Sub-lethal effects of the insecticide, imidacloprid, on the responses of damselfly larvae to chemosensory cues indicating predation risk

Insecticides, including the widely used neonicotinoids, can affect both pest and non-target species. In addition to lethal effects, these insecticides at sub-lethal levels may cause disruption to sensory perception and processing leading to behavioural impairments. In this laboratory experiment, we investigated the effects of a 10-day exposure to the neonicotinoid insecticide, imidacloprid, on the behaviour of larvae of the damselfly, Lestes congener. In tests of baseline activity, imidacloprid concentrations of 1.0 and 10.0 μg/L caused significant reductions in foraging behaviour. Moreover, in response to chemical cues that indicate a potential risk to the larvae, imidacloprid caused the loss of an appropriate antipredator response (reduced foraging) depending on the concentration and duration of exposure. Imidacloprid at 0.1 μg/L caused the loss of responses toward the odour of a beetle (Dytiscus spp.) predator after 10 days of exposure, whereas 1.0 μg/L caused lost responses toward both the predator odour and injured conspecific cues (i.e., alarm cues) and after only 2 days of exposure. However, at 10.0 μg/L, larvae responded appropriately to both cues throughout the duration of the study, suggesting compensatory responses to imidacloprid at higher concentrations. Hence, the lack of appropriate responses at 1.0 μg/L likely resulted from a cognitive impairment rather than chemical alteration of these important chemosensory cues. In the natural environment, such effects will likely cause decreased survivorship in predator encounters. Hence, imidacloprid exposure, even at low concentrations, could have adverse consequences for chemosensory ecology of this damselfly species.

Exposure to the insecticide, imidacloprid, impairs predator-recognition learning in damselfly larvae

Many aquatic organisms use chemosensory information to learn about local predation threats, but contaminants in their environment may impair such cognitive processes. Neonicotinoids are a class of water-soluble systemic insecticides that have become a major concern in aquatic systems. In this study, we explored how a 10-day exposure to various concentrations (0, 0.1, 1.0, or 10.0 μg/L) of the neonicotinoid imidacloprid affects the learned recognition of predator odour by non-target damselfly larvae (Lestes spp). Unexposed larvae and those exposed to the low concentration (0.1 μg/L) demonstrated an appropriate learned response to a novel predator odour following a conditioning with the odour paired with chemical alarm cues. However, such learning failed to occur for larvae that were exposed to imidacloprid concentrations of 1.0 and 10.0 μg/L. Thus, either the cognitive processing of the chemical information was impaired or the chemistry of one or both of the conditioning cues was altered, making them ineffective for learning. In a second experiment, we found evidence for this latter hypothesis. In the absence of background imidacloprid exposure, larvae did not show significant learned responses to the predator odour when the conditioning cues were mixed with imidacloprid (initial pulse solution of 3.0 μg/L) at the start of conditioning (reaching a final concentration of 0.01 μg/L). These findings indicate that even low levels of imidacloprid can have important implications for chemosensory cognition of non-target species in aquatic environments.

Maternal exposure to bisphenol S reduces anxiety and impairs collective antipredator behavior of male zebrafish (Danio rerio) offspring through dysregulation of their serotonergic system

Bisphenol S (BPS) is a common endocrine-disrupting chemical globally used in several consumer and industrial products. Although previous studies suggested that BPS induces multiple effects in exposed organisms, very little is known about its intergenerational effect on offspring behavior and/or the potential underlying mechanisms. To this end, adult female zebrafish Danio rerio were exposed to BPS (0, 10, 30 µg/L) and 1 µg/L of 17-β-estradiol (E2) as a positive control for 60 days. Afterwards, female fish were bred with untreated males, and their offspring were raised to 6 months old in control water. Maternal exposure to BPS decreased male offspring anxiety and antipredator behaviors while boldness remained unaffected. Specifically, maternal exposure to 10 and 30 µg/L BPS and 1 µg/L E2 were found to impact male offspring anxiety levels as they decreased the total time that individuals spent in the dark zone in the light/dark box test and increased the total track length in the center of the open field test. In addition, maternal exposure to all concentrations of BPS and E2 disrupted antipredator responses of male offspring by decreasing shoal cohesion in the presence of chemical alarm cues derived from conspecifics, which communicated high risk. To elucidate the possible molecular mechanism underlying these neuro-behavioral effects of BPS, we assessed 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). The impaired anxiety and antipredator responses were associated with reduced levels of 5-HT1A subtype and MAO mRNA expression within the brain of adult male offspring. Collectively, the results of this study demonstrate that maternal exposure to environmental concentrations of BPS can interfere with the serotonergic signaling pathway in the developing brain, subsequently leading to the onset of a suite of behavioral deficits in adult offspring.

Uncertainty about predation risk: a conceptual review

Uncertainty has long been of interest to economists and psychologists and has more recently gained attention among ecologists. In the ecological world, animals must regularly make decisions related to finding resources and avoiding threats. Here, we describe uncertainty as a perceptual phenomenon of decision-makers, and we focus specifically on the functional ecology of such uncertainty regarding predation risk. Like all uncertainty, uncertainty about predation risk reflects informational limitations. When cues are available, they may be novel (i.e. unknown information), incomplete, unreliable, overly abundant and complex, or conflicting. We review recent studies that have used these informational limitations to induce uncertainty of predation risk. These studies have typically used either over-responses to novelty (i.e. neophobia) or memory attenuation as proxies for measuring uncertainty. Because changes in the environment, particularly unpredictable changes, drive informational limitations, we describe studies assessing unpredictable variance in spatio-temporal predation risk, intensity of predation risk, predator encounter rate, and predator diversity. We also highlight anthropogenic changes within habitats that are likely to have dramatic impacts on information availability and thus uncertainty in antipredator decisions in the modern world.

