A review of predator diet effects on prey defensive responses

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.

Effects of ocean acidification and warming on physiological and behavioural responses of an herbivore snail to waterborne predator cues

Ocean Acidification (OA) and Ocean Warming (OW) represent major climate stressors that may disrupt species interactions. However, despite the knowledge about the impacts of OA and OW on the performance of individual species, it is still unclear how biological interactions can be modified by the combined effects of these stressors. Consequently, in this study, we assess the effects of changes in temperature (12 °C and 20 °C) and pCO2 (500 and 1600 μatm) levels in seawater, along with the presence/absence of waterborne cues from the predator crab Homalaspis plana on the physiological and behavioural performance of the snail Tegula atra. Snail consumption rate was positively affected by OW and negatively by predator cues whereas absorption efficiency (AE) was positively affected by OW without interactions among these stressors. Oxygen uptake of snails reared in OW conditions was greater than those in control conditions, but only at control pCO2 levels. When pCO2 level was also raised, the positive effect of warmer temperature on oxygen uptake was reduced. While biomass was negatively affected by OW, OA and predator cues, without interactions. In the presence of predator cues the self-righting times of snails were significantly slower in individuals reared at OW conditions. Additionally, OA and OW conditions do not affect the prey hunting, efficiency (consumption) and preference, and claw strength of the predatory crab. These results indicate that OA and OW affect physiological and behavioral traits of snails but no the predatory behavior of crab. This environmentally-induced decoupling of co-evolutionary predator-prey dynamics may have important consequences on the structure and stability of coastal communities and ecosystems under the influence of climate change.

Nest box entrance hole size can influence nest site selection and nest defence behaviour in Japanese tits

Birds have the ability to assess the risk of predation in their environment and adjust their antipredation strategies based on this risk information. However, whether nest site selection has effect on subsequent nest defence behaviour has not been studied. In this study, we aimed to determine whether the Japanese tit (Parus minor) exhibits a nest-box hole size preference and whether the entrance hole sizes of nest boxes influence the nest defence behaviour of tits. We hung nest boxes with three different entrance hole sizes (diameters: 6.5 cm, 4.5 cm and 2.8 cm) in our study sites and investigated which nest boxes were occupied by tits. In addition, by using dummy-presentation experiments, we observed the nest defence behaviours of tits that nested in boxes with 2.8 cm and 4.5 cm entrance holes towards common chipmunks (Tamias sibiricus, a small nest predator able to enter these holes) and Eurasian red squirrels (Sciurus vulgaris, a large nest predator unable to enter the 2.8 cm entrance hole). The tits that bred in nest boxes with 2.8 cm entrance holes exhibited more intense nest defence responses to chipmunks than to squirrels. In contrast, the tits that bred in nest boxes with 4.5 cm entrance holes exhibited similar nest defence responses to chipmunks and squirrels. Additionally, Japanese tits that bred in nest boxes with 2.8 cm entrance holes exhibited more intense behavioural responses to chipmunks than those that bred in nest boxes with 4.5 cm entrance holes. Our results suggested that Japanese tits prefer to occupy nest boxes with small holes for breeding and that nest-box characteristics influenced their nest defence behaviour.

Investigating the Relationship Between Body Shape and Life History Traits in Toothed Whales: Can Body Shape Predict Fast-Slow Life Histories?

A widespread pattern in vertebrate life-history evolution is for species to evolve towards either fast or slow life histories; however, the underlying causes of this pattern remain unclear. Toothed whales (Odontoceti) are a diverse group with a range of body sizes and life histories, making them an ideal model to investigate potential drivers of this dichotomy. Using ancestral reconstruction, we identified that certain groups of odontocetes evolved more-streamlined, presumably faster, body shapes around the same time that killer whales (Orcinus orca) evolved into whale predators approximately 1 Mya during the Pleistocene. This suggests that the evolution of a streamlined body shape may have been an adaptation to escape killer whale predation, leading to longer life-history events. To test this hypothesis, we performed a cluster analysis of odontocete whales and confirmed the dual pattern of life-history traits, with one group referred to as 'reproducers' characterized by early age of maturity, short gestation, short interbirth interval, and short lifespan, and the other group referred to as 'bet-hedgers' exhibiting the opposite pattern. However, we found that life history grouping was relatively unrelated to whale shape (i.e., more streamlined or less streamlined). Therefore, we incorporated principal component results into mixed effects models, and the model results indicated that body shape was positively related to neonate length (a measure of investment in progeny), but not significantly related to the temporal life-history traits. Thus, whale body shape is not a sufficient explanation for the evolution of fast-slow life histories in odontocete whales.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11692-023-09605-4.

