Ineffective integration of multiple anti-predator defenses in a rotifer: a low-cost insurance?

To maximize survival, prey often integrates multiple anti-predator defenses. How the defenses interact to reduce predation risk is, however, poorly known. We used the rotifer Brachionus calyciflorus to investigate how morphological (spines) and behavioral (floating) defenses are integrated against a common predatory rotifer, Asplanchna brightwellii, and if their combined use improves survival. To this end, we assessed the cost of the behavioral defense and the efficiency of both defenses, individually and combined, as well as their mutual dependency. The results show that the behavioral defense is costly in reducing foraging activity, and that the two defenses are used simultaneously, with the presence of the morphological defense enhancing the use of the behavioral defense, as does the pre-exposure to predator cues. However, while the morphological defense reduces predation risk, the behavioral defense does not, thus, adding the costly behavioral defense to the morphological defense does not improve survival. It is likely that the cost of the behavioral defense is low given its reversibility—compared to the cost of misidentifying the predator species—and that this has promoted the adoption of both defenses, as general low-cost insurance rather than as a tailored strategy toward specific predators. Thus, the optimal strategy in the rotifer appears to be to express both morphological and behavioral defenses when confronted with the cues of a potential predator.

Inter- and Intraspecific Trait Compensation of Behavioural and Morphological Defences in a Damselfly Genus

Predation is a key driver of phenotypic diversification with prey having evolved sets of correlated anti-predator traits. Changes in anti-predator traits can be studied on an evolutionary as well as on a developmental timescale. Using a common garden setup, we studied inter- and intraspecific correlations of behavioural and morphological defences in four damselfly species that either occur in habitats dominated by predatory fish (fish habitats) or fishless habitats by raising larvae either with predatory fish or in a control treatment. We found inter- as well as intraspecific trait compensation (negative correlations) between behavioural and morphological defences. Compared to fishless habitat species, fish habitat species invested more in behavioural defences and less in morphological defences. This was mirrored by fish habitat species investing more in behavioural defences and less in morphological defences when reared with predatory fish whereas fishless habitat species invested less in morphological defences only. Our results emphasise the role of context-specific combinations of defensive traits to avoid predation. We suggest, considering changes in multiple correlated traits on different timescales when studying the evolution of anti-predator traits.

Environmental Stressors and Pathology of Marine Molluscs

Mollusca is one of the most species-rich phylum of the Animal Kingdom, comprising a wide range of both terrestrial and aquatic organisms [...]

Microplastic leachates induce species-specific trait strengthening in intertidal mussels

Plastic pollution is ubiquitous with increasing recognition of its direct effects on species' fitness. Little is known, however, about its more subtle effects, including the influence of plastic pollution on the morphological, functional and behavioral traits of organisms that are central to their ability to withstand disturbances. Among the least obvious but most pernicious forms of plastic-associated pollution are the chemicals that leach from microplastics. Here, we investigate how such leachates influence species' traits by assessing functional trait compensation across four species of intertidal mussels, through investigations of byssal thread production, movement and aggregation behavior for mussels held in natural seawater or seawater contaminated by microplastic leachates. We found no evidence for compensation of functional traits, but for each species, microplastic leachates reinforced one trait while others remained unaffected. Two species (Perna perna and Mytilus galloprovincialis), were characterized by a resistance strategy to disturbance; they produced more byssal threads in microplastic leachate seawater than in control seawater, while motility and aggregation remained essentially unaffected. In contrast, the other two species (M. edulis and Choromytilus meridionalis), showed a resilience strategy to disturbance through increased motility and aggregation in leachate seawater, while byssal thread production remained unaffected. These results suggest that the competitive abilities of intertidal mussels may be related to their sensitivity to microplastic leachates or other chemical disturbance. Importantly, the trait strengthening observed will affect the ability of these mussels to form spatially patterned beds, with implications for their quality as autogenic ecological engineers or foundation species. Thus, our findings have implications for the ability of mussel beds to tolerate disturbance, and hence for central ecosystem services, such as their ability to support biodiversity and enhance secondary and tertiary production. The results suggest that an inconspicuous aspect of plastic pollution has the potential to influence other communities and ecosystems in powerful ways.

