Anax Junius Research Articles

Phenoloxidase and Melanization Innate Immune Activities in Green Darner Dragonfly Nymphs (<i>Anax junius</i>)

Insects in the Order Odonata are highly subject to infection by gregarine parasites. However, despite the important ecological roles that insects play in every ecosystem in which they exist, little research has been devoted to the description of insect immunity. Insects rely heavily on the rapid actions of innate immune mechanisms to prevent infection. We characterized the melanization response in the hemolymph of green darner dragonfly (Anax junius) nymphs. Incubation of chymotrypsin-activated hemolymph with L-DOPA resulted in volume- and time-dependent production of dopaquinone via the phenoloxidase (PO) enzyme, with biphasic accumulation of product. The PO activity was temperature-dependent, with a stepwise increase from 20℃ - 35℃ and maximum activity measured at 35℃ - 40℃. The formation of product was also inhibited in a concentration-dependent manner by diethylcarbonate, a specific inhibitor of PO activity, which indicated that the observed activity was due to the presence of PO enzyme. The rate of formation and quantity of melanin was dependent on exposure to different titers of bacteria. This is the first characterization of both PO activity and melanization response in green darner dragonflies.

Integrating high-speed videos in capture-mark-recapture studies of insects.

Capture–mark–recapture (CMR) studies have been used extensively in ecology and evolution. While it is feasible to apply CMR in some animals, it is considerably more challenging in small fast‐moving species such as insects. In these groups, low recapture rates can bias estimates of demographic parameters, thereby handicapping effective analysis and management of wild populations. Here, we use high‐speed videos (HSV) to capture two large dragonfly species, Anax junius and Rhionaeschna multicolor, that rarely land and, thus, are particularly challenging for CMR studies. We test whether HSV, compared to conventional “eye” observations, increases the “resighting” rates and, consequently, improves estimates of both survival rates and the effects of demographic covariates on survival. We show that the use of HSV increases the number of resights by 64% in A. junius and 48% in R. multicolor. HSV improved our estimates of resighting and survival probability which were either under‐ or overestimated with the conventional observations. Including HSV improved credible intervals for resighting rate and survival probability by 190% and 130% in A. junius and R. multicolor, respectively. Hence, it has the potential to open the door to a wide range of research possibilities on species that are traditionally difficult to monitor with distance sampling, including within insects and birds.

Stress hormone-mediated antipredator morphology improves escape performance in amphibian tadpoles

Complete functional descriptions of the induction sequences of phenotypically plastic traits (perception to physiological regulation to response to outcome) should help us to clarify how plastic responses develop and operate. Ranid tadpoles express several plastic antipredator traits mediated by the stress hormone corticosterone, but how they influence outcomes remains uncertain. We investigated how predator-induced changes in the tail morphology of wood frog (Rana sylvatica) tadpoles influenced their escape performance over a sequence of time points when attacked by larval dragonflies (Anax junius). Tadpoles were raised with no predator exposure, chemical cues of dragonflies added once per day, or constant exposure to caged dragonflies crossed with no exogenous hormone added (vehicle control only), exogenous corticosterone, or metyrapone (a corticosteroid synthesis inhibitor). During predation trials, we detected no differences after four days, but after eight days, tadpoles exposed to larval dragonflies and exogenous corticosterone had developed deeper tail muscles and exhibited improved escape performance compared to controls. Treatment with metyrapone blocked the development of a deeper tail muscle and resulted in no difference in escape success. Our findings further link the predator-induced physiological stress response of ranid tadpoles to the development of an antipredator tail morphology that confers performance benefits.

