persistent cue emitted from several sources suggests a broader ecological function than the detection and avoidance of a predator.

Time to recognize zebrafish 'affective' behavior

Abstract: Widely used in biomedical research, zebrafish (Danio rerio) are steadily gaining popularity as a model organism for studying neurobehavioral phenomena. Here, we focus on to the growing spectrum of zebrafish behavioral phenotypes and the ‘bigger’ biological problems these models help to address. Emphasizing the developing potential of zebrafish as a model organism in biological psychiatry, we discuss several questions related to this field: Do zebrafish have ‘emotional’-like behaviors? What are their neural circuits, biomarkers, and ontogenetic origins? And, finally, how can we use this knowledge to build translational bridges to understand human emotions, motivation and personality? Representing a joint effort of several established neurobehavioral laboratories, this article outlines the mounting evidence to support emotionality in zebrafish and other fishes. This conclusion is important to justify the validity of zebrafish ‘affective’ paradigms and their utility for basic/translational research of normal and pathological behaviors.

Parasitism and behavioural syndromes in the fish Gobiomorphus cotidianus

Abstract: It is becoming clear that individual animals exhibit behaviours that are repeatable, consistent and predictable across various contexts and time, and that may be correlated to form behavioural syndromes. The influence of parasitism on host behaviour, although well-documented, is only now being examined in a multi-trait context, and behavioural syndromes provide a framework for such investigations. We test the hypothesis that parasites modify host behavioural syndromes by quantifying the relationship between infection by four trematode species and the correlations, repeatability and consistency of three host behaviours (activity, aggression and boldness) in a freshwater fish, Gobiomorphus cotidianus, in the presence and absence of a predator odour. There was a significant correlation between activity and aggression, and both these behaviour showed higher values in the presence of a chemical predator cue. Of the behaviours tested, only aggression responses were significantly related to infection with one of the parasites, Apatemon sp. Activity, aggression and boldness scores were repeatable across test sessions, but much less so in the presence of a predator cue. Interestingly, individual-level consistency in activity and aggression was significantly associated with infection by Telogaster opisthorchis, Deretrema philippae and/or Apatemon sp., with the direction of the association depending on the behaviour tested. These findings suggest that behavioural syndromes may not only be targets for adaptive host manipulation by parasites, but also that, even if through mere pathology, parasites could act as external agents generating variation in behavioural syndromes.

Improved versions of the Levenshtein distance method for comparing sequence information in animals’ vocalisations: tests using humpback whale song

Abstract: Animals can communicate using visual and acoustic displays to convey information to conspecifics. In some cases, such displays are produced in highly stereotyped and repetitive sequences. Here we use a quantitative analysis technique, the Levenshtein distance, to assess similarity in sequences of displays at both the population and individual levels. We review two existing variations of the method and present two new variations that complement and extend these existing techniques. Three of the methods include the use of a median string sequence and three use a normalisation of the original equation. Humpback whale song theme sequences from multiple populations, years and song types (different variations of the display) are used as examples to illustrate the application and success of each variation. A novel outcome of this technique is that it can produce a threshold measure of similarity to assess when behavioural sequences are so dissimilar that they must be considered different, with a measure of the probability of such clusters being distinct. The Levenshtein distance is applicable to all behavioural data produced in sequences and its use should not be limited to acoustical studies.

Effects of animated images of sympatric predators and abstract shapes on fear responses in zebrafish

