Antipredator Defense Research Articles

Female putty-nosed monkeys (Cercopithecus nictitans) vocally recruit males for predator defence.

Alarm calls can trigger very different behavioural changes in receivers and signallers might apply different alarm call strategies based on their individual cost-benefit ratio. These cost-benefit ratios can also vary as a function of sex. For instance, male but not female forest guenons possess loud alarms that serve warning and predator deterrence functions, but also intergroup spacing and male–male competition. In some forest guenons, the context specificity and alarm call repertoire size additionally differs between females and males but it remains unclear if this corresponds to similar sexual dimorphisms in alarm calling strategies. We here experimentally investigated whether general female and more context-specific male alarm calls in putty-nosed monkeys (Cercopithecus nictitans) had different effects on the opposite sex's behaviour and whether they might serve different female and male alarm calling strategies. We presented a leopard model separately to the females or to the male of several groups while ensuring that the opposite sex only heard alarm calls of target individuals. While female alarms led to the recruitment of males in the majority of cases, male alarms did not have a similar effect on female behaviour. Males further seem to vocally advertise their engagement in group defence with more unspecific alarms while approaching their group. Males switched alarm call types once they spotted the leopard model and started mobbing behaviour. Females only ceased to alarm call when males produced calls typically associated with anti-predator defence, but not when males produced unspecific alarm calls. Our results suggest that sexual dimorphisms in the context specificity of alarms most likely correspond to different alarm calling strategies in female and male putty-nosed monkeys.

Oviposition-site shift in phytophagous mites reflects a trade-off between predator avoidance and rainstorm resistance.

Predators can reduce prey population densities by driving them to undertake costly defences. Here, we report on a remarkable example of induced antipredator defence in spider mites that enhances the risk to rainstorms. Spider mites live on the undersides of host plant leaves and usually oviposit on the leaf undersurface. When they are threatened by predatory mites, they oviposit on three-dimensional webs to avoid egg predation, although the cost of ovipositing on webs has not yet been clearly determined. We prepared bean plants harbouring spider mite (Tetranychus kanzawai) eggs on either leaf surfaces or webs and exposed them to rainstorms outdoors. We found that fewer eggs remained on webs than on leaf surfaces. We then examined the synergistic effect of wind and rain by simulating both in the laboratory. We conclude that ovipositing on webs comes at a cost, as eggs are washed off the host plants by wind and rain. This may explain why spider mite populations decrease drastically in the rainy season, although they inhibit leaf undersides where they are not directly exposed to rainfall.

Wing buzzing as a potential antipredator defense against an invasive predator

Blow flies are primary colonizers of carrion and thus interact with many organisms in a highly competitive environment. Due to the large variety of insects that utilize carrion resources, predators are also often in high abundance, placing selective pressures on necrophagous insects to develop antipredator defenses. Blow fly antipredator defenses are largely studied for larval stages as they are heavily predated on when feeding on a carcass. Consequently, our understanding of adult defenses are limited. In this paper, a potential antipredator defense against the red imported fire ant (Solenopsis invicta (Buren) (Hymenoptera: Formicidae)), an invasive species to the Southeastern United States that is known to compete with and prey on necrophagous insects, was observed. During the summer and winter of 2019 in central Texas, USA adult blow flies (Lucilia spp. and Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae)) were observed attempting to colonize chick (Gallus gallus domesticus) and rat (Rattus norvegicus) carcasses already colonized by fire ants. Ovipositing flies approached by fire ants buzzed their wings, seemingly to repel fire ants as they did not buzz their wings for flight unless engagement by fire ants was persistent or severe enough to drive the fly from the carcass. Wing buzzing is a common phenomenon across several insect orders and is thought to be used in part for defensive purposes. The primary non-flight related behavior regarding wing movements in blow flies is a mating display involving wing fanning in Lucilia sericata (Meigen) (Diptera: Calliphoridae). However, this behavior is generally slower and more rhythmic than the aggressive “buzzing” flies exhibited against fire ants. Wing buzzing as an antipredator defense has been shown to increase survivorship in other insects, though wing damage may occur and wing movements cost energy. Further investigation of adult blow fly interactions with native and non-native predators will increase our understanding of wing buzzing as a potential antipredator defense in blow flies, and their consequences in applied fields.

