Ontogenetic Shift in Efficacy of Antipredator Mechanisms in a Top Aquatic Predator,Anax junius (Odonata: Aeshnidae)

The ability of prey to escape predation often lies in the occurrence and efficacy of their predator avoidance and antipredator behaviors, which are often coupled with specialized morphology. How the use and efficacy of these behaviors change throughout ontogeny may be indicative of the vulnerability and ecological roles these animals experience throughout their lives. We examined the antipredator behavior of a large dragonfly nymph, Anax junius, from a historically fishless pond where these animals have traditionally been classified as top predators. These dragonfly nymphs displayed a series of distinct aggressive antipredator behaviors when grasped that involved stabbing with lateral and posterior spines and seizing with labial hooks. Larger (older) nymphs displayed these aggressive behaviors significantly more than smaller (younger) animals in simulated predation trials. During encounters with live larval salamander predators (Ambystoma tigrinum), all large nymphs, but only 12.5% of small nymphs successfully escaped predation attempts by the amphibians through the use of antipredator behavior. Large nymphs were also significantly more active than smaller nymphs in the presence of salamander larvae. Despite often being considered top predators in fishless ponds, our study demonstrates that their true role is more complex, depending on ontogeny and body size, and that effective antipredator behavior is likely necessary for survival in these systems.     

Isolation and characterization of nuclear microsatellite loci for the common green darner dragonfly Anax junius (Odonata: Aeshnidae) to constrain patterns of phenotypic and spatial diversity

Fourteen polymorphic microsatellite loci were developed from an enriched genomic library of the widely distributed migratory North American dragonfly species, the common green darner (Anax junius). For a group of 22 larvae, these loci averaged 16 alleles, with individual loci ranging from nine to 29 alleles. Observed heterozygosity averaged 0.784 per locus.     

Niche partitioning at emergence of two sympatric top-predator dragonflies,Anax imperator and A. parthenope (Odonata: Aeshnidae)

In natural communities, closely related species are phenotypically similar but usually spatially and/or temporally isolated. In odonates, interspecific competition occurs not only at the larval or adult stage but also during emergence. We investigated the emergence of two sympatric Anax species, focusing on the temporal pattern, vertical stratification, and body size trend over time. Anax imperator started to emerge two weeks earlier than A. parthenope but most of the emergence season overlapped. Both species showed an asynchronous emergence and the median emergence date was 10.3 days earlier in A. imperator. Sex ratio at emergence was not significantly different from 1:1. Body size of both species increased significantly over time, which contrasts many previous studies. The height of exuvia fixation was not significantly different between species but the larger species A. parthenope selected longer supports.     

A phylogenetic analysis of the extant Aeshnidae (Odonata: Anisoptera)

Abstract A cladistic analysis of the world Aeshnidae is presented, based on fifty-eight characters of adult and larval anatomy. The ingroup taxa include all the extant genera of Aeshnidae, and the austropetaliid genera Phyllopetalia and Hypopetalia were chosen as the outgroup. The strict consensus tree obtained after successive weighting shows that the subgroups defined traditionally for Aeshnidae are paraphyletic or polyphyletic. The previous reclassification derived from analyses based on wing venation is supported in terms of the monophyly of Aeshnidae, Gomphaeschninae and its sister group comprising the remaining Aeshnidae. Gomphaeschninae is confirmed as sister group of the remaining Aeshnidae (= Aeshnodea Bechly). The sister-group relationships between Gomphaeschna + Sarasaeschna and Linaeschna + Oligoaeschna are corroborated. Within Aeshnodea, three monophyletic groups emerged: Boyeria + ( Petaliaeschna + ( Limnetron + Gynacanthaeschna + Periaeschna )) + (( Cephalaeschna + Caliaeschna ) + ( Allopetalia ( Notoaeschna + Spinaeschna ))); Dendroaeschna + ( Epiaeschna + ( Aeschnophlebia + ( Nasiaeschna + ( Tetracanthagyna + Brachytron )))); and Polycanthagyna + ( Basiaeschna + ( Amphiaeschna + ( Indaeschna + ( Oplonaeschna + ( Racenaeschna + Plattycantha + Agyrtacantha + Triacanthagyna + ( Subaeschna + Austrogynacantha + Gynacantha ) + ( Heliaeschna + ( Neuraeschna + Staurophlebia ))) + (( Castoraeschna + Coryphaeschna + Remartinia ) + ( Oreaeschna + ( Aeshna + ( Anaciaeschna + ((' A .' isosceles + Andaeshna ) + ( Anax + Hemianax )))))). Additional informative characters are required to test the relationships suggested here between the main groups of Aeshnodea and some enigmatic basal taxa ( Antipodophlebia , Austroaeschna , Acanthaeschna , Telephlebia , Austrophlebia and Planaeschna ).     