Abstract: Previously, zebrafish were shown to respond to the presence of a live predator, the sight of a live predator, moving computer images of a predator, and images of different moving objects in a context and stimulus specific manner. For example, zebrafish showed a robust antipredatory reaction towards a sympatric predator, the Indian leaf fish (Nandus nandus) but not towards an allopatric predator or sympatric or allopatric harmless fish species. In a subsequent study, however, we found zebrafish not to show avoidance in response to the image of another sympatric predator, Xenentodon cancila. The results implied that zebrafish may possess genetic predispositions that allow them to effectively evade at least certain sympatric predators without any prior exposure to them. However, it is not known whether zebrafish can respond to other sympatric predators with antipredatory reactions without any prior exposure to such predators. It is also not known whether such responses may be dependent upon, or idiosyncratic to, predator species. To answer these questions, we examined the effect of computer animated (moving) images of five different predator species all sympatric with zebrafish (Nandus nandus, Channa maculata, Xenentodon cancila, Mystus bleekeri, Chitala chitala) and of two abstract shapes (star and rectangle, also animated) on zebrafish behaviour. The results confirmed that the sight of N. nandus is an aversive stimulus and that the image of X. cancila is not. However, the results also revealed that images of three other species (C. maculata, M. bleekeri, C. chitala) and that of a rectangle induce even more robust aversive reactions than what is elicited by N. nandus. At this point we do not know what features of the images may be perceived as aversive by zebrafish or whether the observed behavioural responses would be adaptive or effective in nature. Nevertheless, we argue that image-presentation based fear paradigms will be useful in future translational research. We also conclude that it may be premature to decide whether zebrafish can recognize their sympatric predators.

Sexual signals of the Amazonian frog Allobates paleovarzensis: geographic variation and stereotypy of acoustic traits

Abstract: Because of its close relationship with the process of evolutionary differentiation, it is expected that geographic variability in acoustic sexual traits should be greater among than within populations. This is particularly expected in organisms with typically high population genetic structure and low dispersal abilities, such as anuran amphibians. We studied the acoustic traits of the advertisement call in the small-sized dendrobatoid frog Allobates paleovarzensis through its range in Central Amazonia. We accessed the variability of call traits from the within-male to the among-population levels, and evaluated the degree of stereotypy of the call characteristics. Call variability had comparable magnitudes within and among populations, and was independent of the degree of stereotypy of call measurements. Therefore, none of the call traits stood out as a potential cue for discrimination between populations. Spectral call measurements were static and strongly related with body size, which explained between 30 and 35% of the variation of these acoustic traits. Temporal characters of the notes were dynamic and influenced by environmental temperature (e.g., 27% of note rate variation), whilst temporal measurements of the entire calls were not related to the co-factors analysed. Both spectral and temporal call traits varied among populations and between sides of the Amazon River. Our results also indicate that body size and sampling site jointly affected the variability of the call traits. However, geographic distances among populations and the river barrier had no significant effect on the overall acoustic variation, indicating that local stabilising selective forces may be important in the process of call differentiation.

Territorial defence behaviour in red squirrels is influenced by local density

Abstract: While many animals defend territories to secure resources such as food and mates, little is known about why territory owners of the same species vary in their territorial defence behaviour. We tested whether potential intruder pressure, defence of offspring, resource-holding potential or aggressiveness of the individual territory owner best explained intraspecific differences in territorial defence in a wild population of North American red squirrels (Tamiasciurus hudsonicus). We assessed territorial defence behaviour of individual red squirrels by recording whether or not they produced territorial vocalizations, known as rattles, both in response to a territorial playback and during natural observation sessions without an experimental stimulus. We compared the relative fit of four a priori models to explain territorial defence intensity in red squirrels and found that rattling behaviour in red squirrels under natural conditions was best explained by the intruder pressure hypothesis. Red squirrels were more likely to vocalize if they were surrounded by a higher density of conspecifics on neighbouring territories, indicating that they adjust territorial defence in response to potential intruder pressure. However, vocalization responses of red squirrels to the playback were not affected by local density, which was reflected in similar support for the four a priori models. The differing effects of local density on red squirrel vocalization rate during natural observations and following playbacks indicates that the effects of local density on the territorial behaviour of red squirrels depends on the particular context in which this behaviour is expressed.