Partial submergence: An undescribed behavioral adjustment for thermoregulation at high ambient temperature in Aeshnidae

Many insects including odonates thermoregulate using a combination of behavioral and physiological mechanisms. At high ambient temperature (Ta), these mechanisms include decreased heat production and increased heat loss. Heat production can be reduced by decreasing activity. Heat loss can be enhanced by perching in a shaded microhabitat where temperature is cooler than in the surrounding environment. Aeshnids, which are intermittent endotherms, increase heat loss at high Ta; also by increasing hemolymph circulation from the thorax, where most metabolic heat is produced, to the abdomen, where it dissipates to the environment by convection. While studying two aeshnid species (Anax junius and Rhionaeschna multicolor) at a Sonoran Desert (Arizona, USA) stream, I observed partially submerged mature individuals of both sexes of these species. This heretofore undescribed behavior was seen only at Ta; ≥ 43 °C and almost exclusively during the hottest part of the day (15:00–17:00 hr), when the daily difference between Ta; and water temperature (Tw) was, on average, largest. A cooling effect of partial submergence behavior on body temperature would, therefore, presumably be most effective also during this period. Several percher species of libellulids were present at the study site. These dragonflies are not known to use endothermy for thermoregulation or to increase hemolymph circulation to the abdomen to dissipate heat at high Ta;, and none was ever observed to partially submerge. It is suggested in aeshnids that partial submergence at high Ta; serves a thermoregulatory function by facilitating body heat dissipation from the abdomen.

Phenological and isotopic evidence for migration as a life history strategy in Aeshna canadensis (family: Aeshnidae) dragonflies

1. Investigating dragonfly migration is important for understanding species' life history strategies, migratory connectivity, terrestrial‐aquatic linkages, and for successful species conservation. While migration patterns are well‐documented for some species (e.g., Anax junius), questions remain about potential migratory behaviour of others.2. We investigated the potential for migration of Aeshna canadensis (Walker, 1908; Canada darner) using phenological observations in three study ponds in central Minnesota, 2017–2019. We also conducted probabilistic assignment to natal origins by measuring stable hydrogen isotope values of wing tissue (δ2Hw) of dragonflies collected in Minnesota and acquired through Canadian museum collections.3. This species emerged May–June from study ponds in central Minnesota, with a 10–15 week lag after onset of emergence before mature adults were observed flying and ovipositing in late summer. The probabilistic assignment depictions of emerging tenerals overlapped with the sampling location, confirming accuracy of isotopic assignments of natal origin.4. Late‐flying mature adults collected at our study ponds likely originated from southern Manitoba, suggesting a north–south migration pathway. We found further evidence for migration by analysing δ2Hw of adult dragonflies collected in northern Minnesota and south‐central Canada. Their likely origins were farther north in central Canada (Manitoba/Quebec) or the northeastern reaches of this species' range in eastern Canada.5. We provide the first conclusive evidence of Aeshna migration in North America and demonstrate a robust approach, combining field observations with probabilistic assignment to origin using stable isotope analysis, which can test for migration in other dragonfly populations.

Predators Induce Morphological Changes in Tadpoles of Hyla andersonii

Predators can affect the development, fitness, and behavior of prey species in myriad ways. In response to the threat of predation, tadpoles can alter growth rate, morphology, and foraging behavior. Changes to tadpole development have the potential to alter life history characteristics and are therefore of interest in species of conservation concern. Using experimental mesocosms, we explored how non-lethal predators affected the larval development of the Pine Barrens Treefrog, Hyla andersonii, a near-threatened species in the United States. We found that caged dragonflies (Anax junius) induced darker tail coloration and deeper tail fins in tadpoles of H. andersonii, but the dragonflies did not affect tadpole behavior, survival, or size at metamorphosis. Non-lethal predator presence also induced greater within population variation in the tail color trait compared to populations without predators. This result suggests that there may be underlying genetic variation in the ability to express phenotypically plastic traits, a concept that should be explored further because it has implications for the evolution of inducible defenses. These findings support the existence of an adaptive syndrome among hylid tadpoles, where tadpoles develop conspicuous tail morphology in response to larval dragonfly predators.

The effects of hydroperiod and predator density on growth, development, and morphology of wood frogs (Rana sylvatica)

