Worker policing in the German wasp Vespula germanica

In some ants, bees, and wasps, workers kill or "police” male eggs laid by other workers in order to maintain the reproductive primacy of the queen. Kin selection theory predicts that multiple mating by the queen is one factor that can selectively favor worker policing. This is because when the queen is mated to multiple males, workers are more closely related to the queen's sons than to the sons of other workers. Earlier work has suggested that reproductive patterns in the German wasp Vespula germanica may contradict this theory, because in some colonies a large fraction of the adult males were inferred to be the workers' sons, despite the effective queen mating frequency being greater than 2 (2.4). In the present study, we reexamine the V. germanica case and show that it does support the theory. First, genetic analysis confirms that the effective queen mating frequency is high, 2.9, resulting in workers being more related to the queen's sons than to other workers' sons. Second, behavioral assays show that worker-laid eggs are effectively killed by other workers, despite worker-laid eggs having the same intrinsic viability as queen-laid ones. Finally, we estimate that approximately 58.4% of the male eggs but only 0.44% of the adult males are worker derived in queenright colonies, consistent with worker reproduction being effectively police

Identification and validation of housekeeping genes in brains of the desert locust Schistocerca gregaria under different developmental conditions

<p>Abstract</p> <p>Background</p> <p>To obtain reliable quantitative RT-PCR data, normalization relative to stable housekeeping genes is required. However, in practice, expression levels of 'typical' housekeeping genes have been found to vary between tissues and under different experimental conditions. To date, validation studies of reference genes in insects are extremely rare and have never been performed in locusts. In this study, putative housekeeping genes were identified in the desert locust, <it>Schistocerca gregaria </it>and two different software programs (geNorm and Normfinder) were applied to assess the stability of thesegenes.</p> <p>Results</p> <p>We have identified seven orthologs of commonly used housekeeping genes in the desert locust. The selected genes were the orthologs of actin, <it>EF1a, GAPDH, RP49, TubA1, Ubi</it>, and <it>CG13220</it>. By employing real time RT-PCR we have analysed the expression of these housekeeping genes in brain tissue of fifth instar nymphs and adults. In the brain of fifth instar nymphs geNorm indicated <it>Sg-EF1a</it>, <it>Sg-GAPDH </it>and <it>Sg-RP49 </it>as most stable genes, while Normfinder ranked <it>Sg-RP49</it>, <it>Sg-EF1a </it>and <it>Sg-ACT </it>as most suitable candidates for normalization. The best normalization candidates for gene expression studies in the brains of adult locusts were <it>Sg-EF1a, Sg-GAPDH </it>and <it>Sg-Ubi </it>according to geNorm, while Normfinder determined <it>Sg-GAPDH</it>, <it>Sg-Ubi </it>and <it>Sg-ACT </it>as the most stable housekeeping genes.</p> <p>Conclusion</p> <p>To perform transcript profiling studies on brains of the desert locust, the use of <it>Sg-RP49</it>, <it>Sg-EF1a </it>and <it>Sg-ACT </it>as reference genes is proposed for studies of fifth instar nymphs. In experiments with adult brains, however, the most preferred reference genes were <it>Sg-GAPDH</it>, <it>Sg-Ubi </it>and <it>Sg-EF1a</it>. These data will facilitate transcript profiling studies in desert locusts and provide a good starting point for the initial selection of genes for validation studies in other insects.</p

Reproduction and feeding in insects - the Allatotropin receptor in Tribolium castaneum and the takeout gene in Schistocerca gregaria.