Transgenerational plasticity of exploratory behavior and a hidden cost of mismatched risk environments between parental sexes

We require a better understanding of the relative contribution of different modes of non-genetic inheritance in behavioral trait development. Thus, we investigate variation in exploratory behavior, which is ecologically relevant and a target of selection. The metabolic hypothesis predicts exploratory behavior to be size-dependent across taxa. This size-dependency is cancelled out under high perceived risk, allowing us to determine the transgenerationally integrated estimated level of risk. Using fathead minnows Pimephales promelas, we manipulated perceived risk in mothers, fathers, caring males and offspring through continuous exposure to either conspecific alarm cues or to a control water treatment. In 1000 four-month old offspring, we determined body sizes and exploratory behavior. Perceived high risk in mothers, followed by personal risk, was most effective in eliminating size-dependent behavior whereas effects of paternal risk on offspring behavioral development were substantially weaker. When maternal risk is high, environmental mismatches between parents prevented offspring from responding appropriately to personal high risk. The environment of the caring male also impacted offspring behavior to a greater extent than that of its genetic parents. Our study highlights the high relative importance of maternal, personal and caring male risk environments and showcases potential costs of an environmental mismatch between parental sexes.

Uncertainty about old information results in differential predator memory in tadpoles

As information ages, it may become less accurate, resulting in increased uncertainty for decision makers. For example, chemical alarm cues (AC) are a source of public information about a nearby predator attack, and these cues can become spatially inaccurate through time. These cues can also degrade quickly under natural conditions, and cue receivers are sensitive to such degradation. Although numerous studies have documented predator-recognition learning from fresh AC, no studies have explored learning from aged AC and whether the uncertainty associated with this older information contributes to shortening the retention of learned responses (i.e. the 'memory window'). Here, we found that wood frog tadpoles, Lithobates sylvaticus, learned to recognize a novel odour as a predator when paired with AC aged under natural conditions for up to 1 h. However, only tadpoles conditioned with fresh AC were found to retain this learned response when tested 9 days after conditioning. These results support the hypothesis that the memory window is shortened by the uncertainty associated with older information, preventing the long-term costs of a learned association that was based on potentially outdated information.

Effects of common antiepileptic drugs on teleost fishes

Antiepileptic drugs (AEDs) are globally prescribed to treat epilepsy and many other psychiatric disorders in humans. Their high consumption, low metabolic rate in the human body and low efficiency of wastewater treatment plants (WWTPs) in eliminating these chemicals results in the frequent occurrence of these pharmaceutical drugs in aquatic systems. Therefore, aquatic organisms, including ecologically and economically important teleost fishes, may be inadvertently exposed to these chemicals. Due to their physiological similarity with humans, fishes may be particularly vulnerable to AEDs. Almost all AED drugs are detectable in natural aquatic ecosystems, but diazepam (DZP) and carbamazepine (CBZ) are among the most widely detected AEDs to date. Recent studies suggest that these drugs have a substantial capacity to induce neurotoxicity and behavioral abnormality in fishes. Here we review the current state of knowledge regarding the potential mode of action of DZP and CBZ as well as that of some other AEDs on teleosts and put observable behavioral effects into a mechanistic context. We find that following their intended mode of action in humans, AEDs also disrupt the GABAergic, glutamatergic and serotonergic systems as well as parasympathetic neurotransmitters in fishes. Moreover, AEDs have non-specific modes of action in teleosts ranging from estrogenic activity to oxidative stress. These physiological changes are often accompanied by dose-dependent disruptions of anxiety, locomotor activity, social behaviors, food uptake, and learning and memory, but DZP and CBZ consistently induced anxiolytic effects. Thereby, AED exposure severely compromises individual fitness across teleost fish species, which may lead to population and ecosystem impairment. We also showcase promising avenues for future research by highlighting where we lack data when it comes to effects of certain AEDs, AED concentrations and behavioral endpoints.

Evidence for the Predator Attraction Hypothesis in an amphibian predator-prey system

Many species possess damage-released chemical alarm cues that function in alerting nearby individuals to a predator attack. One hypothesis for the evolution and/or maintenance of such cues is the Predator Attraction Hypothesis, where predators, rather than prey, are the "intended" recipients of these cues. If a predator attack attracts additional predators, these secondary predators might interfere with the predation event, providing the prey with a better chance to escape. In this study, we conducted two experiments to explore this hypothesis in an amphibian predator/prey system. In Experiment 1, we found that tiger salamanders (Ambystoma mavortium) showed a foraging attraction to chemical cues from wood frog (Lithobates sylvaticus) tadpoles. Salamanders that were experienced with tadpole prey, in particular, were strongly attracted to tadpole alarm cues. In Experiment 2, we observed experimental encounters between a tadpole and either one or two salamanders. The presence of the second predator caused salamanders to increase attack speed at the cost of decreased attack accuracy (i.e., increasing the probability that the tadpole would escape attacks). We also found that the mere presence of visual and chemical cues from a second predator did not affect this speed/accuracy trade-off but did cause enough of a distraction to increase tadpole survival. Thus, our findings are consistent with the Predator Attraction Hypothesis for the evolution and/or maintenance of alarm cues.

Disturbance cues function as a background risk cue but not as an associative learning cue in tadpoles

Chemical information has an important role in the sensory ecology of aquatic species. For aquatic prey, chemical cues are a vital source of information related to predator avoidance and risk assessment. For instance, alarm cues are released by prey that have been injured by predators. In addition to providing accurate information about current risk, repeated exposure to alarm cues can elicit a fear response to novel stimuli (neophobia) in prey. Another source of chemical information is disturbance cues, released by prey that have been disturbed or harassed (but not injured) by a predator. While disturbance cues have received much less attention than alarm cues, they appear to be useful as an early warning signal of predation risk and have the potential to be used as a priming cue for learning. In this study, we used wood frog (Lithobates sylvaticus) tadpoles to test whether repeated exposure to disturbance cues during the embryonic stage can induce neophobic behaviour. Three weeks following repeated exposure to disturbance cues, tadpoles showed reduced activity when exposed to a novel odour, but they no longer displayed an antipredator response to disturbance cues. In a second experiment, we found that tadpoles failed to learn that a novel odour was dangerous following a pairing with disturbance cues, whereas alarm cues facilitated such learning. Our results add to the growing body of information about disturbance cues and provide evidence of their function as an embryonic risk cue but not as an associative learning cue.