Does atrazine induce changes in predator recognition, growth, morphology, and metamorphic traits of larval skipper frogs (Euphlyctis cyanophlyctis)?

Atrazine, an info disruptor, interferes with the olfaction of aquatic organisms by impairing the chemosensory system. Consequently, it affects behavior, physiology, and growth increases mortality and infections, and suppresses the immune system of aquatic animals. In this study, we wanted to determine the sensitivity of larval Euphlyctis cyanophlyctis to different concentrations of atrazine by assessing their antipredator behavior, growth, morphology, and metamorphic traits. The results indicate that exposure to atrazine did not affect the survival of tadpoles. However, it caused retarded growth at higher concentrations. Interestingly, the antipredator behavior of tadpoles toward conspecific alarm cues decreased in a dose-dependent manner with an increase in the concentration of atrazine. Tadpoles exposed to low concentrations of atrazine had deeper, wider bodies and tails while those exposed to higher concentrations had shallower and narrower bodies with shallower tail muscles. However, at low and moderate concentrations atrazine did not affect size at metamorphosis, it extended the larval duration at higher concentrations.

On the different role of alarm substances and fish kairomones in diapause induction in a freshwater planktonic crustacean

Many aquatic organisms anticipate predation risk via infochemical detection. In a laboratory experiment, we investigated the expression of life-history responses in planktonic Daphnia magna under long-lasting exposure to various concentrations of fish kairomones (FK) and alarm substances of Daphnia (AS). Daphnia were exposed to one of six concentrations of AS (0, 0.0005, 0.005, 0.05, 0.5, 5 homogenized D. magna/L) mixed with the highest concentration of FK, or to one of six concentrations of FK (diluted fish feces of 0, 0.001, 0.002, 0.01, 0.02, 0.1 fish/L) accompanied by the highest concentration of AS. FK alone at the highest concentration were sufficient to induce diapause in 21% of Daphnia, while AS alone at the highest concentration did not trigger diapause. Mixed at the highest concentrations, both cues induced diapause in 94% of Daphnia, whereas in the control treatment free of infochemicals no ephippial individuals occurred. No significant size or fecundity changes accompanied the diapause response. The graded type of diapause response observed across a wide concentration AS concentrations suggests that Daphnia use AS concentration as a proxy for the level of non-specific predation risk. In contrast, the abrupt change of diapause response across a narrow concentration of FK suggests that they were more critical to identify predator origin than level of risk.

Long-Tailed Pygmy Rice Rats Modify Their Behavioural Response and Faecal Corticosterone Metabolites in Response to Culpeo Fox but Not to Lesser Grison

Simple Summary

Prey species must fine-tune their antipredator responses to survive, but also to achieve a positive net energy balance which will enhance biological fitness. Given this, we investigated if Oligoryzomys longicaudatus would adapt their behavioural and physiological antipredator responses depending on their relative presence in the predator’s diet. By exposing this rodent species to culpeo fox and lesser grison faeces, we found that O. longicaudatus behavioural and physiological strategies were modulated depending on the predator’s diet. Specifically, rodents would trigger their antipredator responses in the presence of the most dangerous predator, the culpeo, which consumes a higher proportion of O. longicaudatus compared to the lesser grison. Our findings could be of importance for the development of more humane and efficient strategies to control rodent populations.

