Presence Of Predation Risk Research Articles

Fish predation risk alters the microbiota of Daphnia in the process of inducing its life‐history defence traits

Abstract Host‐associated microbiota is an essential mediator of host adaptation to changeable environmental conditions. However, whether fish predation risk alters the gut microbiota composition of Daphnia while also of inducing Daphnia's life‐history defence traits remains unclear. Examination of the effect of predation risk on prey‐associated microbiota may help in improving our understanding of induced anti‐predation defence from a microbial perspective. In this study, Daphnia magna was used as the model organism to investigate the changes in the microbiota in the gut of Daphnia as well as in the whole Daphnia and the culture medium during D. magna life‐history anti‐predation defence. The relationship of these changes with the development stage was also assessed. The results showed that predation risk can simultaneously induce anti‐predation defences and reshape the associated microbiota composition of Daphnia. The gut microbiota of D. magna responded to both developmental stages and predation risk. The Shannon diversity of gut microbiota under predation risk decreased significantly with developmental stage. The abundance of dominant bacteria such as Burkholderiaceae and Flavobacteriaceae decreased under predation risk and was further reduced with developmental stage. Functional prediction results showed that the presence of predation risk mainly weakened overall microbial function, especially metabolic function, in the gut of D. magna. The weakening of microbial function was most obvious during sexual maturity. In addition, the number of unique operational taxonomic units in the whole Daphnia and dissected guts under predation risk was significantly higher than those in control. Based on the screening results, the Pantoea genus (Erwiniaceae family) can clearly distinguish dissected gut samples with or without predation risk. The present study provided more insights into the structural features and functional roles of the Daphnia microbiota and improved our understanding of induced anti‐predation defence from a microbial perspective. Furthermore, this study highlights the possible complex correlations that exist between induced defensive traits and altered microbiota, which warrants further investigation.

Transcriptome-wide genotype-phenotype associations in Daphnia in a predation risk environment.

Phenotypic variation plays an important role in how species cope with environmental challenges. Pinpointing which genes and genomic regions are underlying phenotypic variability thus helps to understand the processes of acclimation and adaptation. We used Daphnia as a system to identify candidates playing a role in phenotypic variation related to a predation risk environment with a genome-wide association approach. Furthermore, a gene co-expression network analysis allowed identifying clusters of co-expressed genes which correlated to life history traits. To enhance the understanding of the functional roles of the transcripts, we identified orthologs and paralogs from related species and used ontologies to annotate the candidates of interest. Our study revealed that only one life history trait and two morphometric traits have a genetic association in the presence of predation risk (fish kairomones), whereas most genotype-phenotype associations were detected in a genotype-environment interaction analysis for reproduction-related phenotypic traits. The gene co-expression network analysis identified a total of 44 modules, of which one module correlated to another life history trait namely the 'total number of broods'. The combined use of gene co-expression network and transcriptome-wide association analysis allowed the identification of 131 candidate transcripts associated with life history traits in Daphnia galeata. These results lay the ground for targeted studies to further understand phenotypic variability in this species.

Local predation risk and matrix permeability interact to shape movement strategy

In fragmented landscapes, the reduced connectivity among patches drives the evolution of movement strategies through an increase of transience costs. Reduced movements may further alter heterogeneity in biotic and abiotic conditions experienced by individuals. The joint action of local conditions and matrix permeability may shape emigration decisions. Here, we tested the interactive effects of predation risk and matrix permeability on movement propensity, movement costs and movers’ phenotype in the common toad Bufo bufo. In a full‐crossed experimental design, we assessed the movement propensity of juveniles in three connectivity treatments (from poorly to highly permeable matrix), with or without predation risk in their living patch. We also assessed the relationships between movement propensity and morphological traits (i.e. body and leg length) and how it affected the movement cost (i.e. mass loss). Movement propensity increased in presence of predation risk, while matrix permeability had no effect. However, matrix permeability interacted with predation risk to influence movers’ phenotype and the physiological cost they endured while moving. In particular, a well‐known movement syndrome in toads (i.e. movement propensity positively related to longer legs) depended on the interaction between matrix permeability and predation risk and resulted in differences in mass loss among matrix types. Movers lost more mass on average than residents except when they also displayed longer legs or when they crossed the most permeable matrix in the presence of predation risk. Our results show that matrix permeability shapes the physiological cost of dispersal by changing the identity of individuals moving away from local conditions. As the movers’ phenotype can importantly alter (meta)population dynamics, context‐dependency of dispersal syndromes should be considered in studies predicting the functioning of human‐altered natural systems.

