Phylogeny of the dragonfly genus Sympetrum (Odonata: Libellulidae)

The libellulid dragonfly genus Sympetrum has been recognized since 1833, but lacks any morphological synapomorphies to unite the taxon. Previous researchers have disagreed over which species belong in Sympetrum, bringing the monophyly of the genus into question. We use DNA sequence data from 6 genetic loci (16S, tRNA-valine, 12S, elongation factor 1 alpha, cytochrome oxidase subunit I, and the second internal transcribed spacer region) and 25 morphological characters (mainly genitalic) to test the monophyly of Sympetrum with Bayesian inference and maximum likelihood analyses. Under Bayesian inference, all Sympetrum species included in this study form a clade, which also contains the Hawaiian monotypic genus Nesogonia, often considered a close relative of Sympetrum. Phylogenetic analyses also reveal at least six strongly supported clades (treated as species groups) within Sympetrum, but relationships between these species groups remain unresolved or unsupported. Although the relationships between Sympetrum species groups remain unresolved, several species groups include taxa from multiple biogeographic regions/continents, and the species group sister to the rest of Sympetrum contains migratory species from the New World and Africa. This pattern suggests a complex biogeographic history in Sympetrum shaped by vicariance and dispersal. Preliminary estimates of the divergence dates of Sympetrum species groups outline a rapid radiation of the groups approximately 32-38 million years ago, possibly influenced by cooling and drying climates of the late Eocene and early Oligocene.     

Isotope evidence for latitudinal migrations of the dragonfly Sympetrum fonscolombii (Odonata: Libellulidae) in Middle Asia

• Sympetrum fonscolombii dragonflies are believed to migrate seasonally. In the spring and early summer, the already-mature dragonflies arrive in Middle Asia for reproduction. In the late summer and autumn, summer-generation dragonflies migrate to the south. Their wintering places remain unknown.
• Stable hydrogen (δ²H) and oxygen (δ¹⁸O) isotope analyses were conducted to confirm the migration of S. fonscolombii and determine the wintering area. Stable isotope composition of carbon (δ¹³C) and nitrogen (δ¹⁵N) in wings and legs was used to clarify the habitats in which dragonfly development took place.
• Three cohorts of dragonflies collected in different regions of Middle Asia were used for analysis: (i) immigrants that arrived in the spring, (ii) residents that developed in Middle Asia, and (iii) transit dragonflies migrating to the south during autumn.
• The average δ²H values in the wings were significantly higher in immigrants (−96‰) than in residents (−134‰) and transit individuals (−124‰). High δ¹⁸O and δ¹⁵N values in the tissue of immigrants confirmed their southerly origin.
• Based on the species range and the global distribution of annual averages of δ²H and δ¹⁸O values in precipitation, the latitudinal migrations of S. fonscolombii were inferred to cover the area from the proposed natal regions of immigrants in South-West Asia (below ∼36°N) to Southern Ural and the south of Western Siberia in the north (54–55°N) with a maximum migration distance of more than 4000 km.

     

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.     

Diel changes in habitat use by dragonflies: Nocturnal roosting site selection by the threatened dragonfly Sympetrum depressiusculum (Odonata: Libellulidae)

Although it is well recognized that insects' habitat use and requirements may change during the season, very little attention has been devoted to diel habitat changes in most insects. In this study, we compared habitat utilization patterns of Sympetrum depressiusculum (Selys, 1841) adult dragonflies between daytime activities and nocturnal roosting. During daytime, we captured and marked adult individuals with fluorescent paint in different habitats. At night, we searched, using UV light, for marked individuals that remained on the habitats. We found that habitat selection for daytime activities and that for nocturnal roosting differed significantly. Adults clearly avoided ponds and their immediate surroundings for nocturnal roosting, whereas this habitat type was frequently utilized for daytime activities. We suggest that nocturnal avoidance of the riparian area is associated with lower temperatures, which adversely affect thermoregulation, and that selection of specific habitats for nocturnal roosting is closely associated with vegetation structure providing stability during windy nights and serving as a suitable shelter. Such habitat properties are found especially on fallow land, a habitat type whose representation in agricultural areas has been gradually decreasing in recent decades.     

Two gynandromorphs of Sympetrum striolatum (Charpentier, 1840) (Odonata: Libellulidae)

Two gynandromorphs of the dragonfly Sympetrum striolatum , with different features, are described here, with special emphasis on the genitalic structures.     

Reproductive behavior of the dragonfly,Orthetrum japonicum (Odonata: Libellulidae)

The reproductive behavior of the dragonfly,Orthetrum japonicum, is described. Behavioral processes of turnover of territorial males, simultaneous guarding of 2 females by a male, and copulation by non-territorial males are described. The males with longer hind wings won the territorial conflicts more frequently. The total duration of territorial residence of a given male was correlated with the number of his matings, but not correlated with the length of his abdomen or hind wings. The territorial site with the lower degree of vegetation cover was occupied by males more consistently. Males in more consistently occupied territorial sites did not have longer abdomen and hind wings than males in less consistently occupied sites. The territorial site where the larger number of copulations was observed was not occupied more consistently. Selection episode analysis using the method of Arnold & Wade (1984a, b) showed that direct selection on the hind wing length favored the short wing and that direct selection on the abdomen length favored the long abdomen during mating.     

Mass reproductive wanderings of dragonflies of the genus Sympetrum (Odonata,Libellulidae)

The results of observing mass flights of some dragonflies of the genus Sympetrum forming tandems are presented. These tandems always fly against the wind, some of them landing for oviposition and then joining the flight again. This variant of migration behavior has been unexplained until now. A hypothesis is proposed according to which synchronous mass flights of dragonfly tandems facilitate the most uniform oviposition in all the suitable biotopes. The general direction of the flight depends on the wind. As the wind direction changes, the flight course of the tandems changes accordingly, so that the dragonflies cross the same territory several times, which leads to a denser and more uniform distribution of eggs. It is proposed to refer to this variant of flight as reproductive wanderings. Such a dispersal strategy can maintain the most uniform population density and a more stable abundance of some dragonfly species in the territories with unstable humidity.     

Perch selection in Sympetrum species (Odonata: Libellulidae): importance of vegetation structure and composition

1. Perching dragonflies are closely associated with the physical structure of vegetation because adults utilise plants when foraging, thermoregulating, and mate-seeking. However, little attention has been given to which structural attribute of vegetation is playing a key role within foraging habitat use. 2. This study focused on the influence of different features of perches on their selection by adult dragonflies. As a model group, a typical percher behavioural guild of Sympetrum was used and experimental plots with artificial perches and different structural properties were established. 3. It was found that adults preferred perch sticks with a wider diameter and larger spacing. It is assumed that these perching sites are advantageous because their base is more stable, they provide the best view for successful foraging, and there is no interference among individuals. 4. This study also revealed significant differences between male and female preferences. Females used less structured vegetation formed by thin perches in high densities. It is suggested that female discrimination is influenced by the higher competitiveness of males, which is related to their agonistic behaviour. 5. These results suggest that the availability of perches in the foraging habitat might be an essential requirement for adults. However, within the terrestrial surroundings of breeding sites, the structure of vegetation providing conditions for perching may be associated only with certain habitats. In intensive landscapes, physically structured vegetation can be limited or completely absent.     

The number and arrangement of elements in the lamina cartridge of the dragonfly Sympetrum rubicundulum

Summary Five monopolar cells and two long visual fibres are a consistent component of the lamina cartridge of the ventral half of the eye of the dragonfly Sympetrum rubicundulum. They communicate with the chiasm via a cartridge axon bundle comprising a minimum of ten fibres. The arrangement of these elements is documented with respect to the ommatidial photoreceptor axon bundle innervating them. These relationships are described both within the lamina cortex and in the cross-section of the underlying cartridge.     

Ultrastructure of the aortic diverticula of the adult dragonfly Sympetrum danae (Odonata: anisoptera)

Summary The aorta of Sympetrum danae possesses two dorsal diverticula: one in the mesothorax and one in the metathorax. They are very similar in form and position. Each diverticulum has a dorsal valve through which blood is pumped from the wings down into the aorta. The wall of the aortic diverticula consists of two simple cell layers: an outer epidermis-like layer and an inner muscle layer. The nuclei of the muscle cells are situated close to the lumen of the diverticula. The mitochondria are evenly dispersed between the myofibrils and are often paired up on either side of the Z-band. The Z-bands are thick and fragmented. The length of the sarcomeres varies from 3.3 to 6.1 . The A-band length is about 3 . The myofibrils consist of thick (250 Å) and thin (85 Å) filaments. Each thick filament is surrounded by 9–12 thin filaments. The sarcoplasmic reticulum is well developed and separates the myofibrils with one or two layers. The T-tubules are flattened and branch irregularly like a two-dimensional tree between the lamellar myofibrils. Intercalated discs are observed.The peculiarities of the muscle of aortic diverticula in S. danae are discussed in relation to various muscles of other insects and arthropods.     

Selection and reproductive success in males of the dragonfly,Orthetrum japonicum (Odonata: Libellulidae)

Reproductive success, copulation success, and mating success were measured for a population of male dragonflies,Orthetrum japonicum. Copulation success explained the greatest variation in reproductive success. The proportion of copulations followed by oviposition was positively correlated with the number of oviposited eggs per mating. Directional selection on four morphological characters was estimated. The effect of selection on correlated traits was comparable to that of direct selection. Directional selection varied between traits and between episodes in a single trait. The probability that the observed directional selection on the four morphological traits was expected under the condition of the selective neutrality of traits was not smaller than 5%.     

Neuroendocrine control of vitellogenesis in the dragonfly, Orthetrum chrysis (Selys) (Odonata: Libellulidae).

1. Histological correlative studies on the cerebral neurosecretory cells, the corpora allata and the oocyte development strongly suggest the involvement of cerebral NSM mostly produced by the A cells of pars intercerebralis and the CA hormone in the vitellogenesis. 2. Biochemical studies reveal the incorporation of haemolymph proteins and lipids in the yolk during vitellogenesis. 3. Exogenous administration of the extract of the brain-CC and FME demonstrates, to some extent, the stimulation of protein synthesis during vitellogenesis in the haemolymph by the cerebral NSM and the CA hormone, while the lipid metabolism lies, mostly, under the control of juvenile hormone.     

Neurosecretory system of the ventral ganglia in the dragonfly,Orthetrum chrysis (selys) (Odonata: Libellulidae)

Summary The neurosecretory cells of the ventral ganglia in the adult dragonfly, Orthetrum chrysis, are classified into A, B, C1 and C2 cells. The neurosecretory material in the ventral ganglia is composed of PAS-positive material with 1-, 2-glycol groups and some proteins. The proteins rich in cystine or cysteine occur predominantly in the A cells, moderately in C cells and negligibly in B cells. Proteins containing arginine occur in A and B cells only, and those containing basic amino acids occur in C2 cells. The neurosecretory pathways and the neurohemal organs are also described.     

The influence of temperature on the functional response of the dragonfly Celithemis fasciata (Odonata: Libellulidae)

Summary Four biennial species (Oenothera erythrosepala, Dontostemon dentatus, Erigeron strigosus, and Erigeron sumatrensis) from the dune system at Azigaura, Japan, were sand-cultured in pots with different nutrient levels, and the critical plant size for the development of a flowering stalk was determined. The critical size decreased in the order O. erythrosepala>E. strigosus>D. dentatus=E. sumatrensis, and corresponded to the order of their distribution along the gradient of soil fertility in the dune system. This correspondence is discussed, and it is concluded that in a less fertile environment, biennials producing seeds after attaining a larger size have an advantage over those producing seeds earlier.     

Potential distribution of the critically endangered dragonfly Libellula angelina (Odonata: Libellulidae) under shared socio-economic pathways

Libellula angelina is an endangered dragonfly species that is native to East Asia. Recently, their population has become severely reduced through habitat loss. To protect L. angelina populations, we need to understand which factors determine their distribution and how their potential habitats will change in the future. In this study, the habitat preference of L. angelina was identified through field surveys, and the potential distribution of L. angelina and the impact of integrated climate–land cover changes were simulated using the MaxEnt model. Furthermore, the wetland loss scenario was applied to areas where the current trend in wetland loss will continue in the future. The field survey identified that L. angelina prefers small inland wetlands: permanent freshwater, ponds; permanent rivers, ponds; irrigated land; and estuarine waters. From the MaxEnt results, altitude was the variable with the greatest contribution and distance from wetlands was the most unique variable. MaxEnt described the geographic pattern of occurrences under the current climate well, with few areas requiring any further survey. In the future projection, the potential habitat area was increased by up to 48.8% and 30.6% in the 2050s and 2080s, respectively. However, potential habitat loss was expected if wetlands continue to decline as they have done in the last 20 years. The wetland loss scenario resulted in potential habitat losses of 1.9%–2.3% and 4.5%–6.1% in the 2050s and 2080s, respectively. Therefore, to protect L. angelina populations we must minimize the loss of current populations, secure wetlands and strengthen the connectivity between wetlands.     

