The largest insects to have ever lived were the giant meganeurids of the Late Palaeozoic, ancient stem relatives of our modern dragonflies. With wingspans up to 71 cm, these iconic insects have been the subject of varied documentaries on Palaeozoic life, depicting them as patrolling for prey through coal swamp forests amid giant lycopsids, and cordaites. Such reconstructions are speculative as few definitive details of giant dragonfly biology are known. Most specimens of giant dragonflies are known from wings or isolated elements, but Meganeurites gracilipes preserves critical body structures, most notably those of the head. Here we show that it is unlikely it thrived in densely forested environments where its elongate wings would have become easily damaged. Instead, the species lived in more open habitats and possessed greatly enlarged compound eyes. These were dorsally hypertrophied, a specialization for long-distance vision above the animal in flight, a trait convergent with modern hawker dragonflies. Sturdy mandibles with acute teeth, strong spines on tibiae and tarsi, and a pronounced thoracic skewness are identical to those specializations used by dragonflies in capturing prey while in flight. The Palaeozoic Odonatoptera thus exhibited considerable morphological specializations associated with behaviours attributable to 'hawkers' or 'perchers' among extant Odonata.

• MeSH
• křídla zvířecí anatomie a histologie   MeSH
• let zvířat fyziologie   MeSH
• mandibula anatomie a histologie   fyziologie   MeSH
• paleontologie MeSH
• predátorské chování * MeSH
• vážky anatomie a histologie   fyziologie   MeSH
• velikost orgánu MeSH
• zkameněliny * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Phenotypic plasticity is a common defensive strategy in species experiencing variable predation risk, such as habitat generalists. Larvae of generalist dragonflies can elongate their abdominal spines in environments with fish, but long spines render larvae susceptible to invertebrate predators. Long-spined specialists adapted to fish-heavy habitats are not expected to have phenotypic plasticity in this defence trait, but no empirical studies have been undertaken. Moreover, in comparison to prey responding to multiple predators that induce similar phenotypes, relatively little is known regarding how species react to combinations of predators that favour opposing traits. We examined plasticity of larval dragonfly Sympetrum depressiusculum, a long-spined habitat specialist. In a rearing experiment, larvae were exposed to four environments: (i) no predator control, (ii) fish cues (Carassius auratus), (iii) invertebrate cues (Anax imperator), as well as (iv) a combination of (ii) and (iii). Compared with the control, fish but not invertebrate cues resulted in longer spines for two (one lateral, one dorsal) of the six spines measured. Interestingly, the combined-cue treatment led to the elongation of all four dorsal spines compared with the fish treatment alone, whereas lateral spines showed no response. Our experiment provided evidence of morphological plasticity in a long-spined specialist dragonfly. We showed that nearly all spines can elongate, but also react differently under specific predator settings. Therefore, while spine plasticity evolved in direct response to a single predator type (fish), plasticity was maintained against invertebrate predators as long as fish were also present. Selective spine induction under the combined condition suggests that S. depressiusculum can successfully survive in environments with both predators. Therefore, phenotypic plasticity may be an effective strategy for habitat generalists and specialists. Although more studies are necessary to fully understand how selection shapes the evolution of phenotypic plasticity, we demonstrated that in dragonflies, presence or absence of a specific predator is not the only factor that determines plastic defence responses.

• MeSH
• biologické modely * MeSH
• fenotyp * MeSH
• fyziologická adaptace * MeSH
• larva MeSH
• potravní řetězec * MeSH
• vážky fyziologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Insecticides usually present in low concentrations in streams are known to impair behaviour and development of non-target freshwater invertebrates. Moreover, there is growing awareness that the presence of natural stressors, such as predation risk may magnify the negative effects of pesticides. This is because perception of predation risk can by itself lead to changes on behaviour and physiology of prey species. To evaluate the potential combined effects of both stressors on freshwater detritivores we studied the behavioural and developmental responses of Chironomus riparius to chlorantraniliprole (CAP) exposure under predation risk. Also, we tested whether the presence of a shredder species would alter collector responses under stress. Trials were conducted using a simplified trophic chain: Alnus glutinosa leaves as food resource, the shredder Sericostoma vittatum and the collector C. riparius. CAP toxicity was thus tested under two conditions, presence/absence of the dragonfly predator Cordulegaster boltonii. CAP exposure decreased leaf decomposition. Despite the lack of significance for interactive effects, predation risk marginally modified shredder effect on leaf decomposition, decreasing this ecosystem process. Shredders presence increased leaf decomposition, but impaired chironomids performance, suggesting interspecific competition rather than facilitation. C. riparius growth rate was decreased independently by CAP exposure, presence of predator and shredder species. A marginal interaction between CAP and predation risk was observed regarding chironomids development. To better understand the effects of chemical pollution to natural freshwater populations, natural stressors and species interactions must be taken into consideration, since both vertical and horizontal species interactions play their role on response to stress.