The red flour beetle, Tribolium castaneum and the desert locust, Schistocerca gregaria are important pest insect species. They both can cause a lot of damage to human food supplies; especially locusts, that have the ability to undergo phase transition and can change into voracious swarms. Two of the possible methods to control pests, are to intervene with either feeding or reproduction. In the presented doctoral research, we explored several candidate genes involved in both reproduction and feeding in insects. We characterized a G- protein coupled receptor in T. castaneum that could be activated by the allatotropin-like peptide (ATL) of T. castaneum, as well as by allatotropins (ATs) of other insects, in a dose-dependent and reversible way. AT is particularly known to stimulate the juvenile hormone (JH) synthesis and release by the corpora allata (CA), to inhibit ion transport over larval gut epithelium and to be myostimulatory. The tissue distribution of the allatotropin receptor (ATR) in T. castaneum showed a remarkable male biased transcription pattern and highest levels were present in tissues related to reproduction. By means of an RNAi mediated knockdown of ATR, we confirmed these links to male reproduction, as ATR knockdown in males caused a decrease in progeny and a diminished male accessory gland (MAG) size. As these effects were also seen in a JH acid O-methyl-transferase (JHAMT, enzyme in JH synthesis) knockdown experiment in T. castaneum, this points to a link of ATR with JH synthesis. Recently, more and more studies point to JH production and a function of JH in the adult MAGs. Our study reinforces this theory and suggests an involvement of Trica-ATL in the regulation of JH in male reproduction. When we compared recently characterized allatotropin receptors, Aedes aegypti ATR and Tc-ATR were more alike in tissue distribution and activating ligands than the characterized Manduca sexta ATR. We suggest there are possibly two or more groups of ATRs in insects involved in the different functions linked to AT.To study the link between feeding and reproduction, we performed starvation and re-feeding experiments in the desert locust and compared relative gene transcription of several reproduction linked genes: Jhamt, JH epoxide hydrolase (jheh), at, allatostatin (ast), insulin related peptide (irp), ovary maturating parsin (omp) and adipokinetic hormone II (akh II). By starting starvation before onset of sexual maturation, the later was stopped and postponed to the period following re-feeding. Transcription of JH linked genes Jhamt, jheh, at and ast in control animals all showed a trend that is consistent with JH levels. JH production was already shown to decrease upon starvation. However, starvation had a decreasing effect on transcription of jheh (JH degradation function). We suggest that the lower JH titer during starvation is not due to JH degradation by JHEH. We showed that the effect of starvation onSg at and ast transcript levels was different in male and female, with at levels being influenced in males and ast in females. Previously in S. gregaria, no influence of these peptides was shown on the JH production by the CAs. However, as stated above, we also found several indications of JH involvement in the regulation of the MAGs reproductive functions. We propose an AT and AST influence on JH production but in organs other as the CA, probably MAGs in male and ovaries in females. The reduced jhamt and omp transcription in starved individuals was not restored after re-feeding. It can be suggested that both are responsible for the persistent effect of starvation on reproduction even under re-feeding conditions. Akh II transcription showed a peak upon starvation in females and a peak upon re-feeding in males. By BLAST search in a neural EST database with Drosophila Takeout (TO), we found 3 takeout (to) genes in S. gregaria. One form, Sg-to2, was characterized in detail. Sg-to2 transcript levels displayed a circadian rhythm similar to period and were decreased upon starvation. Transcription of Sg-to2 was highest in cuticular structures with epidermis, with highest levels in antennae and labial palps. This suggests a function in interaction with the environment by intervening in odorant perception. These structures are also involved in male courtship behavior and transcription was mainly male biased. In abdominal cuticle with epidermis a role for Sg-to2 in reproduction was suggested but this only in males. Knockdown of Sg-to2 in males caused a delay in mating. We showed that Sg-to2 is down regulated by knockdown of the sex determination gene fruitless (fru) but not vice versa, suggesting that Sg-to2 is downstream of fru. In non cuticular tissues, transcript level was highest in the AKH producing corpora cardiaca. Female Sg-to2 knockdown locusts ate more compared to control and male Sg-to2 knockdown locusts. We suggest, in similarity with results in Drosophila, a role for TO in energy homeostasis. We further propose TO interacts with AKH in energy mobilization during reproduction. Difference in Sg-to2 transcript levels between solitary and gregarious phases were only observed during starvation, suggesting a role in differentially coping with limited food availability of both phases. In conclusion our study gave more insight in the physiology of insects. These insights can hopefully contribute to improve future pest management strategies.nrpages: 213status: publishe