Abstract

Even though behavioural and physiological reactions to predation risk exhibited by prey species have received considerable attention in scientific journals, there are still many questions still unsolved. Our aim was to broaden the knowledge on one specific question: do long-tailed pygmy rice rats adapt their behavioural and physiological antipredator strategies depending on the predator species? For this question, we live-trapped in a temperate forest in Southern Chile long-tailed pygmy rice rats (Oligoryzomys longicaudatus), which were exposed to three predator odour phases (Phase 0: preliminary, no predator cues; Phase 1: one plot with culpeo fox faeces (Lycalopex culpaeus), one plot with lesser grison (Galictis cuja) faeces and one plot acting as a control with no odour; Phase 2: post treatment, no predator cues). We measured the behavioural response by the capture ratio. To assess the physiological stress response, we collected fresh faecal samples to quantify faecal corticosterone metabolites (FCM). Our results showed that O. longicaudatus increased both the capture ratio and FCM levels in the presence of culpeo cues. Culpeo foxes have higher densities in the study area than G. cuja and exhibit a higher activity pattern overlap with O. longicaudatus. Moreover, it has been also been reported in other regions that L. culpaeus consumption of O. longicaudatus is more frequent compared to G. cuja diet. The increase in capturability could be because traps can be regarded as a shelter in high-risk settings, but it can also be explained by the predator inspection behaviour. The increase in FCM concentrations during culpeo treatment can be linked to the adaptive mobilisation of energy to execute antipredator responses to increase survival chances.

The context dependence of non-consumptive predator effects

Non-consumptive predator effects (NCEs) are now widely recognised for their capacity to shape ecosystem structure and function. Yet, forecasting the propagation of these predator-induced trait changes through particular communities remains a challenge. Accordingly, focusing on plasticity in prey anti-predator behaviours, we conceptualise the multi-stage process by which predators trigger direct and indirect NCEs, review and distil potential drivers of contingencies into three key categories (properties of the prey, predator and setting), and then provide a general framework for predicting both the nature and strength of direct NCEs. Our review underscores the myriad factors that can generate NCE contingencies while guiding how research might better anticipate and account for them. Moreover, our synthesis highlights the value of mapping both habitat domains and prey-specific patterns of evasion success ('evasion landscapes') as the basis for predicting how direct NCEs are likely to manifest in any particular community. Looking ahead, we highlight two key knowledge gaps that continue to impede a comprehensive understanding of non-consumptive predator-prey interactions and their ecosystem consequences; namely, insufficient empirical exploration of (1) context-dependent indirect NCEs and (2) the ways in which direct and indirect NCEs are shaped interactively by multiple drivers of context dependence.

Phenotypic plasticity of senescence in Daphnia under predation impact: no ageing acceleration when the perceived risk decreases with age

Recognising the nature of the predation risk, and responding to it accurately, is crucial to fitness. Yet, even the most accurate adaptive responses to predation risk usually entail costs, both immediate and lifelong. Rooting in life-history theory, we hypothesize that an animal can perceive the nuances of prey size and age selectivity by the predator and modulate its life history accordingly. We test the prediction that-contrary to the faster or earlier senescence under predation risk that increases with prey size and age-under predation risk that decreases with prey size and age either no senescence acceleration or even its deceleration is to be observed. We use two species of indeterminate growers, small crustaceans of the genus Daphnia, Daphnia Pulex and Daphnia magna, as the model prey, and their respective gape-limited invertebrate predators, a dipteran, midge larva Chaoborus flavicans, and a notostracan, tadpole shrimp Triops cancriformis. We analyse age-specific survival, mortality and fertility rates, and find no senescence acceleration, as predicted. With this study, we complete the picture of the expected non-consumptive phenotypic effects of perceived predation pressure of different age-dependence patterns.

Big and bad: how relative predator size and dietary information influence rusty crayfish (Faxonius rusticus) behavior and resource-use decisions

Prey animals use the information that they extract from predator cues to assess risk. Animals can obtain information about the relative size of predators and their dietary constituents from odor cues that predators deposit in the environment. However, it is currently unknown how prey animals respond when presented with two or more pieces of information about a predator. Rusty crayfish (Faxonius rusticus (Girard, 1852)) were exposed to odors from predatory largemouth bass (Micropterus salmoides (Lacepède, 1802)) that were fed four different diets and also varied in size relative to the crayfish subjects. A series of analyses of covariance (ANCOVA) indicated that rusty crayfish altered their macrophyte consumption, foraging behavior, and shelter-use behavior depending on the relative size and dietary information presented by the largemouth bass. This study demonstrates that prey consider and respond to multiple aspects of a predatory threat when making resource-use decisions.