Relative fitness of decoy coloration is mediated by habitat type

Predator-prey interactions can be important drivers of morphological evolution, and antipredator traits in particular. Further, ecological context can be an important factor shaping the evolution of these traits. However, the role of ecological factors such as habitat structure in altering predator-based selection is not well known for antipredator traits such as decoy coloration. We used a combination of a natural history collection survey and a clay model experiment in open- and closed-canopy habitats to study how ecological context alters the fitness benefit of either red or blue decoy coloration in skinks. We found that the development and ecology of red decoy coloration of mole skinks differed substantially from blue tail coloration of other sympatric skink species. Mole skinks do not reach the body size of sympatric species of skinks and retain decoy coloration throughout development. Both patterns of scarring in museum specimens and attacks on plasticine models suggest that red coloration serves as a decoy, attracting attacks to the autotomous tail. While predation rates were similar across habitats, models with red tails were attacked far less frequently in open habitats than models with blue tails, while attack rates were similar in closed habitats. Our results suggest that red decoy coloration in mole skinks could be an adaptation to relatively open-canopy habitats. Our study has important implications for understanding how habitat structure and predator-based selection can alter the evolutionary dynamics of decoy coloration.

Current environmental microplastic levels do not alter emergence behaviour in the intertidal gastropod Littorina littorea

Microplastic ingestion by intertidal fauna is a well-documented phenomenon, with emphasis on the physiological consequences of microplastic exposure. However, the behavioural effects of microplastic ingestion have not been explored to the same degree, even in species with documented microplastic ingestion. In this study, the predator-avoidance emergence response of Littorina littorea was assessed and related to microplastic levels within the samples. This is a novel approach to microplastic behavioural experiments, whereby current environmental L. littorea microplastic levels are assessed, rather than levels vastly in excess of those recorded under field conditions. The results showed no difference in emergence likelihood or emergence latency related to microplastic abundance, sex, or treatment. However, L. littorea size did have a significant effect on emergence likelihood and emergence latency, with smaller individuals emerging faster and more frequently. This study shows that microplastics, at their current environmental levels, do not seem to affect L. littorea emergence behaviour.

Effects of long-term exposure to reduced pH conditions on the shell and survival of an intertidal gastropod

Volcanic CO₂ vents are useful environments for investigating the biological responses of marine organisms to changing ocean conditions (Ocean acidification, OA). Marine shelled molluscs are highly sensitive to changes in seawater carbonate chemistry. In this study, we investigated the effects of reduced pH on the intertidal gastropod, Phorcus sauciatus, in a volcanic CO₂ vent off La Palma Island (Canary Islands, North East Atlantic Ocean), a location with a natural pH gradient ranging from 7.0 to 8.2 over the tidal cycles. Density and size-frequency distribution, shell morphology, shell integrity, fracture resistance, and desiccation tolerance were evaluated between populations from control and CO₂ vent sites. We found no effects of reduced pH on population parameters or desiccation tolerance across the pH gradient, but significant differences in shell morphology, shell integrity, and fracture resistance were detected. Individuals from the CO₂ vent site exhibited a higher shell aspect ratio, greater percentages of shell dissolution and break, and compromised shell strength than those from the control site. Our results highlight that long-term exposure to high pCO₂ can negatively affect the shell features of P. sauciatus but may not have a significant effect on population performance. Moreover, we suggest that loss of shell properties could lead to changes in predator-prey interactions.

Microplastic leachates impair behavioural vigilance and predator avoidance in a temperate intertidal gastropod

Microplastics are a ubiquitous source of contaminations in marine ecosystems, and have major implications for marine life. Much effort has been devoted to assessing the various effects of microplastics on marine life. No evidence exists, however, on the effects of microplastic leachates on chemically mediated predator-prey interactions and the ability of prey to detect and avoid its predator. This study shows that microplastic leachates have direct biological effects by disturbing the behavioural response of the intertidal gastropod Littorina littorea to the presence of Carcinus maenas chemical cues, hence increasing their vulnerability to predation. Leachates from virgin and beached pellets respectively impaired and inhibited L. littorea vigilance and antipredator behaviours. These results suggest that the biological effects from microplastic leachates may have major implications for marine ecosystems on taxa that rely on chemosensory cues to escape predation.

A comparison of survivourship and function (grazing and behaviour) of three gastropod species used as clean-up crew for the marine aquarium trade

Several million gastropods are collected each year for the marine ornamental trade to graze on algae detrimental to aquarium species, however, little is known about popular species' suitability to perform this clean-up crew role. Three commonly traded gastropods, Turbo bruneus, Tectus fenestratus, and Tegula eiseni were assessed on their performance. Their survival was quantified as was their movement, and positioning with respect to water level and growth rates were calculated from the start and end weights. Nitrocellulose-coated slides were impregnated with an algal extract and the amount of grazing by each species was also compared. After 53 days final mortality levels of species were significantly different with all T. bruneus individuals surviving, whilst all T. fenestratus individuals apart from two and 35% of the T. eiseni had died by the end of the experiment. T. bruneus grazed significantly more than individuals of T. eiseni, and T. fenestratus. Both T. bruneus and T. eiseni were heavier after one month with T. bruneus gaining significantly more weight than T. eiseni. Greater percentages of algae were grazed by T. bruneus of increasing weight, although this relationship was not found for T. eiseni and T. fenestratus. All three species were generally active and remained within the water for the vast majority of time, although a small, but significant amount of time was spent out of the water for T. eiseni. T. fenestratus were significantly less active than T. bruneus, although the mean activity of T. eiseni was not significantly different from either species. T. bruneus out performs the other two species as a cleaning organism especially in the context of fluctuating water quality, thus highlighting the varying suitability of organisms for this task. Preference in the ornamental trade should be given to T. bruneus over the other topshells, but accurate species identification is critical.