• MeSH
• Chironomidae účinky léků   růst a vývoj   fyziologie   MeSH
• hmyz účinky léků   růst a vývoj   fyziologie   MeSH
• insekticidy toxicita   MeSH
• larva účinky léků   růst a vývoj   fyziologie   MeSH
• listy rostlin MeSH
• nymfa účinky léků   růst a vývoj   fyziologie   MeSH
• olše MeSH
• ortoaminobenzoáty toxicita   MeSH
• potravní řetězec * MeSH
• predátorské chování * MeSH
• stravovací zvyklosti účinky léků   MeSH
• vážky růst a vývoj   fyziologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

BACKGROUND: Many animals rely on their escape performance during predator encounters. Because of its dependence on body size and temperature, escape velocity is fully characterized by three measures, absolute value, size-corrected value, and its response to temperature (thermal sensitivity). The primary target of the selection imposed by predators is poorly understood. We examined predator (dragonfly larva)-imposed selection on prey (newt larvae) body size and characteristics of escape velocity using replicated and controlled predation experiments under seminatural conditions. Specifically, because these species experience a wide range of temperatures throughout their larval phases, we predict that larvae achieving high swimming velocities across temperatures will have a selective advantage over more thermally sensitive individuals. RESULTS: Nonzero selection differentials indicated that predators selected for prey body size and both absolute and size-corrected maximum swimming velocity. Comparison of selection differentials with control confirmed selection only on body size, i.e., dragonfly larvae preferably preyed on small newt larvae. Maximum swimming velocity and its thermal sensitivity showed low group repeatability, which contributed to non-detectable selection on both characteristics of escape performance. CONCLUSIONS: In the newt-dragonfly larvae interaction, body size plays a more important role than maximum values and thermal sensitivity of swimming velocity during predator escape. This corroborates the general importance of body size in predator-prey interactions. The absence of an appropriate control in predation experiments may lead to potentially misleading conclusions about the primary target of predator-imposed selection. Insights from predation experiments contribute to our understanding of the link between performance and fitness, and further improve mechanistic models of predator-prey interactions and food web dynamics.

• MeSH
• larva anatomie a histologie   fyziologie   MeSH
• ocas anatomie a histologie   fyziologie   MeSH
• plavání MeSH
• potravní řetězec * MeSH
• Salamandridae anatomie a histologie   růst a vývoj   fyziologie   MeSH
• teplota MeSH
• vážky růst a vývoj   fyziologie   MeSH
• velikost těla MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Global change affects individual phenotypes and biotic interactions, which can have cascading effects up to the ecosystem level. However, the role of environmentally induced phenotypic plasticity in species interactions is poorly understood, leaving a substantial gap in our knowledge of the impacts of global change on ecosystems. Using a cladoceran-dragonfly system, we experimentally investigated the effects of thermal acclimation, acute temperature change and enrichment on predator functional response and metabolic rate. Using our experimental data, we next parameterized a population dynamics model to determine the consequences of these effects on trophic interaction strength and food-chain stability. We found that (1) predation and metabolic rates of the dragonfly larvae increase with acute warming, (2) warm-acclimated larvae have a higher maximum predation rate than cold-acclimated ones, and (3) long-term interaction strength increases with enrichment but decreases with both acclimation and acute temperatures. Overall, our experimental results show that thermal acclimation can buffer negative impacts of environmental change on predators and increase food-web stability and persistence. We conclude that the effect of acclimation and, more generally, phenotypic plasticity on trophic interactions should not be overlooked if we aim to understand the effects of climate change and enrichment on species interaction strength and food-web stability.