Skeletomuscular development of genital segments in the dragonfly Anax imperator (Odonata, Aeshnidae) during metamorphosis and its implications for the evolutionary morphology of the insect ovipositor

The skeleton-muscular organisation of abdominal segments 7-9 in female Anax imperator L. (Anisoptera, Aeshnidae) was examined in the stages of ultimate larva, teneral imago, and mature imago, with special emphasis on the transformation of the muscle arrangement. The absence of certain muscles in the genital segments compared to the 7th pre-genital segment was noted on all studied stages. Reductions of certain muscles in adults compared to those in larvae are reported. Some of ovipositor's muscles appear already in larvae. Attachment sites of larval muscles are retained in freshly emerged females concurrently with integument transformations. This situation allows for precise determination of the borders of newly differentiated genital sclerites and, therefore, of the possible origin of certain ovipositor elements in odonates. All changes in the segmental sets of studied abdominal muscles during metamorphosis are tabulated, and displacements of muscles are documented and illustrated. Schematic figures illustrating homologies between the parts of larval and imaginal abdominal sclerites are provided. The origins of the components of the endophytic ovipositor in Odonata as well as their implications for the evolutionary morphology of the insect ovipositor are discussed.     

The mechanoreceptors on the endophytic ovipositor of the dragonfly Aeshna cyanea (Odonata,Aeshnidae)

This study investigates the mechanoreceptors located on the cutting valvulae of the ovipositor of the dragonfly Aeshna cyanea (Aeshnidae), using both SEM and TEM, with the aim of providing an overview of the sensory equipment of an odonatan endophytic ovipositor. Four kinds of sensilla have been described. Notwithstanding their different external and internal morphology, they show features typical of mechanoreceptors. Three of them are evident along the external surface of the two cutting valvulae in the form of sub-spherical pegs, pit organs type 1 (holes) and pit organs type 2 (depressions), these last are similar to amphinematic scolopidia, while the fourth type is represented by subintegumental mononematic scolopidia having no direct relationship with the cuticle. In spite of their structural differences, the morphology of the described mechanoreceptors is consistent with performing a main role in allowing the perception of compression/stretching of the thick cuticle of the valvulae and their bending due to the pressure acting on the distal end of the ovipositor during substrate penetration. Such an organization is coherent with the need of endophytic Odonata to be able to evaluate the stiffness of the plant where to lay eggs.     

福建头蜓属一新种(蜻蜓目:蜓科)

记述采自福建省邵武市的头蜓属1新种,邵武头蜓Cephalaeschnashaowuensis,sp.nov.。模式标本存放在漳州教育学院。     

Tolerance of low pH exposure by the eggs of Odonata (dragonflies and damselflies)

The development times and hatching success of the eggs of four species of Odonata (Ischnura verticalis, Lestes congener, Libellula lydia, and Sympetrum vicinum) were unaffected by exposure to soft water at pH 5.1 and 3.5. Tolerance of low pH, soft water conditions by Odonata eggs may in part account for the widespread distribution of Odonata in potentially acid-stressed regions.     