Accelerated development and metamorphosis allow tadpoles to escape death by leaving the aquatic habitat before it dries. Phenotypic plasticity in response to predators typically includes development of physical and behavioral traits, including changes in tail coloration, activity rate, and tail shape and body size. Responding to predators increases the probability of survival, but lowers growth rate. Responses to two common stressors in ephemeral aquatic habitats appear to be in direct opposition to one another. In this study, we examined the individual and interactive effects of hydroperiod and predator density on the life history, morphology, and metamorphosis of wood frog (Rana sylvatica) tadpoles in an outdoor mesocosm study. Tadpoles were exposed to three hydroperiods (constant, intermediate, and short) and three predator densities (zero, four, and eight Anax junius naiads) using a complete block design. The threat of habitat desiccation resulted in increased developmental rate and shorter larval periods. Increased predator densities resulted in increased size at metamorphosis and development of the induced morphology. Although the threat of predation precluded growth and developmental responses to shortened hydroperiod in tadpoles, it did not negate the metamorphic responses to hydroperiod. It appears that, at least at the treatment levels imposed in this experiment, the interaction between these multiple stressors is complex, with the stressors acting both individually and together on different aspects of tadpole ecology.

Palatability and Defense of Eastern Newt (Notophthalmus viridescens) Larvae and Metamorphic Juveniles against Predatory Dragonfly Nymphs

We examined the predator–prey relationship between nymphs of the predatory dragonfly Anax junius (Common Green Darner) and larval and metamorphic Notophthalmus viridescens (Eastern Newt), some of which may contain the potent neurotoxin, tetrodotoxin. First, we conducted a palatability study to determine which life-history stages were palatable to dragonflies. We also tested the metamorphosis and survival rates of larval newts when exposed to predatory dragonflies in small microcosms. Finally, we tested the predator avoidance behavior of larval newts in response to chemical cues from a control, food stimulus, and predatory dragonflies. All life-history stages (small and large larvae, and recent metamorphs) were palatable to dragonflies. In microcosm trials, we found that newt larvae had a lower chance of surviving and transforming when dragonflies were present compared to a control. Finally, newt larvae decreased movement significantly when exposed to predatory dragonfly stimulus compared to either a control or food stimulus. These results suggest dragonflies are effective predators of newts from hatching through metamorphosis. However, the larvae do possess behavioral avoidance mechanisms that likely reduce the risk of predation by dragonflies.

Chronic Exposure to High Concentrations of Road Salt Decreases the Immune Response of Dragonfly Larvae

Salinization of freshwater ecosystems, due to the application of road salts, is recognized as a potential threat to aquatic communities. Much of the research on the impact of salinity has focused on performance metrics in vertebrates, including respiration and osmoregulation. Here we focus on immune function in of the dragonfly Anax junius, a top predator in fishless aquatic habitats. Impacts on this top predator have the potential to cascade through the community, and immune function is known to be both plastic and sensitive to stress. We injected larvae with monofilaments (simulating a parasite) and placed them in one of three environmentally relevant concentrations of deicing road salt: control (dechlorinated tap water with no added salt), low (1000 mgL-1), or high salt (3000 mgL-1), for either acute (24hr) chronic or (96hr) exposures. We hypothesized that elevated salinity would suppress the immune response and that longer exposure magnifies this effect. As predicted, chronic exposure to high salt concentrations resulted in a significantly reduced larval immune response, however, there was no detectable treatment effects in larvae exposed to low concentrations of road salt or to acute high concentrations. Our results demonstrate that prolonged exposure to high levels of road salt can compromise the immune response of dragonfly larvae. Our findings suggest that insects in aquatic environments that experience sustained environmental salt pollution will be more susceptible to parasites and pathogens, which in turn may affect the impact of this major predator on aquatic community dynamics.

Parasite-induced vulnerability to predation in larval anurans.

Within communities, pathogens and parasites have the potential to indirectly influence predator-prey interactions. For instance, prey that exhibit pathology or altered traits (e.g. behavioral shifts) following infection could be more prone to predation, which is known as parasite-induced vulnerability to predation (PIVP). PIVP has been frequently documented for pathogens with trophic transmission, because predators are often critical in the pathogen's life cycle. However, for pathogens without trophic transmission, PIVP can lead to a healthy herds effect, thereby reducing transmission in the system. In this study, we explored whether the pathogen ranavirus (family Iridoviridae) enhances vulnerability of 4 species of larval amphibians (spring peepers Pseudacris crucifer, gray treefrogs Hyla versicolor, American toads Anaxyrus americanus, and northern leopard frogs Lithobates pipiens) to 2 common tadpole predators (larval green darners Anax junius [hereinafter Anax] and adult water bugs Belostoma flumineum [hereinafter Belostoma]). For each anuran species, we conducted short-term microcosm experiments to assess predation rates on individuals that were or were not exposed to virus. For 3 of the 4 species, we found that exposure to ranavirus decreased survival rates with Anax between 2- and 9-fold. However, we did not see the same trend with Belostoma, which indicates that predator identity is important in this interaction. More specifically, the higher efficiency of Anax in capturing and consuming prey, relative to Belostoma, may allow Anax to capitalize on trait changes induced by virus exposure and enhance the PIVP effect. Our results indicate that trait-mediated indirect effects could play a role in creating healthy herds in amphibian communities.