Long-term study of behaviors of two cohabiting sea urchin species, Mesocentrotus nudus and Strongylocentrotus intermedius, under conditions of high food quantity and predation risk in situ

Background

In the predator–sea urchin–macrophyte trophic cascade, the ecological effect of sea urchins as grazers depends both on their density and the changes in foraging activity, which are influenced by various disturbing factors. However, the complete duration of the alarm reactions of echinoids has not been studied until now. Here, we tested a hypothesis that two cohabiting sea urchins, Mesocentrotus nudus and Strongylocentrotus intermedius, which differ morphologically, might display different behavioral responses to high hydrodynamic activity and predation.

Methods

We used continuous time-lapse video recording to clarify behavioral patterns of M. nudus and S. intermedius in presence of a large quantity of food (the kelp Saccharina japonica) but under different weather conditions and different types of predation threat: (1) calm weather conditions, (2) stormy weather conditions, (3) predation risk associated with the presence of several sea star species and (4) predation risk associated with an alarm stimulus (crushed conspecifics or heterospecifics). Three separate video recording experiments (134 days in total) were conducted under field conditions. Video recording analysis was performed to determine the number of specimens of each sea urchin species in the cameras’ field of view, size of sea urchins’ groups, movement patterns and the duration of the alarm responses of both sea urchin species.

Results

We showed that in the presence of kelp, M. nudus and S. intermedius exhibited both similar and different behavioral responses to hydrodynamics and predation threat. Under calm weather, movement patterns of both echinoids were similar but M. nudus exhibited the higher locomotion speed and distance traveled. Furthermore, S. intermedius but not M. nudus tended to group near the food substrate. The stormy weather caused a sharp decrease in movement activity followed by escape response in both echinoids. Six starfish species failed to predate on healthy sea urchins of either species and only a few attacks on ailing S. intermedius specimens were successful. The alarm response of S. intermedius lasted approximately 90 h and 20 h for starfish attacks on ailing conspecifics and for simulated attacks (crushed conspecifics or heterospecifics), respectively and involved several phases: (1) flight response, (2) grouping close to the food, (3) leaving the food and (4) return to the food. Phase three was the more pronounced in a case of starfish attack. M. nudus only responded to crushed conspecifics and exhibited no grouping behavior but displayed fast escape (during 4 h) and prolonged (up to 19 days) avoidance of the food source. This outcome is the longest alarm response reported for sea urchins.

Discussion

The most interesting finding is that two cohabiting sea urchin species, M. nudus and S. intermedius, display different alarm responses to predation threat. Both alarm responses are interpreted as defensive adaptations against visual predators.

Chemical ecology of the marine plankton

A review of chemically mediated interactions in planktonic marine environments covering new studies from January 2015 to December 2017.

Influence of interspecific interactions on avoidance response to contamination

An increasing number of studies have shown the ability of organisms to escape from toxic effects due to contamination, by moving spatially towards less contaminated habitats. However, this issue has been investigated in monospecific scenarios, without considering possible interactions between species during the contamination avoidance process. It is widely known that the spatial distribution of one species can be affected by another one, in different ways. Therefore, the main question addressed in the present study was as follows: Might interspecific interaction between the freshwater fish Danio rerio (zebrafish) and Poecilia reticulata (guppy) change their behavior patterns in terms of avoidance in the presence of a copper gradient? Zebrafish and guppies exposed to a copper gradient were tested for avoidance responses in a free-choice, non-forced, static, multi-compartmented exposure system, using two distinct approaches: (1) monospecific tests, in which only one species was exposed to the copper gradient, at two different population densities; and (2) multispecific tests, in which both species were tested simultaneously. In the control (with no copper) monospecific tests, both species were randomly distributed; however, in the control multispecific test, P. reticulata tended to aggregate. In the monospecific tests with a copper gradient, both species avoided copper in a similar way, with AC₅₀ (concentration triggering avoidance in 50% of the exposed population) values between 15 and 18 μg·L^-1, irrespective of the population density. However, in the multispecific tests, P. reticulata displaced D. rerio to previously avoided copper levels, consequently increasing the AC₅₀ of D. rerio to 75 μg·L^-1. This study shows the importance of understanding the interactions among species in contaminated areas, and the way that one species can prevent the avoidance behavior of another.

