Aquatic insect larvae as indicators of limiting minimal contents of dissolved oxygen

Minimal concentrations of oxygen are limiting factors for limnic biocenoses. It should therefore be possible to use biocenose structure to infer minimal oxygen concentrations that have occured, provided the tolerance of the organisms concerned is known. A simple apparatus used to measure LC₅₀ of oxygen for aquatic insect larvae with tracheal gills is described. Lethal concentrations found in some Ephemeroptera differ between species. Usually, they are strongly temperature dependent. In the species so far studied, confidence intervals are very small and suggest that such insect larvae could be used as bioindicators of minimal oxygen concentrations (even of short term ones), especially in thermically stable waters.     

Aerial Jumping in the Trinidadian Guppy (Poecilia reticulata)

Many fishes are able to jump out of the water and launch themselves into the air. Such behavior has been connected with prey capture, migration and predator avoidance. We found that jumping behavior of the guppy Poecilia reticulata is not associated with any of the above. The fish jump spontaneously, without being triggered by overt sensory cues, is not migratory and does not attempt to capture aerial food items. Here, we use high speed video imaging to analyze the kinematics of the jumping behavior P. reticulata. Fish jump from a still position by slowly backing up while using its pectoral fins, followed by strong body trusts which lead to launching into the air several body lengths. The liftoff phase of the jump is fast and fish will continue with whole body thrusts and tail beats, even when out of the water. This behavior occurs when fish are in a group or in isolation. Geography has had substantial effects on guppy evolution, with waterfalls reducing gene flow and constraining dispersal. We suggest that jumping has evolved in guppies as a behavioral phenotype for dispersal.     

A century and a half of research on the evolution of insect flight

The gill and paranotal lobe theories of insect wing evolution were both proposed in the 1870s. For most of the 20th century, the paranotal lobe theory was more widely accepted, probably due to the fundamentally terrestrial tracheal respiratory system; in the 1970s, some researchers advocated for an elaborated gill (“pleural appendage”) theory. Lacking transition fossils, neither theory could be definitively rejected.Winged insects are abundant in the fossil record from the mid-Carboniferous, but insect fossils are vanishingly rare earlier, and all earlier fossils are from primitively wingless insects. The enigmatic, isolated mandibles of Rhyniognatha (early Devonian) hint that pterygotes may have been present much earlier, but the question remains open.In the late 20th century, researchers used models to study the interaction of body and protowing size on solar warming and gliding abilities, and stability and glide effectiveness of many tiny adjustable winglets versus a single, large pair of immobile winglets. Living stoneflies inspired the surface-skimming theory, which provides a mechanism to bridge between aquatic gills and flapping wings. The serendipitously discovered phenomenon of directed aerial descent suggests a likely route to the early origin of insect flight. It provides a biomechanically feasible sequence from guided falls to fully-powered flight.     

uninflatable encodes a novel ectodermal apical surface protein required for tracheal inflation in Drosophila

The tracheal system of Drosophila melanogaster has proven to be an excellent model system for studying the development of branched tubular organs. Mechanisms regulating the patterning and initial maturation of the tracheal system have been largely worked out, yet important questions remain regarding how the mature tubes inflate with air at the end of embryogenesis, and how the tracheal system grows in response to the oxygen needs of a developing larva that increases nearly 1000-fold in volume over a four day period. Here we describe the cloning and characterization of uninflatable (uif), a gene that encodes a large transmembrane protein containing carbohydrate binding and cell signaling motifs in its extracellular domain. Uif is highly conserved in insect species, but does not appear to have a true ortholog in vertebrate species. uif is expressed zygotically beginning in stage 5 embryos, and Uif protein localizes to the apical plasma membrane in all ectodermally derived epithelia, most notably in the tracheal system. uif mutant animals show defects in tracheal inflation at the end of embryogenesis, and die primarily as larvae. Tracheal tubes in mutant larvae are often crushed or twisted, although tracheal patterning and maturation appear normal during embryogenesis. uif mutant larvae also show defects in tracheal growth and molting of their tracheal cuticle.     