Predator community and resource use jointly modulate the inducible defense response in body height of crucian carp.

Phenotypic plasticity can be expressed as changes in body shape in response to environmental variability. Crucian carp (Carassius carassius), a widespread cyprinid, displays remarkable plasticity in body morphology and increases body depth when exposed to cues from predators, suggesting the triggering of an antipredator defense mechanism. However, these morphological changes could also be related to resource use and foraging behavior, as an indirect effect of predator presence. In order to determine whether phenotypic plasticity in crucian carp is driven by a direct or indirect response to predation threat, we compared twelve fish communities inhabiting small lakes in southeast Norway grouped by four categories of predation regimes: no predator fish, or brown trout (Salmo trutta), perch (Perca fluviatilis), or pike (Esox lucius) as main piscivores. We predicted the body shape of crucian carp to be associated with the species composition of predator communities and that the presence of efficient piscivores would result in a deeper body shape. We use stable isotope analyses to test whether this variation in body shape was related to a shift in individual resource use—that is, littoral rather than pelagic resource use would favor the development of a specific body shape—or other environmental characteristics. The results showed that increasingly efficient predator communities induced progressively deeper body shape, larger body size, and lower population densities. Predator maximum gape size and individual trophic position were the best variables explaining crucian carp variation in body depth among predation categories, while littoral resource use did not have a clear effect. The gradient in predation pressure also corresponded to a shift in lake productivity. These results indicate that crucian carp have a fine‐tuned morphological defense mechanism against predation risk, triggered by the combined effect of predator presence and resource availability.

Variation in size and shape of toxin glands among cane toads from native-range and invasive populations

If optimal investment in anti-predator defences depends on predation risk, invading new regions (and thus, encountering different predators) may favour shifts in that investment. Cane toads offer an ideal system to test this prediction: expensive anti-predator toxins are stored mainly in parotoid glands whose dimensions are easy to measure, and toad invasions have changed the suites of predators they encounter. Although plasticity may influence parotoid morphology, comparisons between parents and progeny revealed that gland dimensions were highly heritable. That heritability supports the plausibility of an evolved basis to variation in gland dimensions. Measurements of 3779 adult toads show that females have larger glands than males, invasive populations have larger glands than in the native-range, and that parotoid sexual size dimorphism varies strongly among invaded areas. Geographic variation in parotoid morphology may be driven by predation risk to both adult toads and offspring (provisioned with toxins by their mother), with toxins allocated to eggs exacerbating the risk of cannibalism but reducing the risk of interspecific predation. Investment into chemical defences has evolved rapidly during the cane toad’s international diaspora, consistent with the hypothesis that organisms flexibly adjust resource allocation to anti-predator tactics in response to novel challenges.

Numerical Study of One Prey-Two Predator Model Considering Food Addition and Anti-Predator Defense

This article examines the interaction between prey populations, juvenile predators, and adult predators. A mathematical model that considers adding food and anti-predators was developed. The equilibria of the existing system are that the system has four equilibria points with conditions suitable for the locale. Numerical simulations were carried out to describe the dynamics of the system solution. Based on numerical simulations, the varying of parameter causes changes in the extinction of prey or survival of prey populations, juvenile predators, and adult predators. Addfood parameters (A) encourae Hopf Bifurcation and Saddle-node bifurcation Numerical continuity results show that Hopf bifurcation occurs when the parameter value A = 1.00162435 and when the parameter value A = 2.435303 Saddle-node bifurcation occurs.