Larval development of Aeshna cyanea (Müller, 1764) (Odonata: Aeshnidae) in Central Italy

A three-year investigation was carried out on the life cycle of Aeshna cyanea (Müller, 1764) (Odonata, Aeshnidae) in temporary freshwater pools in Central Italy. The instars were discriminated by size and scatter plot, based on measurements of labium length, head width, metafemur length, forewing-pad length and total larval body length. The prolarvae instar was derived by Dyar's law. The mean increase value index between following and previous instar was between 1.26 and 1.33 for isometric variables, and around 1.96 for the wing-pad allometric variable. A. cyanea entered diapause mainly at the F-2 instar, placing it almost intermediate between the Southern Spain populations, which usually overwintered in the F-3 instar, and those of England and Central Europe, who spent their last winter in F-1. A. cyanea appeared to be a `summer species', as defined by Corbet (1962), and the population we studied had a semivoltine life cycle.     

Afrotropical and Nearctic genera of Odonata in the French Oligocene: biogeographic and paleoclimatic implications (Insecta: Calopterygidae,Aeshnidae)

New species of the genera Sapho and Epiaeschna are recorded in the Oligocene of Aix- en-Provence, Bouches-du-Rhône, France. Sapho legrandi n. sp. is the third fossil representative of this recent African genus and Epiaeschna pseudoheros n. sp. is the fifth fossil species of this recent North American genus. The fossil species Triaeschna gossi from the Eocene of England, Epacantha magnifica from the Late Oligocene of Kazakhstan, and Mediaeschna matutina from the Oligocene of China, are considered species of Epiaeschna and the three fossil genera Triaeschna Campion 1916, Mediaeschna Zhang 1989, and Epacantha Martynov 1929 are synonymized with Epiaeschna. The closely related genera Umma and Sapho inhabit warm humid forests of Western Africa. Their presence in two Oligocene deposits of France supports the hypothesis of a warm humid palaeoenvironment for Armissan (Aude, France), and Aix-en-Provence.     

The life history of Boyeria irene (Fonscolombe, 1838) (Odonata: Aeshnidae) in the Sierra Morena Mountains (southern Spain)

The life history of Boyeria irene is inferred fromsize-frequency analyses of sweep-net samples taken during fiveyears in a permanent stream in the Sierra Morena Mountains.There the species is apparently mainly semivoltine, although a fewlarvae require three years to complete development. The instardistribution during winter is that of a summer species (sensuCorbet, 1954). Metamorphosis is confined to spring and thereis a long flying season. Similarities between B. ireneand congeneric species in North America are discussed.     

Effects of aluminum,calcium and low pH on egg hatching and nymphal survival of Cloeon triangulifer McDunnough (Ephemeroptera: Baetidae)

Laboratory experiments were conducted to assess the effects of aluminum, calcium and low pH on egg hatching and nymphal survival of the mayfly Cloeon triangulifer. Percent successful hatch (living nymphs breaking free of the chorion) decreased and percent partial hatch (nymphs dying attached to the chorion) increased with increasing acidity (pH 7.5–3.0). Most hatches occurring below pH 5.0 were partial hatches. Decreased time of exposure to acidic waters increased percent successful hatch and decreased percent partial hatch. Time to first hatch was not affected by pH. Eggs were incubated in acidic waters (pH 4.0 and 5.5) with additions of calcium (10 and 100 mg l^–1) and aluminum (100 and 500 g l^–1). Aluminum decreased percent successful hatch and increased percent partial hatch and calcium increased both percent successful hatch and percent partial hatch. Time to first hatch was increased by both aluminum and calcium. The 96 h LC50 for small nymphs was pH 4.75. Addition of aluminum (100 and 500 µg l^–1) to acidic waters (pH 4.0 and 5.0) reduced nymphal mortality by 8–22%. Toxic effects of low pH on egg hatching and early nymphs may contribute to the absence of mayflies from acidified habitats.Contribution No. 1469 of the Maine Agricultural Experiment Station, University of Maine, Orono, Maine 04469 USA.Contribution No. 1469 of the Maine Agricultural Experiment Station, University of Maine, Orono, Maine 04469 USA.     