Phenotypic plasticity can explain evolution of sympatric polymorphism in the hairy snail Trochulus hispidus (Linnaeus, 1758)

Morphological variation of snails from the genus Trochulus is so huge that their taxonomy is unclear. The greatest variability concerns forms hispidus and sericeus/plebeius, which are often considered as separate species. To evidence the species barriers, we carried out crossbreeding experiments between these two sympatric morphs. Moreover, we compared the shell morphology of laboratory-bred offspring with their wild parents to test if the variation can be explained by the phenotypic plasticity model. We found that the two Trochulus morphs show no reproductive barriers. The fecundity rates, the mean clutch size, and F₁ viability observed for all crosses were not significantly different. In hybrid crosses (in F₂ generation), we also recorded reproduction compatibility, similar fecundity, and hatching success as in their parents. Accordingly, phylogenetic analyses revealed the significant grouping of sequences from these different morphs and supported no constrains in reproduction between them. Comparison of shell morphology between wild and laboratory samples showed that various characters appeared highly plastic. The average shell shape of the hispidus morph changed significantly from flat with wide umbilicus to elevated with narrower umbilicus such as in the sericeus/plebeius morph. All these findings indicate that the examined morphs do not represent separate biological species and the evolutionary process is not advanced enough to separate their genetic pool. Therefore, phenotypic plasticity has played a significant role in the evolution of Trochulus shell polymorphism. The two morphs can evolve independently in separate phylogenetic lineages under the influence of local environmental conditions.

Do physical habitat complexity and predator cues influence the baseline and stress-induced glucocorticoid levels of a mangrove-associated fish?

As human populations continue to expand, increases in coastal development have led to the alteration of much of the world's mangrove habitat, creating problems for the multitude of species that inhabit these unique ecosystems. Habitat alteration often leads to changes in habitat complexity and predation risk, which may serve as additional stressors for those species that rely on mangroves for protection from predators. However, few studies have been conducted to date to assess the effects of these specific stressors on glucocorticoid (GC) stress hormone levels in wild fish populations. Using the checkered puffer as a model, our study sought to examine the effects of physical habitat complexity and predator environment on baseline and acute stress-induced GC levels. This was accomplished by examining changes in glucose and cortisol concentrations of fish placed in artificial environments for short periods (several hours) where substrate type and the presence of mangrove roots and predator cues were manipulated. Our results suggest that baseline and stress-induced GC levels are not significantly influenced by changes in physical habitat complexity or the predator environment using the experimental protocol that we applied. Although more research is required, the current study suggests that checkered puffers may be capable of withstanding changes in habitat complexity and increases in predation risk without experiencing adverse GC-mediated physiological effects, possibly as a result of the puffers' unique morphological and chemical defenses that help them to avoid predation in the wild.

MicroRNA-21 Promotes Proliferation of Fibroblast-Like Synoviocytes through Mediation of NF-κB Nuclear Translocation in a Rat Model of Collagen-Induced Rheumatoid Arthritis

MicroRNA-21 (miR-21) is overexpressed in patients with rheumatoid arthritis (RA). This study was designed to investigate the effect and mechanism of miR-21 on cell proliferation in fibroblast-like synoviocytes (FLS) of RA. FLS were primary-cultured from a rat RA model. RA-FLS and normal FLS were infected with lentivirus (anti-miR-21 or pro-miR-21) for overexpression or downregulation of miR-21, respectively. The effects of miR-21 overexpression or inhibition on nucleoprotein NF-κB levels and FLS cell proliferation were evaluated by western blotting and MTT assays. The effects of an inhibitor of NF-κB nuclear translocation (BAY 11-7082) were also evaluated. The results showed that the levels of miR-21 and nucleoprotein NF-κB were increased in FLS of RA model rats compared to the control group. Downregulation of miR-21 in RA FLS led to a significant decrease in nucleoprotein NF-κB levels and cell proliferation rates compared to the antinegative control (NC) group. However, miR-21 overexpression in normal FLS resulted in a significant increase of nucleoprotein NF-κB levels and cell proliferation rates compared to the pro-NC group. The effects of miR-21 overexpression were reversed by BAY 11-7082. We concluded that upregulated miR-21 in FLS in RA model rats may promote cell proliferation by facilitating NF-κB nuclear translocation, thus affecting the NF-κB pathway.

Consistent long-term behavioural traits are linked to morphological defences in common carp (Cyprinus carpio)

Individual prey often exhibit consistent behavioural differences in responses to risk. Here, we assess whether such behavioural consistency is linked to morphological changes that are known to result in differences in vulnerability to predators. Some fishes increase their depth-to-length ratio when under increased risk of predation, thereby reducing their risk to gape-limited predators. However, the development of these defences is limited by available resources. We asked whether behavioural tendencies associated with shelter seeking and activity are linked to differences in growth patterns. Common carp classified as ‘active/non-sheltering’ or ‘passive/sheltering’ based on their movement patterns and shelter use, showed consistency in behaviour over a 10-month period with active/non-sheltering fish developing a greater depth to length ratio than passive/sheltering fish. The effectiveness of anti-predator strategies in animals is an integrative function of both behaviour and morphology. Our works highlights a fascinating link between behavioural consistency and the development of adaptive morphologies.

Living in a risky world: the onset and ontogeny of an integrated antipredator phenotype in a coral reef fish

Prey individuals with complex life-histories often cannot predict the type of risk environment to which they will be exposed at each of their life stages. Because the level of investment in defences should match local risk conditions, we predict that these individuals should have the ability to modulate the expression of an integrated defensive phenotype, but this switch in expression should occur at key life-history transitions. We manipulated background level of risk in juvenile damselfish for four days following settlement (a key life-history transition) or 10 days post-settlement, and measured a suite of physiological and behavioural variables over 2 weeks. We found that settlement-stage fish exposed to high-risk conditions displayed behavioural and physiological alterations consistent with high-risk phenotypes, which gave them a survival advantage when exposed to predators. These changes were maintained for at least 2 weeks. The same exposure in post-settlement fish failed to elicit a change in some traits, while the expression of other traits disappeared within a week. Our results are consistent with those expected from phenotypic resonance. Expression of antipredator traits may be masked if individuals are not exposed to certain conditions at key ontogenetic stages.

Consumer trait variation influences tritrophic interactions in salt marsh communities

The importance of intraspecific variation has emerged as a key question in community ecology, helping to bridge the gap between ecology and evolution. Although much of this work has focused on plant species, recent syntheses have highlighted the prevalence and potential importance of morphological, behavioral, and life history variation within animals for ecological and evolutionary processes. Many small-bodied consumers live on the plant that they consume, often resulting in host plant-associated trait variation within and across consumer species. Given the central position of consumer species within tritrophic food webs, such consumer trait variation may play a particularly important role in mediating trophic dynamics, including trophic cascades. In this study, we used a series of field surveys and laboratory experiments to document intraspecific trait variation in a key consumer species, the marsh periwinkle Littoraria irrorata, based on its host plant species (Spartina alterniflora or Juncus roemerianus) in a mixed species assemblage. We then conducted a 12-week mesocosm experiment to examine the effects of Littoraria trait variation on plant community structure and dynamics in a tritrophic salt marsh food web. Littoraria from different host plant species varied across a suite of morphological and behavioral traits. These consumer trait differences interacted with plant community composition and predator presence to affect overall plant stem height, as well as differentially alter the density and biomass of the two key plant species in this system. Whether due to genetic differences or phenotypic plasticity, trait differences between consumer types had significant ecological consequences for the tritrophic marsh food web over seasonal time scales. By altering the cascading effects of the top predator on plant community structure and dynamics, consumer differences may generate a feedback over longer time scales, which in turn influences the degree of trait divergence in subsequent consumer populations.

The evolution of antipredator behaviour following relaxed and reversed selection in Alaskan threespine stickleback fish

Changing environments, whether through natural or anthropogenic causes, can lead to the loss of some selective pressures ('relaxed selection') and possibly even the reinstatement of selective agents not encountered for many generations ('reversed selection'). We examined the outcome of relaxed and reversed selection in the adaptive radiation of the threespine stickleback fish, Gasterostues aculeatus L., in which isolated populations encounter a variety of predation regimes. Oceanic stickleback, which represent the ancestral founders of the freshwater radiation, encounter many piscivorous fish. Derived, freshwater populations, on the other hand, vary with respect to the presence of predators. Some populations encounter native salmonids, whereas others have not experienced predation by large fish in thousands of generations (relax-selected populations). Some relax-selected populations have had sport fish, including rainbow trout, Oncorhynchus mykiss, introduced within the past several decades (reverse-selected). We examined the behavioural responses of stickleback from three populations of each type to simulated attacks by trout and birds to determine whether relaxed and reversed selection has led to divergence in behaviour, and whether this divergence was predator specific. Fish from trout-free populations showed weak responses to trout, as predicted, but these responses were similar to those of oceanic (ancestral) populations. Fish from populations that co-occur with trout, whether native or introduced, showed elevated antipredator responses, indicating that in freshwater, trout predation selects for enhanced antipredator responses, which can evolve extremely rapidly. Comparison of laboratory-reared and wild-caught individuals suggests a combination of learned and genetic components to this variation. Responses to a model bird flyover were weakly linked to predation environment, indicating that the loss of predation by trout may partially influence the evolution of responses to birds. Our results reject the hypothesis that the consistent presence of predatory birds has been sufficient to maintain responses to piscivorous fish under periods of relaxed selection.