Assessing the risk effects of native predators on the exotic American bullfrog (Lithobates catesbeianus) and their indirect consequences to ecosystem function

Understanding the factors and mechanisms that affect the impacts of invasive species in invaded environments has been widely debated among researchers. However, few studies about invasive species have explored the effects of predation risks by native predators on exotic prey. Herein, the traditional invasive predator-native prey framework was reversed. We tested if tadpoles, of the worldwide invasive American Bullfrog Lithobates catesbeianus, were affected by the predation risk imposed by native predators. We used two different species of belostomatid predators and tested whether and how predation-induced phenotypic plasticity on L. catesbeianus reverberated in morphological, physiological, and ecosystem-level processes. Individuals of L. catesbeianus modified their morphological (tail muscle width), behavioral (activity and foraging), and physiological (growth and growth efficiency) traits in the presence of predation risk. Based on the observed morphological changes, our results suggest that prey may recognize predator-specific cues. In addition, we observed that L. catesbeianus' responses to predation risk can affect ecosystem-level properties, by inducing trophic cascades and reducing animal-mediated nutrient recycling rates. In summary, our study supports that exotic prey species who are subjected to native predators may display anti-predator responses, with implications for their development, as well as possible ecosystem-level effects.

Mangrove expansion into temperate marshes alters habitat quality for recruiting Callinectes spp.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 573:1-14 (2017) - DOI: https://doi.org/10.3354/meps12176 FEATURE ARTICLE Mangrove expansion into temperate marshes alters habitat quality for recruiting Callinectes spp. Cora A. Johnston1,3,*, Olivia N. Caretti2,4 1Department of Entomology, University of Maryland, College Park, MD 20742, USA 2Department of Biology, St. Mary’s College of Maryland, St. Mary’s City, MD 20686, USA 3Present address: Marine Science Institute, University of California, Santa Barbara, CA 93106, USA 4Present address: Department of Marine, Earth & Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, USA *Corresponding author: coraann.johnston@gmail.com ABSTRACT: Beyond direct habitat loss, climate change can alter habitat quality and availability by stimulating shifts in foundation species ranges. Tropical mangroves are proliferating at the intersection with temperate saltmarshes and continue moving poleward with unknown consequences for inhabitant marine fauna. We expected that mangrove and marsh foundation species differ in habitat quality, due at least in part to differences in their structural attributes, such that shifts from marsh to mangrove wetlands alter habitat availability for wetland inhabitants. We coupled recruitment surveys and laboratory experiments to assess the influences of foundation species’ structural and non-structural attributes on Callinectes spp. recruitment, preference, and survival among mangrove and marsh habitats. Recruitment was evident in Spartina alterniflora and Rhizophora mangle intertidal habitats but not in Avicennia germinans. In laboratory trials, S. alterniflora was preferred in the presence of predation risk and provided the highest probabilities of survival, indicating that settlers can distinguish among ecotone vegetation types and that their choices correspond to habitat quality. Survival probability and recruit persistence were comparatively low in mangrove habitats. The differences in habitat use, preference, and survival identified in this study suggest that mangrove expansion is diminishing wetland habitat for Callinectes spp. It also reveals that changes between habitat-forming species, and not just the loss of structure per se, can affect habitat quality, such that foundation species may not replace one another functionally where they displace each other spatially. KEY WORDS: Foundation species · Climate change · Biogenic habitat · Range shifts · Recruitment · Survival Full text in pdf format Information about this Feature Article Supplementary material NextCite this article as: Johnston CA, Caretti ON (2017) Mangrove expansion into temperate marshes alters habitat quality for recruiting Callinectes spp.. Mar Ecol Prog Ser 573:1-14. https://doi.org/10.3354/meps12176 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 573. Online publication date: June 21, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Resource levels and prey state influence antipredator behavior and the strength of nonconsumptive predator effects

