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Within species, bird parents defend their nests with different levels of intensity. Previous studies have examined several hypotheses for this variation by looking at factors such as morphological characteristics of the parents and the characteristics of the brood, but few have controlled for multiple factors simultaneously. Here we examined a broad range of factors that may influence the nest defense behaviour of Mountain Bluebirds ( Sialia currucoides (Bechstein, 1798)), including the adult's morphology (sex, age, plumage colour, body size, and body condition) and characteristics of their brood (size, hatch date, and stage of nestling development). Parental aggression was triggered using a taxidermy mount of an American red squirrel ( Tamiasciurus hudsonicus (Erxleben, 1777)). We found no relationship between nest defense and any morphological characteristic of adults, but the intensity of nest defense was positively correlated with the stage of offspring development, clutch size, and hatch date consistent with parental investment theory. Males also defended nests more strongly than females, consistent with the premise of the renesting hypothesis that males have fewer future opportunities to breed and, therefore, are more invested in the current brood. Our results provide strong support for parental investment theory and renesting as the primary drivers of nest defense intensity in breeding birds.

Overwintering in shallow habitats presents a serious obstacle for aquatic invertebrates. Here we investigated the little-known ability of water boatmen (Hemiptera: Corixidae), an aquatic insect, to survive the winter encased in air pockets within the ice of shallow wetlands. We extracted and experimentally thawed large blocks of ice from prairie wetlands in Saskatchewan, Canada, from which we examined the species composition and revival of corixids. While multiple corixid species were present in wetlands prior to freeze-up, a single species, Cymatia americana Hussey, 1920, comprised the vast majority of corixids that were found within the ice later in winter. Only 4%–9% of corixids, all Cymatia americana, revived after ice thawing over both study years. Being encased within an air pocket appeared to be necessary for the survival of corixids in the ice, with up to 300 individuals grouped together. Other invertebrate taxa also revived after thawing, including Haliplidae and Dytiscidae (Coleoptera) encased within air pockets both alongside corixids and on their own, as well as Coenagrionidae (Odonata), Phryganeidae and Leptoceridae (Trichoptera), Chironomidae (Diptera), and Physidae and Planorbidae (Basommatophora), which appeared to be encased in solid ice. The ability to overwinter inside ice represents a little understood survival mechanism of aquatic invertebrates in shallow wetlands, which could confer energetic and reproductive advantages to those that endure until spring.

Predator avoidance often comes at the cost of reduced foraging and mating opportunities, and therefore, prey animals are often highly attuned to variation in risk. Indeed, individuals capable of detecting threats early in life are at an advantage because they may be better able to escape risks than their naive peers. Some prey organisms, including embryonic prey, can learn to recognize new predators and may even incorporate information on the degree of threat involved. Prey organisms that evaluate the intensity of a threat and modify their behaviours accordingly should have a distinct advantage by being able to seize opportunities in low-risk situations. Graded behavioural responses that vary depending on threat levels are referred to as threat sensitive. Here we show that embryonic minnows are not only capable of learning to recognize novel predators, but do so in a threat-sensitive manner, such that fish responded with an intensity correlated to the degree of the threat to which they were exposed in the egg. Subsequent to embryonic exposure to one of three different concentrations of alarm cue paired with a novel predator odour, juvenile fish from all three groups responded to predator odour by reducing their movement. However, only those exposed to the pairing with the highest concentration of alarm cue later increased their shelter use. These responses were maintained over the course of 10 months.

Coral reef ecosystems are currently under unprecedented stress due to anthropogenic induced climate change. Such stress causes coral habitats to degrade, which has been found to negatively impact the behaviour of some reef fishes. However, it is unknown whether the same chemical stresses from degraded habitats that impacts fish behaviour also impacts energy supporting swimming performance traits of fishes during the pelagic-to-reef life-history bottleneck. Here, we exposed newly settled juvenile Ambon damselfishes (Pomacentrus amboinensis) to either water that had passed over healthy or degraded coral for 24 h. Fishes were then swum at an ecologically relevant swimming speed for 200 min, and oxygen uptake rates were measured periodically. In general, fish swimming in water from degraded coral depressed oxygen uptake rates by 21%, which suggests that degraded habitats can have strong effects on fish physiology during this ecologically-critical time window.