A panel of microsatellite markers to study sperm precedence patterns in the emperor dragonfly Anax imperator (Odonata: Anisoptera)

Odonates were the first group of organisms where sperm competition and last male sperm precedence have been identified. With the development of 10 microsatellites for the emperor dragonfly Anax imperator, the function and priority patterns of the multiple sperm storage organs of females can be studied and compared between species in natural populations. In addition, two microsatellite loci developed for the sister species Anax parthenope, are also highly polymorphic in A. imperator. For the presented 12 microsatellite loci, the number of alleles per locus ranged from two to 24. Observed heterozygosity ranged from 0.07 to 0.88.     

The effects of temperature and prey density on the development rates and growth of damselfly larvae (Odonata: Zygoptera)

Abstract. 1. The effects of prey density and temperature on the feeding and development rates of several late instars of the larvae of three common European damselflies ( Lestes sponsa (Hansemann), Coenagrion puella (L.) and Ischnura elegans van der Linden) were investigated in a laboratory experiment.
2. Functional responses were used to estimate maximum feeding rates. Maximum feeding rates were compared between species, instars and temperatures by expressing prey consumption in terms of prey biomass consumed per unit predator biomass. Lestes was capable of feeding at almost twice the rate of either Coenagrion or Ischnura.
3. Higher feeding rates led to faster development rates and there was an interaction between species and temperature. With the exception of those with very low feeding rates, larvae maintained at higher temperatures, but similar feeding rates, developed faster. Under similar conditions of temperature and feeding rate, Lestes larvae developed faster than larvae of either Coenagrion or Ischnura.
4. Faster development rates at similar rates of food intake were achieved at the cost of reduced size-increases between instars.
5. The differences in the responses of the three species are discussed in the light of their respective life histories, and with reference to a recent model of population regulation in damselflies.     

Changes in prey preferences of dragonfly naiads of Rhionaeschna multicolour (Hagen, 1861) (Odonata: Aeshnidae) in the presence and the absence of macrophytes

We offered prey consisting of the rotifers, cladocerans, copepods, amphipods, dipterans and ephemeropterans to the pre-starved and sorted in three size groups of naiads of Rhionaeschna multicolour (Hagen, 1861) in the presence of the macrophyte Egeria densa Planchon and without it. The naiads consumed up to 25 prey items or in terms of biomass (wet weight) up to 7 mg within 2 h. Biomass intake increased with increasing predator's size. Prey consumption was significantly lower in presence of plants. The cladocerans Ceriodaphnia dubia Rihcard, 1894, Daphnia mendotae (Taylor and Hebert, 1993) and Ilyocryptus sp. were consistently preferred by the dragonfly naiads while Simocephalus vetulus (Müller, 1776), Alona guttata Sars, 1862 and Scapholeberis kingi Sars, 1888 were avoided with and without macrophytes. This study suggests that dragonfly naiads structure the zooplankton community by selective feeding.     

Counting the spots: a molecular and morphological phylogeny of the spotted darner Boyeria (Odonata: Anisoptera: Aeshnidae) with an emphasis on European taxa

Boyeria irene and Boyeria cretensis are species of spotted dragonflies belonging to the ‘darner’ family, Aeshnidae. In 1991, Peters classified Boyeria from Crete as B. cretensis, based on adult morphological characters. In this study, we used molecular evidence to determine if indeed B. irene and B. cretensis are different species. DNA was sequenced from samples of B. irene (from France, Switzerland, Tunisia, Spain and Italy) and B. cretensis (from Crete). These species were recovered as two different clades with strong support. We conclude that B. irene and B. cretensis are different species, with evidence based on molecular and morphological differences. In addition, we present the first phylogenetic hypothesis for Boyeria for which we have sequenced all but three species. Lastly, we discuss different scenarios that may have led to the present‐day distribution and speciation patterns of Mediterranean Boyeria.     

