Pellets of proof: First glimpse of the dietary composition of adult odonates as revealed by metabarcoding of feces

Recent advances in molecular techniques allow us to resolve the diet of unstudied taxa. Odonates are potentially important top‐down regulators of many insects. Yet, to date, our knowledge of odonate prey use is based mainly on limited observations of odonates catching or eating their prey. In this study, we examine the potential use of metabarcoding in establishing the diet of three adult odonate species (Lestes sponsa, Enallagma cyathigerum, and Sympetrum danae) at a site in southwestern Finland. To this purpose, we compared three different methods for extracting DNA from fecal samples: the Macherey‐Nagel Nucleospin XS kit, a traditional salt extraction, and the Zymo Research Fecal Microprep kit. From these extracts, we amplified group‐specific mitochondrial markers (COI and 16S rRNA) from altogether 72 odonate individuals, and compared them to comprehensive reference libraries. The three odonate species show major overlap in diet, with no significant differences between individuals of different size and/or gender, reflecting opportunistic foraging of adult odonates. Of a total of 41 different prey species detected, the most frequently consumed ones were Diptera, with additional records of six other orders. Based on our data, the best DNA extraction method is the traditional salt extraction, as it provides the most information on prey content while also being the most economical. To our knowledge, this is the first study to resolve the species‐level diet of adult odonates. Armed with the appropriate methodological caveats, we are ready to examine the ecological role of odonates in both terrestrial and aquatic food webs, and in transferring subsidies between these two realms.     

Diel feeding behavior in larvae of four odonate species

The diel feeding behavior of four coexisting odonate larvae, Aeshna juncea, Coenagrion hastulatum, Cordulia aenea,and Leucorrhinia dubiawas studied in the laboratory. C. hastulatumand L. dubiawere equally active during day and night. While C. hastulatumconsumed an equal number of prey during day and night, L. dubiaconsumed more prey during night. In contrast, A. juncealarvae were most active and consumed more prey during day, while C. aenealarvae were most active and consumed more prey during night. In contrast to the other three species, A. junceashowed a longer reactive distance under light conditions. In A. junceaand L. dubiacapture efficiency was higher under light conditions, whereas in C. hastulatumand C. aeneait was the same irrespective of illumination. The results show that the time niche is an important component of the feeding in this guild.     

Are behavioural traits in prey sensitive to the risk imposed by predatory fish?

1. Behavioural differences among prey species may result from evolutionary adaptations that facilitate coexistence with different predators and influence vulnerability to predators. It has been hypothesised that prey species modify their behaviour in relation to the risk posed by particular predators. 2. We examined the relationship between anti‐predator behaviour and predation risk in five species of larval odonates in combination with three predatory fish species (perch, gudgeon and rudd) that differ in foraging behaviour. The odonates, Platycnemis pennipes, Coenagrion puella, Lestes sponsa, Sympetrum striolatum and Libellula depressa, differ with regard to their life cycle and habitat, including water depth, occurrence in temporary ponds and co‐existence with fish. 3. The odonate species differed in their response to fish: (i) Two species showed a flexible response. Larval C. puella reduced activity in the presence of fish, regardless of species, whereas L. depressa altered their activity only in the presence of gudgeon. (ii) Independent of fish species, all odonates except L. depressa exhibited spatial avoidance of fish. This was interpreted as a more general anti‐predator response. (iii) In some cases the odonates showed no response to predators and their behaviour was thus independent of predation risk. 4. Our results confirm that all odonates responded to the presence of at least some predatory fish, and that some odonate species discriminated between fish species. However, we found no significant correlation between behavioural modifications and predation risk, indicating that anti‐predator responses and predation risk depend on the particular predator and the species being preyed on.     

Effects of zooplankton availability and foraging mode on cannibalism in three dragonfly larvae

Summary Cannibalism is likely to operate as a form of population control in dragonfly larvae. I performed aquarium experiments to investigate the effect of foraging activity and zooplankton availability on cannibalism in three dragonfly larvae. Large Cordulia aenea larvae showed low activity, and large Leucorrhinia dubia larvae showed high activity irrespective of zooplankton availability. In contrast, large Coenagrion hastulatum larvae changed from high activity in the absence to low activity in the presence of zooplankton. Small Cordulia aenea larvae were active in the absence of large conspecifics irrespective of zooplankton availability. In the presence of large conspecifics they showed a reduced activity when zooplankton were present. Small L. dubia larvae showed high activity and small Coenagrion hastulatum larvae low activity irrespective of pressence or absence of zooplankton and large conspecifics. In all three species cannibalism was highest in the absence of zooplankton. In the absence of zooplankton cannibalism was low in Coenagrion hastulatum compared to the other two species. On the contrary, in the presence of zooplankton, cannibalism did not differ between the three species.     