A prerequisite for effective antipredator responses is the ability of a prey to distinguish animals that pose a threat from those that do not. Prey often have efficient learning mechanisms to learn threats but learning to recognize nonpredators may be equally or more important. Moreover, the ability to generalize learned information is of key importance for prey animals. Prey take information they know about one species to make ‘educated guesses’ about the predatory/nonpredatory status of other unknown species. Here, we investigate the ability of Whitetail damselfish Pomacentrus chrysurus to learn the identity of non‐predators and then generalize their responses to other unknown animals. Our work is completed within the context of unprecedented habitat degradation in reef ecosystems. When corals die, the remaining skeleton is colonized by algae, cyanobacteria and sessile invertebrates. These opportunistic colonists change the physical and chemical landscape of the reef and hence the background odour in which predator and non‐predator recognition occurs. Our results indicated that Whitetail damselfish learn to classify Moonwrasse Thalasomma lunare as a non‐predator through the process of latent inhibition, whereby the prey are repeatedly exposed to Moonwrasse odour multiple times in the absence of negative reinforcement. These fish subsequently generalized their nonpredator recognition to other unknown wrasse, but not distantly related fish. Of key importance was our finding that the patterns and extent of non‐predator learning and generalization were dramatically altered in dead coral habitats. As predicted, prey that learned the Moonwrasse as a nonpredator in live coral environments did not subsequently respond to Moonwrasse when we tried to teach them Moonwrasse was a predator in live coral. However, this non‐predator recognition was reduced in dead coral environments. Moreover, generalization completely failed when we changed from live to dead coral environments. Juvenile damselfishes need to rapidly catalogue the identity of unknown animals when they arrive at a reef. Changing background odours, that occur with changing tides and currents, means that prey need to learn non‐predator identities separately in each water source. This cognitive challenge likely has significant survival consequence in a changing environment. A free Plain Language Summary can be found within the Supporting Information of this article.

The transmission of many parasites, particularly those with complex life cycles, can only occur when infective stages that are present in one host are consumed by another host. Parasites can enhance rates of transmission by altering the behaviour, coloration or conspicuousness of infected hosts that require ingestion by a predator in which parasite reproduction occurs (i.e. the definitive host). But such enhancement will impose costs if it also facilitates the transmission of infective stages into nonhosts that are incompatible with parasite development and reproduction. We assessed these potential costs in fathead minnows, Pimephales promelas, exposed to larvae of a brain-encysting trematode, Ornithodiplostomum ptychocheilus. We evaluated minnow antipredator escape responses immediately after they received visual stimuli from simulated host and nonhost predators. Our results show that mean response latencies of infected minnows were 12% greater than uninfected minnows when they were threatened with horizontally approaching stimuli (simulating a nonhost predator) regardless of infection level and regardless of parasite development stage. Response latencies of minnows exposed to vertically approaching stimuli (simulating a host predator) were lower than in controls, but the differences were not significant. In this case of parasite-induced alteration of host behaviour, the alteration enhances transmission into nonhosts. Costs associated with enhanced transmission into nonhosts likely constrains the development of specific parasite-induced alterations of host phenotypes in other host–parasite interactions that require predation of infected hosts.

[Extract:] In their study, Clark et al. suggest that previous studies on the effects of elevated levels of CO2 on the behaviour of coral reef fishes are not repeatable and that ocean acidification does not impair the behaviour of coral reef fishes, even though six significant behavioural effects were detected in their study, each of which was dismissed for a different reason. They then compare the means and variances of six previous ocean acidification studies in fish with a data distribution that is derived from a multi-species compilation of their own data to conclude that the results of previous studies are statistically improbable. However, Clark et al. did not closely repeat previous studies, as they did not replicate key species, used different life stages and ecological histories and changed methods in important ways that reduce the likelihood of detecting the effects of ocean acidification.

Neophobia, the fear response of organisms towards novel cues, is a phenotypically plastic trait that manifests among prey that experience uncertain, often high levels of risk. Prey that find themselves in uncertain or highly variable risk environments over ecological and evolutionary time could benefit from reducing the costs associated with ‘making a bad decision’ when they detect novel or unknown predatory threat. Hence, understanding ecological uncertainty in the context of prey decision making is of key interest. While ecological uncertainty remains a poorly defined concept, the degree of uncertainty experienced by prey, and by extension neophobia, should be influenced by the predictability of risk. Here, we test whether prey exposed to the same overall level of predation risk exhibit stronger neophobic responses towards a standardized novel cue when they experience the risk in an unpredictable versus predicable manner. Northern red-bellied dace, Chrosomus eos, exposed to conspecific alarm cues (risk cue) over a 3-day period exhibited a stronger intensity of neophobia than those exposed to low-level risk. However, if the alarm cues were presented as three exposures ranging in volume, the dace exhibited stronger neophobic responses compared to dace exposed to three equal exposures per day. Similarly, our second experiment showed that dace exposed over 3 days to elevated risk at random versus consistent times each day had stronger neophobic response under the random schedule. Combined, our results demonstrate that the degree of predictability of risk is a critical factor determining uncertainty and neophobia exhibited by prey populations.