• MeSH
• aklimatizace MeSH
• bazální metabolismus * MeSH
• biologické modely MeSH
• Daphnia fyziologie   MeSH
• klimatické změny MeSH
• larva růst a vývoj   fyziologie   MeSH
• nízká teplota MeSH
• populační dynamika MeSH
• potravní řetězec * MeSH
• predátorské chování * MeSH
• vážky růst a vývoj   fyziologie   MeSH
• vysoká teplota MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Thermal quality and predation risk are considered important factors influencing habitat patch use in ectothermic prey. However, how the predator's food requirement and the prey's necessity to avoid predation interact with their respective thermoregulatory strategies remains poorly understood. The recently developed 'thermal game model' predicts that in the face of imminent predation, prey should divide their time equally among a range of thermal patches. In contrast, predators should concentrate their hunting activities towards warmer patches. In this study, we test these predictions in a laboratory setup and an artificial environment that mimics more natural conditions. In both cases, we scored thermal patch use of newt larvae (prey) and free-ranging dragonfly nymphs (predators). Similar effects were seen in both settings. The newt larvae spent less time in the warm patch if dragonfly nymphs were present. The patch use of the dragonfly nymphs did not change as a function of prey availability, even when the nymphs were starved prior to the experiment. Our behavioral observations partially corroborate predictions of the thermal game model. In line with asymmetric fitness pay-offs in predator-prey interactions (the 'life-dinner' principle), the prey's thermal strategy is more sensitive to the presence of predators than vice versa.

• MeSH
• biologické modely MeSH
• larva fyziologie   MeSH
• nymfa fyziologie   MeSH
• predátorské chování fyziologie   MeSH
• Salamandridae růst a vývoj   fyziologie   MeSH
• teplota * MeSH
• vážky růst a vývoj   fyziologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

1. Predation is often size selective, but the role of other traits of the prey and predators in their interactions is little known. This hinders our understanding of the causal links between trophic interactions and the structure of animal communities. Better knowledge of trophic traits underlying predator-prey interactions is also needed to improve models attempting to predict food web structure and dynamics from known species traits. 2. We carried out laboratory experiments with common freshwater macroinvertebrate predators (diving beetles, dragonfly and damselfly larvae and water bugs) and their prey to assess how body size and traits related to foraging (microhabitat use, feeding mode and foraging mode) and to prey vulnerability (microhabitat use, activity and escape behaviour) affect predation strength. 3. The underlying predator-prey body mass allometry characterizing mean prey size and total predation pressure was modified by feeding mode of the predators (suctorial or chewing). Suctorial predators fed upon larger prey and had ˜3 times higher mass-specific predation rate than chewing predators of the same size and may thus have stronger effect on prey abundance. 4. Strength of individual trophic links, measured as mortality of the focal prey caused by the focal predator, was determined jointly by the predator and prey body mass and their foraging and vulnerability traits. In addition to the feeding mode, interactions between prey escape behaviour (slow or fast), prey activity (sedentary or active) and predator foraging mode (searching or ambush) strongly affected prey mortality. Searching predators was ineffective in capturing fast-escape prey in comparison with the remaining predator-prey combinations, while ambush predators caused higher mortality than searching predators and the difference was larger in active prey. 5. Our results imply that the inclusion of the commonly available qualitative data on foraging traits of predators and vulnerability traits of prey could substantially increase biological realism of food web descriptions.

• MeSH
• bezobratlí fyziologie   MeSH
• brouci fyziologie   MeSH
• Chironomidae MeSH
• chování zvířat fyziologie   MeSH
• Cladocera MeSH
• Culicidae MeSH
• Heteroptera fyziologie   MeSH
• hmyz MeSH
• Isopoda MeSH
• larva fyziologie   MeSH
• lokomoce MeSH
• Lymnaea MeSH
• masožravci fyziologie   MeSH
• mortalita MeSH
• potravní řetězec MeSH
• predátorské chování * MeSH
• sladká voda MeSH
• tělesná hmotnost fyziologie   MeSH
• vážky fyziologie   MeSH
• vodní organismy fyziologie   MeSH
• žáby MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH