How can dragonflies discern bright and dark waters from a distance? The degree of polarisation of reflected light as a possible cue for dragonfly habitat selection

SUMMARY 1. Based on the findings that some dragonflies prefer either ‘dark’ or ‘bright’ water (as perceived by the human eye viewing downwards perpendicularly to the water surface), while others choose both types of water bodies in which to lay their eggs, the question arises: How can dragonflies distinguish a bright from a dark pond from far away, before they get sufficiently close to see it is bright or dark? 2. Our hypothesis is that certain dragonfly species may select their preferred breeding sites from a distance on the basis of the polarisation of reflected light. Is it that waters viewed from a distance can be classified on the basis of the polarisation of reflected light? 3. Therefore we measured, at an angle of view of 20° from the horizontal, the reflection‐polarisation characteristics of several ponds differing in brightness and in their dragonfly fauna. 4. We show that from a distance, at which the angle of view is 20° from the horizontal, dark water bodies cannot be distinguished from bright ones on the basis of the intensity or the angle of polarisation of reflected light. At a similar angle of view, however, dark waters reflect light with a significantly higher degree of linear polarisation than bright waters in any range of the spectrum and in any direction of view with respect to the sun. 5. Thus, the degree of polarisation of reflected light may be a visual cue for the polarisation‐sensitive dragonflies to distinguish dark and bright water bodies from far away. Future experimental studies should prove if dragonflies do indeed use this cue for habitat selection.     

Evolution of prey behavior in response to changes in predation regime: damselflies in fish and dragonfly lakes

In a large behavioral experiment we reconstructed the evolution of behavioral responses to predators to explore how interactions with predators have shaped the evolution of their prey's behavior. All Enallagma damselfly species reduced both movement and feeding in the presence of coexisting predators. Some Enallagma species inhabit water bodies with both fish and dragonflies, and these species responded to the presence of both predators, whereas other Enallagma species inhabit water bodies that have only large dragonflies as predators, and these species only responded to the presence of dragonflies. Lineages that shifted to live with large dragonflies showed no evolution in behaviors expressed in the presence of dragonflies, but they evolved greater movement in the absence of predators and greater movement and feeding in the presence of fish. These results suggest that Enallagma species have evolutionarily lost the ability to recognize fish as a predator. Because species coexisting with only dragonfly predators have also evolved the ability to escape attacking dragonfly predators by swimming, the decreased predation risk associated with foraging appears to have shifted the balance of the foraging/predation risk trade-off to allow increased activity in the absence of mortality threats to evolve in these lineages. Our results suggest that evolution in response to changes in predation regime may have greater consequences for characters expressed in the absence of mortality threats because of how the balance between the conflicting demands of growth and predation risk are altered.     

Odonate species occupancy frequency distribution and abundance–occupancy relationship patterns in temporal and permanent water bodies in a subtropical area

This paper investigates species richness and species occupancy frequency distributions (SOFD) as well as patterns of abundance–occupancy relationship (SAOR) in Odonata (dragonflies and damselflies) in a subtropical area. A total of 82 species and 1983 individuals were noted from 73 permanent and temporal water bodies (lakes and ponds) in the Pampa biome in southern Brazil. Odonate species occupancy ranged from 1 to 54. There were few widely distributed generalist species and several specialist species with a restricted distribution. About 70% of the species occurred in <10% of the water bodies, yielding a surprisingly high number of rare species, often making up the majority of the communities. No difference in species richness was found between temporal and permanent water bodies. Both temporal and permanent water bodies had odonate assemblages that fitted best with the unimodal satellite SOFD pattern. It seems that unimodal satellite SOFD pattern frequently occurred in the aquatic habitats. The SAOR pattern was positive and did not differ between permanent and temporal water bodies. Our results are consistent with a niche‐based model rather than a metapopulation dynamic model.     

Biodiversity patterns of nutrient-rich fish ponds and implications for conservation

Nutrient-rich water bodies are usually expected to host low species richness at the local scale (water body). Nevertheless, they can support a diverse and sometimes unique biodiversity when diversity is considered at a regional scale. This discrepancy between the two scales is well documented for natural water bodies, but little is known about biodiversity of artificial water bodies, like fish ponds. We hypothesise that nutrient-rich water bodies can collectively host high species richness at the regional scale. Thus, these are important ecosystems for the regional conservation of biodiversity. We investigated 84 fish ponds in the Dombes region, France, with five taxonomic groups: macrophytes, phytoplankton, macroinvertebrates, dragonflies, and amphibians. Species richness patterns were determined for α- (single pond), β- (between ponds), and γ- (regional pond network) levels. For most studied species groups, richness per fish pond and at the regional level proved to be relatively high in comparison with natural ponds in other landscapes. Contribution of α-diversity to regional diversity was highest for dragonflies with 41 %, and lowest for amphibians and macrophytes with 16 and 18 %, respectively. For macroinvertebrate families and phytoplankton genera it was intermediate. Contribution of β-diversity to regional diversity was similar for all species groups with 22–25 %. Furthermore, some ponds hosted a large number of less frequent species and some endangered species, indicating that the conservation of biodiversity of fish ponds must be established at a regional scale.     

A dual layer hair array of the brown lacewing: repelling water at different length scales

Additional weight due to contamination (water and/or contaminating particles) can potentially have a detrimental effect on the flight capabilities of large winged insects such as butterflies and dragonflies. Insects where the wing surface area-body mass ratio is very high will be even more susceptible to these effects. Water droplets tend to move spontaneously off the wing surface of these insects. In the case of the brown lacewing, the drops effectively encounter a dual bed of hair springs with a topographical structure which aids in the hairs resisting penetration into water bodies. In this article, we demonstrate experimentally how this protective defense system employed by the brown lacewing (Micromus tasmaniae) aids in resisting contamination from water and how the micro- and nanostructures found on these hairs are responsible for quickly shedding water from the wing which demonstrates an active liquid-repelling surface.     

Migrations of dragonflies (Odonata) in the south of the West Siberian plain

The paper presents a summary of mass dragonfly migrations observed previously in Russia, in particular in West Siberia. From 1969 to 2009, the authors studied the dynamics of dragonfly population, their spatial distribution and movements in the West Siberian forest-steppe. The main studies were conducted in the Lake Chany basin (the Biological Station of the Institute of Animal Systematics and Ecology, Siberian Division, Russian Academy of Sciences). The spatial redistribution of dragonflies is regarded as a balance of homing and wandering behavior. Homing results in a relative stability of local dragonfly populations and assemblages, while wandering leads to dispersal of dragonflies from their emergence sites and colonization of new habitats; the latter is especially important due to the ephemeral nature of many shallow reservoirs where the nymphs develop. The formation of more or less constant migration routes is a peculiar variant of wandering activities. A special type of dragonfly migrations is mass exodus from native habitats, triggered by excessive population growth and leading to elimination of all or most individuals. Such migrations not only optimize the size of dragonfly populations but also facilitate removal of nutrients and organic matter from eutrophic water bodies. An original generalized classification of dragonfly migrations is proposed.     

Ecological traps for dragonflies in a cemetery: the attraction of Sympetrum species (Odonata: Libellulidae) by horizontally polarizing black gravestones

1. We observed that the dragonfly species Sympetrum flaveolum, S. striolatum, S. sanguineum, S. meridionale and S. danae were attracted by polished black gravestones in a Hungarian cemetery. 2. The insects showed the same behaviour as at water: (i) they perched persistently in the immediate vicinity of the chosen gravestones and defended their perch against other dragonflies; (ii) flying individuals repeatedly touched the horizontal surface of the shiny black tombstones with the ventral side of their body; (iii) pairs in tandem position frequently circled above black gravestones. 3. Tombstones preferred by the dragonflies were in the open and had an area of at least 0.5 m² with an almost horizontal, polished, black surface and with at least one perch in their immediate vicinity. 4. Using imaging polarimetry, we found that the black gravestones, like smooth water surfaces, reflect highly and horizontally polarized light. 5. In double‐choice field experiments with various test surfaces, we showed that the dragonflies attracted to shiny black tombstones display positive polarotaxis and, under natural conditions, detect water by means of the horizontally polarized reflected light. This, and the reflection‐polarization characteristics of black gravestones, explain why these dragonflies are attracted to black tombstones. 6. If females attracted to the black gravestones oviposit on them, the latter constitute ecological traps for dragonflies that are not close to water.     