Considerations Used by Desert Isopods to Assess Scorpion Predation Risk

Animals adjust behaviors to balance changes in predation risk against other vital needs. Animals must therefore collect sensory information and use a complex risk-assessment process that estimates risks and weighs costs and benefits entailed in different reactions. Studying this cognitive process is challenging, especially in nature, because it requires inferring sensory abilities and conscious decisions from behavioral reactions. Our goal was to address this empirical challenge by implementing psychophysical principles to field research that explores considerations used by desert isopods (Hemilepistus reaumuri) to assess the risk of scorpions that hunt exclusively from within their burrows. We introduced various combinations of chemical and physical cues to the vicinity of isopod burrows and recorded their detailed reactions on first encountering the cues. The isopods reacted defensively to scorpion odor but only when accompanied with excavated soil or other odors typically found near scorpion burrows. Isopods also reacted defensively to piles of excavated soil without scorpion olfactory cues, suggesting that isopods take precautions even against physical disturbances that do not necessarily reflect predator activity. Simultaneous presence of different cues provoked graded responses, possibly reflecting an additive increase in risk estimation. We conclude that wild isopods use defensive reactions toward environmental signals only when the integrated perceptual information implies an active scorpion burrow or when they lack data to refute this possibility.

Wild Norway Rats Do Not Avoid Predator Scents When Collecting Food in a Familiar Habitat: A Field Study

The ability to avoid predators is crucial to wild prey animals’ survival. Potential danger is signalled, among others, by the presence of predator scents. These odors are used in research both to trigger and to study fear reactions in laboratory animals; they are also employed as repellents against pest rodent species. In our study, we assessed nine predator-derived odors for their effectiveness in eliciting avoidance responses in a free-living colony of Norway rats (Rattus norvegicus). The rats were studied in a field setting. Food was put in two compartments inside the experimental pen: in one of them, predator scent was introduced on experimental days. The rats did not avoid boxes with predator odor and did not display an increased latency of food-carrying behavior or any other fear-related behavior, such as freezing or increased grooming. The results confirm the hypothesis that the foraging of rodents in a well-known territory and in relative proximity to burrows and other shelters is not affected by indirect cues of predation risk, such as the presence of predator urine or feces. We have also concluded that in a well-established colony living in a familiar territory, predator scent holds little promise as rodent repellent.

Predator recognition of chemical cues in crayfish: diet and experience influence the ability to detect predation threats

Aquatic prey often alter their morphology, physiology, and/or behaviour when presented with predatory chemical cues which are heavily influenced by the diet of the predator. We tested the roles that diet and prey familiarity with predators play in the ability of prey to recognize predator threats. Odours from two fish, bass and cichlid fed a vegetarian, protein, heterospecific, and a conspecific diet, were collected and presented to virile crayfish in a choice arena. Our results show that crayfish altered their behaviour in the presence of odours containing conspecific, as opposed to heterospecific diets, but only from familiar predators. A reduced anti-predator response was measured with odours from an unfamiliar predator fed conspecific crayfish. Therefore, crayfish may be able to determine different threat levels based on the different dietary cues from a potential predator, but only when the prey have familiarity with the predators.

Behavioral responses of CD-1 mice to conspecific and heterospecific blood odors and to a blood odor component

The odor of blood may have both aversive and attractive properties for mammals, depending on the species of the odor donor and the species perceiving the odor. To better understand the informational content of blood odor for a prey species we assessed behavioral responses of male CD-1 mice (n=60) to the odor of blood of same-sex and opposite-sex conspecifics, of a natural predator of mice (cat), and of a herbivore (horse) and an omnivore (human) non-predator of mice. Further, we assessed their behavior towards the mammalian blood odor component trans-4,5-epoxy-(E)-2-decenal which recent studies have shown to be as attractive to mammalian predators as the odor of real blood. A two-compartment test arena was used to record approach/avoidance behavior when the animals were presented with an odor in one compartment and a blank control in the other compartment. We found that both conspecific and heterospecific blood odors elicited significant avoidance behavior in the mice whereas a control odor (n-pentyl acetate) did not. The blood odor component trans-4,5-epoxy-(E)-2-decenal was also significantly avoided and thus appears to play an important role in the perception of mammalian blood odor in this prey species. These results support the notion that mammalian blood odor contains an olfactory warning signal which elicits an adaptive behavioral avoidance response in a prey species, the mouse. Our finding that the mice avoided the mammalian blood odor component trans-4,5-epoxy-(E)-2-decenal to the same degree as the odor of real blood suggests that this volatile compound might be (part of) this warning signal.