Paternal care effects outweigh gamete-mediated and personal environment effects during the transgenerational estimation of risk in fathead minnows

BACKGROUND

Individuals can estimate risk by integrating prenatal with postnatal and personal information, but the relative importance of different information sources during the transgenerational response is unclear. The estimated level of risk can be tested using the cognitive rule of risk allocation, which postulates that under consistent high-risk, antipredator efforts should decrease so that individual metabolic requirements can be satisfied. Here we conduct a comprehensive study on transgenerational risk transmission by testing whether risk allocation occurs across 12 treatments that consist of different maternal, paternal, parental care (including cross-fostering) and offspring risk environment combinations in the fathead minnow Pimephales promelas, a small cyprinid fish with alloparental care. In each risk environment, we manipulated perceived risk by continuously exposing individuals from birth onwards to conspecific alarm cues or a control water treatment. Using 2810 1-month old individuals, we then estimated shoaling behaviour prior to and subsequent to a novel mechanical predator disturbance.

RESULTS

Overall, shoals estimating risk to be high were denser during the prestimulus period, and, following the risk allocation hypothesis, resumed normal shoaling densities faster following the disturbance. Treatments involving parental care consistently induced densest shoals and greatest levels of risk allocation. Although prenatal risk environments did not relate to paternal care intensity, greater care intensity induced more risk allocation when parents provided care for their own offspring as opposed to those that cross-fostered fry. In the absence of care, parental effects on shoaling density were relatively weak and personal environments modulated risk allocation only when parental risk was low.

CONCLUSIONS

Our study highlights the high relative importance of parental care as opposed to other information sources, and its function as a mechanism underlying transgenerational risk transmission.

Exposure to predation risk reduces lateralization in fathead minnows

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).

Reproductive fitness of honey bee queens exposed to thiamethoxam during development

The productivity and survival of honey bee (Apis mellifera) colonies depend on queen bee health. Colony-level neonicotinoid exposure has negative effects on reproductive fitness of honey bee queens. However, it is unclear if the observed effects are a direct outcome of neonicotinoid toxicity or result from suboptimal care of developing queens by exposed workers. The aim of this study was to evaluate larval survival, reproductive fitness, and histopathology of honey bee queens exposed to incremental doses (0, 5, 50 ng) of the neonicotinoid thiamethoxam (THI) applied directly to individual late larvae (7 days post-oviposition) of queens. The 5 ng dose represents a calculated high environmental level of exposure for honey bee queen larvae. Morphometric evaluation revealed that the total area of mandibular gland epithelium in queens exposed to 5 and 50 ng THI was reduced by 14% (P = .12) and 25% (P = .001), respectively. Decreased mandibular gland size may alter pheromone production, which could in part explain previously observed negative effects of THI on the reproductive fitness of queens. We also found that late larval exposure to THI reduced larval and pupal survival and decreased sperm viability in mated queens. These changes may interfere with queen development and reproductive longevity.

Early-life and parental predation risk shape fear acquisition in adult minnows

Exposure to predation risk can induce a fearful baseline state, as well as fear reactions toward novel situations (i.e., neophobia). Some research indicates that risk exposure during sensitive periods makes adults more prone to acquiring long-term fearful phenotypes. However, chronic risk can also lead to ignoring threats in order to maintain other activities. We sought to assess how a relatively long period of low risk, experienced either early in life or by the previous generation, influences fear behaviour acquired from a short period of high risk as adults. We used fathead minnows as study subjects and simulated predation risk with repeated exposures to conspecific chemical alarm cues. The period of high risk experienced by adults induced typical fear behaviour (baseline freezing and neophobia), whereas the early-life low-risk period 1 year prior caused only a reduction in baseline foraging. We found no evidence that the early-life risk significantly altered the fear acquired from the adult-risk period. However, in a second experiment, a low-risk period during the parental generation interacted with a high-risk period experienced by the adult offspring. The combination of both risk periods heightened baseline freezing despite parental risk having little effect independently. Hence, our study provides evidence that parental risk exposure can lead to an additive intergenerational effect on fear acquisition in minnows.

Microplastic exposure interacts with habitat degradation to affect behaviour and survival of juvenile fish in the field

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.

Proportional fitness loss and the timing of defensive investment: a cohesive framework across animals and plants

The risk of consumption is a pervasive aspect of ecology and recent work has focused on synthesis of consumer-resource interactions (e.g., enemy-victim ecology). Despite this, theories pertaining to the timing and magnitude of defenses in animals and plants have largely developed independently. However, both animals and plants share the common dilemma of uncertainty of attack, can gather information from the environment to predict future attacks and alter their defensive investment accordingly. Here, we present a novel, unifying framework based on the way an organism's ability to defend itself during an attack can shape their pre-attack investment in defense. This framework provides a useful perspective on the nature of information use and variation in defensive investment across the sequence of attack-related events, both within and among species. It predicts that organisms with greater proportional fitness loss if attacked will gather and respond to risk information earlier in the attack sequence, while those that have lower proportional fitness loss may wait until attack is underway. This framework offers a common platform to compare and discuss consumer effects and provides novel insights into the way risk information can propagate through populations, communities, and ecosystems.