The risk of predation can drive trophic cascades by causing prey to engage in antipredator behavior (e.g. reduced feeding), but these behaviors can be energetically costly for prey. The effects of predation risk on prey (nonconsumptive effects, NCEs) and emergent indirect effects on basal resources should therefore depend on the ecological context (e.g. resource abundance, prey state) in which prey manage growth/predation risk tradeoffs. Despite an abundance of behavioral research and theory examining state‐dependent responses to risk, there is a lack of empirical data on state‐dependent NCEs and their impact on community‐level processes. We used a rocky intertidal food chain to test model predictions for how resources levels and prey state (age/size) shape the magnitude of NCEs. Risk cues from predatory crabsCarcinus maenascaused juvenile and sub‐adult snailsNucella lapillusto increase their use of refuge habitats and decrease their growth and per capita foraging rates on barnaclesSemibalanus balanoides. Increasing resource levels (high barnacle density) and prey state (sub‐adults) enhanced the strength of NCEs.Our results support predictions that NCEs will be stronger in resource‐rich systems that enhance prey state and suggest that the demographic composition of prey populations will influence the role of NCEs in trophic cascades. Contrary to theory, however, we found that resources and prey state had little to no effect on snails in the presence of predation risk. Rather, increases in NCE strength arose because of the strong positive effects of resources and prey state on prey foraging rates in the absence of risk. Hence, a common approach to estimating NCE strength – integrating measurements of prey traits with and without predation risk into a single metric – may mask the underlying mechanisms driving variation in the strength and relative importance of NCEs in ecological communities.

Cautious versus desperado males: predation risk affects courtship intensity but not female choice in a wolf spider

Understanding the decisions that animals make in the presence of predation risk can reveal their assessment of current and future reproductive options. The wolf spider, Pardosa milvina, has a conspicuous courtship display that is an indicator of male quality. In an initial experiment, we determined that male courtship was highly repeatable and correlated with symmetry. We then used symmetry as an indicator of quality to explore the reactions of males when presented with simulated predation risk and an attractive virgin female. There were no differences in courtship features between risk and no risk treatments unless we took into account male quality. High-quality males reduced courtship intensity under risk conditions suggesting that they estimated their long-term fitness prospects as strong. This response is consistent with the asset protection principle, which suggests that animals with high value traits should behave cautiously. Low-quality males courted at high levels under predation risk, which seemed to be reckless attempts to attract females. This response is analogous to the effect, which is one explanation for vigorous fighting by inferior animals in contests. Although females used behavior to select males when no predator information was present, they seemed to use symmetry in the presence of predator cues. The ability of females to select the most attractive males suggests that they can accurately assess male quality under laboratory conditions. High courting desperado males may occasionally be selected in more complex environments and/or when they are in competition with other males.

Intimidating courtship and sex differences in predation risk lead to sex-specific behavioural syndromes

Behavioural correlations between mating behaviour and antipredator behaviour are expected when sexual behaviour increases predation risk. However, the correlation would be different between males and females, particularly when the sexes experience different levels of predation risk. Here, we tested this idea using a water strider species, Gerris gracilicornis (Heteroptera: Gerridae). G. gracilicornis males employ an unusual intimidating courtship strategy capitalizing on predator behaviours and female response to predators. Since mounted females are more vulnerable than males to predatory attacks from below, we predicted that changes in female mating behaviours across predation contexts (boldness in a mating context) should be associated with female antipredator behaviours (boldness in a nonmating context), but that the correlation would be weaker for male mating behaviours. In a series of behavioural assays, we measured water striders' (1) mating behaviour in the absence of predators, (2) mating behaviour in the presence of predation risk, (3) boldness in the mating context (changes in female mating behaviour after predator attacks) and (4) boldness in the nonmating context. We found that females behaved more cautiously around predators in both the mating and nonmating contexts. We also found that females' boldness in the mating context was significantly correlated with their boldness in the nonmating context. In contrast to females, antipredator behaviour of males in the nonmating context did not correlate with their boldness in the mating context. Thus we suggest that sex differences in boldness across predation contexts appear to cause sex-specific behavioural syndromes.

Mating behavior of Daphnia: impacts of predation risk, food quantity, and reproductive phase of females.

High predation risk and food depletion lead to sexual reproduction in cyclically parthenogenetic Daphnia. Mating, the core of sexual reproduction, also occurs under these conditions. Assessment of the environmental conditions and alteration of mating efforts may aid in determining the success of sexual reproduction. Here, we evaluated the impacts of predation risk, food quantity, and reproductive phase of females on the mating behavior of Daphnia obtusa males including contact frequency and duration using video analysis. Mating–related behavior involved male–female contact (mating) as well as male–male contact (fighting). Mating frequency increased while unnecessary fighting decreased in the presence of predation risk. In addition, low food concentration reduced fighting between males. Males attempted to attach to sexual females more than asexual females, and fighting occurred more frequently in the presence of sexual females. Duration of mating was relatively long; however, males separated shortly after contact in terms of fighting behavior. Thus, assessment of environmental factors and primary sexing of mates were performed before actual contact, possibly mechanically, and precise sex discrimination was conducted after contact. These results suggest that mating in Daphnia is not a random process but rather a balance between predation risk and energetic cost that results in changes in mating and fighting strategies.

Non‐pathogenic aquatic bacteria activate the immune system and increase predation risk in damselfly larvae

SummaryPathogens can increase vulnerability to predation through their harmful effects on hosts. Recently, it was shown that the mere activation of the immune system by pathogens may increase the host's risk of predation. Here, we test whether exposure to non‐pathogenic bacteria also activates the immune system and thereby increases vulnerability to predation.We exposedEnallagma cyathigerumdamselfly larvae to a non‐pathogenic strain of the bacteriumEscherichia coliand measured immune defence, anti‐predator behaviour and survival times in the presence of larval dragonfly predators. To evaluate whether non‐pathogenic bacteria also generated energy‐based trade‐offs leading to other fitness costs, we also quantified growth rate and survival in the absence of predators.Exposure to the non‐pathogenic bacterium did not affect survival in the absence of the predator but increased growth rate, possibly a response to reduce exposure time to the bacterium. Larvae exposed to the bacterium activated their immune response as shown by an increase in the activity of phenoloxidase and the number of haemocytes. The bacterium affected anti‐predator traits involved in avoiding detection by predators as well as traits involved in escape after detection. Pre‐exposed larvae showed higher activity levels and further increased the number of feeding strikes in the presence of predation risk, possibly driven by energetic constraints. Pre‐exposed larvae swam less often when attacked, but faster. This impaired anti‐predator response came at the ecological cost of increased vulnerability to predation.Our study demonstrated that exposure to non‐pathogenic bacteria increases vulnerability to predation, which is a novel type of antagonistic interaction. This highlights the unexplored possibility that non‐pathogens may play a role in maintaining variation in immune defence through insidious effects on predator–prey interactions. Since non‐pathogenic bacteria can be very abundant, this unexplored ecological cost of immune system activation in terms of increased predation may have major consequences in natural systems and may provide an unexplored new force underlying variation in immune defence.