Carotenoids of dragonflies,from the perspective of comparative biochemical and chemical ecological studies

Carotenoids of 20 species of dragonflies (including 14 species of Anisoptera and six species of Zygoptera) were investigated from the viewpoints of comparative biochemistry and chemical ecology. In larvae, β-carotene, β-cryptoxanthin, lutein, and fucoxanthin were found to be major carotenoids in both Anisoptera and Zygoptera. These carotenoids were assumed to have originated from aquatic insects, water fleas, tadpoles, and small fish, which dragonfly larvae feed on. Furthermore, β-caroten-2-ol and echinenone were also found in all species of larvae investigated. In adult dragonflies, β-carotene was found to be a major carotenoid along with lutein, zeaxanthin, β-caroten-2-ol, and echinenone in both Anisoptera and Zygoptera. On the other hand, unique carotenoids, β-zeacarotene, β,ψ-carotene (γ-carotene), torulene, β,γ-carotene, and γ,γ-carotene, were present in both Anisoptera and Zygoptera dragonflies. These carotenoids were not found in larvae. Food chain studies of dragonflies suggested that these carotenoids originated from aphids, and/or possibly from aphidophagous ladybird beetles and spiders, which dragonflies feed on. Lutein and zeaxanthin in adult dragonflies were also assumed to have originated from flying insects they feed on, such as flies, mosquitoes, butterflies, moths, and planthoppers, as well as spiders. β-Caroten-2-ol and echinenone were found in both dragonfly adults and larvae. They were assumed to be metabolites of β-carotene in dragonflies themselves. Carotenoids of dragonflies well reflect the food chain during their lifecycle.     

Variation in size of the dragonefly m-chromosome,with considerations on its significance for the chorogeography and taxonomy of the order odonata,and notes on the validity of the rule of reinig

The morphological and kinetical features of the so-called m-chromosomes in dragonflies are reviewed. The relative size of the m-chromosomes varies in some species, but not in all. It has been demonstrated that the size is peculiar, in some dragonflies, for populations originating from different portions of the species range, and therefore it could be used to advantage in the taxonomy of infraspecific forms. The dragonfly m-chromosomes are considered as fragments of normal autosomes. The break can take place at any time, at any place in the holokinetic chromosome, and in any geographic population, therefore the variation in size of the m-chromosome is only accidental and has no chorogeographic implications. The chorogeographic hypothesis ofReinig (1938, 1939), which has been widely promoted by some distinguished odonatologists, has no connection with the size trend of the m-chromosomes. Its general validity for the determination of the body size of dragonflies is likewise rejected. Paper presented at the Meeting of the Genetical Society of the Netherlands, 28 November 1967, Utrecht. This paper is the third report on the research project supported by grant No. 913-19 of the Netherlands Organization for the Advancement of Pure Research (Z.WW. O.).     

Prey size selection and distance estimation in foraging adult dragonflies

To determine whether perching dragonflies visually assess the distance to potential prey items, we presented artificial prey, glass beads suspended from fine wires, to perching dragonflies in the field. We videotaped the responses of freely foraging dragonflies (Libellula luctuosa and Sympetrum vicinum—Odonata, suborder Anisoptera) to beads ranging from 0.5 mm to 8 mm in diameter, recording whether or not the dragonflies took off after the beads, and if so, at what distance. Our results indicated that dragonflies were highly selective for bead size. Furthermore, the smaller Sympetrum preferred beads of smaller size and the larger Libellula preferred larger beads. Each species rejected beads as large or larger than their heads, even when the beads subtended the same visual angles as the smaller, attractive beads. Since bead size cannot be determined without reference to distance, we conclude that dragonflies are able to estimate the distance to potential prey items. The range over which they estimate distance is about 1 m for the larger Libellula and 70 cm for the smaller Sympetrum. The mechanism of distance estimation is unknown, but it probably includes both stereopsis and the motion parallax produced by head movements.     