Algae associated with coral degradation affects risk assessment in coral reef fishes

Habitat degradation alters the chemical landscape through which information about community dynamics is transmitted. Olfactory information is crucial for risk assessment in aquatic organisms as predators release odours when they capture prey that lead to an alarm response in conspecific prey. Recent studies show some coral reef fishes are unable to use alarm odours when surrounded by dead-degraded coral. Our study examines the spatial and temporal dynamics of this alarm odour-nullifying effect, and which substratum types may be responsible. Field experiments showed that settlement-stage damselfish were not able to detect alarm odours within 2 m downcurrent of degraded coral, and that the antipredator response was re-established 20-40 min after transferral to live coral. Laboratory experiments indicate that the chemicals from common components of the degraded habitats, the cyanobacteria, Okeania sp., and diatom, Pseudo-nitzschia sp.prevented an alarm odour response. The same nullifying effect was found for the common red algae, Galaxauria robusta, suggesting that the problem is of a broader nature than previously realised. Those fish species best able to compensate for a lack of olfactory risk information at key times will be those potentially most resilient to the effects of coral degradation that operate through this mechanism.

Eastern Oysters Crassostrea virginica Produce Plastic Morphological Defenses in Response to Crab Predators Despite Resource Limitation

Many prey react to predation risk by altering their phenotype to reduce their chances of being consumed but incur reductions in growth and fecundity when reacting to predators. To determine when to produce defenses, prey collect information and evaluate the costs and benefits of defense induction. Resource availability can affect prey ability and willingness to incur defense costs. When resources are scarce, defenses may suffer disproportionate decreases in energy allocation if defenses would further reduce prey access to resources or if resources are needed to maintain metabolic functions. We tested the effects of predation risk and resource availability on plastic defenses in eastern oysters Crassostrea virginica and present novel findings that oysters continued to produce defended shells in response to predators when resources were limited, even though they grew smaller, lighter shells when deprived of food in control conditions. Predation risk affected all three tested shell metrics (area, weight, and strength), but food availability did not. Although low food levels often limit expression of predator defenses, predator cues caused oysters to build shells that were larger and heavier, with a similar trend for shell strength, in treatments with both low and high food levels, suggesting that predation is an important pressure in this system. The differences between predator and control treatments were greater under conditions of low food availability, and thus, resource availability may influence interpretations of plastic responses to predators.

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.

Predatory blue crabs induce stronger nonconsumptive effects in eastern oysters Crassostrea virginica than scavenging blue crabs

By influencing critical prey traits such as foraging or habitat selection, predators can affect entire ecosystems, but the nature of cues that trigger prey reactions to predators are not well understood. Predators may scavenge to supplement their energetic needs and scavenging frequency may vary among individuals within a species due to preferences and prey availability. Yet prey reactions to consumers that are primarily scavengers versus those that are active foragers have not been investigated, even though variation in prey reactions to scavengers or predators might influence cascading nonconsumptive effects in food webs. Oysters Crassostrea virginica react to crab predators by growing stronger shells. We exposed oysters to exudates from crabs fed live oysters or fed aged oyster tissue to simulate scavenging, and to controls without crab cues. Oysters grew stronger shells when exposed to either crab exudate, but their shells were significantly stronger when crabs were fed live oysters. The stronger response to predators than scavengers could be due to inherent differences in diet cues representative of reduced risk in the presence of scavengers or to degradation of conspecific alarm cues in aged treatments, which may mask risk from potential predators subsisting by scavenging.

