Stable isotope methods in biological and ecological studies of arthropods

This is an eclectic review and analysis of contemporary and promising stable isotope methodologies to study the biology and ecology of arthropods. It is augmented with literature from other disciplines, indicative of the potential for knowledge transfer. It is demonstrated that stable isotopes can be used to understand fundamental processes in the biology and ecology of arthropods, which range from nutrition and resource allocation to dispersal, food-web structure, predation, etc. It is concluded that falling costs and reduced complexity of isotope analysis, besides the emergence of new analytical methods, are likely to improve access to isotope technology for arthropod studies still further. Stable isotopes pose no environmental threat and do not change the chemistry or biology of the target organism or system. These therefore represent ideal tracers for field and ecophysiological studies, thereby avoiding reductionist experimentation and encouraging more holistic approaches. Considering (i) the ease with which insects and other arthropods can be marked, (ii) minimal impact of the label on their behaviour, physiology, and ecology, and (iii) environmental safety, we advocate more widespread application of stable isotope technology in arthropod studies and present a variety of potential uses

Stable isotope-mass spectrometric determination of semen transfer in malaria mosquitoes

The potential use of stable isotopes to study mosquito mating was investigated by tracing the fate of labelled semen into spermathecae. [13C]glucose was incorporated in the diet of the malaria mosquito Anopheles arabiensis. Treatments included labelling of either the larval water or adult sugar water, or a combination of both. After mating, `spiked' spermathecae were analysed for isotope ratios using mass spectrometry. Results demonstrated that spermathecae positive for semen could successfully be distinguished from empty ones or controls (i.e. filled with unlabelled semen) using the raw 13C values. Labelling during larval development and combined labelling of larvae and adults resulted in detectable values. The label persisted in spermathecae for up to 7 days after mating, and unlabelled sugar feeding of males labelled in the larval stage did not result in a detectable turnover of the semen label. There were no detrimental effects of the addition of labelled glucose on larval development and survival, adult size, male longevity and mating performance. We have proved that it is possible to label male mosquitoes and detect the semen label in females after insemination. This method offers great potential to study mating in mosquitoes and other insects and could prove useful in genetic control studies of medical or agricultural pest insects, with male mating success in the field as a critical verifiable indicator for a positive outcome of the intervention

DNA-based stable isotope probing enables the identification of active bacterial endophytes in potatoes.

* A (13)CO(2) (99 atom-%, 350 ppm) incubation experiment was performed to identify active bacterial endophytes in two cultivars of Solanum tuberosum, cultivars Desirée and Merkur. We showed that after the assimilation and photosynthetic transformation of (13)CO(2) into (13)C-labeled metabolites by the plant, the most directly active, cultivar-specific heterotrophic endophytic bacteria that consume these labeled metabolites can be identified by DNA stable isotope probing (DNA-SIP). * Density-resolved DNA fractions obtained from SIP were subjected to 16S rRNA gene-based community analysis using terminal restriction fragment length polymorphism analysis and sequencing of generated gene libraries. * Community profiling revealed community compositions that were dominated by plant chloroplast and mitochondrial 16S rRNA genes for the 'light' fractions of (13)CO(2)-incubated potato cultivars and of potato cultivars not incubated with (13)CO(2). In the 'heavy' fractions of the (13)CO(2)-incubated endophyte DNA, a bacterial 492-bp terminal restriction fragment became abundant, which could be clearly identified as Acinetobacter and Acidovorax spp. in cultivars Merkur and Desirée, respectively, indicating cultivar-dependent distinctions in (13)C-label flow. These two species represent two common potato endophytes with known plant-beneficial activities. * The approach demonstrated the successful detection of active bacterial endophytes in potato. DNA-SIP therefore offers new opportunities for exploring the complex nature of plant-microbe interactions and plant-dependent microbial metabolisms within the endosphere