Risk‐taking behaviour may explain high predation mortality of GH‐transgenic common carp Cyprinus carpio

The competitive ability and habitat selection of juvenile all-fish GH-transgenic common carp Cyprinus carpio and their size-matched non-transgenic conspecifics, in the absence and presence of predation risk, under different food distributions, were compared. Unequal-competitor ideal-free-distribution analysis showed that a larger proportion of transgenic C. carpio fed within the system, although they were not overrepresented at a higher-quantity food source. Moreover, the analysis showed that transgenic C. carpio maintained a faster growth rate, and were more willing to risk exposure to a predator when foraging, thereby supporting the hypothesis that predation selects against maximal growth rates by removing individuals that display increased foraging effort. Without compensatory behaviours that could mitigate the effects of predation risk, the escaped or released transgenic C. carpio with high-gain and high-risk performance would grow well but probably suffer high predation mortality in nature.

The role of ecological context and predation risk-stimuli in revealing the true picture about the genetic basis of boldness evolution in fish

To showcase the importance of genotype × environment interactions and the presence of predation risk in the experimental assessment of boldness in fish, we investigated boldness in terms of feeding behavior and refuge use in two genetically different populations of juvenile carp (Cyprinus carpio) in two replicated experimental conditions in ponds and laboratory tanks. The populations were expected to exhibit genetic differences in boldness due to differential evolutionary adaptation to low-predation-risk pond aquaculture conditions. Boldness was measured in variants of open-field trials with and without implementation of additional predation risk-stimuli by angling on feeding spots. Without explicit implementation of risk, genotypes adapted to low-risk environments, i.e., domesticated mirror carp behaved consistently bolder than their less domesticated scaled conspecifics in the pond environment, but not in the laboratory environment. When we implemented artificial risk-stimuli by angling on previously safe feeding spots, boldness differences among genotypes also emerged in the laboratory environment, indicating strong genotype × environment effects on boldness behavior of carp. The expected genetic basis of boldness differences among genotypes was clearly supported in the pond environment, while the laboratory study revealed these patterns only under inclusion of explicit risk-stimuli. Our study thus underscores that boldness may involve both a basal component that is expressed independently of obvious predation risk (e.g., in open fields) and a component revealed in relation to explicit predation risk, and both dimensions may respond differently in behavioral tests.

Effects of species‐specific interactions with predation risk on the relative species sensitivities to a pesticide in water boatmen (Corixidae)

There is increasing concern that synergistic interactions between stressors may result in accelerated biodiversity loss. Yet, the prevalence and magnitude of these interactions remain one of the largest uncertainties in projections of future ecological change. Synergistic interactions between pesticide stress and predation risk are receiving increasing attention because they indicate that standard pesticide tests in the absence of predation risk may underestimate effects that occur under natural conditions. We questioned whether synergisms (or interactions in general), by differently shaping individual species’ sensitivities, can modulate species sensitivity rankings (SSRs) in survival and growth rate. Using laboratory and outdoor mesocosm experiments with five species of water boatmen (Hemiptera: Corixidae) we studied mortality and growth rate over seven days of exposure. We evaluated the presence and nature of interactions between the pesticide endosulfan and predation risk and tested to what extent this affected the SSRs to endosulfan. The combined exposure to the pesticide and predation risk resulted in synergistic effects for survival (Sigara lateralis) and growth rate (Sigara iactans) and in an antagonistic effect for growth rate (Hesperocorixa linnaei and female Sigara striata). These results suggest that standard tests may underestimate the pesticide effect in a natural predator environment for some species. While the effects of these interactions on SSRs were not strong and SSRs remained largely similar in the absence and presence of predation risk, some obvious species rank shifts occurred for growth rate which may potentially affect community structure through changed competitive strength. The study of SSRs and their dependency on biotic stressors may provide a simple conceptual and predictive framework to increase our understanding of how stressors like pesticides may differentially affect community structure in the absence and presence of another stressor.

