Hormones regulating structural changes in the adipocytes of the female earwig Labidura riparia

Changes in periovarian fat body fine structure occur during the reproductive cycle of the female earwig Labidura riparia. During the process of vitellogenesis, high levels of protein synthesis are seen in the adipocytes. Simultaneously, the formerly osmiophilic lipid droplets become non-osmiophilic, while an osmiophilic material diffuses from lipid droplets to the cisternae of the rough endoplasmic reticulum (RER). These structural features alter during non-vitellogenic periods: RER and Golgi apparatus regress and seem to be inactive. Lipid droplets are once again osmiophilic and no material enters into RER cisternae. Using microsurgical manipulations, hormonal treatments and light and electron microscopy, we have investigated the regulation of these changes. The neuroendocrine cerebral centre pars intercerebralis, by the action of the juvenile hormone of the corpus allatum. triggers protein metabolism. Another neuroendocrine center, the pars lateralis. and the hormone 20-hydroxyecdysone, regulate structural lipid droplet changes in the adipocytes.     

Identification of 10 microsatellite loci in the earwig Labidura riparia (Dermaptera,Labiduridae)

Ten microsatellite loci were isolated from the earwig Labidura riparia (Pallas, 1773). The polymorphism of the loci was assessed in 24 individuals from one population. The number of alleles ranged from four to 11 alleles and observed and expected heterozygosities from 0.250 to 0.833 and from 0.551 to 0.861, respectively.     

Allatostatin-like peptide in the brain-retrocerebral complex of the earwig Labidura riparia: cyclic variations related to the reproductive cycle

Summary

A polyclonal antibody raised against allatostatin-3 of Blattella germanica (BLAST-3) has been used to immunolocalize allatostatin-like peptides in the brain-retrocerebral complex of Labidura riparia adult females. Strongly stained immunoreactive cells are observed in the pars intercerebralis (14 cells) and mainly in the pars lateralis (32 cells). Fibres leading to the corpus allatum are also stained. In the deutocerebrum, one cell is immunostained at the root of each antennal nerve. In the tritocerebmm two cells in each brain hemisphere are weakly immunostained. During the reproductive cycle, these cells and their axons show immunoreactivity at previtellogenic, ovulation and ovarian arrest periods. During vitellogenesis, immunoreactivity is restricted to only four perikarya in the pars intercerebralis.

When young vitellogenic females are injected with 20-hydroxyecdysone (20E), which inhibits vitellogenesis, full immunoreactivity reappears, suggesting sensibility of these cells to 20E as is expected for a negative feed-back loop (Sayah et al., 1995).

These results show that BLAST-3-like material is produced periodically in Labidura in correlation with low levels of juvenile hormone and the absence of vitellogenesis. This study contributes to provide information on the degree of homology of allatostatins across various insects.     

Effect of Azadirachtin on vitellogenesis of Labidura riparia (Insect Dermaptera)

This study investigates the effects of the insect growth regulator Azadirachtin (AZA) on the ultrastructure of ovaries and fat body of the earwig Labidura riparia. Ovarian development is severely reduced in AZA-injected females in a dose-dependent manner. Follicles exhibit degenerative changes, separation of follicle cells from the oocyte, and lack of pinocytotic vesicles as of yolk spheres in cortical ooplasm. Adipocytes show fragmented rough endoplasmic reticulum (RER), numerous autophagic vacuoles, multivesicular bodies, osmiophilic lipid droplets, and many large glycogen areas. Gel electrophoresis reveals that vitellogenin is absent from both fat body and hemolymph, and that vitellin is not deposited in the ovary. These pathological effects are not linked to an absence of feeding. The effect of AZA on vitellogenesis is rescuable by Juvenile hormone (JH) treatment. The inhibition of vitellogenesis by AZA is discussed on the basis of its direct cytotoxic effect as well as its interference with the neuroendocrine system.     