Morphometric analysis of the larval branchial chamber in the dragonfly Aeshna cyanea Müller (Insecta, Odonata, Anisoptera)

The aquatic larvae of anisopteran dragonflies possess tracheal gills located in the rectum. Using stereological methods, we estimated the morphometric diffusing capacity for oxygen (D(MO2)) across the gill epithelium, i.e., from rectal water to the gill tracheoles, in the larvae of Aeshna cyanea. A 271-mg larva has a total branchial surface area of approximately 12 cm(2). Tracheoles make up 6% of the epithelial volume of the gills; the harmonic mean thickness of the water-tracheolar diffusion barrier is 0.27 microm and consists mainly of cuticle. The calculated D(MO2) is 23.0 microl min(-1) g(-1) kPa(-1), which, using published values for oxygen consumption in a similar species, would result in a mean driving pressure of 0.2 kPa at rest and 1.3 kPa during activity. Since these driving pressures are similar to those reported for other arthropods, we conclude that the D(MO2) of the gill is not rate-limiting for aerobic metabolism in Aeshna cyanea larvae. J Morphol. 261:81-91, 2004.     

条背萤幼虫水生适应性形态与游泳行为研究

研究了条背萤Luciolasubstriata幼虫的形态特征及其对游泳行为的适应。形态及扫描电镜观察发现,条背萤幼虫存在二态现象。1～2龄幼虫虫体扁平,多毛。有7对呼吸鳃,分别位于腹部第1～7节。3～6龄幼虫虫体扁平呈船形,无呼吸鳃,靠气管呼吸。二者均具有扁平桨状的足、燕尾状尾节及位于尾节末端的圆柱形粘附器官。条背萤幼虫游动时身体腹面朝上,呈仰泳姿态,足向后划水。3～6龄幼虫仰泳时足共有8种摆动姿势。幼虫仰泳时足摆动1个周期所需时间为(0.611±0.16)s。腹部末端可上下左右摆动,当幼虫向前游动时,尾部上下摆动1个周期所需时间为(1.795±0.44)s。幼虫的游泳速度为(0.85±0.16)mh。仰泳中的幼虫改变方向时,头部和尾部同时向身体的一侧弯曲,当头部与尾部呈近90°时,幼虫用力将尾部伸直,此时水产生一个反作用力继续推动幼虫转向,幼虫转向的范围为0～90°。条背萤2种类型幼虫呼吸系统的不同决定着幼虫外部形态的差异及游泳行为的不同,而导致这种呼吸系统、形态及运动行为不同的原因很可能是条背萤对环境的适应性进化。     

雷氏黄萤幼虫呼吸系统和呼吸行为

研究雷氏黄萤Luciola leii Fu and Ballantyne幼虫的呼吸系统及其呼吸行为。结果表明:雷氏黄萤幼虫的呼吸系统中只有气管无气囊。前胸、中胸和后胸均分布有气门,无气管鳃,腹部1~8节分布有气门和气管鳃,气门腔基部和气管鳃基部相连,呈"√"状,气管鳃内气管与气门气管相连通。雷氏黄萤幼虫的呼吸行为分为3种:利用胸部气门呼吸、腹部气门呼吸和气管鳃呼吸,其中以腹部气门呼吸为主。     

Factors affecting the distribution and abundance of Cloeon and Caenis (Ephemeroptera) larvae in a tropical impounded river, Nigeria