The impacts of habitat disturbance on adult and larval dragonflies (Odonata) in rainforest streams in Sabah,Malaysian Borneo

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湿地植被对北京地区蜻蜓生态分布的影响

蜻蜓目（Odonata）昆虫是半变态类（Hemimetabola）昆虫,它的一生经过卵、若虫和成虫3个阶段。和其他水生昆虫一样,蜻蜓目昆虫是淡水生物群落的重要组成部分,对淡水生态系统起到重要作用。蜻蜓目昆虫在其生活史中,取食、交配等活动离不开水生植物和水域附近的植被。为了研究蜻蜓栖息生境中的湿地植被特征对蜻蜓生态分布影响,对北京地区不同湿地类型的17块样地中296个样方分布的蜻蜓种类、多度以及湿地植被的特征和植物多样性进行调查,记录到蜻蜓6科26属36种,维管植物40科99属150种。应用TWINSPAN对蜻蜓种类和样地进行双向聚类分析,所有样地被划分成为四组。同时,将植被特征因子和湿地植物的多样性视为影响蜻蜓数量及分布的因子进行CCA分析。结果表明：湿地植物的丰富度与植物群落结构的完整性是影响蜻蜓分布的主要因素;各湿地植被特征因子对于蜻蜓生态分布的影响不一,依贡献率由大及小依次为浮水植物层盖度、湿生植物盖度、G1eason丰富度指数、沉水植物层盖度、G-F多样性指数、挺水植物层盖度。并且首次应用G-F多样性指数分析湿地植物的多样性。对于蜻蜓栖息地的保护、城市中对于湿地的兴建和改造也提出了相关保护建议。     

Export of biomass and metals from aquatic to terrestrial ecosystems via the emergence of dragonflies (Insecta: Odonata)

Long-term monitoring of the abundance and spatial distribution of 18 widespread species of Odonata has made it possible to assess their contribution to the export of aquatic productivity that entered the Barabinsk forest-steppe ecosystem. The annual emergence of Odonata varies from 0.8 to 4.9 g/m² of the land area and from 2.3 to 13.3 g/m² of the water area, which is 4–5 times larger than that in Diptera. The total flux of organic matter from water to terrestrial ecosystems remains relatively stable (sixfold interannual variability) irrespective of large interannual variations in the abundance of separate species (e.g., 42-fold interannual variability in Libellula quadrimaculata). The metal content was determined in nine Odonata species. Export of metals by dragonflies decreases in the series K > Na > Mg > Ca > Fe > Zn > Cu > Mn > Pb > Ni > Cr > Cd. Therefore, odonates appear to be quantitatively and qualitatively important providers of aquatic resources to the forest-steppe landscape of Western Siberia.     

Not going with the flow: a comprehensive time‐calibrated phylogeny of dragonflies (Anisoptera: Odonata: Insecta) provides evidence for the role of lentic habitats on diversification

Ecological diversification of aquatic insects has long been suspected to have been driven by differences in freshwater habitats, which can be classified into flowing (lotic) waters and standing (lentic) waters. The contrasting characteristics of lotic and lentic freshwater systems imply different ecological constraints on their inhabitants. The ephemeral and discontinuous character of most lentic water bodies may encourage dispersal by lentic species in turn reducing geographical isolation among populations. Hence, speciation probability would be lower in lentic species. Here, we assess the impact of habitat use on diversification patterns in dragonflies (Anisoptera: Odonata). Based on the eight nuclear and mitochondrial genes, we inferred species diversification with a model‐based evolutionary framework, to account for rate variation through time and among lineages and to estimate the impact of larval habitat on the potentially nonrandom diversification among anisopteran groups. Ancestral state reconstruction revealed lotic fresh water systems as their original primary habitat, while lentic waters have been colonized independently in Aeshnidae, Corduliidae and Libellulidae. Furthermore, our results indicate a positive correlation of speciation and lentic habitat colonization by dragonflies: speciation rates increased in lentic Aeshnidae and Libellulidae, whereas they remain mostly uniform among lotic groups. This contradicts the hypothesis of inherently lower speciation in lentic groups and suggests species with larger ranges are more likely to diversify, perhaps due to higher probability of larger areas being dissected by geographical barriers. Furthermore, larger range sizes may comprise more habitat types, which could also promote speciation by providing additional niches, allowing the coexistence of emerging species.     