1. An increasing number of coral reefs throughout the world have become degraded as a result of climate change. This degradation has resulted in a significant decline in local biodiversity. Studies have shown that some fishes (non‐responders) within these altered habitats are not able to adequately access olfactory cues, specifically chemical alarm cues that are crucial in mediating predation risk. 2. We propose that the inability to access this crucial information is a potential mechanism for increased mortality of these species under natural conditions. However, we posit that the presence of certain key species (responders that are unaffected by degradation) may buffer the handicap of non‐responders by providing an alternate source of information. 3. To explore this hypothesis, we investigated if a high ratio of responders to non‐responders could mitigate the impact of information loss for the affected species. Using mesocosms, we manipulated the ratio of two damselfish species, Pomacentrus chrysurus (responder) and P. moluccensis (non‐responder), to determine if community composition can be predictive of information transfer about predation threats in nearby non‐responder individuals. 4. Our results indicate that, in degraded environments, the magnitude of fear effects seen in P. moluccensis exposed to a predator was proportional to the number of P. chrysurus present and consumed by the predator in the community. This indicates that P. chrysurus became the only functional source of predation‐related information for P. moluccensis in degraded habitats. These results contrasted with those from live coral environments, where all individuals exhibited fear effects, regardless of community composition. 5. Our study provides evidence that the presence of non‐affected species in the community provides a potential mechanism allowing increased resilience by affected species, therefore providing another example of the way biodiversity affects ecological resilience of species in changing ecosystems.

Lateralization of cognitive functions impacts many behaviours related to fitness and, in most species, varies greatly among individuals. Laboratory and field studies have suggested that within-species variation in lateralization is partly due to phenotypic plasticity. For example, in fish, prey that have experienced predation risk during early ontogeny develop highly lateralized phenotypes, and this lateralization often favours prey in evading predators. In contexts other than predation, plasticity of lateralization has also been reported for adult fish. Therefore, we asked whether adult fathead minnows, Pimephales promelas, exposed to high predation risk would also show plasticity linked to increase lateralization. We exposed minnows to conspecific alarm cues for up to 8 days to simulate predation risk and tested their lateralization with a standard detour test. The treatment affected lateralization but in an unexpected direction: Individuals exposed to high predation risk showed lower lateralization scores compared to control fish. In addition, fish within groups exposed to risk reduced the variability in their directionality of lateralization; that is, they showed a similar turning preference in the detour task. Our study suggests that lateralization can vary in response to predation risk in adult fish. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

The ability of prey to assess predation risk is fundamental to their success. It is routinely assumed that predator cues do not vary in reliability across levels of predation risk. We propose that cues can differ in how precisely they indicate different levels of predation risk. What we call danger cues precisely indicate high risk levels, while safety cues precisely indicate low risk levels. Using optimality modeling, we find that prey fitness is increased when prey pay more attention to safety cues than to danger cues. This fitness advantage is greater when prey need to protect assets, predators are more dangerous, or predation risk increases at an accelerating rate with prey foraging efforts. Each of these conditions lead to prey foraging less when estimated predation risk is higher. Danger cues have less value than safety cues because they give precise information about risk when it is high, but prey behavior varies little when risk is high. Safety cues give precise information about levels of risk where prey behavior varies. These results highlight how our fascination with predators may have biased the way that we study predator-prey interactions and focused too exclusively on cues that clearly indicate the presence of predator rather than cues that clearly indicate their absence.

Lake food web structure dictates the flow of energy and contaminants to top predators, and addition of invasive species can shift these flows. We examined trophic position (TP), proportional reliance on the littoral zone (Proplittoral), and mercury (Hg) concentrations across the life-span of two predatory fishes, walleye (Sander vitreus) and northern pike (Esox lucius), in lakes with and without invasive virile crayfish (Faxonius virilis). The littoral zone was the dominant foraging zone for both species regardless of size, accounting for 59% and 80% of the diet of walleye and pike, respectively. Both species increased in TP and Hg with body size, as did crayfish. Walleye in crayfish-present lakes had lower Proplittoral, TP, and Hg concentrations compared with non-present lakes, but trophic magnification of Hg through the food web was consistent across all six lakes. These findings underscore a strong role for the littoral zone in channeling energy and contaminants to higher trophic levels and how invasive species can occupy new habitats at low abundance while altering food web structure and contaminant bioaccumulation.

Aquatic prey can gauge predation risk using chemical information, including chemical alarm cues — released when prey are injured, disturbance cues — released when prey are threatened, or the odour of the predator itself. While a lot of work has focused on alarm cues, disturbance cues remained poorly studied in freshwater systems, and has been virtually omitted in marine ones. In the current study, we document the first evidence of disturbance cue use in a marine fish. Juvenile damselfish Pomacentrus nagasakiensis were exposed to cues from undisturbed or disturbed conspecifics, a water control (negative control) and conspecific alarm cues (positive control). Juveniles displayed increased antipredator responses when exposed to alarm cues and disturbed conspecifics, but not when exposed to undisturbed ones. In addition, we demonstrated that disturbance cues, just like alarm cues, could mediate learned predator recognition, a phenomenon undemonstrated in freshwater fishes. Given disturbance cues are thought to be comprised of nitrogenous waste, it has been hypothesised that the constant and dilute release of such products in the hypotonic freshwater environment results in a high level of ‘background chemical’ noise masking subsequent releases. Extending this hypothesis, we propose that in the marine environment, disturbance cues are more easily detected due to low background noise. Prey animals must accurately assess their current predation risk. Aquatic prey rely on chemical cues to gain information on risk. These cues can include odours released when nearby prey are damaged or disturbed, or the odour of a known predator. Prey exposed to a novel odour for the first time must learn if the odour is an indication of risk or benign. This is accomplished when the odour of a known risk (e.g. cues released from a damaged individual) is paired with a novel odour (e.g. a novel predator). In the current paper, we show for the first time that coral reef fishes can use disturbance cues (cues released when prey are chased or otherwise disturbed) as a ‘known risk’ and when paired with a novel odour, are subsequently able to respond to the novel odour when presented alone.