Impoundment of rivers affects the mayfly (Ephemeroptera) fauna inhabiting such water bodies, especially with respect to their distribution and abundance. A two‐year study of the mayfly fauna and some of the physicochemical parameters of the Opa stream–reservoir revealed that there are two mayfly genera inhabiting it, Cloeon and Caenis. The number of Cloeon larvae collected was 10,930 while the number of Caenis larvae was 450. It was observed that although both genera occurred at all the sampling stations, their numbers were reduced in the stream below the dam due to increased water current velocity. There were significant differences in the abundance of Cloeon among the stations, but none for Caenis. Submerged aquatic plants and water current velocity were found to be the major factors responsible for the significant differences. There were significant correlations between the number of Cloeon larvae and pH as well as between dissolved oxygen concentration and Caenis. These findings are discussed with reference to inter‐specific differences in patterns of response to environmental parameters. A species‐specific approach is suggested for studies on the strategies that enable mayfly species maintain their populations in stressed and unstable aquatic ecosystems.     

普通齿蛉幼虫的游泳行为（英文）

为了探究广翅目昆虫幼虫在水中的游泳能力, 以丰富其水生习性的行为学资料, 选取中国特有种普通齿蛉Neoneuromus ignobilis幼虫为研究对象, 通过室内试验对其游泳的姿势、 刺激因素、 不同龄期游泳能力及在外界刺激下的游泳行为进行了观察和测定。结果表明： 普通齿蛉幼虫有垂直、 平行、 仰面和侧面等4种游泳姿势, 出现的频率分别为89.08%, 5.49%, 4.40%和0.61%。游泳时身体呈不同程度的“S”形, 利用头部和尾部方向的改变实现虫体的上升、 下沉和游泳姿势的改变。普通齿蛉幼虫利用身体的摆动游泳, 游泳时3对足以固定的姿势靠紧身体。不同龄期的幼虫游泳能力差异很大, 6龄幼虫的游泳能力远强于2龄和末龄幼虫。在游泳时, 普通齿蛉幼虫还具有比较复杂和独特的防御行为, 如其腹部末端会喷射出化学物质。据此认为, 普通齿蛉拥有较强的游泳能力, 有助于其逃生和防御。     

Rowing locomotion by a stonefly that possesses the ancestral pterygote condition of co-occurring wings and abdominal gills

A leading hypothesis for the origin of insect wings is that they evolved from thoracic gills that were serial homologues of the abdominal gills present in fossil pterygotes and in the nymphs of some modern mayflies, damselflies and stoneflies. Co-occurrence of thoracic wings and abdominal gills is the primitive condition for fossil pterygote insects, whereas the winged stage of modern insects almost exclusively lacks abdominal gills. Here we examine the locomotor behaviour and gill morphology of a stonefly, Diamphipnopsis samali (Plecoptera), which retains abdominal gills in the winged adult stage. This species can fly, but also uses its forewings as oars to accomplish rowing locomotion along the surface of water. The abdominal gills are in contact with both air and water during rowing, and their elaborately folded surface suggests an ability to contribute to gas-exchange. D. samali nymphs also have behaviours that place them in locations where their gills are exposed to air; they forage at night at the stream margin and within bubble curtains in rapids. These traits may exemplify an early pterygote condition in which gill and protowing function overlapped in an amphibious setting during a transition from aquatic to aerial locomotion and gas exchange. Rowing locomotion provides a novel and mechanically intermediate stage for the wings-from-gills and surface-skimming hypotheses for the origin of insect wings and flight.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79, 341–349.     

湘西峒河流域星齿蛉幼虫分子鉴定与体表呼吸结构观察

星齿蛉属Protohermes隶属于广翅目Megaloptera齿蛉科Corydalidae,是一类原始的完全变态昆虫,幼虫水生,常作为指示生物用于水质监测。本文对湘西峒河流域两种星齿蛉幼虫进行了分子鉴定和体表呼吸结构观测。结果表明两种星齿蛉幼虫COⅠ基因序列分别与花边星齿蛉Protohermes costalis和炎黄星齿蛉Protohermes xanthodes同源性较高;遗传距离分析和系统发育分析进一步证实两种星齿蛉幼虫分别属于花边星齿蛉和炎黄星齿蛉,分子鉴定结果与成虫形态鉴定结果一致。花边星齿蛉和炎黄星齿蛉幼虫体表呼吸结构气门、毛簇、气管鳃和臀足侧突均与气管相连,毛簇是主要的水下呼吸结构。本研究结果为峒河流域星齿蛉昆虫资源的保护和开发利用提供了科学数据。     