Do Hind Wing Eyespots of Caligo Butterflies Function in Both Mating Behavior and Antipredator Defense? (Lepidoptera, Nymphalidae)

Abstract In general, butterfly ventral hind wing eyespots are considered to play a role in predator–prey interactions. These eyespots are prominent wing pattern elements in Brassolini butterflies, and they vary in size, position, and number across taxa. Female Caligo Hübner, 1819 (Lepidoptera, Nymphalidae) appear to use the large eyespots of lekking males as a mate-locating cue, but female Opsiphanes Doubleday, 1849 (Lepidoptera, Nymphalidae) do not because males patrol to find mates. These behaviors led us to predict that male Caligo should have larger eyespots than females, but eyespot size would not differ between sexes in Opsiphanes. Our analyses supported these predictions. As displacement of the eyespots to the center of the wing might make them more conspicuous, we asked if eyespot position and size covaried across the Brassolini phylogeny. While we found a positive association between position and size, the relationship of these two variables contained significant phylogenetic signal. Two Brassolini species show strong sexual dimorphism where females converge on the color pattern of sympatric species of Caligo. Their ventral hind wing eyespots are much larger than those of close relatives, approximating those of Caligo, and further reinforcing the importance of ventral hind wing eyespots as a visual signal in this group of butterflies. Importantly, our results suggest that, in addition to antipredation defense, ventral hind wing eyespots can function in mating activities, and consequently they might be evolving under both natural and sexual selection in Caligo butterflies.

Towards an ecology of protective coloration.

The strategies underlying different forms of protective coloration are well understood but little attention has been paid to the ecological, life-history and behavioural circumstances under which they evolve. While some comparative studies have investigated the ecological correlates of aposematism, and background matching, the latter particularly in mammals, few have examined the ecological correlates of other types of protective coloration. Here, we first outline which types of defensive coloration strategies may be exhibited by the same individual; concluding that many protective coloration mechanisms can be employed simultaneously, particularly in conjunction with background matching. Second, we review the ecological predictions that have been made for each sort of protective coloration mechanism before systematically surveying phylogenetically controlled comparative studies linking ecological and social variables to antipredator defences that involve coloration. We find that some a priori predictions based on small-scale empirical studies and logical arguments are indeed supported by comparative data, especially in relation to how illumination affects both background matching and self-shadow concealment through countershading; how body size is associated with countershading, motion dazzle, flash coloration and aposematism, although only in selected taxa; how immobility may promote background matching in ambush predators; and how mobility may facilitate motion dazzle. Examination of nearly 120 comparative tests reveals that many focus on ecological variables that have little to do with predictions derived from antipredator defence theory, and that broad-scale ecological studies of defence strategies that incorporate phylogenetics are still very much in their infancy. We close by making recommendations for future evolutionary ecological research.

The antipredator benefits of postural camouflage in peppered moth caterpillars

Camouflage is the most common form of antipredator defense, and is a textbook example of natural selection. How animals’ appearances prevent detection or recognition is well studied, but the role of prey behavior has received much less attention. Here we report a series of experiments with twig-mimicking larvae of the American peppered moth Biston betularia that test the long-held view that prey have evolved postures that enhance their camouflage, and establish how food availability and ambient temperature affect these postures. We found that predators took longer to attack larvae that were resting in a twig-like posture than larvae resting flat against a branch. Larvae that were chilled or food restricted (manipulations intended to energetically stress larvae) adopted a less twig-like posture than larvae that were fed ad libitum. Our findings provide clear evidence that animals gain antipredator benefits from postural camouflage, and suggest that benefits may come at an energetic cost that animals are unwilling or unable to pay under some conditions.

Sex-specific plasticity across generations II: Grandpaternal effects are lineage specific and sex specific.