Living in mix-species aggregations provides animals with substantive anti-predator, foraging and locomotory advantages while simultaneously exposing them to costs, including increased competition and pathogen exposure. Given each species possess unique morphology, competitive ability, parasite vulnerability and predator defences, we can surmise that each species in mixed groups will experience a unique set of trade-offs. In addition to this unique balance, each species must also contend with anthropogenic changes, a relatively new, and rapidly increasing phenomenon, that adds further complexity to any system. This complex balance of biotic and abiotic factors is on full display in the exceptionally diverse, yet anthropogenically degraded, Great Barrier Reef of Australia. One such example within this intricate ecosystem is the inability of some damselfish to utilize their own chemical alarm cues within degraded habitats, leaving them exposed to increased predation risk. These cues, which are released when the skin is damaged, warn nearby individuals of increased predation risk and act as a crucial associative learning tool. Normally, a single exposure of alarm cues paired with an unknown predator odour facilitates learning of that new odour as dangerous. Here, we show that Ambon damselfish, Pomacentrus amboinensis, a species with impaired alarm responses in degraded habitats, failed to learn a novel predator odour as risky when associated with chemical alarm cues. However, in the same degraded habitats, the same species learned to recognize a novel predator as risky when the predator odour was paired with alarm cues of the closely related, and co-occurring, whitetail damselfish, Pomacentrus chrysurus. The importance of this learning opportunity was underscored in a survival experiment which demonstrated that fish in degraded habitats trained with heterospecific alarm cues, had higher survival than those we tried to train with conspecific alarm cues. From these data, we conclude that redundancy in learning mechanisms among prey guild members may lead to increased stability in rapidly changing environments.

Antidepressant (AD) drugs are widely prescribed for the treatment of psychiatric disorders, including depression and anxiety disorders. The continuous use of ADs causes significant quantities of these bioactive chemicals to enter the aquatic ecosystems mainly through wastewater effluent discharge. This may result in many aquatic organisms being inadvertently affected by these drugs. Fluoxetine (FLX) and venlafaxine (VEN) are currently among the most widely detected ADs in aquatic systems. A growing body of experimental evidence demonstrates that FLX and VEN have a substantial capacity to induce neurotoxicity and cause behavioral dysfunctions in a wide range of teleost species. At the same time, these studies often report seemingly contradictory results that are confounding in nature. Hence, we clearly require comprehensive reviews that attempt to find overarching patterns and establish possible causes for these variable results. This review aims to explore the current state of knowledge regarding the neurobehavioral effects of FLX and VEN on fishes. This study also discusses the potential mechanistic linkage between the neurotoxicity of ADs and behavioral dysfunction and identifies key knowledge gaps and areas for future research. Copyright © 2021 Elsevier B.V. All rights reserved.

Organisms are exposed to a wealth of chemical information during their development. Some of these chemical cues indicate present or future dangers, such as the presence of predators that feed on either the developing embryos or their nearby parents. Organisms may use this information to modify their morphology or life-history, including hatching timing, or may retain information about risk until it gains relevance. Previous research has shown predation-induced alterations in hatching among embryonic minnows that were exposed to mechanical-injury-released alarm cues from conspecific embryos. Here, we test whether minnows likewise hatch early in response to alarm cues from injured adult conspecifics. We know that embryonic minnows can detect adult alarm cues and use them to facilitate learned recognition of predators; however, it is unknown whether these adult alarm cues will also induce a change in hatching time. Early hatching may allow animals to rapidly disperse away from potential predators, but late hatching may allow animals to grow and develop structures that allow them to effectively escape when they do hatch. Here, we found here that unlike embryonic fathead minnows (Pimephales promelas) exposed to embryonic cues, embryonic minnows exposed to adult alarm cues do not exhibit early hatching. The ability of embryos to recognize adult alarm cues as a future threat, but not a current one, demonstrates sophisticated ontogenetic specificity in the hatching response of embryonic minnows.

Within tropical coastal habitats such as coral reefs and seagrass meadows, sea anemones (Actiniaria) provide microhabitats for a diverse range of fauna. However, the mechanisms that enable these interactions, and how actiniarian diversity and abundance mediates associate assemblages, remains poorly understood. Here, we compared sea anemone species richness and abundance with that of their associated decapod crustaceans and teleost fishes across adjacent coral reef and seagrass habitats at Carrie Bow Cay, Belize. At least 16 decapod and seven fish species were associated with anemones across both habitats, including several previously undocumented associations. While overall anemone-associate richness did not differ between habitats, seagrass anemones had the greatest mean abundance and diversity of both decapod and fish associates. This suggests that the importance of anemones as microhabitat reflected broader benthic complexity and shelter availability, with species aggregating on sea anemones when access to alternative shelter, such as corals, was limited. Patterns of associate distributions on anemones were also highly structured, in terms of both associate and anemone species, with these patterns likely reflecting a combination of associate specialization, intraspecific competition, and anemone morphology and toxicity. The diverse multi-species associate complexes observed suggest that sea anemones provide an important refuge for both specialized and generalist species and so have the potential to increase faunal diversity and abundance within tropical coastal habitats.