Individual variation in habituation: behaviour over time toward different stimuli in threespine sticklebacks (Gasterosteus aculeatus)

Abstract: Habituation, or the relatively permanent waning of a response as a result of repeated stimulation, is a form of behavioural plasticity that allows animals to filter out irrelevant stimuli and to focus selectively on important stimuli. Individuals that fail to habituate might be at a disadvantage if they continue to respond to irrelevant stimuli; therefore, habituation can have adaptive significance. In this study we compared rates of behaviour over time toward three different ecologically-relevant stimuli (food, a male intruder and a gravid female) in threespine sticklebacks (Gasterosteus aculeatus). We detected evidence for habituation to the stimuli, and males in this study were especially aggressive toward both male and female conspecifics. Although there were some clear temporal patterns that could be detected by looking at average behaviour, not all individuals behaved in the same ‘average’ way. We detected substantial inter-individual variation in behaviour toward all three stimuli, inter-individual variation in rates of habituation to both male and female conspecifics, but no evidence for correlations between behaviours across stimuli (behavioural syndromes). These results suggest that individual animals vary in rates of habituation, and prompt hypotheses about the causes and consequences of variation in rates of habituation.

Structural consistency of behavioural syndromes: does predator training lead to multi-contextual behavioural change?

Abstract: Behavioural syndromes are suites of behaviours that are correlated across multiple contexts. Syndromes may occur in populations because behaviours are tightly linked by underlying mechanisms, such as genetics or physiology, which constrain flexibility and preclude multi-contextual plasticity. Alternatively, correlated behaviours may not share a common mechanism and may be able to change independently, allowing for potentially maladaptive combinations of traits to be broken apart. We tested these two hypotheses by training Trinidadian guppies (Poecilia reticulata) which possessed a behavioural syndrome encompassing three contexts, to avoid a potential predator. While we found no difference in magnitude of behavioural change between the trained and control groups, we did find that all subjects generally became shyer toward a potential predator following training and hypothesise that this resulted from sensitization and a predisposition to quickly recognize and adjust behaviour to predator-like stimuli. Importantly, behavioural changes in response to a potential predator did not generate changes in ‘general activity’ or ‘exploration’, and a tri-contextual syndrome broke apart. Our results suggest that in this population of guppies, individuals differ in behavioural plasticity in terms of their response to experience with predation risk and behaviours across contexts are domain specific and are able to change independently of each other. Future research should focus on populations that evolved in high predation environments and, therefore, may possess more rigid syndromes, to determine whether behavioural flexibility is limited.

Is there a difference in reproductive performance between cooperative and non-cooperative species? A southern African comparison

Abstract: For cooperative breeding to be a strategy under positive selection, individuals should accrue some benefit, or at least not suffer a loss, compared to alternative breeding strategies. Cooperative breeding is often associated with habitat saturation (where the opportunities for pairs to establish new territories are limited), and such species are, thus, assumed to have lower per capita reproductive success than their non-cooperative counterparts. To test whether different breeding strategies affect reproductive success and progression through each breeding stage, we compared cooperative versus non-cooperative breeding strategies across a range of small to medium-sized birds in semi-arid open and grassland habitats in southern Africa. We found that in general, cooperative breeders fledged their young significantly earlier and raised more broods per season than non-cooperative species of similar body mass. Within phylogenetic families, we found cooperative species had shorter nestling periods, and that the duration of the nestling period tended to decline as cooperative group size increased. We then examined in detail two species sharing the same habitat and similar foraging niches, but with different breeding strategies: a cooperative breeder and a biparental breeder. In each species, we followed the fate of breeding attempts from incubation until nutritional independence of young. We found that the cooperative breeder fledged young earlier and invested in overlapping broods more often, resulting in lower nest predation and multiple clutches successfully raised to independence per season. This resulted in more offspring surviving per adult. These results suggest that, due to changes in breeding behavior as a consequence of helper presence (earlier fledging, overlapping broods), cooperative breeding could provide equivalent reproductive success to non-cooperative breeding strategies.