Radio-tracking reveals how wind and temperature influence the pace of daytime insect migration.

Insects represent the most diverse and functionally important group of flying migratory animals around the globe, yet their small size makes tracking even large migratory species challenging. We attached miniaturized radio transmitters (less than 300 mg) to monarch butterflies ( Danaus plexippus) and common green darner dragonflies ( Anax junius) and tracked their autumn migratory movements through southern Ontario, Canada and into the United States using an automated array of over 100 telemetry towers. The farthest estimated distance a monarch travelled in a single day was 143 km at a wind-assisted groundspeed of 31 km h-1 (8.7 m s-1) and the farthest estimated distance a green darner travelled in a single day was 122 km with a wind-assisted groundspeed of up to 77 km h-1 (21.5 m s-1). For both species, increased temperature and wind assistance positively influenced the pace of migration, but there was no effect of precipitation. While limitations to tracking such small animals remain, our approach and results represent a fundamental advance in understanding the natural history of insect migration and environmental factors that govern their movements.

Consumption of the eggs, hatchlings, and tadpoles of Green Frogs (Lithobates clamitans) by native and non-native predators

Abstract Predation by native and non-native predators on the eggs, embryos, and early stage tadpoles can affect the recruitment of offspring into a population. We examined the effects of native (Little Brown Mudbugs, Cambarus thomai; overwintered Rana tadpoles; Common Green Darner, Anax junius, larvae) and non-native (Western Mosquitofish, Gambusia affinis) potential predators on the eggs, hatchlings, and early tadpoles of the Green Frog (Lithobates clamitans). The predators had no effect on survivorship or hatching of L. clamitans eggs. However, tadpole survivorship was significantly reduced by dragonfly larvae and crayfish, but not G. affinis or the overwintered ranid tadpoles. Our observation that invertebrates consumed Green Frog tadpoles while vertebrates did not is consistent with palatability contributing to the tadpoles’ susceptibility to different predators. Our results therefore suggest Green Frog tadpoles, but not eggs or embryos, from some populations may be subject to differential predation by invertebrate and vertebrate predators.

Space Use of Predatory Larval Dragonflies and Tadpole Prey in Response to Chemical Cues of Predation

Chemical cues are frequently a key source of information to aquatic organisms. Both predators (kairomones digestive metabolites) and prey (alarm and damage-released cues) may generate chemical cues during their interactions, and different cue types can have different informational values. How predators and prey use the information from chemical cues to make spatial movement decisions influences both their direct interaction rates and their interactions with other species. We measured the spatial response of predatory larval dragonflies (Anax junius) and predator-naive green frog (Lithobates clamitans) tadpoles exposed to several types of chemical cues using experimental mesocosms. We found tadpoles only responded with spatial avoidance when exposed to both Anax kairomones and conspecific alarm cues together, whereas Anax did not exhibit consistent spatial responses to any cue type. Our results suggest tadpole prey selectively respond to environmental information from chemical cues (possibly to minimize costly antipredator behavior due to responding to insufficient information or reflecting a need for associative learning). They also show predatory dragonflies may use nonchemical information to make space use decisions (possibly due to inability to detect the same chemical cues as tadpoles).

Tracking dragons: stable isotopes reveal the annual cycle of a long-distance migratory insect.