Minimizing predation risk, especially for young or naïve individuals, can be achieved by learning to recognize predators. Embryonic learning may optimize survival by allowing for the earliest possible response to predation threats posthatch. However, predatory threats often change over an individual’s lifetime, and using old information can be detrimental if it becomes outdated. Adaptive forgetting allows an individual to discount obsolete information in decision-making and instead emphasize newer, more relevant information when responding to predation threats. Little is known about the extent to which young individuals can learn and forget information about predation threats. Here we demonstrate that rainbow trout 1) are capable of learning from both conspecific and heterospecific alarm cues as embryos, newly hatched larvae, and free-swimming larvae, 2) exhibit adaptive forgetting of predator information at all stages, and 3) display dynamic adaptive forgetting based on the ontogeny of learning. Specifically, fish that learned information as embryos retained the information for longer periods than those that learned the same information as newly hatched alevins.

The change in coral reefs from live coral to algal-dominated seascapes prevents some fish species from using chemical alarm cues to gain information about their risk of predation. Field experiments showed that Ambon damselfish, Pomacentrus amboinensis, were able to learn the identity of individual novel predators from a cocktail of odours from three predators derived from digestive products. Learning only occurred when the predators had been fed conspecifics of the prey species in the presence of water that had passed over live hard coral. This allows novel predators to be identified long after the immediate capture and ingestion event. Fish that had the same learning opportunity in degraded water took more risk and died faster on habitat patches in the field. Ambon damselfish respond to chemical alarm cues from closely related Pomacentrus nagasakiensis, in both live and degraded water, yet experiments suggested they cannot use the congeneric diet odours to label predators. However, we did find a modest survival benefit under natural conditions, suggesting some limited learning occurred. Findings suggest that as coral habitats degrade, fishes that are affected by the changing chemistry will have a greatly reduced range of mechanisms for obtaining and updating threat information, altering the resilience of communities.

There are numerous examples of species introductions that have caused declines in native populations. In many cases, exotic species are predators of native prey which do not respond correctly to these new and often much different threats. Amphibians, as a group, have been strongly affected by introductions of fish and other aquatic predators such as crayfish. Our goal in this study was to explore the potential impacts of exotic crayfish on the behaviour, morphology, and survival of naive wood frog tadpoles, Lithobates sylvaticus. In mesocosms, groups of tadpoles were exposed to either a native predator (larval beetle or dragonfly nymph) or an exotic crayfish, Orconectes virilis. Tadpoles were the largest following exposure to dragonflies, indicating that dragonflies were selecting smaller tadpoles. Vertical space use of tadpoles was highest in the presence of crayfish, suggesting that tadpoles were learning to avoid crayfish in the benthos. Mortality was highest in the presence of beetles and lowest with crayfish, and hence in isolation, exotic crayfish were poorer predators of wood frog tadpoles. However, half way through the experiment, we replaced each predator with a new predator of either the same species or a different species to assess how the impact of the new predator was affected by experience with the first predator. When crayfish were added following beetles, the mortality due to crayfish increased significantly, possibly due to differences in predator space use and foraging mode.

The fear of predation can have marked effects on an individual's phenotype, and the resulting phenotype is selected to increase an individual's chance of survival during a predator encounter. However, for species with inducible defences, such defensive phenotypes must be costly enough to prevent them from becoming constitutive. While morphological and life-history adaptations have been shown to incur costs, much less research has been done on the costs of behavioural adaptations, which are often thought of as plastic, with limited associated costs. In this study, we document the costs of a high-risk behavioural phenotype. Under high-risk conditions, damselfish are known to exhibit a high-risk phenotype, which among other traits, confer a significant survival advantage during encounters with predators. We exposed juvenile damselfish to a high-risk or low-risk environment for 4 days. We then set up competitive encounters between size-matched pairs of high-risk and low-risk conspecifics. To test for context dependency, we also ran trials when the pair was exposed to a novel predator odour during the competitive encounter. Our results indicate that low-risk fish were the superior competitors in a low-risk environment, but not in a high-risk environment. This result may be explained by an increase in motivation by high-risk individuals to seek shelter from a potential predation threat. Our results highlight (1) the existence of significant costs, even for rapidly induced behavioural phenotypes, and (2) the importance of investigating the adaptive value of phenotypes within the context in which they develop.