Life history influences the vulnerability of New Zealand galaxiids to invasive salmonids

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Large net cage for captive breeding and behavioural studies of damselfly Lestes sponsa (Hansemann, 1823) (Odonata: Lestidae): submerged oviposition as a model behaviour

Odonata have a strong potential as model organisms for testing ecological and evolutionary hypotheses because of their short life history, relative ease and cost-effectiveness of care. Unfortunately, very few studies have examined how to create a semi-natural environment for odonates, limiting the biological validity of laboratory manipulation. To better study odonate life cycle and behaviour under controlled conditions, we designed a large net cage that imitated the natural terrestrial as well as aquatic habitat of the damselfly Lestes sponsa (Hansemann, 1823). This species is thought to be capable of submerged oviposition, an unusual behaviour in odonates. We compared multiple variables across natural conditions and the net cage. We demonstrated that between-year variability under natural conditions was generally greater than variability between natural and artificial environments. Overall, semi-natural conditions did not substantially change the L. sponsa life cycle (including the unique behaviour of submerged oviposition), suggesting that results from the net cage are likely generalisable to the field.     

Critical periods in the life cycle and the effects of a severe spate vary markedly between four species of elmid beetles in a small stream

1. The chief objectives were: (i) to describe quantitatively the life cycles of four species of Elmidae, Elmis aenea, Esolus parallelepipedus, Oulimnius tuberculatus and Limnius volkmari; (ii) to use life tables to identify critical periods for survival in the life cycle of each species; (iii) to evaluate the immediate and longer‐term effects of a severe spate on densities of the four species. Monthly samples were taken over 63 months at two contrasting sites in a small stream: one in a deep section with macrophytes abundant, and the other in a shallow stony section. 2. There were five larval instars for O. tuberculatus, seven for L. volkmari and six for the other two species. The life cycle of each species took 1 year from egg hatching (chiefly in June for E. aenea and O. tuberculatus, and July for the other species) to pupation in the stream bank and a further year before the adults in the stream matured and laid their eggs. Mature adults were present in most months, but were rare or absent in January and February and attained maximum densities in April for O. tuberculatus and May for the other species. 3. Laboratory experiments provided data on egg hatching and pupation periods and the number of eggs laid per female. Life tables compared maximum numbers per square metre for key life‐stages. Within each species, mortality rates between adjacent life‐stages were fairly constant among six cohorts and between sites, in spite of large differences in numbers. The only exception for all species was the high adult, but not larval, mortality during a severe spate. 4. Standardised life tables, starting with 1000 eggs, identified key life‐stages with the highest mortality, namely the early life‐stages for E. aenea (36% mortality), start of the overwintering period to pupation for O. tuberculatus (41%) and L. volkmari (51%), start of pupation to the maximum number of immature adults for E. parallelepipedus (41%) and between the maximum numbers of immature and mature adults for O. tuberculatus (41%). Therefore, critical periods for survival in the life cycle differed between species, presumably because of their different ecological requirements. Similarly, the effects of the spate on adult mortality, and hence egg production, varied between species, being most severe and long‐term for E. aenea and O. tuberculatus, less severe for E. parallelepipedus and least severe with a rapid recovery for L. volkmari. Possible reasons for these discrepancies are discussed, but more data are required on the food and microhabitat requirements of the elmids before satisfactory explanations can be found.     

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

Abstract 1. 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 in Erythromma najas, which has a slow lifestyle, than in Lestes sponsa, which has a fast lifestyle. Similarly, anti‐predator behaviours were fixed at safer levels in E. najas than in L. 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.     

Foraging modes in an assemblage of odonate larvae — effects of prey and interference

The foraging behaviour of four coexisting odonate larvae; Coenagrion hastulatum (Charp.) Zygoptera, Aeshna juncea (L.) Anisoptera, Cordulia aenea (L.) Anisoptera and Leucorrhinia dubia (v d Lind.) Anisoptera was analysed under various conditions of prey type and abundance. Coenagrion and Aeshna used a sit and wait mode when the prey density was high and when the prey was evasive. When the prey abundance was low an active mode was used. In Aeshna an active mode was also used when prey was sedentary. Cordulia exhibited a sit and wait mode and Leucorrhinia an active mode under all prey treatments performed. The results indicate that a niche differentiation in foraging behaviour may be one of several ways to reduce food competition between these coexisting species. However a literature study on prey selectivity did not reveal any support for this suggestion. Interference from Aeshna altered the foraging behaviour of Coenagrion whereas that of Leucorrhinia remained unchanged. Further, Aeshna preyed heavily on Leucorrhinia and to a lesser extent on Coenagrion during interference trials. A field study did not show any negative correlation in abundance between Aeshna and Leucorrhinia or Coenagrion larvae. The results indicate interference competition may be more important than exploitation competition in the shaping of odonate larval communities.     