Insect migration is globally ubiquitous and can involve continental-scale movements and complex life histories. Apart from select species of migratory moths and butterflies, little is known about the structure of the annual cycle for migratory insects. Using stable-hydrogen isotope analysis of 852 wing samples from eight countries spanning 140 years, combined with 21 years of citizen science data, we determined the full annual cycle of a large migratory dragonfly, the common green darner ( Anax junius). We demonstrate that darners undertake complex long-distance annual migrations governed largely by temperature that involve at least three generations. In spring, the first generation makes a long-distance northbound movement (further than 650 km) from southern to northern range limits, lays eggs and dies. A second generation emerges and returns south (further than 680 km), where they lay eggs and die. Finally, a third resident generation emerges, reproducing locally and giving rise to the cohort that migrates north the following spring. Since migration timing and nymph development are highly dependent on temperature, continued climate change could lead to fundamental changes in the biology for this and similar migratory insects.

The interactive effects of predator stress, predation, and the herbicide Roundup

AbstractAs the number of studies examining the effects of contaminants grows, ecologists are becoming increasingly aware that contaminants can interact with natural stressors (e.g., competition and predator cues) in their effects on nontarget animals. In amphibians, predator cues can make contaminants more lethal under laboratory conditions, but the opposite outcome has been observed under more natural conditions with stratified water columns; stratification causes more pesticide to be present near the surface while predator cues scare spring‐breeding amphibians down to the benthos. I examined whether this phenomenon also occurs in three species of summer‐breeding amphibians (Hyla versicolor, Rana clamitans, and Rana catesbeiana) that were raised in outdoor mesocosms. Specifically, I asked how amphibian survival was affected by multiple concentrations of a common herbicide (glyphosate; commercial name: Roundup), the herbicide combined with chemical cues from predators (caged larval dragonflies; Anax junius), and the herbicide combined with lethal predators. Environmentally relevant concentrations of the herbicide caused high rates of tadpole mortality, but this outcome was substantially reversed by the addition of predator cues. With lethal predators, the tadpoles experienced such high mortality that the herbicide caused no additional effect. Roundup also induced morphological changes in Hyla versicolor, and the induced traits were different from those induced by predators. Collectively, these results suggest that while predator cues can make pesticides less lethal when thermal stratification occurs, highly lethal predators can overwhelm these effects. Thus, the impacts of such contaminants can be dramatically different in environments that do or do not contain high‐risk predators.

Animal behaviour and algal camouflage jointly structure predation and selection.

Trait variation can structure interactions between individuals, thus shaping selection. Although antipredator strategies are an important component of many aquatic systems, how multiple antipredator traits interact to influence consumption and selection remains contentious. Here, I use a common larval dragonfly (Epitheca canis) and its predator (Anax junius) to test for the joint effects of activity rate and algal camouflage on predation and survival selection. I found that active and poorly camouflaged Epitheca were more likely to be consumed, and thus, survival selection favoured inactive and well-camouflaged individuals. Notably, camouflage dampened selection on activity rate, likely by reducing attack rates when Epitheca encountered a predator. Correlational selection is therefore conferred by the ecological interaction of traits, rather than by opposing selection acting on linked traits. I suggest that antipredator traits with different adaptive functions can jointly structure patterns of consumption and selection.

Threat of predation alters aggressive interactions among spotted salamander (Ambystoma maculatum) larvae.

Intraspecific aggression represents a major source of mortality for many animals and is often experienced alongside the threat of predation. The presence of predators can strongly influence ecological systems both directly by consuming prey and indirectly by altering prey behavior or habitat use. As such, the threat of attack by higher level predators may strongly influence agonistic interactions among conspecifics via nonconsumptive (e.g., behaviorally mediated) predator effects. We sought to investigate these interactions experimentally using larval salamanders (Ambystoma maculatum) as prey and dragonfly nymphs (Anax junius) as predators. Specifically, we quantified salamander behavioral responses to perceived predation risk (PPR) from dragonfly nymphs and determined the degree to which PPR influenced intraspecific aggression (i.e., intraspecific biting and cannibalism) among prey. This included examining the effects of predator exposure on the magnitude of intraspecific biting (i.e., extent of tail damage) and the resulting change in performance (i.e., burst swim speed). Salamander larvae responded to PPR by reducing activity and feeding, but did not increase refuge use. Predator exposure did not significantly influence overall survival; however, the pattern of survival differed among treatments. Larvae exposed to PPR experienced less tail damage from conspecifics, and maximum burst swim speed declined as tail damage became more extensive. Thus, escape ability was more strongly compromised by intraspecific aggression occurring in the absence of predation risk. We conclude that multitrophic indirect effects may importantly modulate intraspecific aggression and should be considered when evaluating the effects of intraspecific competition.