Nocturnal migration of dragonflies over the Bohai Sea in northern China

Abstract.  1. A sudden increase and subsequent sharp decrease of catches of dragonflies in a searchlight trap, with Pantala flavescens Fabricius (Odonata: Libellulidae) predominating, observed at Beihuang Island in the centre of the Bohai Gulf, in 2003 and 2004, indicated a seasonal migration of these insects over the sea during the night in China. The movements were associated with the onset of fog.
2. Simultaneous radar observations indicated that the nocturnally migrating dragonflies generally flew at altitudes of up to 1000 m above sea level, with high density concentrations at about 200–300 or 500 m; these concentrations were coincident with the temperature inversion.
3. During early summer, the dragonflies oriented in a downwind direction, so that the displacement direction varied between different altitudes. In contrast, during late summer, the dragonflies were able to compensate for wind drift, even headwind drift, so as to orient south-westward no matter how the wind changed, and thus the displacement direction was towards the south-west.
4. The duration of flight, estimated from the variation of area density derived from radar data and hourly catches in the searchlight trap through the night, was about 9–10 h. The displacement speed detected using radar was ≈5–11 m s⁻¹. Therefore, the dragonflies might migrate 150–400 km in a single flight.
5. The dragonflies were thought to originate in Jiangsu province and they migrated into north-east China to exploit the temporary environment of paddy fields in early summer. Their offspring probably migrated back south during late summer and autumn.     

Effect of juvenile hormone analog in a natural host-parasite system

Hormones mediate the physiological responses of animals to environmental changes. Consequently, hormones can be responsible of trade offs between different life history traits. Juvenile hormone (JH) is thought to mediate resource allocation in insects: specifically, it is thought to enhance the expression of condition-related traits like sexual signals, whilst reducing immune responsiveness. Here, we experimentally test whether a JH analog (JHa) had an effect on immunity of male dragonflies Celithemis eponina, and if such effects are translated into faster growth or development of a natural parasite (water mite). We also tested the effects of JHa on host condition (muscular mass and fat reserves) of mature male dragonflies. Mites from JHa treated dragonflies grew faster than mites from control dragonflies receiving just an acetone carrier. However, there was no effect of JHa on measures of host immune response (melanization of a nylon implant) or condition of mature males. We suggest that better parasite growth in JHa treated males does not result from the JH immunosuppressive function, but instead it appears that parasites receive hormone signals from the host and alter their development without affecting host condition measurably. Our work highlights the importance of measuring both immune parameters and response to real parasites when studying evolutionary trade offs.     

Procedure for Predicting the Trajectory of Species Recovery Based on the Nested Species Pool Information: Dragonflies in a Wetland Restoration Site as a Case Study

Restoration of seminatural habitats in the rural agricultural landscape has become an urgent matter in environmental conservation. We propose here a procedure for predicting the trajectory of species recovery and for specifying the priority of habitat types for restoration of a rural agricultural landscape. We then apply it as a case study to the recovery of dragonfly species in the Azame restoration project that began in 2003 in northern Kyushu, Japan. We examined the nestedness of the regional distribution of dragonflies using a national database on wildlife distribution and listed the recorded species in order of their prevalence in the region. We also conducted a census of adult dragonflies currently found at the restoration site to assess species richness. By comparing these data, we identified species potentially capable of inhabiting the restoration site and, based on their habitat requirements, suggest what type of habitat (e.g., bogs and marshes, ponds, and bodies of slow‐moving water) should be restored preferentially. We observed significant nestedness in the presence–absence matrix for dragonfly species and thus predict that species recovery at the restoration site will follow the regional order of prevalence of the species. The required habitat types did not differ significantly between the currently observed species and the potential species, which indicates that all these habitat types should be restored in the project.     