Transgenerational plasticity (TGP) occurs when the environment encountered by one generation (F0) alters the phenotypes of one or more future generations (e.g. F1 and F2). Sex selective TGP, via specific lineages or to only male or female descendants, has been underexplored in natural systems, and may be adaptive if it allows past generations to fine-tune the phenotypes of future generations in response to sex-specific life-history strategies. We sought to understand if exposing males to predation risk can influence grandoffspring via sperm in three-spined stickleback Gasterosteus aculeatus. We specifically tested the hypothesis that grandparental effects are transmitted in a sex-specific way down the male lineage, from paternal grandfathers to F2 males. We reared F1 offspring of unexposed and predator-exposed F0 males under 'control' conditions and used them to generate F2s with control grandfathers, a predator-exposed maternal grandfather (i.e. predator-exposed F0 males to F1 daughters to F2s), a predator-exposed paternal grandfather (i.e. predator-exposed F0 males to F1 sons to F2s) or two predator-exposed grandfathers. We then assayed male and female F2s for a variety of traits related to antipredator defence. We found little evidence that transgenerational effects were mediated to only male descendants via the paternal lineage. Instead, grandpaternal effects depended on lineage and were mediated largely across sexes, from F1 males to F2 females and from F1 females to F2 males. When their paternal grandfather was exposed to predation risk, female F2s were heavier and showed a reduced change in behaviour in response to a simulated predator attack relative to grandoffspring of control, unexposed grandparents. In contrast, male F2s showed reduced antipredator behaviour when their maternal grandfather was exposed to predation risk. However, these patterns were only evident when one grandfather, but not both grandfathers, was exposed to predation risk, suggesting the potential for non-additive interactions across lineages. If sex-specific and lineage effects are common, then grandparental effects are likely underestimated in the literature. These results draw attention to the importance of sex-selective inheritance of environmental effects and raise new questions about the proximate and ultimate causes of selective transmission across generations.

Exploring the complexity and chaotic behavior in plankton–fish system with mutual interference and time delay

Anti-predator defense is an important mechanism that preys use to reduce the stress of constant struggle in a high concentration of predator and commonly established through evolution that supports prey organisms against predators. In the current study, we explore a three-tier plankton–fish interaction model using two kinds of function form, Monod–Haldane and Beddington–DeAngelis type. We introduce a discrete-time delay in the top predator population due to gestation. Our main objective persuades in this article is to address the role of inhibitory effect, mutual interference and gestation delay on the system dynamics in the presence of intermediate and top predators population. We perform theoretical analyses such as positivity and boundedness along with the local stability conditions of the delayed plankton–fish system. We also derive the condition of stability and direction of Hopf-bifurcation by using normal form theory and center manifold theorem. Our numerical computation demonstrates the dynamical outcome such as periodic and chaotic solutions of the model system without and with time delay validates our analytical findings. We also draw bifurcation diagrams that show the complexity of different parameters of model system. Interestingly, extinction is noticed in the top predator owing to the defense of phytoplankton. Model system exhibits irregular behavior when the inhibitory effect of phytoplankton is high or the value of gestation period of fish is high. We explore the significance of time delay with defense in our study which promotes chaotic phenomena in plankton system. Further, we notice the occurrence of double Hopf-bifurcation in a certain range of predator’s interference with variation in the coefficient of time delay.

Modelling the fear effect in a two-species predator–prey system under the influence of toxic substances

Effect of anti-predator defense due to fear of predator felt by prey and effect of toxic substance released by external sources on prey–predator system is a serious mater of concern in mathematical biology. In the proposed model we have discussed a prey–predator system in which both the species are infected by environmental toxicant. In our consideration prey species is directly infected by environmental toxicant and predator gets infected by consuming infected prey. Prey’s growth rate is assumed to be affected by fear of predator. In this work the proposed predator–prey model is analyzed in presence of environmental fluctuation, i.e., stochastic analysis of this model is discussed. Using Ito formula: positivity, boundedness, uniform continuity criterion and global attractivity of solutions of this system have been established. Conditions for which the prey as well as the predator goes extinct have been derived. Conditions for persistence of the system have also been discussed. Mathematical findings have been validated in numerical simulation by MATLAB. Different effects of different levels of toxicant and different levels of fear have been demonstrated by depicting figures in numerical simulation using MATLAB.

Life-History Modeling Reveals the Ecological and Evolutionary Significance of Autotomy.

