Damselfly Larvae Research Articles

Predation and disease: understanding the effects of predators at several trophic levels on pathogen transmission

Summary Predators can directly and indirectly influence host–parasite interactions by consuming infected individuals, by removing infectious parasite stages and by changing host traits (e.g. behaviour). Because such effects can affect infection positively or negatively, understanding the net effects of predation on pathogen transmission under natural conditions is important. We conducted a mesocosm experiment to examine the effects of predators on interactions between tadpole hosts (Pseudacris regilla) and trematode parasites (Ribeiroia ondatrae). We manipulated the presence of (non‐lethal, i.e., caged) predators of tadpoles (dragonfly larvae) and (potentially lethal) parasite predators (damselfly larvae) to evaluate their individual and combined effects on host infection. We expected that dragonflies would reduce tadpole activity and thereby increase parasite infection through a reduction in antiparasite behaviour. Because damselflies can consume parasites in the laboratory, we predicted that damselflies would lower infection by consuming parasites before they infected tadpoles. Our goal was to evaluate the net consequences of these predator‐mediated effects for host/prey infection. The presence of caged dragonflies reduced tadpole activity, resulting in a ˜50% increase in average infection load compared to treatments without predators. In contrast to our prediction that damselflies would reduce infection, damselflies elicited behavioural and morphological changes in hosts similar to dragonflies, with a comparable increase in parasite transmission. Thus, predator‐mediated effects were evident predominantly through changes in host/prey behaviour, rather than through changes in the abundance of parasites. The lack of a direct effect of predators on infection (i.e. via consumption of parasites) could be the result of the presence of alternative prey (zooplankton) or a mismatch in timing between visual predators feeding during the day and parasites released from the first intermediate host and infecting amphibians at night. The presence of predators also stimulated morphological defences in their tadpole prey, including increased tail and body depth. Interestingly, we found that parasite infection also induced morphological changes in tadpole tail and body depth, similar to changes produced by (non‐lethal) cues from predators. Parasites caused malformations in tadpoles, but there were no effects on tadpole growth or development from either parasites or predators. This research has key implications for linking predation and infectious disease in aquatic ecosystems. Our results emphasise the importance of indirect effects of predators on infection and highlight possible trade‐offs in mitigating the concurrent risks of predation and disease. Parasites can also alter host morphology through trait‐mediated effects similar to predators, supporting a broader inclusion of parasites in the study of the ecology of natural enemies.

Damselfly larvae select quick release lamellae for survival

Adult damselflies are a spectacular vision of summer, streaking through the air above pond surfaces. Yet survival through their earlier aquatic life stages is extremely precarious. Equipped with leaf-like lamellae hinged at the end of the abdomen for propulsion, the structures provide the perfect appendages for passing predators to grab onto. But the larval insects have a self-preservation mechanism that helps them to escape hungry predators: they self amputate – autotomize – trapped lamellae. Jennifer Gleason, Douglas Fudge and Beren Robinson from the University of Guelph, Canada, explain that the ability of a larva to shed its lamellae with ease improves its chances of survival, which might lead larvae that inhabit heavily predated waters to develop relatively fragile lamellar joints to increase their chances of survival (p. 185). To test the theory, the Canadians measured the force required to break damselfly larvae lamellar joints, as well as the size and cuticle thickness of the joint. They discovered that the joints of damselfly larvae from fishless ponds – where carnivorous dragonfly larvae flourish – were much more fragile than the joints of larvae from ponds where there were few dragonfly larvae. ‘This suggests that autotomy may evolve in larval damselflies under selection from small grasping predators like larval dragonflies by favouring smaller joint size or reduced cuticle area of lamellae joints’, says the team.

Competitive displacement alters top-down effects on carbon dioxide concentrations in a freshwater ecosystem

Climate change and invasive species have the potential to alter species diversity, creating novel species interactions. Interspecific competition and facilitation between predators may either enhance or dampen trophic cascades, ultimately influencing total predator effects on communities and biogeochemical cycling of ecosystems. However, previous studies have only investigated the effects of a single predator species on CO2 flux of aquatic ecosystems. In this study, we measured and compared the individual and joint effects of predatory damselfly larvae and diving beetles on total prey biomass, leaf litter processing, and dissolved CO2 concentrations of experimental bromeliad ecosystems. Damselfly larvae created strong trophic cascades that reduced CO2 concentrations by ~46% relative to no-predator treatments. Conversely, the effects of diving beetles on prey biomass, leaf litter processing, and dissolved CO2 were not statistically different to no-predator treatments. Relative to multiplicative null models, the presence of damselfly larvae and diving beetles together resulted in antagonistic relations that eliminated trophic cascades and top-down influences on CO2 concentrations. Furthermore, we showed that the antagonistic interactions between predators occurred due to a tactile response that culminated in competitive displacement of damselfly larvae. Our results demonstrate that predator identity and predator-predator interactions can influence CO2 concentrations of an aquatic ecosystem. We suggest that predator effects on CO2 fluxes may depend on the particular predator species removed or added to the ecosystem and their interactions with other predators.