An ecological framework of neophobia: from cells to organisms to populations

Neophobia is the fear of novel stimuli or situations. This phenotype has recently received much ecological attention, primarily in the context of decision making. Here, we explore neophobia across biological levels of organisation, first describing types of neophobia among animals and the underlying causes of neophobia, highlighting high levels of risk and uncertainty as key drivers. We place neophobia in the framework of Error Management Theory and Signal Detection Theory, showing how increases in overall risk and uncertainty can lead to costly non-responses towards novel threats unless individuals lower their response threshold and become neophobic. We then discuss how neophobic behaviour translates into population and evolutionary consequences before introducing neophobia-like processes at the cellular level, where some phenomena such as allergy and autoimmunity can parallel neophobic behaviour. Finally, we discuss neophobia attenuation, considering how a sudden change in the environment from dangerous to safe can lead to problematic over-responses (i.e. the 'maladaptive defensive carry-over' hypothesis), and discuss treatment methods for such over-responses. We anticipate that bridging the concept of neophobia with a process-centered perspective can facilitate a transfer of insight across organisational levels.

Time-dependent latent inhibition of predator-recognition learning

To optimally manage an environment with predators, prey must correctly distinguish between cues that are risky and cues that are safe. Even a specific cue that is safe in one area or at a certain time may be dangerous in other situations, and vice versa. Latent inhibition is a cognitive mechanism by which animals fail to learn that a stimulus as risky because they have already learned it as non-threatening via previous encounters with the stimulus in the absence of negative consequences. Here, we demonstrate that latent inhibition of predator-recognition learning in wood frog tadpoles, Lithobates sylvaticus, depends on the timing of their learning opportunities. For 6 days, tadpoles were exposed daily to an initially novel stimulus (salamander odour), either in the morning (11.00-13.00 h) or evening (16.00-18.00 h). The following day, we conditioned tadpoles to recognize the salamander odour as a predator by pairing it with injured tadpole cues, either at the same time as their previous experience or at the opposite time. When tested the following day, latent inhibition occurred under each scenario where the timing of conditioning matched the timing of the pre-exposure. However, tadpoles tested in the morning showed learned fright responses when conditioned in the morning if their pre-exposure had occurred in the evening, whereas individuals tested in the evening showed learned fright responses when conditioned in the evening if their pre-exposure had occurred in the morning. This is the first report of time-dependent latent inhibition of predator-recognition learning, which is likely an important mechanism for correctly managing predation risk and safety.

Microhabitat complexity influences fear acquisition in fathead minnows

Habitat varies in structure, with animals often preferring a certain degree of microhabitat complexity that facilitates fitness-related activities such as predator avoidance. Environments with high predation risk can induce elevated baseline fear and neophobia in prey, but whether microhabitat complexity influences the acquisition of neophobia has yet to be reported. Here, we tested whether exposure to predation risk induces different levels of fear in microhabitats that differed in complexity. We exposed fathead minnows, Pimephales promelas, to predation risk repeatedly (12 times over 4 days) in the form of damage-released chemical alarm cues (compared to water control) in tanks with vertical plant structure distributed either throughout the tank (complex habitat) or clumped together (simple habitat). Then, we tested minnows before and after exposure to a novel odor in tanks with either the same microhabitat complexity (i.e., familiar habitats) or in tanks with novel habitat that had different substrate structure and no vertical structure. Minnows in the complex habitat showed less overall movement one day after the background risk period, whereas individuals in the simple habitat showed reduced movement regardless of prior risk exposure. We observed stronger effects in the novel habitat, where background risk in both simple and complex habitats caused neophobia. However, individuals from the simple background habitat showed higher baseline fear behaviors. Hence, for minnows, low microhabitat complexity appears to lead to elevated fear, which remains even after a habitat change.

High background risk induces risk allocation rather than generalized neophobia in the fathead minnow

To cope with the heterogeneous nature of predation and the trade-off between predator avoidance and foraging, prey animals have evolved several cognitive rules. One of these is the risk allocation hypothesis, which predicts that in environments with long periods of sustained high risk, individuals should decrease their antipredator effort to satisfy their metabolic requirements. The neophobia hypothesis, in turn, predicts increased avoidance of novel cues in high-risk habitats. Despite the recent interest in predator-induced neophobia across different sensory channels, tests of such generalized neophobia are restricted to a single fish taxon, the Cichlidae. Hence, we retested the generalized neophobia hypothesis in fathead minnows Pimephales promelas, a small schooling North American cyprinid fish. From hatching onward, minnows were exposed to conspecific alarm cues, which indicate predation risk, or distilled water in a split-clutch design. After 1 month, shoaling behavior was examined prior and subsequent to a mechanical predator disturbance. Fish previously exposed to elevated background risk formed compact shoals for a shorter time interval after the stimulus compared with controls. These results contrast previous studies of generalized neophobia but match the risk allocation hypothesis. Consequently, risk allocation and generalized neophobia are not ubiquitous cognitive rules but instead evolved adaptations of different taxa to their respective environments.

Evaluating adaptive, carry-over, and plastic antipredator responses across a temporal gradient in Pacific chorus frogs

The development of antipredator traits is dependent on the frequency and intensity of predator exposure over evolutionary and ecological time. We hypothesized that prey species would respond with increasing accuracy when exposed to predators across generational, ontogenetic, and immediate time scales. We assessed larval Pacific chorus frog (PSRE; Pseudacris regilla) individuals that varied in population sympatry, embryonic conditioning, and immediate exposure to stocked populations of rainbow trout (Oncorhynchus mykiss). Using PSRE populations from sites with and without resident rainbow trout, we conditioned embryos to trout odor, PSRE alarm cues, trout odor in combination with alarm cues, or control water. After being hatched and reared in control water, individuals were exposed to the four predator cue treatments using a fully factorial design. Tadpoles from populations with resident rainbow trout did not behave or develop differently than tadpoles originating from fishless sites. However, we found evidence that PSRE reduced predation risk with a combination of carry-over effect (i.e., transfer of information across life history stages) and within-life stage phenotypically plastic mechanisms. We found both developmental and behavioral carry-over effects: tadpoles conditioned with trout odor as embryos grew more slowly and took refuge more often than control animals. Within-life-stage behavioral plasticity was observed in tadpoles from all treatment groups, responding to predator cues with increased refuge use. Potentially additive effects of predator exposure on prey response should be considered when predicting the ability of prey to recognize novel threats.