AbstractAutotomy, the self-amputation of body parts, serves as an antipredator defense in many taxonomic groups of animals. However, its adaptive value has seldom been quantified. Here, we propose a novel modeling approach for measuring the fitness advantage conferred by the capability for autotomy in the wild. Using a predator-prey system where a land snail autotomizes and regenerates its foot specifically in response to snake bites, we conducted a laboratory behavioral experiment and a 3-year multievent capture-mark-recapture study. Combining these empirical data, we developed a hierarchical model and estimated the basic life-history parameters of the snail. Using samples from the posterior distribution, we constructed the snail's life table as well as that of a snail variant incapable of foot autotomy. As a result of our analyses, we estimated the monthly encounter rate with snake predators at 3.3% (95% credible interval: 1.6%-4.9%), the contribution of snake predation to total mortality until maturity at 43.3% (15.0%-95.3%), and the fitness advantage conferred by foot autotomy at 6.5% (2.7%-11.5%). This study demonstrated the utility of the multimethod hierarchical-modeling approach for the quantitative understanding of the ecological and evolutionary processes of antipredator defenses in the wild.

Experimental predator intrusions in a cooperative breeder reveal threat-dependent task partitioning

AbstractIn cooperatively breeding species, nonbreeding individuals provide alloparental care and help in territory maintenance and defense. Antipredator behaviors of subordinates can enhance offspring survival, which may provide direct and indirect fitness benefits to all group members. Helping abilities and involved costs and benefits, risks, and outside options (e.g., breeding independently) usually diverge between group members, which calls for status-specific differentiated behavioral responses. Such role differentiation within groups may generate task-specific division of labor, as exemplified by eusocial animals. In vertebrates, little is known about such task differentiation among group members. We show how breeders and helpers of the cooperatively breeding cichlid Neolamprologus savoryi partition predator defense depending on intruder type and the presence of dependent young. In the field, we experimentally simulated intrusions by different fish species posing a risk either specifically to eggs, young, or adults. We used intrusions by harmless algae eaters as a control. Breeders defended most when dependent young were present, while helper investment hinged mainly on their body size and on the potential threat posed by the respective intruders. Breeders and helpers partitioned defense tasks primarily when dependent young were exposed to immediate risk, with breeders investing most in antipredator defense, while helpers increased guarding and care in the breeding chamber. Breeders’ defense likely benefits helpers as well, as it was especially enhanced in the treatment where helpers were also at risk. These findings illustrate that in a highly social fish different group members exhibit fine-tuned behavioral responses in dependence of ecological and reproductive parameter variation.

Testing the hypothesized antipredator defence function of stridulation in the spiny orb-weaving spider, Micrathena gracilis

The observable diversity of antipredator defences across organisms demonstrates predation's impact on trait evolution. The functions of many traits that are presumed to have an antipredator function have never been directly tested. The spiny orb-weaving spider, Micrathena gracilis, for example, stridulates when grasped. While stridulation was first hypothesized to be an antipredator defence nearly 50 years ago, no data exist to support this hypothesis. To explore the form and function of M. gracilis stridulation, we first quantified the behavioural and acoustical properties of sound production. Next, using laboratory assays, we directly tested the effect of stridulation on survival with an avian predator – blue jays, Cyanocitta cristata . Finally, we conducted a large mark–recapture field study in which we compared the natural survival of experimentally manipulated adult female M. gracilis that could not stridulate (silenced) versus could stridulate (control). Stridulatory pulses produced broadband frequency spectra, consistent with acoustic antipredator defences in other taxa. We also observed stridulation by male M. gracilis for the first time. In staged laboratory interactions with captive blue jays, we found no differences in survival between silenced and control M. gracilis . Similarly, in our mark–recapture field study, we found no differences in survival estimates between silenced and control groups, nor an effect of stridulation rate. While M. gracilis stridulation closely resembles antipredator stridulation in other arthropods, our behavioural data do not yet provide solid support for an antipredator function in M. gracilis . • We tested whether M. gracilis uses stridulation in antipredator defence. • We quantified behavioural and acoustical properties of stridulation. • We tested survival of silenced and control adult females in the laboratory/field. • Survival of silenced and control females did not differ. • Stridulation may not serve an antipredator function in M. gracilis.