Inducible defenses in Olympia oysters in response to an invasive predator

The prey naiveté hypothesis suggests that native prey may be vulnerable to introduced predators because they have not evolved appropriate defenses. However, recent evidence suggests that native prey sometimes exhibit induced defenses to introduced predators, as a result of rapid evolution or other processes. We examined whether Olympia oysters (Ostrea lurida) display inducible defenses in the presence of an invasive predator, the Atlantic oyster drill (Urosalpinx cinerea), and whether these responses vary among oyster populations from estuaries with and without this predator. We spawned oysters from six populations distributed among three estuaries in northern California, USA, and raised their offspring through two generations under common conditions to minimize effects of environmental history. We exposed second-generation oysters to cue treatments: drills eating oysters, drills eating barnacles, or control seawater. Oysters from all populations grew smaller shells when exposed to drill cues, and grew thicker and harder shells when those drills were eating oysters. Oysters exposed to drills eating other oysters were subsequently preyed upon at a slower rate. Although all oyster populations exhibited inducible defenses, oysters from the estuary with the greatest exposure to drills grew the smallest shells suggesting that oyster populations have evolved adaptive differences in the strength of their responses to predators. Our findings add to a growing body of literature that suggests that marine prey may be less likely to exhibit naiveté in the face of invasive predators than prey in communities that are more isolated from native predators, such as many freshwater and terrestrial island ecosystems.

Social cues may advertise habitat quality to refuge-seeking conspecifics

Individuals travelling through landscapes may use the presence of conspecifics to evaluate habitat quality. Juvenile Atlantic salmon (Salmo salar L., 1758) are usually territorial and exhibit some degree of density-dependent regulation in wild populations. They are also vulnerable to heat stress and may need to locate a thermal refuge to offset metabolic costs above certain temperature thresholds. During July 2010, a heat wave resulted in water temperatures in the Miramichi River system exceeding 30 °C. During this period, salmon parr were observed aggregating in cold-water refugia at densities several orders of magnitude greater than usual. We tested whether groups of wild-caught salmon parr held at high densities (160 parr/m2) would have an attractant effect on free-swimming parr at three sites differing in temperature between 16.5 and 24 °C. Although neither temperature nor site influenced the number of parr that we observed, there were significantly more parr in close proximity (<1 m) to the artificial aggregations than to the controls. These results suggest that social cues from high-density aggregations of conspecifics during extreme temperature events may advertise the location of thermal refugia to others. Understanding how heat-stressed salmon locate refugia may prove valuable to ongoing conservation efforts given the likelihood of increasingly frequent and extreme high-temperature events.

You Are What you Eat: a Metabolomics Approach to Understanding Prey Responses to Diet-Dependent Chemical Cues Released by Predators

Prey responses to predator cues are graded in intensity in accordance with the degree of threat presented by the predator. In systems in which prey gather information on predators by using chemicals, prey often respond more to the odor of predators that have consumed conspecifics, as opposed to heterospecifics. We investigated the response of a prey species, the mud crab, Panopeus herbstii, to urine of blue crab, Callinectes sapidus, fed mud crabs or oysters. Behavioral analysis was combined with metabolomics to characterize bioactive deterrents in the urine of predators fed different diets. Urine from blue crabs fed oysters or mud crabs depressed mud crab foraging when presented singly, with the urine derived from a mud crab diet being more potent. The magnitude of foraging depression increased with urine concentration. When urine from blue crabs fed oysters or mud crabs was combined, response to the urine mixture was no different from that to urine derived only from a mud crab diet. Metabolomics analysis indicated diet-dependent differences were related to a set of shared spectral features that differed in concentration in the respective urines, likely consisting of aromatic compounds, amino acids, and lipids. Taken together, these results suggest mud crabs distinguish diet of, and therefore the risk imposed by, predators through detection of a suite of compounds that together represent what the predator has recently consumed.

Risk assessment and predator learning in a changing world: understanding the impacts of coral reef degradation

Habitat degradation is among the top drivers of the loss of global biodiversity. This problem is particularly acute in coral reef system. Here we investigated whether coral degradation influences predator risk assessment and learning for damselfish. When in a live coral environment, Ambon damselfish were able to learn the identity of an unknown predator upon exposure to damselfish alarm cues combined with predator odour and were able to socially transmit this learned recognition to naïve conspecifics. However, in the presence of dead coral water, damselfish failed to learn to recognize the predator through alarm cue conditioning and hence could not transmit the information socially. Unlike alarm cues of Ambon damselfish that appear to be rendered unusable in degraded coral habitats, alarm cues of Nagasaki damselfish remain viable in this same environment. Nagasaki damselfish were able to learn predators through conditioning with alarm cues in degraded habitats and subsequently transmit the information socially to Ambon damselfish. Predator-prey dynamics may be profoundly affected as habitat degradation proceeds; the success of one species that appears to have compromised predation assessment and learning, may find itself reliant on other species that are seemingly unaffected by the same degree of habitat degradation.