What can aquatic gastropods tell us about phenotypic plasticity? A review and meta-analysis

There have been few attempts to synthesise the growing body of literature on phenotypic plasticity to reveal patterns and generalities about the extent and magnitude of plastic responses. Here, we conduct a review and meta-analysis of published literature on phenotypic plasticity in aquatic (marine and freshwater) gastropods, a common system for studying plasticity. We identified 96 studies, using pre-determined search terms, published between 1985 and November 2013. The literature was dominated by studies of predator-induced shell form, snail growth rates and life history parameters of a few model taxa, accounting for 67% of all studies reviewed. Meta-analyses indicated average plastic responses in shell thickness, shell shape, and growth and fecundity of freshwater species was at least three times larger than in marine species. Within marine gastropods, species with planktonic development had similar average plastic responses to species with benthic development. We discuss these findings in the context of the role of costs and limits of phenotypic plasticity and environmental heterogeneity as important constraints on the evolution of plasticity. We also consider potential publication biases and discuss areas for future research, indicating well-studied areas and important knowledge gaps.

Meek males and fighting females: sexually-dimorphic antipredator behavior and locomotor performance is explained by morphology in bark scorpions (Centruroides vittatus)

Sexual dimorphism can result from sexual or ecological selective pressures, but the importance of alternative reproductive roles and trait compensation in generating phenotypic differences between the sexes is poorly understood. We evaluated morphological and behavioral sexual dimorphism in striped bark scorpions (Centruroides vittatus). We propose that reproductive roles have driven sexually dimorphic body mass in this species which produces sex differences in locomotor performance. Poor locomotor performance in the females (due to the burden of being gravid) favors compensatory aggression as part of an alternative defensive strategy, while male morphology is coadapted to support a sprinting-based defensive strategy. We tested the effects of sex and morphology on stinging and sprinting performance and characterized overall differences between the sexes in aggressiveness towards simulated threats. Greater body mass was associated with higher sting rates and slower sprinting within sexes, which explained the greater aggression of females (the heavier sex) and, along with longer legs in males, the improved sprint performance in males. These findings suggest females are aggressive to compensate for locomotor costs of reproduction while males possess longer legs to enhance sprinting for predator evasion and mate finding. Sexual dimorphism in the metasoma ("tail") was unrelated to stinging and sprinting performance and may best be explained by sexual selection.

Plastic proteans: reduced predictability in the face of predation risk in hermit crabs

Variation in behaviour occurs at multiple levels, including between individuals (personality) and between situations (plasticity). Behaviour also varies within individuals, and intra-individual variation (IIV) in behaviour describes within-individual residual variance in behaviour that remains after the effects of obvious external and internal influences on behaviour have been accounted for. IIV thus describes how predictable an individual's behaviour is. Differences in predictability, between individuals and between situations, might be biologically significant. For example, behaving unpredictably under predation threat might reduce the chance of capture. Here, we investigated the duration of startle responses in hermit crabs, in the presence and absence of a predator cue. Individuals differed in startle response duration (personality) and while individuals also varied in their sensitivity to risk, mean response time was greater in the presence of a predator (plasticity). Moreover, IIV was greater in the presence of a predator, providing some of the first evidence that the facultative injection of unpredictability into behaviour might represent a strategy for dealing with risk.