Retention of learned predator recognition in embryonic and juvenile rainbow trout

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 Effects of Selenomethionine on the Escape Behaviours of Fathead Minnows

Selenium (Se) is an essential micronutrient for animals and yet becomes toxic with only a small increase in concentration. Toxicological studies have reported various effects of Se on fishes, including developmental impacts and deformities of the musculature and sensory systems. This paper investigates the impact of sublethal concentrations of Se on the ability of the Fathead Minnow (Pimephales promelas) to perform escape responses, a routine behaviour important to predator-prey dynamics. Predation is among the strongest evolutionary driving forces in nature. Changes to this dynamic can have effects that cascade through the ecosystem. We used responses to mechanical and visual stimuli to determine the impact of environmentally relevant concentrations of dietary selenomethionine on the behaviour of minnows. Latency to respond to the stimulus and kinematic performance were assessed. Our results indicated that there was no significant effect of selenomethionine on either the visual response to a threat or burst swimming behaviours of the fast-start response in minnows. Levels of Se in tissues approached that of tissue-specific guidelines set by regulatory bodies across North America. This suggests that current regulations are adequately protecting this key component of predator avoidance in Fathead Minnows.

Coral degradation alters predator odour signatures and influences prey learning and survival

Habitat degradation is a key factor leading to the global loss of biodiversity. This problem is particularly acute in coral reef ecosystems. We investigated whether recognition of predator odours by damselfish was influenced by coral degradation and whether these changes altered survival in the wild. We taught whitespot damselfish to recognize the odour of a predator in the presence of live/healthy coral or dead/degraded coral. Fish were tested for a response to predator odours in environments that matched their conditioning environment or in environments that were mismatched. Next, we taught blue damselfish to recognize the odour of three common reef predators in live and degraded coral environments and then stocked them onto live or degraded patch reefs, where we monitored their subsequent response to predator odour along with their survival. Damselfish learned to recognize predator odours in both coral environments, but the intensity of their antipredator response was much greater when the conditioning and test environments matched. Fish released on degraded coral had about 50% higher survival if they had been trained in the presence of degraded coral rather than live coral. Altering the intensity of antipredator responses could have rather profound consequences on population growth.

A novel alarm signal in aquatic prey: Familiar minnows coordinate group defences against predators through chemical disturbance cues

Animal signalling systems outside the realm of human perception remain largely understudied. These systems consist of four main components: a signalling context, a voluntary signal, receiver responses and resulting fitness benefits to both the signaller and receiver(s). It is often most difficult to determine incidental cues from voluntary signals. One example is chemical disturbance cues released by aquatic prey during predator encounters that may serve to alert conspecifics of nearby risk and initiate tighter shoaling. We aimed to test whether disturbance cues are released incidentally (i.e. as a cue) or are produced voluntarily depending on a specific signalling context such as the audience surrounding the individual, and thus constitute a signal. We hypothesized that if receivers use disturbance cues to communicate risk among themselves, they would produce more (or more potent) disturbance cues when present in a group of conspecifics rather than when they are isolated (presence/absence of an audience) and use disturbance cues more when present alongside familiar rather than unfamiliar conspecifics (audience composition effect). We placed fathead minnows (Pimephales promelas) in groups with familiar fish, unfamiliar fish or as isolated individuals with no audience present, and then simulated a predator chase to evoke disturbance cues. We used bioassays with independent receivers to assess whether the disturbance cues produced differed depending on the signallers' audience. We found evidence of voluntary signalling, as minnows responded to disturbance cues from groups of fish with tighter shoaling while disturbance cues from isolated minnows did not evoke a significant shoaling response (presence/absence audience effect). Receivers also increased shoaling, freezing and dashing more in response to disturbance cues from familiar groups compared to disturbance cues from unfamiliar groups or isolated minnows (audience composition effect). Together, these findings support our hypothesis that disturbance cues are used as an antipredator signal to initiate coordinated group defences among familiar conspecifics involving shoaling, freezing and dashing. This study represents the strongest evidence to date that chemicals released by aquatic prey upon disturbance by predators serve as voluntary signals rather than simply cues that prey have evolved to detect when assessing their risk of predation.

School is out on noisy reefs: the effect of boat noise on predator learning and survival of juvenile coral reef fishes

Noise produced by anthropogenic activities is increasing in many marine ecosystems. We investigated the effect of playback of boat noise on fish cognition. We focused on noise from small motorboats, since its occurrence can dominate soundscapes in coastal communities, the number of noise-producing vessels is increasing rapidly and their proximity to marine life has the potential to cause deleterious effects. Cognition-or the ability of individuals to learn and remember information-is crucial, given that most species rely on learning to achieve fitness-promoting tasks, such as finding food, choosing mates and recognizing predators. The caveat with cognition is its latent effect: the individual that fails to learn an important piece of information will live normally until the moment where it needs the information to make a fitness-related decision. Such latent effects can easily be overlooked by traditional risk assessment methods. Here, we conducted three experiments to assess the effect of boat noise playbacks on the ability of fish to learn to recognize predation threats, using a common, conserved learning paradigm. We found that fish that were trained to recognize a novel predator while being exposed to 'reef + boat noise' playbacks failed to subsequently respond to the predator, while their 'reef noise' counterparts responded appropriately. We repeated the training, giving the fish three opportunities to learn three common reef predators, and released the fish in the wild. Those trained in the presence of 'reef + boat noise' playbacks survived 40% less than the 'reef noise' controls over our 72 h monitoring period, a performance equal to that of predator-naive fish. Our last experiment indicated that these results were likely due to failed learning, as opposed to stress effects from the sound exposure. Neither playbacks nor real boat noise affected survival in the absence of predator training. Our results indicate that boat noise has the potential to cause latent effects on learning long after the stressor has gone.