Developmental- and food-dependent foraging transcript levels in the desert locust

Drastic changes in the environment during a lifetime require developmental and physiological flexibility to ensure animal survival. Desert locusts, Schistocerca gregaria, live in an extremely changeable environment, which alternates between periods of rainfall and abundant food and periods of drought and starvation. In order to survive, locusts display an extreme form of phenotypic plasticity that allows them to rapidly cope with these changing conditions by converting from a cryptic solitarious phase to a swarming, voracious gregarious phase. To accomplish this, locusts possess different conserved mediators of phenotypic plasticity. Recently, attention has been drawn to the possible roles of protein kinases in this process. In addition to cyclic AMP-dependent protein kinase (PKA), also cyclic GMP-dependent protein kinase (PKG), which was shown to be involved in changes of food-related behavior in a variety of insects, has been associated with locust phenotypic plasticity. In this article, we study the transcript levels of the S. gregaria orthologue of the foraging gene that encodes a PKG in different food-related, developmental and crowding conditions. Transcript levels of the S. gregaria foraging orthologue are highest in different parts of the gut and differ between isolated and crowd-reared locusts. They change when the availability of food is altered, display a distinct pattern with higher levels after a moult and decrease with age during postembryonic development.status: publishe

Worker policing in the German wasp Vespula germanica

In some ants, bees, and wasps, workers kill or "police" male eggs laid by other workers in order to maintain the reproductive primacy of the queen. Kin selection theory predicts that multiple mating by the queen is one factor that can selectively favor worker policing. This is because when the queen is mated to multiple males, workers are more closely related to the queen's sons than to the sons of other workers. Earlier work has suggested that reproductive patterns in the German wasp Vespula germanica may contradict this theory, because in some colonies a large fraction of the adult males were inferred to be the workers' sons, despite the effective queen mating frequency being greater than 2 (2.4). In the present study, we reexamine the V. germanica case and show that it does support the theory. First, genetic analysis confirms that the effective queen mating frequency is high, 2.9, resulting in workers being more related to the queen's sons than to other workers' sons. Second, behavioral assays show that worker-laid eggs are effectively killed by other workers, despite worker-laid eggs having the same intrinsic viability as queen-laid ones. Finally, we estimate that approximately 58.4% of the male eggs but only 0.44% of the adult males are worker derived in queenright colonies, consistent with worker reproduction being effectively policed. Copyright 2008, Oxford University Press.

More than two decades of research on insect neuropeptide GPCRs: an overview

This review focuses on the state of the art on neuropeptide receptors in insects. Most of these receptors are G protein-coupled receptors (GPCRs) and are involved in the regulation of virtually all physiological processes during an insect's life. More than 20 years ago a milestone in invertebrate endocrinology was achieved with the characterization of the first insect neuropeptide receptor, i.e., the Drosophila tachykinin-like receptor. However, it took until the release of the Drosophila genome in 2000 that research on neuropeptide receptors boosted. In the last decade a plethora of genomic information of other insect species also became available, leading to a better insight in the functions and evolution of the neuropeptide signaling systems and their intracellular pathways. It became clear that some of these systems are conserved among all insect species, indicating that they fulfill crucial roles in their physiological processes. Meanwhile, other signaling systems seem to be lost in several insect orders or species, suggesting that their actions were superfluous in those insects, or that other neuropeptides have taken over their functions. It is striking that the deorphanization of neuropeptide GPCRs gets much attention, but the subsequent unraveling of the intracellular pathways they elicit, or their physiological functions are often hardly examined. Especially in insects besides Drosophila this information is scarce if not absent. And although great progress made in characterizing neuropeptide signaling systems, even in Drosophila several predicted neuropeptide receptors remain orphan, awaiting for their endogenous ligand to be determined. The present review gives a précis of the insect neuropeptide receptor research of the last two decades. But it has to be emphasized that the work done so far is only the tip of the iceberg and our comprehensive understanding of these important signaling systems will still increase substantially in the coming years.status: publishe