The ontogenetic scaling of bite force and head size in loggerhead sea turtles (Caretta caretta): implications for durophagy in neritic, benthic habitats

Ontogenetic studies of vertebrate feeding performance can help address questions relevant to foraging ecology. Feeding morphology and performance can either limit access to food resources or open up new trophic niches in both aquatic and terrestrial systems. Loggerhead sea turtles are long-lived vertebrates with complex life histories that are marked by an ontogenetic shift from an oceanic habitat to a coastal neritic habitat, and a transition from soft oceanic prey to hard, benthic prey. Although considered durophagous and strong biters, bite performance has not been measured in loggerheads, nor has the ontogeny of bite performance been characterized. In the present study, we collected measurements of bite force in loggerhead turtles from hatchlings to adults. When subadults reach the body size at which the ontogenetic shift occurs, their crushing capability is great enough for them to consume numerous species of hard benthic prey of small sizes. As loggerheads mature and bite performance increases, larger and harder benthic prey become accessible. Loggerhead bite performance eventually surpasses the crushing capability of other durophagous carnivores, thereby potentially reducing competition for hard benthic prey. The increasing bite performance and accompanying changes in morphology of the head and jaws are likely an effective mechanism for resource partitioning and decreasing trophic competition. Simultaneous measurements of body and head size and the use of non-linear reduced major axis regression show that bite force increases with significant positive allometry relative to body size (straight carapace length, straight carapace width and mass) and head size (head width, height and length). Simple correlation showed that all recorded morphometrics were good predictors of measured bite performance, but an AICc-based weighted regression showed that body size (straight carapace width followed by straight carapace length and mass, respectively) were more likely predictors of bite force than head size morphometrics (head width and head length).

Interpopulation variation in predator avoidance behavior of a freshwater snail to the same predator

The New Zealand mud snail ( Potamopyrgus antipodarum (J.E. Grey, 1843)) responds to the presence of predatory fish by moving to a safer environment. These experiments attempted to determine if predator detection by the snail results in specific responses to light and (or) gravity by the snail and if snails respond more or less to fish from their native lake compared with fish from a foreign lake. Snails and fish (Gobiomorphus cotidianus McDowall, 1975) were collected from lakes Alexandrina and Peorua from the South Island of New Zealand. Snails were placed in behavioral chambers and tested for their responses to the direction of light, vertical orientation with respect to gravity, and rate of movement in light and dark conditions. Snails from each lake were exposed to one of three treatments: plain water, water from fish from Lake Alexandrina, and water from fish from Lake Peorua. Results showed no effect of direction of light on behavior. Snails from Lake Alexandrina were not found to alter their up or down movements in response to the detection of fish. However, snails from Lake Peorua moved down more in response to fish from their own lake than fish from Lake Alexandrina or no fish. Both snail populations increase their speed in the light more when detecting Alexandrina fish compared with Peorua fish and no fish. Both snail populations show some evidence of enhanced response to local predator populations. Interestingly, different behavioral mechanisms appear to be responsible for the avoidance behaviors in each population.

Intraspecific trait cospecialization of constitutive and inducible morphological defences in a marine snail from habitats with different predation risk

1. Studies examining the integration of constitutive and inducible aspects of multivariate defensive phenotypes are rare. 2. I asked whether marine snails (Nucella lamellosa) from habitats with and without abundant predatory crabs differed in constitutive and inducible aspects of defensive shell morphology. 3. I examined multivariate shell shape development of snails from each habitat in the presence and absence of waterborne cues from feeding crabs (Cancer productus). I also examined the influence of constitutive and inducible shell morphology on resistance to crushing. 4. Regardless of the presence of crabs, snails from high-risk (HR) habitats developed rotund, short-spired shells, while snails from low-risk habitats developed elongate shells, tall-spired shells, indicating among-habitat divergence in constitutive shell shape. Moreover, allometry analyses indicated that constitutive developmental patterns underlying this variation also differed between habitats. However, snails from HR habitats showed greater plasticity for apertural lip thickness and apertural area in the presence of crab cues, indicating among-habitat variation in defence inducibility. 5. Both shell shape and apertural lip thickness contributed to shell strength suggesting that constitutive shell shape development and inducible lip thickening have evolved jointly to form an effective defence in habitats where predation risk is high.

Behavioral plasticity in an invaded system: non-native whelks recognize risk from native crabs

Inducible defenses have the potential to affect both invasion success and the structure of invaded communities. However, little is known about the cues used for risk-recognition that influence the expression of inducible defenses in invasive prey, because they involve a novel threat. In laboratory experiments, we investigated behavioral defenses induced by a native crab on two invasive oyster drills (marine whelks Urosalpinx cinerea and Ocinebrina inornata). Both drills hid more often and reduced their feeding rates when they detected predators consuming conspecific prey. Examination of the responses of U. cinerea to specific cue sources (predator kairomones, conspecific alarm cues) indicated that this species had the strongest responses to cues from injured conspecifics, but that it did recognize the novel crab predator. Our observation of native predator (per se) recognition by an invasive marine prey is novel. In addition, we observed that neither species of drill reduced their defensive behavior to reflect predation risk shared by a group of prey. The lack of density dependence in risk-assessment could cause populations of invasive prey to transmit both quantitatively and qualitatively different community effects over the course of an invasion as abundance changes. Together, these findings demonstrate several ways that the risk-assessment strategies could be important in establishment and post-establishment dynamics of invasive prey.