Maternal Exposure to Dietary Selenium Causes Dopaminergic Hyperfunction and Cognitive Impairment in Zebrafish Offspring

Maternal exposure to environmental contaminants is a predisposing factor for neurodevelopmental disorders with associated cognitive and social deficits in offspring. In this study, we investigated the effects of maternal exposure to selenium (Se), a contaminant of potential environmental concern in aquatic ecosystems, on cognitive performance and the underlying mechanisms in F1-generation adult zebrafish. Adult female zebrafish were exposed to different concentrations of dietary Se (3.5, 11.1, or 27.4 μg Se/g dry weight) for a period of 60 days. Fish were subsequently bred, and their offspring were collected and raised for 6 months on a normal diet. Maternal exposure to all concentrations of dietary Se induced learning impairment in F1-zebrafish tested in a latent learning task. The results also showed a hyperfunctioning dopaminergic system in fish exhibiting the learning deficit. The hyperfunction of the dopaminergic system was associated with enhanced oxidative stress and alterations in the mRNA abundance of several immediate early and late response genes in the zebrafish brain. Taken together, these results suggest that maternal exposure to dietary Se via alterations in the dopaminergic system leads to persistent neurobehavioral deficits in F1-generation adult zebrafish.

The socially mediated recovery of a fearful fish paired with periodically replaced calm models

Social learning is an important mechanism for acquiring knowledge about environmental risk. However, little work has explored the learning of safety and how such learning outcomes are shaped by the social environment. Here, we exposed minnows, Pimephales promelas, to a high-risk environment to induce behavioural responses associated with fear (e.g. neophobia). We then used the presence of calm conspecific models (low-risk individuals) to weaken these responses. When observers (individuals from the high-risk environment) and models were paired consistently in a one-on-one setting, the observers showed no recovery (i.e. no weakening of the fear responses), and instead the models indirectly acquired those responses (i.e. a socially transmitted state of fear). However, observers paired with models that were periodically replaced with new calm models showed a significant recovery, and each new model showed diminished socially transmitted fear. We argue that our understanding of predation-related fear and social information transfer can prove fruitful in understanding problems with fear and stress across animal taxa, including among humans who experience post-traumatic stress and secondary trauma. Our findings indicate that the periodic replacement of models can promote fear recovery in observers and reduce socially transmitted fear in models.

Dopaminergic dysregulation and impaired associative learning behavior in zebrafish during chronic dietary exposure to selenium

A growing body of evidence indicates that exposure to selenium (Se) can cause neurotoxicity, and this can occur because of its interference with several neurotransmitter systems in humans and animals. Dopamine is a critical modulator of a variety of brain functions and a prime target for environmental neurotoxicants. However, effects of environmentally relevant concentrations of Se on dopaminergic system and its neurobehavioral effects are still largely unknown. For this purpose, we exposed zebrafish, a model organism, to different concentrations of dietary l-selenomethionine (control, 3.5, 11.1, 27.4, and 63.4 μg Se/g dry weight) for a period of 60 days. Cognitive performance of fish was evaluated using a plus maze associative learning paradigm. Oxidative stress, as the main driver of Se neurotoxicity, was assessed by measuring the ratio of reduced to oxidized glutathione (GSH:GSSG), lipid peroxidation (LPO) levels, and mRNA expression of several antioxidant enzymes in the zebrafish brain. Dopamine levels in the brain and the expression of genes involved in dopamine synthesis, storage, reuptake, metabolism, and receptor activation were examined. Moreover, transcription of several synaptic plasticity-related immediate-early and late response genes was determined. Overall, fish fed with the two highest concentrations of dietary Se displayed impaired associative learning. Se exposure also induced oxidative stress in the zebrafish brain, as indicated by a reduction in GSH:GSSG ratio, increased LPO levels, and up-regulation of antioxidant genes in fish treated with the two highest concentrations of Se. An increase in brain dopamine levels associated with altered expression of dopaminergic cell markers was evident in different treatment groups. Moreover, Se exposure led to the down-regulation of immediate-early and late response genes in fish that exhibiting learning impairment. Taken together, the results of this study imply that the induction of oxidative stress and dysregulation of dopaminergic neurotransmission may underlie Se-induced impairment of associative learning in zebrafish.

Trust thy neighbour in times of trouble: background risk alters how tadpoles release and respond to disturbance cues

In aquatic environments, uninjured prey escaping a predator release chemical disturbance cues into the water. However, it is unknown whether these cues are a simple physiological by-product of increased activity or whether they represent a social signal that is under some control by the sender. Here, we exposed wood frog tadpoles (Lithobates sylvaticus) to either a high or low background risk environment and tested their responses to disturbance cues (or control cues) produced by tadpoles from high-risk or low-risk backgrounds. We found an interaction between risk levels associated with the cue donor and cue recipient. While disturbance cues from low-risk donors did not elicit an antipredator response in low-risk receivers, they did in high-risk receivers. In addition, disturbance cues from high-risk donors elicited a marked antipredator response in both low- and high-risk receivers. The response of high-risk receivers to disturbance cues from high-risk donors was commensurate with other treatments, indicating an all-or-nothing response. Our study provides evidence of differential production and perception of social cues and provides insights into their function and evolution in aquatic vertebrates. Given the widespread nature of disturbance cues in aquatic prey, there may exist a social signalling system that remains virtually unexplored by ecologists.

