Andreas Martens

A field study of larval development in a dragonfly assemblage in African desert ponds (Odonata)

Aquatic animals distributed along a habitat-permanence gradient (HPG), differ in life history (Wellborn et al., 1996. Annual Revue of Ecology and Systematics 27: 337--363). Dragonflies that occur in hot arid regions often occur in temporary waters and consequently perform direct and rapid development. Dragonfly species of the Namibian desert do differ in their selection of habitats along the HPG and therefore may also differ in life cycle. Here, we attempt to monitor colonisation, larval growth and emergence in a temporary pond of known history. We studied the development of dragonfly species that laid eggs in artificial ponds constructed by us in March 2001. The assemblage consisted of species that originate from different habitats along the HPG. To obtain data on larval development we took samples from the ponds at 10-day intervals. Most species showed rapid development. By regressing the maximum sizes attained by larvae on each sampling date against time we estimated growth rates for five species and were thereby able to estimate that total duration of development from oviposition to emergence ranged between 38 and 70 days. Observation of first oviposition and first emergence for three of these species corroborated our estimates based on growth rate. Of few species, which laid eggs in the ponds no larvae or adults were found. For some this may have been the result of predation whereas others may not have grown fast enough to emerge before the ponds dried up. Our results indicate that dragonflies cannot recognise whether a pond will retain water long enough for full larval development and oviposit in waters that will not allow larval development.

Female aggregation in Platycypha caligata (odonata: chlorocyphidae): a tactic to evade male interference during oviposition

Abstract Females of the African damselfly Platycypha caligata (Selys) oviposit on barkless driftwood in streams. Territorial males perform conspicuous courtship displays at these sites. Approaching males can interrupt the oviposition and force the female to fly off. In this study, receptive females landed on perches near the oviposition site where tandem formation and copulation took place. Non-receptive females showed behavioural adaptations to repulse the males courtship and to evade further copulations. At locations with several potential oviposition sites most females aggregated at only a few. Ovipositions in groups lasted longer than those in solitary females. The presence of ovipositing females influenced other females in their choice of site. Approaching females preferred sites with already ovipositing individuals. Females forced to fly off by courting males tried to land near resident females again. Joining a group was advantageous, as solitary egg-laying individuals were intercepted more frequently by males than were females within groups. Group formation and the wing-spreading display of the courted female and her neighbours are interpreted as collective defence mechanisms against male interference.

Simultaneous determination of Cd and Fe in beans and soil of different regions of Brazil using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sampling.

A fast routine screening method for the simultaneous determination of cadmium and iron in bean and soil samples is proposed, using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sampling. The primary absorption line at 228.802 nm has been used for the determination of cadmium, and an adjacent secondary line, at 228.726 nm, for iron. Fourteen bean samples and 10 soil samples from nine states all over Brazil have been analyzed. The limits of detection (3 sigma, n = 10) were 2.0 microg kg(-1) for Cd and 4.5 mg kg(-1) for Fe. The relative standard deviation ranged from 4 to 7% for Cd and from 5 to 28% for Fe, which is usually acceptable for a screening method. The accuracy of the method has been confirmed by the analysis of two certified reference materials; the results were in agreement with the certified values at a 95% confidence interval.

Egg distribution, mate-guarding intensity and offspring characteristics in dragonflies (Odonata)

We studied how egg size, larval size and egg development time are related to oviposition site selection and mate guarding in a dragonfly assemblage of the Namib desert. Species that oviposited mainly in tandem flight (Pantala flavescens and Sympetrum fonscolombii) spread their eggs over several ponds, which we interpreted as spatial risk spreading. Other species (Orthetrum chrysostigma, Trithemis kirbyi, T. annulata and Crocothemis erythraea) performed noncontact guarding and localized their eggs, usually in a single pond, which we interpreted as distinct habitat selection. Because long oviposition durations increase the risk of disruption by rival males, we predicted that in species that localize their eggs to a distinct oviposition habitat the first-laid eggs of a clutch should be the largest, indicating high quality. Species that perform risk spreading should distribute large eggs randomly over all oviposition sites. We tested our hypothesis at artificial ponds using experimental manipulations of oviposition. In O. chrysostigma and T. kirbyi, egg size and larval size decreased significantly with order of laying, and the time to hatch was randomly distributed. As predicted, within the clutches of P. flavescens and S. fonscolombii, egg size was randomly distributed over a clutch and we found no trend of decrease in larval size or increase in the time to hatch in relation to order of laying.

Method development and optimization for the determination of selenium in bean and soil samples using hydride generation electrothermal atomic absorption spectrometry

The present investigation is the first part of an initiative to prepare a regional map of the natural abundance of selenium in various areas of Brazil, based on the analysis of bean and soil samples. Continuous-flow hydride generation electrothermal atomic absorption spectrometry (HG-ET AAS) with in situ trapping on an iridium-coated graphite tube has been chosen because of the high sensitivity and relative simplicity. The microwave-assisted acid digestion for bean and soil samples was tested for complete recovery of inorganic and organic selenium compounds (selenomethionine). The reduction of Se(VI) to Se(IV) was optimized in order to guarantee that there is no back-oxidation, which is of importance when digested samples are not analyzed immediately after the reduction step. The limits of detection and quantification of the method were 30 ng L(-1) Se and 101 ng L(-1) Se, respectively, corresponding to about 3 ng g(-1) and 10 ng g(-1), respectively, in the solid samples, considering a typical dilution factor of 100 for the digestion process. The results obtained for two certified food reference materials (CRM), soybean and rice, and for a soil and sediment CRM confirmed the validity of the investigated method. The selenium content found in a number of selected bean samples varied between 5.5±0.4 ng g(-1) and 1726±55 ng g(-1), and that in soil samples varied between 113±6.5 ng g(-1) and 1692±21 ng g(-1).

Egg deposition rates and duration of oviposition in Platycnemis pennipes (Pallas) (Insects: Odonata)

Platycnemis pennipes deposits eggs into plant tissue at or just below the water surface. On a number of different plant species egg deposition rate was found to be similar, while oviposition duration varied. Eggs were not always to be found in the substrate after a female had probed the substrate with her ovipositor. Actual oviposition took place only during longer stays.

Selenium status in preschool children receiving a Brazil nut–enriched diet

OBJECTIVEnThe Brazilian Amazon region has selenium (Se)-rich soil, which is associated with higher Se levels in populations fed locally grown produce. Brazil nuts are a major source of dietary Se and are included with meals offered to children enrolled in public preschool in Macapá. The aim of this study was to examine Se intake and status of these children.nnnMETHODSnThe Macapá group consisted of 41 children from a public preschool who received 15 to 30xa0g of Brazil nuts 3xa0d/wk. The control group included 88 children from the nearby city of Belém who did not receive Brazil nut-enriched meals. In both groups, school meals comprised ≥90% of the childrens total food consumption. Selenium was assessed using hydride generation quartz tube atomic absorption spectroscopy in plasma, erythrocytes, nails, hair and urine. Dietary intakes (macronutrients and Se) were evaluated using the duplicate-portion method.nnnRESULTSnBoth groups received inadequate intakes of energy and macronutrients. Selenium intake was excessive in both groups (155.30 and 44.40xa0μg/d, in Macapá and Belém, respectively). Intake was potentially toxic in Macapá on days when Brazil nuts were added to meals. Although biomarkers of Se exposure exceeded reference levels in the Macapá group, no clinical symptoms of Se overload (selenosis) were observed.nnnCONCLUSIONSnThe inclusion of Brazil nuts in school meals provided to children with already high dietary Se intakes increased Se levels and may result in an increased risk for toxicity. As selenosis is associated with some chronic diseases, we recommend continued monitoring of Se intake and status in this population.

For consistency's sake? A reply to Bybee et al.

1Ecology and Environmental Science, Halmstad University, Halmstad, Sweden, 2Institut für Geoökologie, Technische Universität Braunschweig, Braunschweig, Germany, 3Institut für Biologie und Schulgartenentwicklung, Pädagogische Hochschule Karlsruhe, Karlsruhe, Germany, 4Zoological Institute: Functional Morphology and Biomechanics, Kiel University, Kiel, Germany and 5Ecology and Evolutionary Biology Program, Department of Biology, University of Oklahoma, Norman, OK, U.S.A.

Critical species of Odonata in the Comoros, Seychelles, Mascarenes and other small western Indian Ocean islands

Abstract For the Odonata species known from islands in the western Indian Ocean - excluding Madagascar - comments on 33 species of conservation concern are given.

The feeding action of Forcipomyia paludis (Diptera: Ceratopogonidae), a parasite of Odonata imagines

Abstract Females of Forcipomyia paludis were studied microscopically during their feeding action on Odonata wings where they were mostly attached to main veins in the basal half of the wings. In some individuals rhythmic nodding of the head was noted. Conspicuously many midges lifted the abdominal tip every one or two minutes and from the anus fast growing gas bubbles appeared that burst after about half a second. We suppose that the insects, having punctured the hosts veins with their stout proboscis, sucked much air (as well as haemolymph) from the tracheae which they had to get rid of afterwards. From these observations, combined with further indications, it is inferred that F. paludis acts as a true parasite of Odonata and that the association is not only phoretic as previously assumed.