Trait Variation in Moths Mirrors Small-Scaled Ecological Gradients in A Tropical Forest Landscape

Simple SummaryTropical rainforests are still lost at alarming rates due to timber extraction or conversion into plantations. While losses of species diversity are well documented, less is known about how the functional integrity of insect communities changes with such interventions. Using light-trap samples taken from species-rich moth assemblages in one region in SW Costa Rica, we asked whether the body size of moths and the contribution of warningly colored species change from old-growth forest across disturbed forest toward oil palm plantations. Across three topographic types of old-growth forest, differences were small. Moth species occurring in plantations were substantially smaller than their relatives thriving in natural forest. Similarly, the incidence of warning coloration dropped massively in plantations. Two different types of mimicry (moths imitating wasps or poisonous beetles, respectively) showed their own patterns of variation across ecosystems, yet both color types were very rare in plantations. These results confirm that not only insect species diversity becomes greatly diminished when tropical forests are destroyed: the functional composition and integrity of the insect fauna that remains in plantations is eroding as well.Along environmental gradients, communities are expected to be filtered from the regional species pool by physical constraints, resource availability, and biotic interactions. This should be reflected in species trait composition. Using data on species-rich moth assemblages sampled by light traps in a lowland rainforest landscape in Costa Rica, we show that moths in two unrelated clades (Erebidae-Arctiinae; Geometridae) are much smaller-sized in oil palm plantations than in nearby old-growth forest, with intermediate values at disturbed forest sites. In old-growth forest, Arctiinae predominantly show aposematic coloration as a means of anti-predator defense, whereas this trait is much reduced in the prevalence in plantations. Similarly, participation in Müllerian mimicry rings with Hymenoptera and Lycidae beetles, respectively, is rare in plantations. Across three topographic types of old-growth forests, community-weighted means of moth traits showed little variation, but in creek forest, both types of mimicry were surprisingly rare. Our results emphasize that despite their mobility, moth assemblages are strongly shaped by local environmental conditions through the interplay of bottom–up and top–down processes. Assemblages in oil palm plantations are highly degraded not only in their biodiversity, but also in terms of trait expression.

Antipredatory Responses of Mosquito Pupae to Non-Lethal Predation Threat—Behavioral Plasticity Across Life-History Stages

Antipredatory behavioral responses tend to be energetically expensive, and prey species thus need to resolve trade-offs between these behaviors and other activities such as foraging and mating. While these trade-offs have been well-studied across taxa, less is known about how costs and benefits vary in different life-history contexts, and associated consequences. To address this question, we compared responses of the yellow fever mosquito (Aedes aegypti [Diptera: Culicidae]) to predation threat from guppy (Poecilia reticulata [Cyprinodontiformes: Poeciliidae]) across two life-history stages-larvae (data from previous study) and pupae (from this study). Pupae are motile but do not feed and are comparable to larvae in terms of behavior. To understand how physiological costs affect the threat sensitivity of pupae, we used sex (with size as a covariate) as a proxy for stored energy reserves, and quantified movement and space use patterns of male (small-sized) and female (large-sized) pupae when exposed to predation threat. We found that pupae did not alter movement when exposed to predator cues but instead altered spatial use by spending more time at the bottom of the water column. We found no effect of pupa sex (or size) on the behavioral responses we measured. We conclude that pupa behavior, both antipredatory and otherwise, is primarily targeted at minimizing energy expenditure, as compared with larval behavior, which appears to balance energy expenditure between the opposing pressures of foraging and of avoiding predation. We suggest that antipredatory defenses in metamorphosing prey are modulated by varying energetic trade-offs associated with different life-history stages.

The evolution of startle displays: a case study in praying mantises.

Anti-predator defences are typically regarded as relatively static signals that conceal prey or advertise their unprofitability. However, startle displays are complex performances that deter or confuse predators and can include a spectacular array of movements, colours and sounds. Yet, we do not fully understand the mechanisms by which they function, their evolutionary correlates, or the conditions under which they are performed and evolve. Here, we present, to our knowledge, the first phylogenetically controlled comparative analyses of startle displays including behavioural data, using praying mantises as a model system. We included 58 species that provide a good representation of mantis diversity and estimated the strength of phylogenetic signal in the presence and complexity of displays. We also tested hypotheses on potential evolutionary correlates, including primary defences and body size. We found that startle displays and morphological traits were phylogenetically conserved, whereas behavioural traits were highly labile. Surprisingly, body size was not correlated with display presence or complexity in phylogenetically controlled analyses. Species-rich clades were more likely to exhibit displays, suggesting that startle displays were probably involved in lineage diversification. We suggest that to further elucidate the conditions under which startle displays evolve, future work should include quantitative descriptions of multiple display components, habitat type, and predator communities. Understanding the evolution of startle displays is critical to our overall understanding of the theory behind predator-prey dynamics.