Prey can greatly improve their odds of surviving predator encounters by eavesdropping on conspecific risk cues, but the reliability of these cues depends on both previous accuracy as well as the cue's relevance. During a predator chase, aquatic prey release chemical disturbance cues that may vary in their reliability depending on the individuals receiving them. Thus, prey may rely differentially on disturbance cues from familiar individuals (due to previous experience) or from kin (due to their relatedness). We examined the responses of wood frog (Lithobates sylvaticus) tadpoles to disturbance cues from familiar versus unfamiliar conspecifics and kin versus non-kin. In accordance with our prediction, tadpoles responded differently to disturbance cues from familiar versus unfamiliar conspecifics. Tadpoles receiving disturbance cues from unfamiliar individuals displayed a fright response, whereas tadpoles ignored disturbance cues from familiar individuals. Tadpoles may have habituated to familiar cues since they were unaccompanied by a true threat, hence rendering these cues functionally unreliable. Tadpoles responded similarly to disturbance cues from related and unrelated individuals suggesting they were similarly reliable and this mirrors the matching reliability of prey responses to damage-released alarm cues from kin and non-kin. Our findings shed light on a seldom-studied chemical communication system in aquatic prey.

Human-induced noise has a pervasive influence on the behaviour of animals in their natural environment, but little scientific attention has gone toward noises that regularly affect animals being maintained in captivity for research purposes. Here, we assessed underwater aquarium noise produced from two types of aeration equipment (an airstone diffuser attached to an air pump vs. aeration from a mounted aquarium filter) and used recordings from a hydrophone to characterize these two noise stimuli. For several months, we maintained fathead minnows, Pimephales promelas, in a laboratory environment with aeration and noise from an airstone. Then minnows were moved into tanks with either the familiar airstone noise or novel filter noise for four days. We then measured the latency of minnows to emerge from an isolation chamber as a standard measure of boldness behaviour. Exposure to novel filter noise resulted in decreased boldness (P

Elevated levels of contaminants from human activities have become a major threat to animals, particularly within aquatic ecosystems. Selenium (Se) is a naturally occurring element with a narrow range of safe intake, but excessive Se has toxicological effects, as it can bioaccumulate and cause cognitive and behavioural impairments. In this study, we investigated whether exposure to Se would also have transgenerational effects, causing changes in the descendants of exposed individuals. We exposed adult female zebrafish to either a control diet or environmentally relevant concentrations of dietary Se-Met (3.6, 12.8, 34.1 μg Se/g dry weight) for 90 days. Then, females from each treatment group were bred with untreated males, and the offspring (F1-generation) were raised to adulthood (6 months old) without Se exposure. In behavioural tests, offspring that were maternally exposed to 34.1 μg Se/g showed signs of elevated stress, weaker group preferences, and impaired social learning. Maternal exposure to high levels of Se-Met also led to dysregulation of the serotonergic system via changes in mRNA expression of serotonin receptors, including the 5-HT1A, 5-HT1B, and 5-HT1D subtypes, the serotonin transporter, and monoamine oxidase (MAO). Such perturbations in the serotonergic system, thus, appear to underlie the neurobehavioural deficits that we observed. These findings suggest that Se contamination can have important transgenerational consequences on social behaviour and cognition.

Recent studies show that bisphenol S (BPS) induces multiple adverse effects in exposed organisms; however, the maternal effects of BPS exposure remain poorly understood. Here, we expose adult female zebrafish to environmentally relevant concentrations of BPS (0, 1, 10, 30 μg/L) and 1 μg/L of 17-β-estradiol (E2) as a positive control for 60 days. Females were then paired with BPS-unexposed males and their offspring were raised in control water for 6 months. Maternal exposure to BPS was found to alter social behavior and anxiety response in a dose-specific manner in male offspring. Group preferences and social cohesion were significantly reduced by maternal exposure to 1 and 10 μg/L BPS, respectively. Additionally, maternal exposure to 1 and 30 μg/L BPS and E2 decreased offspring stress responses during the novel tank test. The impaired social behavior was associated with elevated arginine-vasotocin (AVT) level as well as with the altered expression of genes involved in AVT signaling pathway (AVT, avpr1aa) and enzymatic antioxidant genes (cat and Mn-sod) in the brain. Collectively, these results suggest that maternal exposure to environmentally relevant concentrations of BPS alters social behavior in zebrafish offspring, which is likely mediated by oxidative stress and disruption of neuropeptide signaling pathways in the brain.