Heterogeneity in body size and habitat complexity influence community structure

ABSTRACTFood web studies commonly ignore individual variation within a population and variation in the environment and assume these factors have insignificant effects on community dynamics relative to interspecific interactions. However, variation in body sizes within a population (size structure) and the physical structure of habitats (habitat complexity) can both affect interspecific interactions independently, with possible interactive effects. Using experimental mesocosms, we examined effects of predator size structure and habitat complexity on predation by two common predators in fishless ponds: larval aquatic beetles (Cybister fimbriolatus) and larval dragonflies (Anax junius). Cannibalism, intraguild predation, and predation on shared prey were measured at two levels of habitat complexity crossed with six size-structured pairs of predators. We found that highly complex habitats sustain a higher prey density because prey can take refuge from predators. Additionally, size structure had direct (size better predicted predation rate than did species identity) and indirect (IGP and cannibalism lowered predation rates) effects on consumptive interactions, which changed the composition and density of the predator guild. The identified size- and habitat-mediated mechanisms can change the frequencies of intraguild vs. interguild predation (a balance important in determining top–down control of predators), and therefore we argue that these sources of heterogeneity should be included in community ecology studies where possible.

Changes in hemolymph total CO2 content during the water-to-air respiratory transition of amphibiotic dragonflies.

Dragonflies (Odonata, Anisoptera) are amphibiotic; the nymph is aquatic and breathes water using a rectal gill before metamorphosing into the winged adult, which breathes air through spiracles. While the evolutionary and developmental transition from water breathing to air breathing is known to be associated with a dramatic rise in internal CO2 levels, the changes in blood-gas composition experienced by amphibiotic insects, which represent an ancestral air-to-water transition, are unknown. This study measured total CO2 (TCO2) in hemolymph collected from aquatic nymphs and air-breathing adults of Anax junius, Aeshna multicolor (Aeshnidae), Libellula quadrimaculata and Libellulaforensis (Libellulidae). Hemolymph PCO2 was also measured in vivo in both aeshnid nymphs and marbled crayfish (Procambarus fallax. f. virginalis) using a novel fiber-optic CO2 sensor. The hemolymph TCO2 of the pre- and early-final instar nymphs was found to be significantly lower than that of the air-breathing adults. However, the TCO2 of the late-final instar aeshnid nymphs was not significantly different from that of the air-breathing adults, despite the late-final nymphs still breathing water. TCO2 and PCO2 were also significantly higher in the hemolymph of early-final aeshnid nymphs compared with values for the water-breathing crayfish. Thus, while dragonfly nymphs show an increase in internal CO2 as they transition from water to air, from an evolutionary standpoint, the nymph's ability to breathe water is associated with a comparatively minor decrease in hemolymph TCO2 relative to that of the air-breathing adult.

Larval body condition regulates predator-induced life-history variation in a dragonfly.

Organisms with complex life cycles commonly exhibit adaptive plasticity in the timing of transitions between life stages. While the threat of predation is predicted to induce earlier transitions, empirical support has been equivocal. When predation risk affects both the propensity to transition to the next life stage and the ability to reach the energetic thresholds necessary to complete the transition, only those individuals in the best physiological condition may be able to accelerate development and emerge earlier. To test this hypothesis, we followed uniquely marked dragonfly larvae (Pachydiplax longipennis) through emergence in pools where we factorially manipulated the presence of a large heterospecific predator (Anax junius) and cannibalism risk via conspecific size variation. Consistent with our hypothesis, high-condition larvae were more likely to emerge in the presence of the heterospecific predator than in its absence, and low-condition larvae were more likely to emerge in its absence than in its presence. Moreover, high-condition larvae emerged earlier when cannibalism risk was high than when it was low. Predation risk therefore has condition-dependent effects on emergence. As predation risk frequently affects resource accumulation, similar mechanisms across taxacould commonly underlie the incongruence between empirical results and theoretical expectations for predator-induced life-history variation.