When rank counts — dominant dogs learn better from a human demonstrator in a two-action test

Abstract: Dogs can learn effectively from a human demonstrator in detour tests as well as in different kinds of manipulative tasks. In this experiment we used a novel two-action device from which the target object (a ball) was obtained by tilting a tube either by pulling a rope attached to the end of the tube, or by directly pushing the end of the tube. Tube tilting was relatively easy for naive companion dogs; therefore, the effect of the human demonstration aimed to alter or increase the dogs’ initial preference for tube pushing (according to the behaviour shown by naive dogs in the absence of a human demonstrator). Our results have shown that subjects preferred the demonstrated action in the two-action test. After having witnessed the tube pushing demonstration, dogs performed significantly more tube pushing than the dogs in the rope pulling demonstration group. In contrast, dogs that observed the rope pulling demonstration, performed significantly more similar actions than the subjects of the other demonstration group. The ratio of rope pulling was significantly higher in the rope pulling demonstration group, than in the No Demo (control) group. The overall success of solving the task was also influenced by the social rank of the dog among its conspecific companions at home. Independently of the type of demonstration, dominant dogs solved the task significantly more often than the subordinate dogs did. There was no such difference in the No Demo group.This experiment has shown that a simple two-action device that does not require excessive pre-training, can be suitable for testing social learning in dogs. However, effects of social rank should be taken into account when social learning in dogs is being studied and tested, because dominant and subordinate dogs perform differently after observing a demonstrator.

Aversion to violation of expectations of food distribution: the role of social tolerance and relative dominance in seven primate species

Abstract: Studies on how animals behave when two partners receive different amounts of food have produced variable results, with individuals responding negatively to specific food distributions in some cases (e.g., when food is distributed unequally between partners), but not in others. In this study, we used a simple experimental approach to (i) assess the strictness of dominance relationships based on the degree of social tolerance and (ii) compare the behavioural responses of seven primate species (chimpanzees, Pan troglodytes; bonobos, Pan paniscus; gorillas, Gorilla gorilla; orangutans, Pongo pygmaeus; brown capuchin monkeys, Cebus apella; spider monkeys, Ateles geoffroyi; long-tailed macaques, Macaca fascicularis), when two partners received different amounts of food and no effort was required. We predicted that negative responses (i.e., refusal to participate in the task or avoidance of proximity to the food source) would be elicited by food distributions that violate the individual expectations based on tolerance levels and subject’s dominance rank relative to the partner. In the ‘tolerance’ task, we found that species with less strict dominance relationships were chimpanzees and bonobos, followed by orangutans, spider monkeys, gorillas, brown capuchin monkeys and long-tailed macaques. In the ‘food distribution’ task, capuchin monkeys and especially macaques showed their aversion by refusing to participate in most conditions, including the ones with equal food distribution. When dominants received more food than the partner, subjects of all species maintained a comparable amount of proximity to the food source, possibly reflecting the general acceptance of such a food distribution across species. When dominants received less than or as much as their partners, dominant capuchin monkeys maintained less proximity than other species, possibly because having different expectations of food distributions (i.e., more/all food to the dominant). Our study highlights the importance of the species’ degree of social tolerance and the relative dominance rank between partners in the study of violation of expectations of different food distributions.

Predation pressure and food abundance during early life alter risk-taking behaviour and growth of guppies (Poecilia reticulata)

Abstract: The trade-off between predation risk and the need to feed is one of the major constraints animals have to cope with. Virtually all animals have a higher risk of being preyed upon when being active (e.g., searching for food or mating partners), compared with being inactive (e.g., staying at their burrows, nests, etc.). Yet, staying safe leads to a higher risk of starvation and may reduce reproductive success and body growth. Hence selection on behaviour optimizing the search, handling and digestion of food while avoiding the risk of predation is strong and should lead to strategies maximising survival chances and inclusive fitness. These facts call for integrative studies manipulating both, abundance of food and predation risk in a factorial set up, analysing the effects of both factors on behaviour and physiological parameters. We present results of a 2 × 2 factorial experiment, manipulating risk of predation and food abundance in guppies. We found that the two factors have an additive effect on body growth, but that predation risk by a pike cichlid is the main factor affecting the expression of behavioural strategies in guppies. Low food availability and high predation risk led to lower body growth. High predation risk affected swimming depth and risk sensitivity of guppies and might represent adaptive behavioural changes to the environmental context experienced in early life. Our study shows that integrative studies, analysing multiple interdependent and interconnected factors in the wild and in the lab are needed to further understand animal behaviour and development.