深圳市基本生态控制线划定对生态系统服务价值的影响

基于深圳市2002、2005和2010年的土地变更调查数据,分析了基本生态控制线划定前后深圳市土地利用面积变化特征,运用基于单位面积价值当量因子的方法对生态系统服务价值进行评估,并采用倍差法研究了基本生态控制线政策对生态系统服务价值的影响。结果表明:2002—2010年深圳市土地利用总体呈现耕地、园地、草地和水域面积减小,建设用地面积增大,林地面积先减小后增大的趋势;该区生态系统服务价值总体减小,但基本生态控制线划定之后总价值减小的速率降低;各土地利用类型中,林地和水域是构成深圳市生态系统服务价值的主要来源,而各项生态系统服务中,水源涵养产生的价值最大;生态系统服务价值低值范围不断扩大,蚕食价值高的地区,尤其以西部沿海、宝安北部、光明新区、龙华北部以及龙岗南部地区价值降低最为明显;基本生态控制线内生态系统服务价值以中、较高为主,价值变化不明显,线外以低、较低为主,且呈现不断降低的趋势;倍差法结果表明基本生态控制线政策对生态系统服务价值的提高存在促进作用,提升幅度约为1.6%。     

Optimal strategies for insects migrating in the flight boundary layer: mechanisms and consequences

Directed aerial displacement requires that a volant organism'sairspeed exceeds ambient wind speed. For biologically relevantaltitudes, wind speed increases exponentially with increasedheight above the ground. Thus, dispersal of most insects isinfluenced by atmospheric conditions. However, insects thatfly close to the Earth's surface displace within the flightboundary layer where insect airspeeds are relatively high. Overthe past 17 years, we have studied boundary-layer insects byfollowing individuals as they migrate across the Caribbean Seaand the Panama Canal. Although most migrants evade either droughtor cold, nymphalid and pierid butterflies migrate across Panamanear the onset of the rainy season. Dragonflies of the genusPantala migrate in October concurrently with frontal weathersystems. Migrating the furthest and thereby being the most difficultto study, the diurnal moth Urania fulgens migrates between Centraland South America. Migratory butterflies and dragonflies arecapable of directed movement towards a preferred compass directionin variable winds, whereas the moths drift with winds over water.Butterflies orient using both global and local cues. Consistentwith optimal migration theory, butterflies and dragonflies adjusttheir flight speeds in ways that maximize migratory distancetraveled per unit fuel, whereas the moths do not. Moreover,only butterflies adjust their flight speed in relation to endogenousfat reserves. It is likely that these insects use optic flowto gauge their speed and drift, and thus must migrate wheresufficient detail in the Earth's surface is visible to them.The abilities of butterflies and dragonflies to adjust theirairspeed over water indicate sophisticated control and guidancesystems pertaining to migration.     

Data uncertainty and the selectivity of extinction risk in freshwater invertebrates

Aim

To investigate the impact of different treatments of the IUCN Data Deficient (DD) category on taxonomic and geographical patterns of extinction risk in crayfish, freshwater crabs and dragonflies.

Location

Global.

Methods

We used contingency tables to evaluate taxonomic and geographical selectivity of data deficiency and extinction risk for three invertebrate taxonomic groups (crayfish, dragonflies and damselflies, and freshwater crabs) based on their IUCN Red List status. We investigated differences in patterns of data deficiency and extinction risk among taxonomic families, geographical realms and taxonomic families within geographical realms for each of the three groups. At each level, we evaluated the impact of uncertainty conferred by the conservation status of DD species on extinction risk patterns exhibited by that group. We evaluated three scenarios: excluding DD species, treating all DD species as non‐threatened and treating all DD species as threatened.

Results

At the global scale, DD species were taxonomically non‐randomly distributed in freshwater crabs and dragonflies, and geographically non‐randomly distributed in all three taxonomic groups. Although the presence of under‐ or over‐threatened families and biogeographical realms was generally unchanging across scenarios, the strength of taxonomic and geographical selectivity of extinction risk varied. There was little consistent evidence for taxonomic selectivity of extinction risk at sub‐global scales in freshwater crabs and dragonflies, either among biogeographical realms or among scenarios.

Main conclusions

Global patterns of taxonomic selectivity and geographical selectivity were generally consistent with one another and robust to different treatments of DD species. However, sub‐global scale conservation prioritization from these types of data sets will require increased investment to make accurate decisions. Given the current levels of data uncertainty, the relative importance of biological characteristics and threatening processes in driving extinctions in freshwater invertebrates cannot be easily determined. We recommend that DD species should be given high research priority to determine their true status.