Susceptibility to predation affects trait-mediated indirect interactions by reversing interspecific competition

Numerous studies indicate that the behavioral responses of prey to the presence of predators can have an important role in structuring assemblages through trait-mediated indirect interactions. Few studies, however, have addressed how relative susceptibility to predation influences such interactions. Here we examine the effect of chemical cues from the common shore crab Carcinus maenas on the foraging behavior of two common intertidal gastropod molluscs. Of the two model consumers studied, Littorina littorea is morphologically more vulnerable to crab predation than Gibbula umbilicalis, and it exhibited greater competitive ability in the absence of predation threat. However, Littorina demonstrated a greater anti-predator response when experimentally exposed to predation cues, resulting in a lower level of foraging. This reversed the competitive interaction, allowing Gibbula substantially increased access to shared resources. Our results demonstrate that the susceptibility of consumers to predation can influence species interactions, and suggest that inter-specific differences in trait-mediated indirect interactions are another mechanism through which non-consumptive predator effects may influence trophic interactions.

The perception of stress alters adaptive behaviours in Lymnaea stagnalis

Stress can alter adaptive behaviours, and as well either enhance or diminish learning, memory formation and/or memory recall. We show here that two different stressors have the ability to alter such behaviours in our model system, Lymnaea stagnalis. One, a naturally occurring stressor - the scent of a predator (crayfish) - and the other an artificially controlled one - 25 mmol l(-1) KCl - significantly alter adaptive behaviours. Both the KCl stressor and predator detection enhance long-term memory (LTM) formation; additionally predator detection alters vigilance behaviours. The predator-induced changes in behaviour are also accompanied by specific and significant alterations in the electrophysiological properties of RPeD1 - a key neuron in mediating both vigilance behaviours and memory formation. Naive lab-bred snails exposed to crayfish effluent (CE; i.e. the scent of the predator) prior to recording from RPeD1 demonstrated both a significantly reduced spontaneous firing rate and fewer bouts of bursting activity compared with non-exposed snails. Importantly, in the CE experiments we used laboratory-reared snails that have not been exposed to a naturally occurring predator for over 250 generations. These data open a new avenue of research, which may allow a direct investigation from the behavioral to the neuronal level as to how relevant stressful stimuli alter adaptive behaviours, including memory formation and recall.

Predator detection in Lymnaea stagnalis

Laboratory-reared Lymnaea are capable of detecting and responding to the scent of a crayfish predator. The present investigation is a first attempt to characterize multiple stress-related behavioural responses resulting from predator detection and to depict the neurophysiological correlates of one of these illustrated behaviours. Snails respond to crayfish effluent (CE) by increasing the following behaviours: aerial respiration, exploratory/searching phase and sensitivity to the shadow-elicited full-body withdrawal response. In contrast, when snails detect CE they decrease both their righting response time when dislodged from the substratum and their basal cutaneous oxygen consumption. Interestingly, basal heart rate does not change in response to CE exposure. Finally, we directly measured the activity of the neuron that initiates aerial respiratory behaviour, RPeD1, in semi-intact preparations. Naïve snails exposed to CE prior to recording demonstrated both a significantly reduced spontaneous firing rate and fewer bouts of bursting activity compared with non-exposed snails. These data show that laboratory-reared Lymnaea that have never experienced a natural predator are still capable of detecting and responding to the presence of a historically sympatric predator. These data open a new avenue of research, which may allow a direct investigation from the behavioural to the neuronal level as to how an ecologically relevant stressful stimulus alters behaviour.

Phylogenetic relatedness and ecological interactions determine antipredator behavior

Interspecific recognition of alarm cues among guild members through "eavesdropping" may allow prey to fine-tune antipredator responses. This process may be linked to taxonomic relatedness but might also be influenced by local adaptation to recognize alarm cues from sympatric species. We tested this hypothesis using antipredator responses of a freshwater gastropod Lymnaea stagnalis (L.) to alarm cues from damaged conspecific and 10 heterospecific gastropod species. As predicted, the magnitude of antipredator response decreased significantly with increasing phylogenetic distance, but increased when species were naturally sympatric (defined as species cohabiting in the same water body) with the source population of L. stagnalis. The responses to sympatric species were higher overall, and the relationship between genetic distance and alarm cue response was stronger when tested with sympatric species. This is the first study to demonstrate that population sympatry influences innate antipredator responses to alarm cues from intraguild members and suggests that responses based on phylogenetic relationships can be modified through local adaptation. Such adaptation to heterospecific alarm cues suggests that species could be at a disadvantage when they encounter novel intraguild members resulting from species invasion or range expansion due to a reduction in the presence of reliable information about predation risk.