Local adaptation and the potential effects of a contaminant on predator avoidance and antipredator responses under global warming: a space‐for‐time substitution approach

The ability to deal with temperature-induced changes in interactions with contaminants and predators under global warming is one of the outstanding, applied evolutionary questions. For this, it is crucial to understand how contaminants will affect activity levels, predator avoidance and antipredator responses under global warming and to what extent gradual thermal evolution may mitigate these effects. Using a space-for-time substitution approach, we assessed the potential for gradual thermal evolution shaping activity (mobility and foraging), predator avoidance and antipredator responses when Ischnura elegans damselfly larvae were exposed to zinc in a common-garden warming experiment at the mean summer water temperatures of shallow water bodies at southern and northern latitudes (24 and 20°C, respectively). Zinc reduced mobility and foraging, predator avoidance and escape swimming speed. Importantly, high-latitude populations showed stronger zinc-induced reductions in escape swimming speed at both temperatures, and in activity levels at the high temperature. The latter indicates that local thermal adaptation may strongly change the ecological impact of contaminants under global warming. Our study underscores the critical importance of considering local adaptation along natural gradients when integrating biotic interactions in ecological risk assessment, and the potential of gradual thermal evolution mitigating the effects of warming on the vulnerability to contaminants.

Antihistamines and aquatic insects: Bioconcentration and impacts on behavior in damselfly larvae (Zygoptera)

Because aquatic insects use histamines as neurotransmitters, adverse impacts on aquatic insects living in aquatic environments that receive antihistamines with wastewater effluent are plausible. In this study, we exposed damselfly larvae to low concentrations of two commonly used antihistamines (Hydroxyzine and Fexofenadine, 360±42 and 2200±43 ng l−1, respectively), and recorded damselfly larvae behavior before and after exposure. Further, after the second set of behavioral assays was performed, we quantified bioconcentration of the antihistamines in the damselfly bodies. Our results showed significant changes in damselfly behavior following antihistamine exposure. After Hydroxyzine exposure, the damselfly larvae became less active, and they showed reduced fleeing response (i.e. increased boldness) after being exposed to Fexofenadine, the latter also being significantly different from the non-exposed (control) individuals. Further, we found high levels of bioconcentration in the damselflies; Hydroxyzine showed an average bioconcentration factor (BCF) of 2000. As such, our results indicate that low concentrations of antihistamines can have sub-lethal effects on aquatic insects manifested as behavioral changes, and that bioconcentration of these substances can be high. Therefore, the need to investigate the impact of emergent aquatic contaminants also on aquatic insects, and on behaviors that are of ecological importance, is further highlighted.

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.

Latitudinal patterns of phenology and age‐specific thermal performance across six Coenagrion damselfly species

Using a combination of computer simulations and laboratory experiments we test if the thermal sensitivity of growth rates change during ontogeny in damselfly larvae and if these changes can be predicted based on the natural progression of average temperature or thermal variability in the field. The laboratory experiment included replicated species from Southern, Central, and Northern Europe. Although annual fluctuations in temperature represent a key characteristic of temperate environments, few studies of thermal performance have considered the ecological importance of the studied traits within a seasonal context. Instead, thermal performance is assumed to remain constant throughout ontogeny and to reflect selection acting over the whole life cycle. The laboratory experiment revealed considerable variation among species in the strength and direction of ontogenetic performance shifts. In four species from Southern and Central Europe, reaction norms were steepest during early ontogeny, becoming less steep during later ontogenetic stages (indicative of low‐temperature acclimation). In one Northern European species, the slope of reaction norms did not change during ontogeny. In the other North European species, reaction norms became steeper during ontogeny (indicative of high‐temperature acclimation). We had expected high‐latitude species to show strong low‐temperature acclimation responses, because they have a short flight season and inhabit a strongly seasonal environment. Instead, we found the reversed pattern: Low‐latitude species displayed strong low‐temperature acclimation responses, and high‐latitude species displayed weak, or even reversed, acclimation responses to low temperatures. These findings suggest that low‐temperature acclimation may be less beneficial and possibly more costly in habitats with rapid seasonal transitions in average temperature. We conclude that thermal performance traits are more dynamic than typically assumed and caution against using results from single ontogenetic stages to predict species' responses to changing environmental conditions.