In vivo inhibition of vitellogenesis in the Dermapteran Labidura riparia by 20-hydroxyecdysone

In previous studies we have described the existence of cyclical changes in ecdysteroid levels during the female reproductive life of the earwig Labidura riparia. High levels of ecdysteroids are observed at the end of each vitellogenic period just before follicle degeneration, in coincidence with the beginning of each non-vitellogenic period. In the present work, using in vivo [(35)S]methionine incorporation, electrophoresis and electron microscopy, we study the effects on fat body and ovaries of 20-hydroxyecdysone (20E) injections into young vitellogenic females. This resulted in a reduction of proteosynthetic organelles (scarce Golgi complexes and fragmented RER cisternae), inhibition of vitellogenin synthesis in adipocytes, vitellogenesis arrest and premature follicular atresy. All these effects are suppressed when juvenile hormone treatment is associated with 20E injections. 20E does not inhibit vitellogenesis when applied to pars lateralis deprived females, which display continuous vitellogenesis. Thus, 20E does not act directly on ovaries nor on corpus allatum: the presence of the pars lateralis cells is required for 20E to inhibit vitellogenesis. These findings are explained in terms of the existence of a 20E feed back loop. This hormone acts via lateral neurosecretory cells of the brain which probably have an allatostatic effect.     

Activity of corpora allata,endocrine balance and reproduction in female Labidura riparia (Dermaptera)

Summary The reproductive activity of Labidura riparia females involves, after a 5-day maturation stage, a regular alternation of ovarian cycles and egg-care stages averaging 10 days each. Vitellogenesis is characterized by an increase in the size of the corpora allata (CA) where structured SER bodies appear, and by a rise of juvenile hormone (JH III) content in the hemolymph which is followed by an increase in the level of ecdysteroids. During the egg-care periods, the CA are inactive; structured bodies generate autophagic vacuoles, the titer of JHs and later that of ecdysteroids in the hemolymph decreases and remains stationary. Ovariectomy causes hypertrophy and hyperactivity of the CA for about two months. Subsequently, the titer of JH decreases and old females may display parental behaviour; the level of ecdysteroids falls and remains unchanged. After cauterization of the pars intercerebralis (PI) of the protocerebrum, the ovarian activity stops, the ovary shrinks, the JHs rapidly disappear but ecdysteroids remain at the same or even higher levels than those of normal females of the same age. On the basis of these data, we postulate the existence of a center located in the PI, inhibiting the production of ecdysteroids, and of a stimulating center located outside this area. The PI also exhibits an allatotropic function.

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Résumé L'activité sexuelle des femelles de Labidura riparia comporte au terme d'une phase de maturation sexuelle de 5 jours une alternance régulière de cycles ovariens et de phases de soins aux oeufs d'une durée moyenne de 10 jours. La vitellogenèse est caractérisée par l'accroissement des CA oú apparaissent des amas structurés de RE, par une élévation du titre hémolymphatique de la JH III, puis des ecdystéroïdes. En période de soins aux oeufs, les CA sont inactifs (rejet des amas de reticulum sous la forme de vacuoles autophagiques), le titre hémolymphatique de l'hormone juvénile puis des ecdystéroïdes diminue puis reste stationnaire. L'ovariectomie détermine une hypertrophie et pendant 2 mois environ une hyperactivité des CA; ultérieurement, le titre de l'hormone juvénile diminue et les femelles âgées peuvent manifester un comportement parental; le titre des ecdystéroïdes ne s'annule pas chez les femelles ovariectomisées. Après parsectomie, l'activité ovarienne cesse, l'ovaire régresse, le titre de l'hormone juvénile s'annule rapidement mais les ecdystéroïdes restent présents à des titres égaux, voire supérieurs à ceux appréciés chez les femelles normales de même âge. Ces données permettent d'envisager l'existence d'un centre inhibiteur de la production des ecdystéroïdes situé dans la PI et d'un centre excitateur situé en dehors de cette région. La PI a également une fonction allatotrope.