Dual function of egg-covering in the Kentish plover Charadrius alexandrinus

Abstract: Many bird species take recesses during incubation, and while the nests are unattended, the eggs may both be vulnerable to predation and reach suboptimal temperatures for embryo development. Perhaps to avoid these negative possibilities, some birds cover their eggs with materials when they depart from nests. We examined experimentally, using the ground-nesting Kentish plover as model species, whether egg-covering allows egg temperatures to remain within optimal limits for embryogenesis in unattended nests, thus reducing the requirements of contact incubation, and simultaneously maintain the eggs’ camouflage. There was a negative relationship between nest attendance and ambient temperature, but only during mid-morning, the period of the day when eggcovering was most frequent. Indeed, during mid-morning egg-covering not only served to better camouflage the eggs, but also to maintain egg temperatures within optimal thermal thresholds for embryogenesis while the nests remained unattended. During other periods of the day, covered eggs in unattended nests overheated (e.g., afternoon) or did not reach the optimal temperature for embryogenesis (e.g., early morning). During periods in which eggs may be uncovered to alleviate overheating, unattended nests may be easier to locate by predators, because the eggs are less well camouflaged. Therefore, camouflage and appropriate thermal environment are inseparable functions of egg-covering in the ground-nesting Kentish plover.

Vocal behavior of the Mongolian gerbil in a seminatural enclosure

Abstract: This study represents the first effort to obtain a comprehensive library of adult Mongolian gerbil (Meriones unguiculatus) vocalizations recorded in a variety of behavioural contexts. In Phase I of the study, a gerbil colony was introduced into a seminatural enclosure and allowed to breed naturally over an observation period of 19 months. During this period, detailed observations of gerbil social and vocal behaviour were made. In Phase II, this knowledge was used to stage natural behavioural scenarios among adult gerbils in which high-quality recordings of vocalizations could be obtained, and the spectro-temporal properties of these vocalizations analysed. Calls generally occurred in interactive social situations, such as same-sex aggression, mating, food dispute, alarm, and disturbance by conspecifics. Additionally, brief ultrasonic calls were associated with investigation of a new setting and were named ‘contact calls’. Vocalizations were classified by behavioural context and analysed with respect to spectral and temporal characteristics. Calls encompassed a broad range of frequencies (approx. 3-45 kHz); most calls possessed significant energy at two or more harmonics in addition to the fundamental frequency. Calls generally lasted approx. 4-500 ms and were emitted in sequences of 3-20 variants with silent intervals. Such natural call series had significant low-frequency AM content below 8 Hz. Calls within an individual behavioural class had substantial variability in both spectral and temporal properties, but were significantly different from all other call classes in one or more of average fundamental frequency, frequency sweep range, duration, or frequency sweep direction.

Behavioral characteristics of pair bonding in the black tufted-ear marmoset (Callithrix penicillata)

Abstract: The present study describes how the development of a pair bond modifies social, sexual and aggressive behavior. Five heterosexual pairs of marmosets, previously unknown to each other, were formed at the beginning of the study. At the onset of pairing, social, sexual, exploratory and aggressive behaviors were recorded for 40 min. The animals were then observed for 20 min, both in the morning and afternoon for 21 days. The frequency and/or duration of behaviors recorded on Day 1 were compared to those recorded at later observations. The behavior displayed shortly after pairing should be completely unaffected by the pair bond, while such a bond should be present at later observations. Thus, it was possible to determine how the behavior between the pair was modified by the development of a pair bond. Social behaviors increased from Day 1 to Days 2-6 and all subsequent days observed. Conversely, other behaviors, such as open mouth displays (usually considered to be an invitation to sexual activity), had a high frequency during the early part of cohabitation but declined towards the end. Consequently, pair bonding manifests itself in an increased intensity of social behaviors. It is suggested that the intrinsically rewarding properties of grooming and perhaps other social behaviors turn the pair mate into a positive incentive, activating approach and further interactions when possible. Thus, the pair bond may be a motivational state activated by the conditioned incentive properties of the partner. This notion can explain all forms of pair bonds, including those occurring between individuals of the same sex and in promiscuous species.