Behavioural, physiological and biochemical markers in damselfly larvae (Ischnura elegans) to assess effects of accumulated metal mixtures

Currently it is not known at which organismal level effects of metal mixtures in nature can best be detected, which is relevant to develop accurate monitoring schemes and quality standards. The present study investigated relationships between accumulated metals with different levels of biological organisation in the aquatic larval stage of the damselfly Ischnura elegans. Larvae were collected in seven Flemish ponds differing in metal load. In each field-collected larva we quantified concentrations of accumulated metals and a set of biochemical markers (acetylcholinesterase (AChE) and glutathione-S-transferase (GST)), physiological endpoints (energy storage), and behavioural responses (locomotory activity and the feeding rate). Accumulated metal levels and the measured endpoints significantly differed among ponds, however, a large variation in metal load index was observed within individuals of the same population. Only GST and energy availability could be partly predicted by the observed variation in metal load index on individual damselfly level. However, no single endpoint could be used to detect the observed variation in metal load index among populations. In conclusion, the sublethal endpoints cannot be used as reliable biomarkers to monitor the toxicity of accumulated metal mixtures in natural populations of I. elegans.

Susceptibility to a metal under global warming is shaped by thermal adaptation along a latitudinal gradient

Global warming and contamination represent two major threats to biodiversity that have the potential to interact synergistically. There is the potential for gradual local thermal adaptation and dispersal to higher latitudes to mitigate the susceptibility of organisms to contaminants and global warming at high latitudes. Here, we applied a space-for-time substitution approach to study the thermal dependence of the susceptibility of Ischnura elegans damselfly larvae to zinc in a common garden warming experiment (20 and 24°C) with replicated populations from three latitudes spanning >1500km in Europe. We observed a striking latitude-specific effect of temperature on the zinc-induced mortality pattern; local thermal adaptation along the latitudinal gradient made Swedish, but not French, damselfly larvae more susceptible to zinc at 24°C. Latitude- and temperature-specific differences in zinc susceptibility may be related to the amount of energy available to defend against and repair damage since Swedish larvae showed a much stronger zinc-induced reduction of food intake at 24°C. The pattern of local thermal adaptation indicates that the predicted temperature increase of 4°C by 2100 will strongly magnify the impact of a contaminant such as zinc at higher latitudes unless there is thermal evolution and/or migration of lower latitude genotypes. Our results underscore the critical importance of studying the susceptibility to contaminants under realistic warming scenarios taking into account local thermal adaptation across natural temperature gradients.

Differential survival rates of damselfly larvae in the presence of newt and dragonfly predators

The damselfly species Paracercion melanotum has been found to be the most abundant species in damselfly larval communities on Okinawa-zima Island in southwest Japan. To clarify differential susceptibility to predation, a possible factor affecting relative population densities in larval communities, between Paracercion melanotum and a less common damselfly species, Ischnura senegalensis, laboratory experiments were conducted using three abundant predator species: the sword-tailed newt (Cynops ensicauda popei), anisopteran larvae (Crocothemis servilia servilia), and a planktivorous fish (Poecilia reticulata). Paracercion melanotum survived predation by the newt and the dragonfly well compared to I. senegalensis. Fishes consumed approximately equal numbers of the two damselfly species. From these results, the newt and the dragonfly were suggested as the most probable predators regulating damselfly larval communities on Okinawa-zima Island. Predators could be a crucial factor determining relative abundance in...

Predator cues magnify effects of the pesticide endosulfan in water bugs in a multi-species test in outdoor containers

Pesticides have become major stressors in many aquatic communities. Laboratory studies suggest their impact may be further magnified in the presence of cues from predators. Despite their importance for ecological risk assessment, synergisms between pesticides and predator cues have not been confirmed under semi-natural outdoor conditions. We evaluated how the presence of predator cues and the presence of a non-corixid community affect the pesticide sensitivity of five water bug (Corixidae) species in an outdoor, multi-species container experiment. The experiment employed a full factorial design with two pesticide treatments, two predator cue treatments and two (non-corixid) community treatments (absence versus presence of Cloeon dipterum mayfly larvae, Ischnura elegans damselfly larvae and Physa acuta snails). The pesticide treatment negatively affected survival in Cymatia coleoptrata, and to a lesser extent, Sigara lateralis, but not in the other three Corixidae species (Hesperocorixa linnaei, Sigara iactans and Sigara striata). The addition of pesticides did not significantly affect body mass in the latter four species, unless combined with predator cues. To our knowledge this is the first report of this synergism under semi-natural, outdoor conditions. Neither lethal nor sublethal pesticide effects in the Corixidae depended on the community context, yet the presence of the non-corixid community when combined with predator cues reduced survival and body mass. Our results suggest that the here documented synergism between pesticides and predator cues may occur in nature.