     

Changes in the lipid and fatty acid composition of hemolymph and ovaries during the reproductive cycle of Labidura riparia

Lipid metabolism was investigated during the reproductive cycle of Labidura riparia (Pallas). The lipid classes and their constitutive fatty acids present in hemolymph and ovaries were measured using thin‐layer chromatography and gas‐liquid chromatography. In the hemolymph, total lipids increase steadily from the previtellogenic period to vitellogenic arrest. These lipids are predominantly diacylglycerols and phospholipids. In the ovaries, total lipids increase during vitellogenesis then decrease during the vitellogenesis arrest period. The major lipids are triacylglycerols, followed by phospholipids. In both hemolymph and ovaries, all lipid classes contained variable proportions of seven main fatty acids: the saturated fatty acids myristic acid (14:0), palmetic acid (16:0), and stearic acid (18:0); the monounsaturated fatty acids palmitoleic acid (16:1) and oleic acid (18:1); and the polyunsaturated fatty acids linoleic acid (18:2) and linolenic acid (18:3). Unsaturated fatty acids predominate throughout the reproductive cycle. The percentage compositions of total and triacylglycerol fatty acids do not change markedly during the reproductive cycle in hemolymph nor in ovaries, with 18:2, 18:1 and 16:0 fatty acids being the major components. However, for diacylglycerols and phospholipids, the proportions of fatty acids vary systematically. For phospholipids during the vitellogenesis period, 18:2 increases considerably whereas other fatty acids decrease; for diacylglycerols, these fatty acids vary in the reverse way.     

Lipid and fatty acid composition of the fat body during the female reproductive cycle of Labidura riparia (Insecta Dermaptera)

During the reproductive cycle of the female Labidura riparia, cytological observations show cyclical modifications of lipid droplets in the periovarian adipocyte. Fat body lipids and their constitutive fatty acids are analyzed. The lipids are predominantly triacylglycerols, which increase after adult ecdysis during vitellogenic and non-vitellogenic periods. Small amounts of diacylglycerols and phospholipids are found. Diacylglycerols increase during vitellogenesis and decrease during the non-vitellogenic period. Cytological modifications of lipid droplets are probably related to diacylglycerol fluctuations. Gas-liquid chromatography of fatty acid methyl esters shows oleic acid to be the predominant fatty acid in total lipids and triacylglycerols; unsaturated acids are approximately twice as abundant as saturated acids all along the reproductive cycle. Fatty acid composition of diacylglycerols and phospholipids differs from triacylglycerols and total lipids composition. Palmitic, stearic, oleic and linoleic acids represent the major fatty acids; their relative amounts vary during the different periods of the reproductive cycle. The correlations between fat body lipid changes and ovarian development were discussed and compared with observations made on other insect species. Accepted: 23 April 1997     

Ultrastructural changes in the corpus allatum after azadirachtin and 20-hydroxyecdysone treatment in adult females of Labidura riparia (Dermaptera)

In previous reports, we have shown that the injection of azadirachtin (AZA) as well as 20-hydroxyecdysone (20E) into vitellogenic females of Labidura riparia induces inhibition of vitellogenin synthesis and ovarian development. Juvenile hormone (JH) treatment rescues vitellogenin synthesis and ovarian growth (Sayah et al., 1995, 1996). In this work, we have studied ultrastructural changes of corpus allatum (CA) after injection of 200, 400, and 600 ng of 20E or 1, 3, and 5 microg of AZA. CA cells exhibit signs of inactivity in both AZA and females treated with 20E at doses of 3 microg and 400 ng, respectively. Conspicuous cytological effects consisting of multivesicular bodies with dense contents, abnormally large intercellular spaces comprising myelinic structures, and rare smooth endoplasmic reticula occurred in cytoplasm of CA glandular cells in both experimental females. However, the CA ultrastructure of females injected with 20E differs from CA cells of females injected with AZA in having a cytoplasm containing numerous electron-lucent intracellular areas and marked glycogen zones. They also differ in having abundant microtubules and well-developed junctional membranes. At a dose of 600 ng of 20E or 5 microg of AZA, the intensity of the cytotoxic effects is more apparent. CA cells display pycnotic nuclei, spherical mitochondria, large multivesicular bodies, and vacuolization of the cytoplasm. These results are discussed and compared with observations made on other insect species.     