At odds with the group: changes in lateralization and escape performance reveal conformity and conflict in fish schools

Many vertebrates are known to show behavioural lateralization, whereby they differentially use one side of their body or either of their bilateral organs or limbs. Behavioural lateralization often manifests in a turning bias in fishes, with some individuals showing a left bias and others a right bias. Such biases could be the source of considerable conflict in fish schools given that there may be considerable social pressure to conform to the group to maintain effective group evasion. Here, we show that predation pressure is a major determinant of the degree of lateralization, both in a relative and absolute sense, in yellow-and-blueback fusiliers (Caesio teres), a schooling fish common on coral reefs. Wild-caught fish showed a bias for right turning. When predation pressure was experimentally elevated or relaxed, the strength of lateralization changed. Higher predation pressure resulted in an increase in the strength of lateralization. Individuals that exhibited the same turning bias as the majority of individuals in their group had improved escape performance compared with individuals that were at odds with the group. Moreover, individuals that were right-biased had improved escape performance, compared with left-biased ones. Plasticity in lateralization might be an important evolutionary consequence of the way gregarious species respond to predators owing to the probable costs associated with this behaviour.

Making the dead talk: alarm cue-mediated antipredator behaviour and learning are enhanced when injured conspecifics experience high predation risk

Due to the costs of antipredator behaviour, prey have the ability to finely modulate their response according to the risk they have experienced, and adjust it over different scales of ecological time. Information on which to base their responses can be obtained from direct experience, but also indirectly from nearby conspecifics. In aquatic environments, alarm cues from injured conspecifics are an important and reliable source of information about current predation risk. We used wood frog tadpoles, Lithobates sylvaticus, to investigate whether prey responses to alarm cues match the level of background predation risk experienced by injured conspecifics. We found that tadpoles exposed to alarm cues from conspecifics raised in a high-risk environment showed a stronger antipredator response and an enhanced learned response to novel predators, when compared with tadpoles exposed to alarm cues from conspecifics raised in a low-risk environment. Alarm cues not only allow prey to cope with an ongoing predation event, but also to adjust their behaviour to match background risk in the environment.

Not equal in the face of habitat change: closely related fishes differ in their ability to use predation-related information in degraded coral

Coral reefs are biodiversity hotpots that are under significant threat due to the degradation and death of hard corals. When obligate coral-dwelling species die, the remaining species must either move or adjust to the altered conditions. Our goal was to investigate the effect of coral degradation on the ability of coral reef fishes to assess their risk of predation using alarm cues from injured conspecifics. Here, we tested the ability of six closely related species of juvenile damselfish (Pomacentridae) to respond to risk cues in both live coral or dead-degraded coral environments. Of those six species, two are exclusively associated with live coral habitats, two are found mostly on dead-degraded coral rubble, while the last two are found in both habitat types. We found that the two live coral associates failed to respond appropriately to the cues in water from degraded habitats. In contrast, the cue response of the two rubble associates was unaffected in the same degraded habitat. Interestingly, we observed a mixed response from the species found in both habitat types, with one species displaying an appropriate cue response while the other did not. Our second experiment suggested that the lack of responses stemmed from deactivation of the alarm cues, rather than the inability of the species to smell. Habitat preference (live coral versus dead coral associates) and phylogeny are good candidates for future work aimed at predicting which species are affected by coral degradation. Our results point towards a surprising level of variation in the ability of congeneric species to fare in altered habitats and hence underscores the difficulty of predicting community change in degraded habitats.

Patterns of predator neophobia: a meta-analytic review

Neophobia, the fear of novel stimuli, plays a major role in animal ecology. Here, we review studies on predator neophobia and explore its underlying patterns within an ecological framework. Predator neophobia is typically assessed by observing behaviours in novel areas that bring potential risk from unknown predators, or by observing behaviours towards certain kinds of objects and odours that are novel. We conducted a literature review across taxa, surveying research on baseline and induced neophobia versus controls. We calculated effect sizes for the intensity of neophobic responses, and categorized data according to six factors (taxa, age class, background type, trophic position, test cue type and experimental treatment type). While accounting for each of the other factors, we found that baseline neophobia was stronger among birds and mammals, and towards novel areas, relative to other taxa and cue types. Baseline neophobia was lower for wild-caught animals and for those that were higher in trophic position, compared with those reared in captivity and from lower trophic levels. By contrast, induced neophobia was similar in intensity across taxa, background types and testing cue types, while again being lower among upper trophic-level members and among juvenile animals. Although induced neophobia occurred across all treatment types, brain lesions induced stronger neophobia than predation risk or social isolation. We discuss potential mechanisms underlying these results and highlight gaps in the literature.

Exposure to a contextually neutral stressor potentiates fear conditioning in juvenile rainbow trout, Oncorhynchus mykiss

Organisms faced with stressors deploy a suite of adaptive responses in the form of behavioral, physiological and cognitive modifications to overcome the challenge. Interactive effects of these responses are known to influence learning and memory processes and facilitation is thought to be dependent, in part, upon contextual relevance of the stressor to the learning task. Predation is one such stressor for prey animals, and their ability to manage reliable information about predators is essential for adaptive antipredator strategies. Here, we investigated (i) the influence cortisol has on the ability of juvenile rainbow trout to learn and retain conditioned antipredator responses to predatory cues, and (ii) whether conditioned behavioral and physiological responses to predator cues are fixed or deployed in a threat-sensitive manner. Trout were fed cortisol-coated pellets minutes prior to a conditioning event where they were exposed to novel predator odor paired with chemical alarm cues (unconditioned stimulus). We tested for conditioned responses by exposing trout to predator cues after 2, 4 or 10days and subsequently documented physiological and behavioral responses. Both control and cortisol-fed trout learned the predator odor and responded 2 and 4days post conditioning. However, at 10days only cortisol-fed trout maintained strong behavioral responses to predator cues. Interestingly, we failed to find conditioned physiological responses to predator odor despite the presence of threat-sensitive cortisol responses to the unconditioned stimulus. Our findings suggest cortisol exposure prior to predator-learning may enhance retention of conditioned responses, even without a contextual link between stressor source and learning task.