Synergistic effects between pesticide stress and predator cues: Conflicting results from life history and physiology in the damselfly Enallagma cyathigerum

There is increasing awareness that the negative effects of anthropogenic stressors may be magnified in the presence of natural stressors. Very few of these studies have included physiology, yet including physiological studies may help learning about the mechanistic base of such synergisms at the life history level and identify synergistic interactions not translated in life history traits. We studied in Enallagma cyathigerum damselfly larvae potential synergistic effects between exposure to the pesticide glyphosate and predator cues on a key life history trait, growth rate, its associated behavioural trait, food intake, and three types of physiological traits known to be affected by both stressors in isolation: the stress protein Hsp70, energy storage and variables related to oxidative stress and damage. The pesticide and predator cues reduced growth rate in an additive way. Food intake increased under pesticide exposure and was not affected by the predator cues, indicating physiological mediation of the growth reduction. One potential physiological mechanism was that both stressors additively increased Hsp70 levels, this may also have contributed to the reduced levels of total carbohydrates when exposed to predator cues. Chronic exposure to predator cues reduced oxygen consumption, possibly to avoid too high costs of an increased metabolic rate. This reduction did not occur in the presence of the pesticide, reflecting the need for energetically expensive defence mechanisms (such as Hsp70 upregulation). When both stressors were combined, there was a reduction of the antioxidant enzyme superoxide dismutase activity (SOD) and an associated increase of oxidative damage in lipids. While synergistic interactions were not present for growth rate and food intake, they were identified for antioxidant defence and oxidative damage. This novel type of “hidden” synergistic interaction may have profound fitness implications, and when ignored will lead to underestimations of the impact of pollutants in natural populations where predators are omnipresent.

Hypoxia and lost gills: Respiratory ecology of a temperate larval damselfly

Damselfly larvae, important predators and prey in many freshwater communities, may be particularly sensitive to hypoxia because their caudal lamellae (external gills) are frequently lost. In this study, we address how lost lamellae interact with low oxygen to affect respiration and behavior of the widespread North American damselfly Ischnura posita. Results showed no effect of lost lamellae on resting metabolic rate or critical oxygen tension. Ventilation behaviors increased only when dissolved oxygen (DO) was at or below 25% saturation and these behaviors were not affected by the number of lamellae. Use of the oxygen-rich surface layer occurred almost exclusively at the lowest dissolved oxygen level tested (10% saturation, 2.0kPa). Damselflies that were missing lamellae spent more time at the surface than individuals with intact lamellae. The negative relationship between body size and time at the surface, and the negative relationship between body mass and critical oxygen tension suggest that larger I. posita may be more hypoxia tolerant than smaller individuals. Overall, I. posita was minimally affected by missing lamellae and seems well-adapted to low DO habitats. Average critical oxygen tension was very low (0.48kPa, 2.4% saturation), suggesting that individuals can maintain their metabolic rate across a broad range of DO, and behaviors changed only at DO levels below the hypoxia tolerance thresholds of many other aquatic organisms.

Responses of three species of mosquito larvae to the presence of predatory dragonfly and damselfly larvae