Asymmetrical signal content of egg shape as predictor of egg rejection by great reed warblers, hosts of the common cuckoo

Abstract: The size, patterning and coloration of bird eggs may signal different information content to nest owners, mates, predators, hosts, or brood parasites. Recent studies suggested that the pigmentation at one pole of the typically asymmetrical avian egg plays a critical role in the discrimination of own and foreign eggs by several host species parasitized by the common cuckoo (Cuculus canorus). Typically, both eggshell maculation and background colour are more consistent on the blunt pole, and hosts react more strongly to experimental changes in coloration of the blunt pole compared to the sharp pole. However, it remains unclear whether the asymmetrical shape of natural eggs per se enhances the behavioural responses of hosts to foreign eggs. To evaluate the salience of asymmetrical egg shape, we studied reactions of a rejecter cuckoo host, the great reed warbler (Acrocephalus arundinaceus), to artificial shapes of model eggs painted a non-mimetic blue colour. Artificial eggs with two blunt poles were rejected significantly more often than those with a single blunt pole or two sharp poles. These results corroborate the hypothesis that the different egg poles have different signal salience and may have implications for the evolution of diversity of not only egg coloration but also of egg shape in the arms race between hosts and brood parasitic birds.

Chimpanzee interactions with nonhuman species in an anthropogenic habitat

Abstract: Interactions between wildlife species are numerous and diverse, ranging from commensalism to predation. Information on cross-species interactions in anthropogenic habitats are rare but can serve to improve our understanding of animal behavioural and ecological flexibility in response to human-induced changes. Here we report direct observations of interactions between chimpanzees (Pan troglodytes verus) and wild and domesticated species in a forest-farm mosaic at Bossou, Guinea, recorded between 1997 and 2009. The low diversity and abundance of wildlife, in particular typical chimpanzee prey species, are reflected in both the low interaction rates (one interaction per 400 observation hours) and the low number of species with which chimpanzees interacted (nine species, mostly mammals, but also birds and reptiles). Chimpanzees generally chose either to make direct physical contact with a species or not; interactions that involved direct contact lasted longer than noncontacts. Interactions with mammals showed the greatest diversity in nature and duration. Adults most often consumed a captured animal, while immatures most often engaged in playful behaviours with other species. Immatures also exhibited distinctive accompanying behaviours whereas adults rarely did so. Species-specific behaviours that depend on the age-class of the interactant are consistent with the idea that chimpanzees categorise different animals. We anticipate that chimpanzee interactions with sympatric species inhabiting humanised habitats will change over time to include more domesticated species. Conservation management strategies should anticipate behavioural flexibility in response to changing landscapes.

Song repertoire size correlates with measures of body size in Eurasian blackbirds

Abstract: In most oscine bird species males possess a repertoire of different song patterns. The size of these repertoires is assumed to serve as an honest signal of male quality. The Eurasian blackbird’s (Turdus merula) song contains a large repertoire of different element types with a flexible song organisation. Here we investigated whether repertoire size in Eurasian blackbirds correlates with measures of body size, namely length of wing, 8th primary, beak and tarsus. So far, very few studies have investigated species with large repertoires and a flexible song organisation in this context. We found positive correlations, meaning that larger males had larger repertoires. Larger males may have better fighting abilities and, thus, advantages in territorial defence. Larger structural body size may also reflect better conditions during early development. Therefore, under the assumption that body size is linked to overall male quality, our results are in accordance with the hypothesis that repertoire size represents an honest signal in Eurasian blackbirds that has evolved in response to sexual selection.