Risk-sensitive information gathering by cyprinids following release of chemical alarm cues

In aquatic environments, chemical cues released during a predator attack reliably inform prey about the presence of predation risk. Prey with information about predation risk are more successful in surviving encounters with predators than are unwary prey. To remain prepared for attack, prey should continue to monitor the status of predation risk, presenting a behavioural trade-off for prey: increased distance from areas labelled with alarm cues reduces exposure to predation risk but also reduces access to information about predation risk. In two laboratory experiments we used the presence and absence of water flow in a laboratory fluvarium to test alarm response and subsequent risk-sensitive information gathering by zebrafish (Danio rerio). In response to chemical alarm cues, fish significantly reduced activity and increased use of shelters. In the absence of flow, fish sought out the shelter nearest the cue source. In the presence of flow, fish preferred to seek shelter downstream, but not upstream, of the cue source. This allowed fish to gather information about predation risk from a relatively safe distance. In a field experiment on natural populations of stream fishes, fish avoided areas where chemical alarm cues were released (versus blank water control) but primarily because they avoided the region immediately upstream of the cue source. Fish use of the area immediately downstream of cue release did not decrease. Taken together, these laboratory and field data are consistent with a trade-off between risk avoidance and information gathering.

Purple sea urchins Strongylocentrotus purpuratus reduce grazing rates in response to risk cues from the spiny lobster Panulirus interruptus

The classical view of trophic cascades is that predators, by consuming herbivores, exert a positive indirect effect on plants. Although this form of trophic cascade has been demonstrated in a variety of terrestrial, aquatic, and marine systems, growing evidence suggests many trophic cascades are driven by anti-predator behaviors in prey. Despite abundant evidence of behavioral responses by sea urchins to predators, there has been little examination of how predation risk may influence urchin grazing rates. To determine if purple sea urchins Strongylocentrotus purpuratus graze less in the presence of predation risk, I monitored individual urchin grazing on the kelp Macrocystis pyrifera in the presence and absence of waterborne cues from damaged conspecifics and the predatory spiny lobster Panulirus interruptus. Sea urchin grazing rates were similar in the presence and absence of damaged conspecifics, but sea urchins exposed to lobster cues, regardless of lobster diet, reduced grazing rates by 44%. Given that trophic cascades involving herbivorous sea urchins exert an impor- tant influence on primary production in kelp forests, these results suggest that predation risk may play an important but under-appreciated role in the dynamics of kelp forest food webs and primary production.

Predator Effects in Predator-Free Space: the Remote Effects of Predators on Prey

Predators can have effects on prey populations that are connected by migration (i.e. prey metapopulations) because predator-mediated changes in prey behavior and abundance effectively transmit the impact of predators into predator-free prey populations. Behavioral changes in prey that might give rise to effects are altered rates of migration or activity in the presence of predation risk (called non-consumptive effects, fear- or µ-driven effects, and risk effects). Changes in prey abundance that may result in effects arise from changes in prey density due to direct predation (i.e. consumptive effects, also called N-driven effects and predation effects). Remote effects provide a different perspective on both predator-prey interactions and spatial subsidies, illustrating how the interplay among space, time, behavior, and consumption generates emergent spatial dynamics in places where we might not expect them. We describe how strong effects of predators may essentially generate remote control over the dynamics of local populations, alter the persistence of metapopulations, shift the importance of particular paradigms of metacommunity structure, alter spatial subsidies, and affect evolutionary dynamics. We suggest how experiments might document effects and predict that effects will be an important component of prey dynamics under several common scenarios: when predators induce large changes in prey dispersal behavior, when predators dramatically reduce the number of prey available to disperse, when prey movement dynamics occur over greater distances or shorter timescales than predator movement, and when prey abundance is not already limited by competitors or conspecifics.

Active space of chemical alarm cue in natural fish populations

AbstractChemical cues released from injured fish skin during a predator attack provide reliable information about the presence of predation risk. Here, I report estimates of the area avoided by littoral fishes after experimental release of chemical alarm cues in two small lakes in northern Minnesota. Minnow traps were labeled chemically with either water (control) or skin extract (chemical alarm cue) made from 2 cm2 of cyprinid skin (redbelly dace in experiment 1, fathead minnows in experiment 2). Traps labeled with water were placed 1, 2, or 8 m from traps labeled with alarm cue. After 2 h, water-traps that were either 1 or 2 m distant from an alarm-trap caught significantly fewer fish than water-traps 8 m distant from alarm-traps. Conspecific and heterospecific skin extract produced similar area avoidance by fathead minnows. Redbelly dace showed a larger active space in response to conspecific than heterospecific alarm cues. Brook stickleback showed reduced catches within 2 m of skin extract of fathead minnows. Overall, the radius of active space was between 2 and 8 m under lake conditions with average subsurface currents of 0.82 cm/s. These data are the first field estimates of active space of ostariophysan chemical alarm cues.