AbstractAlthough predators have been extensively used in the biological control of mosquito larvae, their efficacy will be reduced if the larvae are able to detect and respond to their presence. This ability to detect and respond to the unseen presence of dragonfly or damselfly larvae was investigated for the larvae of three mosquito species (all Diptera: Culicidae) to see whether they either altered their rate of development or their feeding behaviour. The development of Culex quinquefasciatus Say and Culiseta longiareolata Macquart larvae was not affected by exudates from either predator, but Culex sinaiticus Kirkpatrick developed significantly slower when reared in the presence of a caged dragonfly larva and produced adults that were significantly smaller, indicating that they probably reduced feeding activity to make themselves less detectable to the predator. This only occurred when the dragonflies were fed in situ (in the presence of the mosquito larva) and not when removed for feeding, so that although this removed predator kairomones, other cues such as vibrations caused by movement of the predator may also be involved. In addition, the mosquito larvae responded to dragonfly larvae, but not to damselfly larvae. The depth of the water in which the mosquito larvae were reared had no effect on their response to the dragonfly. All three mosquito species significantly increased surface filter‐feeding, when a predator was present in the water (compared with controls where no predator was present), at the expense of bottom scraping. In Cx. sinaiticus (but not the other two species), surface filter‐feeding was greater when a dragonfly was present, compared with a damselfly. In the experimental conditions of one predator per 250 ml water, all three mosquito species were thus able to detect dragonfly and damselfly larvae (and distinguish between the two), but their response varied among species.

Behaviour and physiology shape the growth accelerations associated with predation risk, high temperatures and southern latitudes in Ischnura damselfly larvae

1. To better predict effects of climate change and predation risk on prey animals and ecosystems, we need studies documenting not only latitudinal patterns in growth rate but also growth plasticity to temperature and predation risk and the underlying proximate mechanisms: behaviour (food intake) and digestive physiology (growth efficiency). The mechanistic underpinnings of predator-induced growth increases remain especially poorly understood. 2. We reared larvae from replicated northern and southern populations of the damselfly Ischnura elegans in a common garden experiment manipulating temperature and predation risk and quantified growth rate, food intake and growth efficiency. 3. The predator-induced and temperature-induced growth accelerations were the same at both latitudes, despite considerably faster growth rates in the southern populations. While the higher growth rates in the southern populations and the high rearing temperature were driven by both an increased food intake and a higher growth efficiency, the higher growth rates under predation risk were completely driven by a higher growth efficiency, despite a lowered food intake. 4. The emerging pattern that higher growth rates associated with latitude, temperature and predation risk were all (partly or completely) mediated by a higher growth efficiency has two major implications. First, it indicates that energy allocation trade-offs and the associated physiological costs play a major role both in shaping large-scale geographic variation in growth rates and in shaping the extent and direction of growth rate plasticity. Secondly, it suggests that the efficiency of energy transfer in aquatic food chains, where damselfly larvae are important intermediate predators, will be higher in southern populations, at higher temperatures and under predation risk. This may eventually contribute to the lengthening of food chains under these conditions and highlights that the prey identity may determine the influence of predation risk on food chain length.

Preference of larvae of Enallagma cyathigerum (Odonata: Coenagrionidae) for habitats of varying structural complexity

In macrophyte-rich lentic ecosystems, higher numbers of damselfly larvae occur in areas where there is structurally complex vegetation than in those where the plant architecture is relatively simple. Biotic interactions rather than morphological constraints are considered to underlie this pattern. We investigated whether the preference of the larvae of the damselfly Enallagma cyathigerum for a particular habitat was retained in absence of prey, predators and/or conspecifics. A series of laboratory choice experiments was conducted in which combinations of sediment and artificial plants differing in structural complexity were offered simultaneously to the larvae. Larvae preferred patches with structurally complex vegetation over patches with simply structured vegetation or lacking vegetation. Patches with simply structured vegetation were preferred over those with bare sediment, but the number of larvae showing a clear choice, which is regarded as an indication of the strength of the preference for a particular habitat, was relatively low compared to the number of individuals responding when complex vegetation was present. Based on the results presented, we conclude that the preference of E. cyathigerum larvae for structurally complex vegetation is independent of the presence of predators, prey or competitors. This suggests that this behaviour of the larvae is either learned or an innate response.

Levels of persistent organic pollutants in larvae of the damselfly Ischnura elegans (Odonata, Coenagrionidae) from different ponds in Flanders, Belgium