Embryonic learning and developmental carry-over effects in an invasive anuran

Carry-over effects influence trait responses in later life stages as a result of early experience with environmental cues. Predation risk is an influential stressor and selection exists for early recognition of threats. In particular, invasive species may benefit from carry-over effects by preemptively recognizing and responding to novel predators via latent developmental changes and embryonic learning. In a factorial experiment, we conditioned invasive American bullfrog embryos (Lithobates catesbeianus) to the odor of a novel fish predator, largemouth bass (Micropterus salmoides) alone or in combination with injured conspecific cues. We quantified developmental carryover in the larval life stage and found that individuals conditioned to the highest risk (fish and injured conspecific cues) grew into longer bodied larvae relative to larvae from lower risk treatments. We also assessed embryonic learning, a behavioral carry-over effect, and found an interaction between embryonic conditioning and larval exposure. Behavioral responses were only found in scenarios when predation risk varied in intensity across life history stages, thus requiring a more flexible antipredator strategy. This indicates a potential trade-off between the two strategies in larval growth and development rates, and time until metamorphosis. Our results suggest that early predator exposure and carry-over effects have significant impacts on life history trajectories for American bullfrogs. This research contributes to our understanding of a potentially important invasion mechanism in an anuran species of conservation concern.

Mechanisms underlying the control of responses to predator odours in aquatic prey

In aquatic systems, chemical cues are a major source of information through which animals are able to assess the current state of their environment to gain information about local predation risk. Prey use chemicals released by predators (including cues from a predator's diet) and other prey (such as alarm cues and disturbance cues) to mediate a range of behavioural, morphological and life-history antipredator defences. Despite the wealth of knowledge on the ecology of antipredator defences, we know surprisingly little about the physiological mechanisms that control the expression of these defensive traits. Here, we summarise the current literature on the mechanisms known to specifically mediate responses to predator odours, including dietary cues. Interestingly, these studies suggest that independent pathways may control predator-specific responses, highlighting the need for greater focus on predator-derived cues when looking at the mechanistic control of responses. Thus, we urge researchers to tease apart the effects of predator-specific cues (i.e. chemicals representing a predator's identity) from those of diet-mediated cues (i.e. chemicals released from a predator's diet), which are known to mediate different ecological endpoints. Finally, we suggest some key areas of research that would greatly benefit from a more mechanistic approach.

Habitat degradation disrupts neophobia in juvenile coral reef fish

Habitat degradation not only disrupts habitat-forming species, but alters the sensory landscape within which most species must balance behavioural activities against predation risk. Rapidly developing a cautious behavioural phenotype, a condition known as neophobia, is advantageous when entering a novel risky habitat. Many aquatic organisms rely on damage-released conspecific cues (i.e. alarm cues) as an indicator of impending danger and use them to assess general risk and develop neophobia. This study tested whether settlement-stage damselfish associated with degraded coral reef habitats were able to use alarm cues as an indicator of risk and, in turn, develop a neophobic response at the end of their larval phase. Our results indicate that fish in live coral habitats that were exposed to alarm cues developed neophobia, and, in situ, were found to be more cautious, more closely associated with their coral shelters and survived four-times better than non-neophobic control fish. In contrast, fish that settled onto degraded coral habitats did not exhibit neophobia and consequently suffered much greater mortality on the reef, regardless of their history of exposure to alarm cues. Our results show that habitat degradation alters the efficacy of alarm cues with phenotypic and survival consequences for newly settled recruits.

Duration of Exposure to Elevated Temperature Affects Competitive Interactions in Juvenile Reef Fishes

Climate change will affect key ecological processes that structure natural communities, but the outcome of interactions between individuals and species will depend on their thermal plasticity. We tested how short- and long-term exposure to projected future temperatures affects intraspecific and interspecific competitive interactions in two species of coral reef damselfishes. In conspecific contests, juvenile Ambon damselfish, Pomacentrus amboinensis, exhibited no change in aggressive interactions after 4d exposure to higher temperatures. However, after 90d of exposure, fish showed a nonadaptive reduction in aggression at elevated temperatures. Conversely, 4d exposure to higher temperature increased aggression towards conspecifics in the lemon damselfish, Pomacentrus moluccensis. 90d exposure began to reduce this pattern, but overall there was little effect of temperature. Aggression in interspecific contests increased with short-term exposure, but was significantly lower after long-term exposure indicative of acclimation. Our results show how the length of exposure to elevated temperature can affect the outcome of competitive interactions. Furthermore, we illustrate that results from intraspecific contests may not accurately predict interspecific interactions, which will challenge our ability to generalise the effects of warming on competitive interactions.

Risk-induced neophobia: does sensory modality matter?

Recent studies have documented that exposure to high levels of background risk can induce neophobic predator avoidance in prey animals, whereby they respond to any novel cue with an anti-predator response. Such phenotypically plastic predator avoidance may allow prey to maximize anti-predator benefits in variable risk environments. It remains poorly understood whether risk assessment information from different sensory modalities can be integrated to induce generalized, cross-sensory system neophobic responses. Here, we directly test this hypothesis by exposing juvenile convict cichlids (Amatitlania nigrofasciata) to high- versus low-risk environments using either conspecific alarm cue (chemosensory risk) or a model avian predator (visual/mechanical risk) and testing their response to a novel chemosensory cue (Experiment 1) or visual cue (Experiment 2). Our results suggest that regardless of the sensory modality used to increased perceived risk, cichlids pre-exposed to high-risk conditions exhibited increased predator avoidance in response to any novel visual or chemical cue. As expected, cichlids pre-exposed to low-risk conditions did not display any neophobic responses. Our results suggest that induced neophobia is not cue specific; rather, it may function as a generalized response to perceived predation risk.