Structural changes in light- and dark-adapted compound eyes of the australian earwig Labidura riparia truncata (dermaptera)

The apposition acone eye of Labidura is relatively small—550–600 facets—with a thick corneal lens and shallow retina. The retinula cell columns are each formed of six peripheral cells plus two central cells, a partially fused rhabdom, and dense pigment in two or three cell types. Upon adaptation from light to dark, the most striking photomechanical response is a proximal broadening of the cone cells, which results in a 38-fold increase in cross-sectional area of the aperture. While longitudinal rhabdom movement is small, microvillar diameters swell in response to light and contract in the dark. Irregularities of facet pattern and shape, and in ommatidial alignment were found, particularly towards eye margins. Three types of interommatidial sense organs on the eye surface are described, one of which has not been previously reported. An argument is presented to explain how the field of view and sensitivity are both apparently decreased in the acone eye by exposure to light.     

The evolution of sexually dimorphic earwig forceps: social interactions among adults of the toothed earwig, Vostox apicedentatus

Earwigs (Insecta, Dermaptera) are characterized by uniquelyelaborated cerci, commonly called forceps, the function of whichremains unclear. We studied intrasexual and intersexual interactionsin the laboratory to examine the context and pattern of forcepsuse in the toothed earwig. Vostox apictdenlatus (Caudell). Interactionsbetween pairs of earwigs were recorded in four social situations:(1) two males, (2) two males plus a virgin female, (3) two females,and (4) one male and one female. Forceps were used as both weaponsand display structures by males and females in all of thesesocial contexts. During pairwise male-male interactions, onemale clearly dominated the other male. Dominant males were moreactive and more likely to use their forceps in intrasexual interactionsthan were subordinate males. In interactions where there weretwo males and one female present, the male that dominated male-maleinteractions was able to maintain exclusive access to the female.There was no indication of active female choice during or aftercourtship. During intersexual interactions, only males usedtheir forceps during courtship. The behavioral repertoire involvingforceps was greater for males than for females, especially inintrasexual contests. There was no clear outcome of intrasexualinteractions among females. These results suggest that forcepsfunction mainly as weapons in male-male interactions and mayhave evolved, at least in part, as a result of sexual selection.Further research is required to test for female mate choiceand to separate the various mechanisms of sexual selection ifmate choice exists. Comparative studies are needed to determineif sexual selection was the original evolutionary mechanismleading to the development of these unusual structures or ifsexual selection is relegated to a secondary effect, leadingto the elaboration and sexualdimorphism of these structuresin selected groups of earwigs.     

Cadmium in Chinese coals: Abundance,distribution, occurrence,and environmental effects

Cadmium (Cd) in coals has attracted much attention due to its potential toxicity. In the present study, we reviewed up-to-date information on the abundance, distribution, and modes of occurrence of Cd in Chinese coals, as well as its environmental effects. With the 3110 sets of data rearranged, the arithmetic and weighted mean of Cd concentration in Chinese coals were calculated. Using coal reserves in individual province and coal-forming ages as weighting factors, the estimated average Cd abundances in Chinese coals are 0.25 mg/kg and 0.42 mg/kg, respectively. Variations in Cd coal abundances in different geographical locations, coal-forming ages, and coal ranks are taken into account. The Cd abundances in northern Chinese coals are significantly lower than those in the southern Chinese coals. Sulfides, especially sphalerite, are the most common Cd carriers in coals. As a semi-volatile element, Cd can be partially transformed into a volatilized form during highly thermal process, which could enrich surrounding fly ash. The combination of electrostatic precipitator and flue gas desulphurization is proved to be a better effective method for reducing emissions of Cd. Heavy loadings of Cd in environmental compartments due to anthropogenic activities have posed a great challenge to atmosphere–land–ocean systems.     