We investigated the accumulation of persistent organic pollutants in damselfly larvae (Ischnura elegans) in sixteen ponds in Flanders (Belgium), widely differing in the surrounding land use. Concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) and hexachlorobenzene (HCB) were measured. From all targeted PBDE-congeners, only three congeners (IUPAC nos. 47, 99, 100) were above the limit of quantification (LOQ). The ∑PBDE concentrations ranged from <LOQ up to 0.51ngg−1 ww. From the targeted PCB-congeners, thirteen were detectable (IUPAC nos. 95, 99, 101, 105, 118, 138, 149, 153, 156, 170, 180, 183, and 187). A high variation in ∑PCB concentrations was observed between the ponds, ranging from <LOQ (0.67ngg−1 ww) up to 9.91ngg−1 ww in the damselflies from the pond at Sijsele. In all investigated Flemish ponds, p,p'-DDE concentrations were >LOQ (0.20ngg−1 ww) with values up to 3.30ngg−1 ww in the pond at Hamme. In fifteen ponds, the HCB concentrations were >LOQ (0.05ngg−1 ww) with values up to 0.24ngg−1 ww. For the available data in the literature a comparison with different species was done for some of the sampled ponds. The monitored ponds can be separated in three groups based on their contamination. The first group is characterised by a relative low POP content (∑PBDEs, ∑PCBs, HCB). Group 2 contained more HCB and p,p'-DDE than the overall mean while this was the case for PBDEs and PCBs in group 3. The vectors of both contaminated groups are situated nearly perpendicular which is suggesting a different pollution sources.

Early stadium damselfly larvae (Odonata: Coenagrionidae) as prey of an aquatic plant, Utricularia australis

Abstract Two third stadium larvae of Coenagrionidae (probably Coenagrion puella or Ischnura elegans) were recorded in the bladders of U. australis sampled from a garden pond in Karlsruhe, Germany, in June 2010. These are the first records of odonate larvae as prey of carnivorous aquatic macrophytes. Keywords: Odonata, dragonfly, bladderwort, carnivorous plants, macrophytes, predation Issue section: Article

The Role of Damselflies (Odonata: Zygoptera) as Paratenic Hosts in the Transmission of Halipegus eccentricus (Digenea: Hemiuridae) to Anurans

Halipegus eccentricus is a common hemiurid trematode in the eustachian tubes of North America frogs. However, the life cycle of this species has never been completely elucidated. Studies on H. eccentricus suggest that it has a 3-host life cycle. Here, we show through fieldwork and host specificity experimental infections that the life cycle of Halipegus eccentricus utilizes 4 hosts. Metamorphosed anurans become infected with H. eccentricus by feeding on infected damselflies; worms reside in the stomach of anurans, migrate to the eustachian tubes within 32-39 days post-exposure (DPE), and release eggs 50-60 DPE. Cystophorous cercariae develop in Physa gyrina snails within 32-35 DPE, infect ostracod ( Cypridopsis sp.) second intermediate hosts, and develop to metacercariae. Fifteen- to 19-day-old metacercariae from ostracods are infective to both damselfly larvae and metamorphosed anurans. Field surveys of damselflies and tadpoles, along with laboratory exposure of damselfly larvae, metamorphosed anurans, and tadpoles with infected ostracods, indicated that only metamorphosed anurans and damselflies become infected with H. eccentricus , whereas field-collected tadpoles and laboratory-exposed tadpoles were never infected with H. eccentricus . Because little morphological change occurred in the metacercaria stage of H. eccentricus between the ostracod second intermediate host and damselfly host, and metamorphosed anurans became infected with H. eccentricus metacercariae recovered from both host groups, we suggest that odonates serve as paratenic hosts in this life cycle. Additionally, our field work and experimental infections provide data on the use of odonates as the route of infection by another North American Halipegus sp. that matures in the stomach of frogs. Our data indicate that when the life cycles are known, the use of odonates as the route of infection to anurans is common in the life cycles of Halipegus spp., and all species exhibit remarkable infection site fidelity in their amphibian hosts.

Behavioural activity levels and expression of stress proteins under predation risk in two damselfly species

Abstract1. It has become apparent that predators may strongly decrease prey fitness without direct contact with the prey, as they induce the development of defence systems that limit the availability of energy for growth and reproduction. Recent studies suggest that stress proteins may help prey organisms deal with this stress. The pattern is not general, however, and little is known about species differences in physiological traits in coping with predator stress, and covariation of physiological with other antipredator traits.2. To explore these issues, we quantified levels of constitutive and fish‐induced stress proteins (Hsp60 and Hsp70) and anti‐predator behaviours in larvae of two damselfly species that differ in lifestyle. Both stress proteins were fixed at higher levels inErythromma najas, which has a slow lifestyle, than inLestes sponsa, which has a fast lifestyle. Similarly, anti‐predator behaviours were fixed at safer levels inE. najasthan inL. sponsa.3. These results suggest that stress proteins may be part of anti‐predator syndromes of damselfly larvae, and there may be trait co‐specialisation between stress proteins and behavioural anti‐predator traits. Studies formally testing these hypotheses in more species may prove rewarding in advancing our understanding of the functional integration of physiological anti‐predator traits in relation to the prey’s lifestyle.