A micro-CT approach for determination of insect respiratory volume

Variation in the morphology of the insect tracheal system can strongly affect respiratory physiology, with implications for everything from pest control to evolution of insect body size. However, the small size of most insects has made measuring the morphology of their tracheal systems difficult. Historical approaches including light microscopy and scanning and transmission electron microscopy (SEM, TEM) are technically difficult, labor intensive, and can introduce preparation artifacts. More recently, synchrotron X-ray microtomography (SR-μCT) has allowed for detailed analysis of tracheal morphology of diverse insects. However, linear accelerators required for SR-μCT are not readily available, making the approach unavailable for most labs. Recent advancements in microcomputed tomography (μCT) have made possible fine resolution of internal morphology of very small insects. However, μCT has never been used to quantify insect tracheal system dimensions. We measured respiratory volume of a grasshopper (Schistocerca americana) by analysis of high resolution μCT scans. Volume estimates from μCT closely matched volume estimates by water displacement as well as literature estimates for this species. The μCT approach may thus provide a widely available, cost-effective, and straightforward approach to characterizing the internal morphology of insect respiratory systems.     

Surviving submerged—Setal tracheal gills for gas exchange in adult rheophilic diving beetles

The gas exchange in adult diving beetles (Coleoptera: Dytiscidae) relies on a subelytral air store, which has to be renewed in regular intervals at the water surface. The dive duration varies from a few minutes to 24 h depending on the species, activity, and temperature. However, some species remain submerged for several weeks. Stygobiont species do not ascend to the surface and gas exchange of these species remains unclear, but it is assumed that they require air filled voids for respiration or they use cutaneous respiration. In this study, we investigate the gas exchange in the running water diving beetle Deronectes aubei, which survive submerged for over 6 weeks. The diffusion distance through the cuticle is too great for cutaneous respiration. Therefore, the dissolved oxygen uptake of submerged beetles was determined and an oxygen uptake via the rich tracheated elytra was observed. Fine structure analyses (SEM and TEM) of the beetles showed tracheated setae mainly on the elytral surface, which acts as tracheal gills. Prevention of the air bubble formation at the tip of the abdomen, which normally act as physical gill in Dytiscidae, resulted in no effect in oxygen uptake in D. aubei, but this was the sole way for a submerged Hydroporus palustris to get oxygen. The setal gas exchange technique explains the restriction of D. aubei to rivers and brooks with high oxygen concentration and it may also be used by subterran living diving beetles, which lack access to atmospheric oxygen. The existence of setal tracheal gills in species in running water which are often found in the hyporheic zone and in stygobiont species supports the known evolution of stygobiont Dytiscidae from species of the hyporheic zone. For species in running water, setal tracheal gills could be seen as an adaptation to avoid drifting downstream by the current. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Patch size drives colonization by aquatic insects,with minor priority effects of a cohabitant