Group-living prey rely on social information such as alarm signals and other social cues to avoid predation. By definition, “signals” imply that a message is voluntarily directed at receivers (i.e., the audience), whereas “cues” are released incidentally regardless of the audience composition. Thus, audience effects can be used to differentiate between signals and cues when communication is difficult to observe or quantify. In at least two fish species, chemical disturbance cues are released during a predator attack to signal to familiar audiences about predation risk. Here, we examined whether audience composition affects disturbance cue release in wood frog (Lithobates sylvaticus) tadpoles to better understand the function of disturbance cues across aquatic prey. Groups of tadpoles underwent simulated predator attacks to obtain disturbance cues. The groups were either familiar and related, unfamiliar and related, familiar and unrelated, or unfamiliar and unrelated. To assess the relative potency of each cue, we used a behavioral bioassay design involving activity changes in independent tadpole receivers (unfamiliar and unrelated to the donors). If tadpoles use disturbance cues to signal related and/or familiar individuals, we predicted increased fright responses in receivers to cues obtained from those groups. However, we detected no effect of audience composition, indicating that tadpoles release similar disturbance cues regardless of audience kinship or familiarity. Nevertheless, disturbance cues evoked a consistent antipredator response in receivers indicating that these chemicals still act as reliable risk cues. Further comparative studies using audience effects are necessary to understand how disturbance cues have evolved across aquatic prey. When aquatic prey encounter predators and are frightened, they release chemicals known as “disturbance cues” into the water. These chemicals alert other prey nearby of potential danger. For example, wood frog tadpoles release disturbance cues when they are being chased by a predator. Tadpoles that smell the disturbance cues of other tadpoles are less likely to be eaten by predators. Since wood frog tadpoles are often found in shallow ponds filled with both familiar siblings as well as other tadpoles that are unfamiliar and unrelated, we wondered if tadpoles would produce more disturbance cues when familiar or related tadpoles were nearby. Here, we show that no matter who the audience members are, familiar siblings or not, tadpoles release disturbance cues that cause similar fright. This suggests that disturbance cues are not released differently depending on the audience in this species.

Coral reefs are degrading globally due to increased environmental stressors including warming and elevated levels of pollutants. These stressors affect not only habitat-forming organisms, such as corals, but they may also directly affect the organisms that inhabit these ecosystems. Here, we explore how the dual threat of habitat degradation and microplastic exposure may affect the behaviour and survival of coral reef fish in the field. Fish were caught prior to settlement and pulse-fed polystyrene microplastics six times over 4 days, then placed in the field on live or dead-degraded coral patches. Exposure to microplastics or dead coral led fish to be bolder, more active and stray further from shelter compared to control fish. Effect sizes indicated that plastic exposure had a greater effect on behaviour than degraded habitat, and we found no evidence of synergistic effects. This pattern was also displayed in their survival in the field. Our results highlight that attaining low concentrations of microplastic in the environment will be a useful management strategy, since minimizing microplastic intake by fishes may work concurrently with reef restoration strategies to enhance the resilience of coral reef populations.

For many species, social learning is crucial for fitness-related activities, but human-induced environmental changes can impair such learning processes. For instance, mining can release the element, selenium (Se), that is vital for physiological functions but also has toxicological properties at elevated concentrations. In this study, we investigated the effects of chronic exposure to Se on social learning outcomes and potential underlying molecular mechanisms in adult zebrafish. After exposure to different levels of dietary selenomethionine (control, 3.6, 12.8, 34.1 μg Se/g dry weight) for 90 days, we examined the ability of observer fish to follow demonstrators (experienced individuals) in escaping an oncoming trawl. Social learning outcomes were then assessed in the absence of demonstrators. Our results indicated that fish in the highest exposure group (34.1 μg/g) displayed significantly slower escape responses compared to fish in the control and lower exposure groups (3.6 and 12.8 μg Se/g). This impaired behavior was associated with higher oxidative stress and dysregulation in genes that are key in the serotonergic pathway, indicating that oxidative stress and alteration in the serotonergic system lead to impairment of social learning.

As animals move through their environment, they must respond to different levels of predation risk in different habitats. We demonstrate that tadpoles use habitat odors to learn about the overall risk associated with specific habitats. Tadpoles adjusted their antipredator behavior to match the risk experienced in different habitats, becoming neophobic (fearful of novel odors) in high-risk habitats. However, responses were not consistent across habitat types, and tadpoles did not use habitat cues when learning about predators.

Exposure of prey animals to high background risk environments generates high-risk behavioural phenotypes characterized by prey that often display transient neophobic responses to novel stimuli. To manipulate background risk, researchers have most often used chemical alarm cues from injured conspecifics because these cues provide a general indication of a high-risk environment but no information regarding the identity of the source of the threat. Here, we hypothesized that the expression of neophobia (fear of unknown stimuli) may not be the result of elevated background risk per se, but rather the result of high uncertainty associated with the predation environment. Here we showed that woodfrog, Lithobates sylvaticus, tadpoles exposed to alarm cues alone for several days subsequently displayed neophobic phenotypes. The same was true for tadpoles exposed to alarm cues paired with the odour of a new novel predator each day for several days. However, tadpoles exposed to alarm cues paired with the same predator cue everyday did not develop the neophobic phenotype. This suggests that if the predator environment is certain (i.e. the alarm cue and predator cues always coincide), then the ratio of costs to benefits of neophobia is high and limits its expression. However, if the prey's uncertainty regarding the predator environment is high (i.e. the alarm cues are often associated with new unknown predators), then the potential survival benefits of expressing neophobia likely override the costs. The prey's perception of uncertainty may be a key driver of the expression of neophobic phenotypes.