HOW FLEXIBLE IS PHENOTYPIC PLASTICITY? DEVELOPMENTAL WINDOWS FOR TRAIT INDUCTION AND REVERSAL

Inducible defenses allow prey to modulate their phenotypic responses to the level of predation risk in the environment and reduce the cost of constitutive defenses. Inherent in this statement is that prey must alter their phenotypes during development in order to form these defenses. This has lead many ecologists and evolutionary biologists to call for studies that examine developmental plasticity to provide insights into the importance of development in controlling the trajectories of trait formation, the integration of phenotypes over ontogeny, and the establishment of developmental windows for trait formation and reversal. By moving away from studies that focus on a single point in development, we can obtain a more complete understanding of the phenotypic decisions and limitations of prey. We exposed freshwater snails (Helisoma trivolvis) to environments in which predatory water bugs (Belostoma flumineum) were always absent, always present, or added and removed at different points in development. We discovered that snails formed morphological defenses against water bugs. Importantly, after the initial induction of defenses, snails showed similar developmental trajectories as snails reared without predators. Further, the snails possessed wide developmental windows for inducible defenses that extended past sexual maturity. However, being induced later in development appeared to have an associated cost (i.e., decreased shell thickness) that was not found when water bugs were always present. This epiphenotype (i.e., new shell formation as an extension of the current shell) suggests that resource limitation plays an important role in responses to temporal variation in predation risk and may have critical ecological costs that limit the benefits of the inducible defense. Lastly, the ability of snails to completely reverse their defenses was limited to early in ontogeny due to the constraints associated with modular growth of shell material. In sum, we demonstrate that taking a developmental perspective is extremely valuable for understanding the ecology of inducible defenses.

Optimizing Time and Resource Allocation Trade‐Offs for Investment into Morphological and Behavioral Defense

Prey organisms are confronted with time and resource allocation trade-offs. Time allocation trade-offs partition time, for example, between foraging effort to acquire resources and behavioral defense. Resource allocation trade-offs partition the acquired resources between multiple traits, such as growth or morphological defense. We develop a mathematical model for prey organisms that comprise time and resource allocation trade-offs for multiple defense traits. Fitness is determined by growth and survival during ontogeny. We determine optimal defense strategies for environments that differ in their resource abundance, predation risk, and defense effectiveness. We compare the results with results of simplified models where single defense traits are optimized. Our results indicate that selection acts in favor of integrated traits. The selective advantage of expressing multiple defense traits is most pronounced at intermediate environmental conditions. Optimizing single traits generally leads to a more pronounced response of the defense traits, which implies that studying single traits leads to an overestimation of their response to predation. Behavioral defense and morphological defense compensate for and augment each other depending on predator densities and the effectiveness of the defense mechanisms. In the presence of time constraints, the model shows peak investment into morphological and behavioral defense at intermediate resource levels.

HABITAT-SPECIFIC VARIATION AND PERFORMANCE TRADE-OFFS IN SHELL ARMATURE OF NEW ZEALAND MUDSNAILS

Studies documenting phenotypic variation among populations show that ecological performance in one activity is sometimes traded off against another. Identifying environment-specific costs and benefits associated with performance trade-offs is fundamental to knowing how conflicting selection pressures shape phenotype-environment matching in populations. We studied phenotypic variation in shell armature (spininess) of the New Zealand mudsnail, Potamopyrgus antipodarum (Gray), and explored how this variability relates to performance trade-offs between flow resistance and predator deterrence. Smooth- and spiny-shell morphotypes exist in populations in New Zealand streams and lakes, but the patterns and correlates of spatial variation of these phenotypes, and the possible hydrodynamical constraints and antipredatory benefits associated with spiny shell armature, are unknown. Samples from 11 rivers and nine lakes on the South Island showed that, on average, nearly 70% of snails in streams were smooth-shelled, whereas >80% of snails in lakes were spiny, suggesting dissimilar selective pressures between habitats. A laboratory flume experiment revealed that spines collected seston (i.e., suspended algae) at current speeds <40 cm/s, making spiny morphs more prone to flow-induced dislodgment than smooth morphs. However, a fish feeding experiment showed that one benefit of spines on shells was a decrease in predation risk from the common bully (Gobiomorphus cotidianus), a widespread predator of mudsnails in both streams and lakes. All snails egested by bullies were dead, further suggesting that these fishes may exert strong lethal effects on mudsnail populations in nature. Spine expression in lakes also appeared to be temperature related. We conclude that functional trade-offs between risk of flow-induced dislodgment and risk of fish predation affect shell armature frequencies of Potamopyrgus in freshwater habitats.