Patch size is one of the most important factors affecting the distribution and abundance of species, and recent research has shown that patch size is an important niche dimension affecting community structure in aquatic insects. Building on this result, we examined the impact of patch size in conjunction with presence of larval anurans on colonization by aquatic insects. Hyla chrysoscelis (Cope''s gray treefrog) larvae are abundant and early colonists in fishless lentic habitats, and these larvae can fill multiple ecological roles. By establishing larvae in mesocosms prior to colonization, we were able to assess whether H. chrysoscelis larvae have priority effects on aquatic insect assemblages. We conducted a series of three experiments in naturally colonized experimental landscapes to test whether (1) H. chrysoscelis larval density affects insect colonization, (2) variation in patch size affects insect colonization, and (3) the presence and larval density of H. chrysoscelis shift colonization of insects between patches of different size. Larval density independently had almost no effect on colonization, while patch size had species‐specific effects consistent with prior work. When larvae and patch size were tested in conjunction, patch size had numerous, often strong, species‐specific effects on colonization; larval density had effects largely limited to the assemblages of colonizing beetles and water bugs, with few effects on individual species. Higher larval densities in large mesocosms shifted some insect colonization to smaller patches, resulting in higher beta diversity among small patches in proximity to high density large mesocosms. This indicates establishing H. chrysoscelis larvae prior to insect colonization can likely create priority effects that slightly shape insect communities. Our results support the importance of patch size in studying species abundances and distributions and also indicate that colonization order plays an important role in determining the communities found within habitat patches.     

Respiratory adaptations to running-water microhabitats in mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis, Ephemeroptera

The mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis inhabit either fast-flowing or, for the latter species, calm zones of running water. We studied (1) mechanisms and limitations of oxygen transport in single individuals (oxygen consumption rate, occurrence and rate of gill movements, and heartbeats) in running water of different oxygen concentrations and (2) capacities for anaerobiosis (L-lactate production). Our aim was to look for specific adaptations in the two species to slightly different microhabitats. Epeorus sylvicola, whose immovable gills are not able to generate ventilatory convection, proved to be an oxyconformer at both test temperatures (11 degrees and 15 degrees C). Ecdyonurus torrentis showed a progressively stronger oxyregulatory behavior at higher temperatures. In this species an onset of gill beating was found at moderate hypoxia (below 16 kPa). Ventilating individuals reached maximum rates (300 min-1) of 5-14 kPa. In the case of a further reduction of oxygen partial pressure, the ventilatory rate started to decrease. Ventilatory activity, however, was maintained down to very low oxygen concentrations. Neither in E. sylvicola nor in E. torrentis was experimental evidence found to confirm the hypothesis of a respiratory function of hindgut movements. During hypoxia, the heart rate was constant in both species (E. sylvicola: 80 min-1; E. torrentis: 60 min-1): bradycardia occurred either below 1.5 kPa or below 4 kPa. Anaerobiosis, that is, lactate production, was not detected in either species.     

Damage to the gills and integument of Litoria fallax larvae (Amphibia: Anura) associated with ionoregulatory disturbance at low pH

In fish, exposure to waters of low pH causes significant damage to the gill resulting in fatal iono- and osmoregulatory disturbance. In amphibians, exposure to acid waters also disrupts ionic homeostasis, however the extent and nature of injuries to amphibian larvae from acid exposure are poorly understood. Changes in gross morphology and ultrastructure of the gills and integument were examined, together with measures of Na⁺ efflux/uptake, in larval Litoria fallax (Amphibia: Anura) following acute acid exposure. Examination of tissues revealed significant changes in morphology and ultrastructure of both gills and the integument following acutely lethal exposure to low pH water. Changes to the gills of acid-exposed L. fallax larvae included lifting of the branchial epithelium and opening of tight junctions between pavement cells (with a consequent reduction in tight junction length). Damage to epithelial cell–cell tight junctions was also apparent at the integument along with widespread oncosis and localised epithelial necrosis. Mucous secretory activity at the gills and body surface was largely unaffected by acid exposure, with little or no difference in density, cross-sectional area and number of epithelial mucous secretory vesicles in acid-exposed and control larvae. Changes in morphology and ultrastructure at low pH were accompanied by significant Na⁺ loss (up to 50% of the total body Na⁺ content) attributable in large part to increased paracellular ionic efflux across the gills as well as increased transcellular and paracellular efflux of ions across the integument.     