Muscular hypertrophy of urinary bladders in dominant tilapia facilitates the control of aggression through urinary signals

Abstract: The urination pattern of the Mozambique tilapia (Oreochromis mossambicus) depends on social context, and the olfactory potency of urine released depends on social rank (males) and reproductive status (females). This strongly suggests that urine mediates chemical communication in this species. The current study tested, firstly, whether urine production rate depends on sex or social status and, secondly, whether differences in urination pattern and volume of urine stored are associated with variation in the morphology of the urinary bladder. Finally, the effect of urination during aggressive male–male interactions was assessed. Urine production in catheterized fish depended neither on sex nor social status (males). Nevertheless, males had larger kidneys than females. Dominant males had heavier urinary bladders than subordinate males or females, mainly due to enlarged muscle fibres, thicker urothelium and a thicker smooth muscle layer. In male pairs wherein urination was prevented by temporary constriction of the genital papillae, social interaction escalated to aggression (mouth-to-mouth fighting) more rapidly and frequently than control pairs. This was accompanied by elevated plasma testosterone and 11-ketotestosterone levels. In control encounters, the male that initiated the aggressive behaviour was usually the winner of the subsequent fight; this did not happen when the males could not urinate. These results suggest that the larger, more muscular bladder of dominant males is an adaptation, facilitating higher urination frequency, post-renal modulation and storage of larger urine volumes for longer. It is likely that urinary pheromones modulate aggression in male–male encounters by providing information on the social rank and/or motivation of the emitter; males are unlikely to invest in costly highly aggressive

The role of various sensory inputs in establishing social hierarchies in crayfish

Abstract: Crayfish form social hierarchies through agonistic interactions. During formation of social hierarchies, individual crayfish establish dominance by signalling status through olfaction, vision and touch. Our study investigated which of these three sensory modalities played the most important role in establishing dominance in rusty crayfish (Orconectes rusticus). Olfaction, vision and touch were systematically impaired in staged triadic and dyadic agonistic interactions to determine the relative contribution of each sensory input. Our results suggest that olfaction is the most important sensory modality during the initial formation of dominance hierarchies in rusty crayfish. Using olfaction alone, crayfish were capable of communicating social status with sensory competent crayfish; without full olfactory ability crayfish were unable to effectively establish dominance. Vision and touch were also found to play practical roles in reducing unnecessary risk; with antennae for touch, functionally reducing the number of fight initiations, and vision allowing a crayfish under imminent attack to ready itself, strike first, or retreat.

Exploring novelty: a component trait of behavioural syndromes in a colonial fish.

Abstract: Individual differences in exploratory behaviour have been shown to be consistent across contexts and suggested to be part of behavioural syndromes in a diversity of species, including fish. Exploration has also been shown to be a key factor in understanding complex ecological processes such as sexual selection and cooperation. Another important question in ecology is why animals breed in colonies. Exploration syndromes, by affecting prospecting behaviour, dispersal and public information use may also contribute to our understanding of coloniality. This study aims at investigating whether an exploration syndrome exists in a colonial fish species, Neolamprologus caudopunctatus. Individuals of this species were subjected to two consecutive tests, a novel environment and a novel object test. Results show that more explorative individuals in a novel environment are also less neophobic in the presence of a novel object, suggesting that the tendency to engage with novelty per se is a consistent trait and part of an exploration syndrome. These results are discussed in light of the contribution of an exploration syndrome to explain colony formation in animals.

Energetics of calling in the male treefrog Hyla arborea: when being large means being sexy at low cost

Abstract: Female mate choice is often thought to be based on signals that honestly reflect male quality as a potential mate. However, while particularly costly acoustic signals have often been studied, the existence of differences in energetic costs among males has rarely been considered. These differences may be decisive in many ‘income breeding’ species in which males face a trade-off between calling in order to attract females and foraging to renew their energetic reserves. We thus examined calling energetic costs in an income breeder, Hyla arborea (L.), known to produce costly energetic calls, in order to explore the sources of inter-individual variability. After an arginine vasotocin injection, we determined the relationships between energetic costs (via oxygen consumption), call characteristics and male morphology. We found a strong variation in male calling energetic costs. For the same call rate, some males consumed oxygen at a rate four times greater than others. This difference was mainly explained by male size, bigger males consuming less oxygen per gram of tissues than smaller ones during calling. In addition, an acoustic parameter, within bout call rate, also influenced the energetic cost of emitted signals. These findings highlight the importance of calling energetic cost in income breeding species which have strong consequences on sexual selection processes. Indeed, energetic constraints are key parameters to understand the inter-individual variation in call characteristics. Males with a reduced cost may increase their chorus tenure and/or the attractiveness of their calls. Regarding female mate choice, choosing a big male may involve indirect benefits linked both to male size and to calling cost.