Sniffing the trade-off: Effects of eel odours on nocturnal foraging activity of native and introduced crayfish juveniles

Efficient predator avoidance has to be balanced with other fitness-related behaviours such as foraging. Many aquatic animals coexisting with predators can recognise them through chemical cues and respond adaptively. Invasive or introduced species may lack this ability which may result in competitive disadvantage in the presence of predation risk. We investigated behavioural responses of predator-naïve juveniles of two co-occurring crayfish species to chemical cues of European eel (Anguilla anguilla). The native noble crayfish (Astacus astacus) has a long coevolutionary history with eel in Finland and the introduced signal crayfish (Pacifastacus leniusculus) a short one. We found that in the presence of odours from food deprived eels, noble crayfish increased shelter use and reduced nocturnal foraging activity. In contrast, signal crayfish reduced shelter use and increased their foraging activity when exposed to eel odours. These results indicate that signal crayfish would face a stronger risk of predation in waters with eel but the risk is reduced by their overall higher tendency to stay in shelter at night.

Potential risks of olfactory signaling: the effect of predators on scent marking by beavers

Mammals scent mark their territories to advertise occupancy and ownership. However, signaling with scent for territorial defense can have a negative effect by advertising an individual’s presence and location to predators. In this study, we measured responses to a simulated territorial intrusion by conspecific adult male Eurasian beavers (Castor fiber) either in the localized presence or in the absence of odor of a predator to test the hypothesis that the territorial defense of free-living beavers would be disrupted by the presence of predation risk in their natural environment. We predicted that beavers would significantly reduce their willingness to countermark intruder’s scent in the presence of the scent of predators (wolf [Canis lupus] and lynx [Lynx lynx]), compared with a control (no odor), as responses are in general stronger to predator scent marks than nonpredator scent. Therefore, we also predicted that the effects of nonpredatory mammal scent (neophobic control) (eland [Taurotragus oryx] and horse [Equus cabalus]) are to be expected somewhere in between the effects of the predator odor and a control. Our results suggest that both predator and nonpredator scents reduce beavers response to a simulated intruder’s scent mounds and therefore disrupt their territorial defense. However, predator scent had a stronger effect than nonpredator scent. Beavers may therefore be at great risk on territories with predators present because of the trade-off between predator avoidance and territorial defense. Our study demonstrates the potential of predation risk as a powerful agent of counterselection on olfactory signaling behavior.

Mating behaviour of male rock shrimp, Rhynchocinetes typus (Decapoda: Caridea): effect of recent mating history and predation risk

When males mate so often that they risk sperm depletion, strategic allocation of sperm across multiple matings should be favoured. Recent studies have demonstrated that past mating history and predation risk can affect both male and female mating behaviour, but the interaction between these two factors has not been addressed explicitly. We allowed some socially dominant male rock shrimp, Rhynchocinetes typus (the robustus morph), to mate and prevented others from doing so. We then added them to an assemblage of individuals of mixed sex and social rank and gave them the opportunity to mate again in both the absence and the presence of predation risk. Recently mated males guarded females for significantly less time and they transferred significantly fewer spermatophores to these females than did unmated males. However, neither predation risk nor recent mating history affected the rate of spermatophore transfer, and there was no interaction between these variables. The results suggest that recently mated robustus males change their mating behaviour according to their perceived mating opportunities. The behaviour that we observed in robustus male R. typus is consistent with that of males of other species. Females and males are affected differently by mating history: with multiple matings, females become choosier and search for higher-quality mates, but males appear to conserve their reproductive resources to be able to increase mate quantity.