Ionic and osmotic regulation of the haemolymph of the dragonfly, Libellula quadrimaculata (Odonata : Libellulidae)

Larvae of the widespread dragonfly, Libellula quadrimaculata, were adapted to a series of salt solutions, and the osmotic pressure, and sodium, potassium and chloride concentrations in the haemolymph measured. The regulation of potassium is extremely efficient over the range 0–50 m-mole/l. external concentration. Above this, larvae die. Sodium and chloride are regulated to a lesser extent, the larvae being able to withstand considerable changes in the concentration of these ions in the haemolymph. However, at higher external concentrations, the haemolymph concentration of these ions is maintained below that of the external medium. The osmotic pressure is regulated in parallel with sodium concentration over most of the range tested. However, in higher salinities, the osmotic pressure of the haemolymph does not fall below that of the external medium. This is seen as a strategy to limit the amount of drinking in saline media. Overall, the osmoregulatory system of L. quadrimaculata resembles that of brackish-water insects, rather than that of the more strictly freshwater dragonflies that have been studied.     

Mechanism of the wing colouration in the dragonfly Zenithoptera lanei (Odonata: Libellulidae) and its role in intraspecific communication

Zenithoptera dragonflies are known for their remarkable bluish colouration on their wings and unique male behaviour of folding and unfolding their wings while perching. However, nothing is known about the optical properties of such colouration and its structural and functional background. In this paper, we aimed to study the relationship between the wing membrane ultrastructure, surface microstructure and colour spectra of male wings in Zenithoptera lanei and test the hypothesis that colouration functions as a signal in territorial fights between males. The results show that the specific wing colouration derives from interference in alternating layers of melanized and unmelanized cuticle in the wing membrane, combined with diffuse scattering in two different layers of wax crystals on the dorsal wing surface, one lower layer of long filaments, and one upper layer of leaf-shaped crystals. The results also show that the thicker wax coverage of the dorsal surface of the wings results in increased brightness and reduced chroma. In the field experiments, we have demonstrated that there is a reduction of aggressive reactions of rivals towards individuals with experimentally reduced amount of blue wing colouration.     

A dragonfly in the desert: genetic pathways of the widespread Trithemis arteriosa (Odonata: Libellulidae) suggest male-biased dispersal

Water-dependent species inhabiting desert regions seem to be a contradiction in terms. Nevertheless, many species have evolved survival strategies for arid conditions. In Odonates (dragonflies and damselflies), both larvae and adults require very different and complex water-associated habitat conditions. The present study investigates the genetic diversity, population structure and dispersal patterns of a desert inhabiting odonate species, the Red-veined Dropwing dragonfly, Trithemis arteriosa. Eight populations from the arid Namibia and four population sites in the more tropical Kenya were compared by using nine microsatellite loci, one non-coding nuclear fragment and the mtDNA fragment ND1. Microsatellite analyses as well as the nuclear fragment reveal a high allelic diversity in all populations with almost no genetic sub-structuring. In contrast, ND1 sequence analyses show sub-structuring and??with two exceptions??only private haplotypes. The conflicting patterns of nuclear versus mitochondrial markers suggest a male-biased dispersal in this species. Results indicate that male dispersal is dependent on the environmental stability of the habitat, while females are philopatric. This life history adaptation would allow females to save energy for mating and oviposition in the demanding environment of a desert region. The results give direct insights into the dispersal pathways of a desert-inhabiting, strongly water dependent flying insect.     

Short and flat grass preferred by adults of the endangered dragonfly <Emphasis Type="Italic">Sympetrum pedemontanum elatum</Emphasis> (Odonata: Libellulidae)

Sympetrum pedemontanum (Müller in Allioni) (Odonata: Libellulidae) is widely distributed across the Eurasian continent and its neighboring islands. However, the populations of its subspecies S. pedemontanum elatum (Selys) in Japan have been rapidly decreasing with the loss of habitats in rural and suburban areas since the 1970s. For the conservation of this subspecies, which is now listed as endangered in many prefectures, it is important to understand the habitat preferences of the adults. Previous studies indicate that adult males of this species tend to fly on the flat surface of rice paddy fields. Thus, we hypothesized that they preferred short and flat grass. Field experiments in the Sakasegawa River, Hyogo Prefecture, Japan, showed that adult S. p. elatum significantly preferred the trimmed grass of Phragmites japonicus to untreated shaggy grass, regardless of sex. Our results indicate the importance of grass management for the conservation of this species, not only in and around paddy fields but also in fluvial habitats, which are abundant in Japan.