Red-crested cardinal defences against shiny cowbird parasitism

Abstract: Avian brood parasites reduce the reproductive success of the host, which favours the evolution of antiparasitic defences, such as aggression towards parasites or rejection of their eggs. The red-crested cardinal, Paroaria coronata, is a potential good-quality host of the shiny cowbird, Molothrus bonariensis. However, the frequency of cowbird parasitism in cardinal nests is very low and there are no records of this host raising parasite’s chicks, which suggest that it may have evolved effective antiparasitic defences. We studied cardinal antiparasitic defences by: (1) presenting dummy models of a female cowbird and non-predator and predator control species to nests during laying and incubation, and (2) conducting experiments of artificial parasitism with natural cowbird eggs of different morphs and conspecific eggs during laying and early and late incubation. We found that: (1) the frequency of cowbird parasitism in cardinal nests was 7%, (2) cardinals did not exhibit aggressive behaviours towards cowbird or nonpredator models but responded aggressively towards a predator model, (3) they rejected parasite eggs in 98.5% of the cases (mostly through egg ejection), but conspecific eggs in only 6% of the cases, (4) there were no costs (breakage or ejection of their own eggs) associated with ejection of the parasite’s eggs, and (5) a relatively low frequency of parasitism is enough selection pressure to maintain egg rejection at a high level. The antagonistic expression of antiparasitic defences in red-crested cardinals suggests that they may have lost the behaviour of aggression towards the parasite as a result of associated costs.

Zebrafish (Danio rerio) models of substance abuse:: harnessing the capabilities

Abstract: Zebrafish are fast becoming one of the most widely used animal models in systems biology and developmental genetics, but their potential as models for behavioural neuroscience is only just beginning to be realised. This progress is dependent upon the rate at which behavioural assays for adult zebrafish are designed, reported and validated. As models for drug abuse and addiction, this species has been shown thus far to show high face validity, in that they show robust place preference for drug-related cues, as well as evidence for withdrawal, relapse and compulsive drug seeking. This review will outline the case for using zebrafish as models to study endophenotypes relating to drug addiction.

Why fight? Selective forces favoring between-group aggression in a variably pair-living primate, the white-faced saki (Pithecia pithecia)

Abstract: Between-group aggression is a common feature of many group-living animals. Yet aggressive behaviors are often costly, involving risk of injury, increased energy expenditure and the potential to reduce feeding time. For aggression to be evolutionarily advantageous these costs must be outweighed by the benefits gained from exclusive access to resources and/or mates, or through committing infanticide. However, the dynamics favoring aggression in species living in small groups may differ from those in larger groups since mating exclusivity is higher and the potential to numerically dominate opponents is lower. We examined the selective factors influencing between-group aggression in a primate that lives in both pairs and small groups, the white-faced saki monkey (Pithecia pithecia). Data were collected on three free-ranging groups at Brownsberg Naturepark (Suriname) over 17 months. Intergroup encounter frequency and intensity of aggression during encounters were compared to temporal changes in diet, variation in ovarian hormones, frequency of copulations and the presence of dependent infants. Participation in between-group aggression was heavily male-biased and the presence of cycling females was a significant predictor of aggression frequency. Percentage of mesocarp in the diet also had a significant effect on the frequency and the intensity of aggression, with high mesocarp consumption corresponding to increased aggression. Presence of dependent infants did not affect between-group aggression. Our results support both the male mate defense and male resource defense hypotheses, suggesting that male reproductive interests are the principle selective pressures acting on between-group aggression in white-faced sakis. White-faced sakis’ rigid conformity to traditional expectations of male intrasexual intolerance appears to be unique among primates living in small groups with variable mating systems.