Biology of the mayfly <Emphasis Type="Italic">Bleptus fasciatus</Emphasis> Eaton (Insecta: Ephemeroptera,Heptageniidae), with special reference to the distribution,habitat environment,life cycle,and nuptial behavior

As the habitats of the mayfly Bleptus fasciatus (Ephemeroptera, Heptageniidae) are unique and specialized, information on the distribution and biology of the mayfly is very poor. In this article, the biology of the mayfly is described, with special reference to the distribution and life cycle: the voltinism, emergence and reproductive season, nuptial behavior (i.e., swarming), egg period, and the early stage of postembryogenesis. The life cycle of the mayfly was judged as semivoltine, in contrast to the previous interpretation. Also, the unique nuptial behavior or the swarming of the mayfly is revealed.     

Preferential Feeding and Occupation of Sunlit Leaves Favors Defense Response and Development in the Flea Beetle,Altica brevicollis coryletorum – A Pest of Corylus avellana

The monophagous beetle, Altica brevicollis coryletorum, is a major leaf pest of Corylus avellana (common hazel). In contrast to majority of the other studied species of shrubs, sunlit leaves are grazed to a much greater extent than shaded leaves. Since the observation of a link between leaf irradiance level and A. brevicollis feeding is unique, we hypothesized that feeding preference of this beetle species is related to the speed needed to escape threats i.e. faster jumping. We also hypothesized that sunlit leaves are more nutritious and easier to consume than the leaves of shaded shrubs. Results indicated that beetle mass was greater in beetles occupying sunlit leaves, which is consistent with our second hypothesis. The study also confirmed under laboratory conditions, that larvae, pupae and beetles that were fed full-light (100% of full light) leaves were significantly heavier than those fed with shaded leaves (15% of full light). In the high irradiance conditions (higher temperature) duration of larval development is also reduced. Further results indicated that neither the concentration of soluble phenols, leaf toughness, or the number of trichomes could explain the insect’s preference for sunlit leaves. Notably, measurements of jump length of beetles of this species, both in the field and under laboratory conditions, indicated that the defense pattern related to jumping was associated with light conditions. The jump length of beetles in the sun was significantly higher than in the shade. Additionally, in laboratory tests, beetle defense (jumping) was more strongly affected by temperature (15, 25, or 35°C for 24h) than by leaf type. The effect of sunlit, higher nutrient leaves (greater level of non-structural carbohydrates) on defense (jumping) appears to be indirect, having a positive effect on insect mass in all developmental stages.     

Fungal symbionts (Harpellales) in Norwegian aquatic insect larvae

Collections of aquatic insect larvae in Norway, over a 40 d period in May and Aug 2002, resulted in finding more than 25 species and one new genus of Harpellales (Trichomycetes). Nine new fungal symbionts are described and named: Ephemerellomyces aquilonius (a new monotypic genus), Glotzia stenospora and Legeriosimilis europaeus in mayfly nymphs (Ephemeroptera); Genistelloides amplispora and G. communis in stonefly nymphs (Plecoptera); and Smittium biforme, Sm. precipitiorum, Stachylina acutibasilaris and St. lentica in midge larvae (Diptera: Chironomidae). Two possibly new species of Smittium in Chironomidae larvae are described but not formally named. New hosts and biogeographical distributions are recorded for 14 previously described species, including the rare occurrence of Smittium simulii in mosquito larvae.     

Trichomycetes from China and the description of three new Smittium species

Trichomycetes were recovered from the guts of aquatic insect larvae collected from a stream in the Qinling Mountains in western China. These collections included Smittium hecatei, known only from Spain, as well as Smittium simulii and Stachylina penetralis, which appear to be more widely distributed. Caudomyces japonicus, previously recorded only from Japan, also is reported from crane fly larvae (Antocha sp.) from China. We describe three new species, Smittium chinliense from a tipulid host, as well as Smittium naiadis and Smittium nodifixum, both from chironomid larvae. A probable new species of Gauthieromyces was collected in mayfly nymphs and is illustrated but not described here.