Sub-lethal effects of disturbance on a predatory net-spinning caddisfly

1. The sub-lethal effects of hydrologic disturbances on stream invertebrates are poorly understood, but integral to some models of how disturbances influence population and community dynamics. Carnivorous larvae of a net-spinning caddisfly, Plectrocnemia conspersa , have a strong predatory impact in some streams. Their silken nets, however, are vulnerable to high flow disturbance and the consequent destruction of nets could reduce predatory impacts and have life history consequences.
2. In a laboratory experiment, we manipulated the frequency of disturbances that destroyed the nets of P. conspersa , in the presence and absence of potential prey. Animals were housed individually and each trial lasted 8 days. We estimated net size, cumulative mass of silk produced, net allocation (net mass expressed as a proportion of body mass), per capita prey consumption and growth or mass loss of larvae.
3. In the absence of prey, increased disturbance frequency was accompanied by increased loss of body mass, a reduction of net size and an increase in the cumulative mass of silk produced. At the highest disturbance frequency, larvae eventually gave up producing nets. The ratio of net mass to body mass decreased with increasing disturbance, suggesting a trade-off in the allocation of resources, with a decreasing proportion of resources available for foraging. In the presence of prey, increased disturbance frequency was accompanied by a reduction in per capita prey consumption. Although foraging success offset the costs of silk production, growth rate decreased with increasing disturbance and could eventually lead to reduced body size and fecundity of adults.
4. These sub-lethal effects suggest that hydrologic disturbances could impose metabolic costs and reduce foraging efficiency of this predator. Thus, disturbances may reduce predator impact on prey populations and reduce predator population size without any direct mortality or loss of individuals.     

Scale dependent effects of predatory fish on stream benthos

In open predation experiments the effects of predators on prey densities can be influenced by predator consumption and by prey movements in to and out of experimental arenas. A published model predicts that the predator effects observed in such experiments are scale dependent over the scale range where there is a transition from movement control (of prey densities) to consumption control. The scale dependence follows from the assumption that per capita rate of emigration out of an experimental arena decreases with increasing arena size.
To test this model the effects of a small benthic fish ( Cottus gobio ) on densities of stream invertebrates was investigated in instream channels of different length (0.5, 2 and 8 m). The effect of fish predation was scale dependent for four prey taxa. For three of these taxa predator effects increased with experimental scale, which is in agreement with model predictions. However, this proved to be a case of making the right prediction for the wrong reason as the basic assumption of scale dependent emigration rate was not upheld. By analyzing the behaviour of the model, parameterized with emigration and consumption rates observed in the experimental channels, it was found that observed scale effects occurred because prey emigration in response to the predator treatment was modified by the experimental scale. Further analysis of the parameterized model suggested that the densities of most prey taxa were controlled by prey movements and not by consumption by the sculpins.     

Sexual selection and the allometry of earwig forceps

Summary Positive intraspecific allometry, the tendency for large individuals to have relatively larger morphological traits, is thought to be more likely for secondary sexual traits than naturally selected traits. This is because secondary sexual traits are often used to signal individual quality and positive allometry should arise where the costs and/or benefits of signalling are size dependent. Here we examine the allometric relationships between forceps length, a sexually selected trait and elytra length, a naturally selected trait, in 42 species of earwig. Both forceps and elytra showed positive allometry. However, the degree of allometry was greater for forceps as predicted. If allometry arises due to sexual selection we would predict a greater degree of allometry in species with more exaggerated secondary sexual traits. Across species, the degree of forcep allometry did increase with forcep exaggeration. The relevance of positive allometry to reliable signalling is discussed.     

RNA and protein synthesis in the earwig ovary

Cytochemical and autoradiographic studies on the ovaries of Labidura riparia indicate that the oöcyte is supplied with RNA synthesized in the nurse cell nucleus. There is no indication that the oöcyte synthesizes its own RNA. Neither DNA nor protein can be shown to enter the oöcyte from external sources. Although largely cytoplasmic, the incorporation of lysine into protein also localizes in the nucleolus of older oöcytes.