Macroparasite Burden of Obligate and Facultative Symbionts in Symbiotic Communities of Scleractinian Corals

A variety of symbionts inhabit colonies of scleractinian corals, the main component of coral reef ecosystems. Obligate symbionts spend almost their whole lives (except the pelagic larvae stage) on or in the host, while facultative symbionts are less tightly associated with the host and easily leave them when food becomes scarce and competition and predation increase. The influence of parasites on the life traits of obligate and facultative symbionts has not yet been studied. The first step in this direction is the study of basic parameters of parasite infracommunities associated with coral symbionts. It was suggested that obligate symbionts that are tightly associated with their hosts and their symbiotic communities are more often infected. An alternative hypothesis suggests that facultative symbionts are more frequently infected because they easily change habitats and consume a broad food spectrum. For several years, we studied parasites of obligate and facultative symbionts (fish, decapods crustaceans, mollusks) associated with the corals Acropora and Pocillopora in the Nha Trang Bay (South China Sea). The highest abundance and diversity of macroparasites (Monogenea, Cestoda, Trematoda, Nematoda, Copepoda) were found in facultative symbionts of corals, fish-parabionts. Obligate fish-inbionts were infected much less often (Cestoda, Trematoda, Nematoda). Obligate symbionts predominated in the invertebrate symbionts, which were also weakly infected. The low abundance and diversity of parasites in obligate symbionts suggest that there should be significant investments in antiparasitic defense, which, together with efficient antipredation defense, minimize the mortality of obligate symbionts. Their fecundity and population number are usually low. Facultative symbionts presumably suffer higher mortality than obligate symbionts, but a more intensive use of resources and higher population numbers may compensate for this. A significant increase in the infection rate with an increase in host body size is typical of facultative symbionts, which are less protected than obligate symbionts. The latter showed low infection levels in all size groups. The results suggest that the role of parasites in shaping the life strategies of symbionts is no less important than the role of predators.

Exposure to predators, but not intraspecific competitors, heightens herbivore susceptibility to entomopathogens

Prey commonly must compete with conspecifics for resources while also defending themselves against predators. Both competition and defense can reduce feeding opportunities, or otherwise strain prey energy reserves, even when the prey is not killed. This suggests that stress from competition and anti-predator defense might yield non-lethal harm that differs quantitatively rather than qualitatively. We examined this possibility for an herbivorous prey species, the Colorado potato beetle (Leptinotarsa decemlineata), feeding among differing numbers of intraspecific competitors while also avoiding predation by Nabis alternatus and Hippodamia convergens. In a field cage experiment, predators and intraspecific competitors similarly reduced the herbivores’ larval survival. Yet, only exposure to predators heightened the risk of beetles later being killed by entomopathogenic nematodes and fungi, as the beetles pupated in the soil. This suggests that the threat of predation was exerting physiological harm to the prey, although it was also possible that a tradeoff existed where those beetles most resistant to predator attack were most susceptible to pathogen infection. In a second experiment, we found that regular touching of larvae by predatory Nabis or Hippodamia, in the absence of actual predation, consistently induced predator-avoidance behaviors by the larvae (e.g., rearing, vomiting, wiggling, etc.) that might be energetically costly. Indeed, only being touched by predators, but not by a wooden dowel as a disturbance control, led to greater susceptibility to entomopathogens as pupae. Altogether, our findings suggest that non-lethal interactions with predators might carry a particular cost to beetles in heightened pathogen susceptibility, not seen when facing competitors or simple disturbance. Additional work is needed to determine the specific physiological mechanism underlying this apparent synergism in the effects of predators and entomopathogens, which spans prey life stages.