Neophobic predator avoidance allows prey to reduce the risk of predation but is costly in terms of reduced foraging or courtship opportunities if the novel cues do not represent an actual threat. Consequently, neophobic responses to novel cues should wane with repeated exposures in the absence of an actual threat. We tested the prediction that individual personality traits shape the retention of neophobic predator avoidance in wild-caught guppies. Using extinction trials, we demonstrate that personality (measured as latency to escape or approach a novel object) did not influence the initial response of wild-caught Trinidadian guppies to a novel odour; bolder and shyer guppies both exhibited similarly strong avoidance responses. However, after several exposures, shyer guppies maintain an avoidance response, and bolder guppies no longer respond. Our results highlight the complex nature of the antipredator algorithm of prey, whereby past experience, acute risk, and individual tactics shape neophobic predator avoidance patterns.

The response of prey to predation threats is often plastic and can vary with the individual's perceived level of threat. To determine whether prey escape responses can be modulated by background levels of risk or short-term acute risk, we maintained juvenile damselfish, Acanthochromis polyacanthus, under high- or low-risk background conditions for several days and then exposed them to an acute risk (high-risk alarm cues or a low-risk saltwater control) minutes prior to startling them with a mechanical disturbance. Fish responded in one of two ways: they either made a C-start escape response or backed away from the threat. While exposure to either background high risk or acute high risk increased the proportion of C-starters, surprisingly the frequency of C-starters decreased when background high risk and acute risk types were combined. Exposure to an acute high-risk cue increased the escape performance for both types of escape responses. However, when the acute high-risk cue occurred within high-risk background conditions, this only increased the performance of C-start escape responses. Non-C-starters reacted similarly in both background risk conditions. Background risk and acute risk acted in a simple additive manner, as seen by the lack of interaction between the two factors. Results showed that escape responses are amplified as the level of perceived risk increases.

As an essential micronutrient, selenium (Se) exerts its biological function as a catalytic entity in a variety of enzymes. From a toxicological perspective, however, Se can become extremely toxic at concentrations slightly above its nutritional levels. Over the last few decades, there has been a growing level of concern worldwide regarding the adverse effects of both inorganic and organic Se compounds on a broad spectrum of neurological functions. A wealth of evidence has shown that exposure to excess Se may compromise the normal functioning of various key proteins, neurotransmitter systems (the glutamatergic, dopaminergic, serotonergic, and cholinergic systems), and signaling molecules involved in the control and regulation of cognitive, behavioral, and neuroendocrine functions. Elevated Se exposure has also been suspected to be a risk factor for the development of several neurodegenerative and neuropsychiatric diseases. Nonetheless, despite the various deleterious effects of excess Se on the central nervous system (CNS), Se neurotoxicity and negative behavioral outcomes are still disregarded at the expense of its beneficial health effects. This review focuses on the current state of knowledge regarding the neurobehavioral effects of Se and discusses its potential mode of action on different aspects of the central and peripheral nervous systems. This review also provides a brief history of Se discovery and uses, its physicochemical properties, biological roles in the CNS, environmental occurrence, and toxicity. We also review potential links between exposure to different forms of Se compounds and aberrant neurobehavioral functions in humans and animals, and identify key knowledge gaps and hypotheses for future research.

The present study was designed to investigate the effects of chronic dietary exposure to selenium (Se) on zebrafish cognition and also to elucidate possible mechanism(s) by which Se exerts its neurotoxicity. To this end, adult zebrafish were exposed to different concentrations of dietary l-selenomethionine (control, 2.3, 9.7, 32.5, or 57.7 μg Se/g dry weight) for 30 days. Cognitive performance of fish was tested using a latent learning paradigm in a complex maze. In addition, we also evaluated oxidative stress biomarkers and the expression of genes involved in dopaminergic neurotransmission in the zebrafish brain. Fish treated with higher dietary Se doses (32.5 and 57.5 μg Se/g) exhibited impaired performance in the latent learning task. The impaired learning was associated with the induction of oxidative stress and altered mRNA expression of dopamine receptors, tyrosine hydroxylase, and dopamine transporter genes in the zebrafish brain. Collectively, our results illustrate that cognitive impairment in zebrafish could be associated with Se-induced oxidative stress and altered dopaminergic neurotransmission in the brain.

Many animals respond differentially to stimuli on one side of their body compared to the other. This is a reflection of being lateralized, and is a feature common in vertebrates. Given that any particular stimulus that an animal encounters, be it food, a predator or a competitor, has an equal probability of coming from either side of the body, there may be negative selection for lateralization. However, the costs of lateralization may be offset if being lateralized confers a considerable advantage in other contexts, including cognition. Here, we showed that learned responses of juvenile ambon damselfish, Pomacentrus amboinensis, to a novel predator was strongly influenced by the degree of lateralization. While both lateralized and nonlateralized fish were able to learn the predator, lateralized fish showed much stronger responses to the learned predator than nonlateralized fish. When we paired lateralized and nonlateralized fish and allowed them to interact over a shelter resource, we observed that lateralized fish were poorer competitors. They attacked less often, showed fewer displays and exhibited greater avoidance of their competitor. For many gregarious species, the expression of lateralization likely reflects a fine balance of competing selection pressures. Our work highlights the need for integrative studies.