Competition between Moina macrocopa and Ceriodaphnia dubia: a Life Table Demography Study

We analyzed the effect of competition on survival‐ and reproduction‐related parameters under two (0.5 · 10⁶ and 1.5 · 10⁶ cells ml^—1 of Chlorella) food densities between Moina macrocopa and Ceriodaphnia dubia using the life table demography approach. In general, regardless of the presence of Moina, the average lifespan and generation time were higher for C. dubia. However, rate of population increase (r) and values of reproductive effort were higher for M. macrocopa. The net reproductive values of C. dubia grown alone varied from 7.6 to 36.6 offspring female^—1 lifetime^—1, depending on Chlorella density. Corresponding values for Moina varied little (16.4 and 17.4 offspring female^—1 lifetime^—1). Values of gross reproductive rate, net reproductive rate and the generation time of both cladoceran species were higher in mixed cultures than when grown alone. The negative effect of competition was evident for both the cladoceran species, not in their reproductive rates, but in their generation times, and thus population growth rates. The role of competition and facilitation occurring between the two species was discussed in relation to different algal food levels.     

Determinant landscape‐scale factors on pond odonate assemblages

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Ontogenetic changes in the drifting of four species of elmid beetles elucidate the complexity of drift-benthos relationships in a small stream in Northwest England

1. This study aimed to quantify ontogenetic changes in the drifting of Elmis aenea, Oulimnius tuberculatus, Esolus parallelepipedus and Limnius volkmari (Coleoptera: Elmidae), and to relate their drift to benthic density. Monthly samples were taken over 39 months, using three surface nets at each of two contrasting sites in a small stream: one in a deep section with abundant macrophytes, and the other in a shallow stony section. 2. Most larvae and adults were taken in the drift at night with little variation between catches in the three nets at each site. Day catches were very low, often zero. No significant relationships could be established between mean numbers in the drift catches and benthic densities. 3. When night catches were converted to drift densities (number caught per 100 m³ of water sampled), the latter were positively related to monthly losses in the benthos, but not to benthic densities. A linear regression described the relationship, and equations for the different life‐stages within each species were not significantly different from the equation for all life‐stages combined. However, drift losses were only about 0.07% of total losses in the benthos. A severe spate in October 1967 increased the number of larvae and adults in the drift, but not drift densities, except for immature adults of E. aenea, O. tuberculatus and E. parallelepipedus. 4. Key life‐stages with the highest drift density were the earliest life‐stage soon after egg hatching for E. aenea, the start of the larval overwintering period for O. tuberculatus and L. volkmari, and mature adults during the mating season for all three species. Drift density for E. parallelepipedus was too low to identify a key life‐stage. These key life‐stages corresponded with critical periods for survival in the life cycle, as identified in an earlier study in the same stream. Mortality was high during these critical periods, hence the strong relationship between drift density and benthic losses. The latter relationship was very consistent for different life‐stages within each species, and partially supported the rarely‐tested hypothesis that drift represents surplus production in the benthos.     

Impacts of freshwater aquaculture on fish communities: A whole‐ecosystem experimental approach

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Annual and non-annual fish assemblages respond differently to environmental and spatiotemporal variations of temporary wetlands from southern Brazil

• The fish community of temporary wetlands is highly dynamic due to the marked seasonal changes in hydrological and limnological conditions. In this study, we evaluated spatiotemporal variation in the fish community and the influence of environmental factors on this variation in temporary wetlands in southern Brazil.
• Two different life cycles—annual and non-annual fishes—were recorded among species. Variation in the fish community appeared to be associated with differences in the life history strategy of species. While species of annual fish were present throughout the hydroperiod, gradually decreasing in density over time, non-annual fish species had an opposite pattern, with higher densities in the final phase of the hydrological cycle.
• Variations in the composition and abundance of fish community in temporary wetlands were related to habitat and landscape attributes (area, number of microhabitats and isolation between temporary wetlands) and climate indicators of water availability (air temperature, average rainfall, and water level of the São Gonçalo channel), but not to water conditions (dissolved oxygen, pH, conductivity and water temperature).
• We concluded that the ichthyofauna of temporary wetlands are composed both of rare species, highly specialised for life within these ephemeral environments, and widespread generalist species that reach the wetlands opportunistically for short periods. Habitat and landscape attributes and changes in climate and hydrological variables over the hydroperiod are the factors that had the greatest influence on spatiotemporal variation of the fish community.
• Maintaining physical characteristics and the hydrological cycle of temporary wetlands is critical for the conservation of fish species inhabiting these vulnerable environments in southern Brazil. Habitat and landscape attributes and climate and hydrology fluctuations affect the annual and non-annual fishes inhabiting temporary wetlands differently.

     

Trait flexibility of generalist invertebrates exposed to contrasting predation and drying stressors

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Regional vs local drivers of phylogenetic and species diversity in stream fish communities

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Morphology,metabolism and behaviour: responses of three fishes with different lifestyles to acute hypoxia

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Fish reduce anuran abundance and decrease herpetofaunal species richness in wetlands

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Juvenile growth of a macrohabitat generalist tied to hydrological character of large‐river system

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Comparative use of side and main channels by small‐bodied fish in a large,unimpounded river

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