Systenostrema alba Larsson 1988 (Microsporidia, Thelohaniidae) in the Dragonfly Aeshna viridis (Odonata, Aeshnidae) from South Siberia: morphology and molecular characterization

An octospore microsporidium was found in the nymphs of Aeshna viridis, collected in intermittent streams near Novosibirsk, Siberia, Russia in 2003. Spores were uninucleate and measured 6.1+/-0.07 x 3.0+/-0.04 microm on fresh smears. The polar filament was anisofilar having 10-11 anterior coils (thicker filament diam.) and 10-11 posterior (thinner filament diam.) coils. Sporophorous vesicles were persistent and measured 12.3+/-0.23 x 11.9+/-0.20 microm. The infection was restricted to the adipose tissue and caused the formation of whitish "cysts" containing mature octospores. Based on ultrastructural similarity we consider this Siberian isolate to be Systenostrema alba, a species described from Aeshna grandis collected in Sweden (Larsson 1988). Maximum likelihood, neighbor joining, and maximum parsimony analyses of the small subunit rDNA all placed Systenostrema alba (Accession no. AY953292) as the sister taxon to a clade consisting of Thelohania solenopsae, Tubulinosema ratisbonensis, and Tubulinosema acridophagus.     

Effects of pH and temperature on myocardial calcium-activation in Pterygoplichthys (catfish)

Fish are chronically exposed to a wide range of temperatures and acidic environments. Fish hearts have to therefore adapt to these changes in order to maintain contractility. Myofibrillar responsiveness to Ca²⁺ is exquisitely sensitive to both temperature and pH in mammalian myocardium. To evaluate myofilament calcium-activation, we chemically skinned ventricular myocardium from catfish (Pterygoplichthys). A decrease in pH from 7.5 to 6.8, irrespective of temperature change, shifted the calcium-force curve towards higher calcium concentrations without affecting maximal Ca²⁺-activated force. The contractile elements are therefore sensitive to changes in pH. In intact muscle preparations the active twitch force was decreased with increasing temperature (10–22 °C). However, the sensitivity of the myofilaments to Ca²⁺ was independent of temperature. These data suggest a possible role of the sarcoplasmic reticulum (SR) in mediating the effects of temperature. The response of intact muscle preparations to changes in temperature is therefore not likely due to temperature-dependent changes in myofilament calcium responsiveness. Accepted: 11 May 1998     

Influence of temperature and photoperiod on embryonic development in the dragonfly Sympetrum striolatum (Odonata: Libellulidae)

Temperature and photoperiod play major roles in insect ecology. Many insect species have fixed degree‐days for embryogenesis, with minimum and maximum temperature thresholds for egg and larval development and hatching. Often, photoperiodic changes trigger the transfer into the next life‐cycle stadium. However, it is not known whether this distinct pattern also exist in a species with a high level of phenotypic plasticity in life‐history traits. In the present study, eggs of the dragonfly Sympetrum striolatum Charpentier (Odonata: Libellulidae) are reared under different constant and fluctuating temperatures and photoperiodic conditions in several laboratory and field experiments. In general, and as expected, higher temperatures cause faster egg development. However, no general temperature or light‐days for eyespot development and hatching are found. The minimum temperature thresholds are distinguished for survival (2 °C), embryogenesis (6 °C) and larval hatching (above 6 °C). Low winter temperatures synchronize hatching. Above 36 °C, no eyespots are visible and no larvae hatch. In laboratory experiments, light is neither necessary for eyespot development, nor for hatching. By contrast to the laboratory experiments, the field experiment show that naturally changing temperature and photoperiod play a significant role in the seasonal regulation of embryonic development. The post‐eyespot development is more variable and influenced by temperature and photoperiod than the pre‐eyespot development. This developmental plasticity at the end of the embryogenesis might be a general pattern in the Libellulidae, helping them to cope with variation in environmental conditions.