Different effects of paternal trans-generational immune priming on survival and immunity in step and genetic offspring

Paternal trans-generational immune priming, whereby fathers provide immune protection to offspring, has been demonstrated in the red flour beetle Tribolium castaneum exposed to the insect pathogen Bacillus thuringiensis. It is currently unclear how such protection is transferred, as in contrast to mothers, fathers do not directly provide offspring with a large amount of substances. In addition to sperm, male flour beetles transfer seminal fluids in a spermatophore to females during copulation. Depending on whether paternal trans-generational immune priming is mediated by sperm or seminal fluids, it is expected to either affect only the genetic offspring of a male, or also their step offspring that are sired by another male. We therefore conducted a double-mating experiment and found that only the genetic offspring of an immune primed male show enhanced survival upon bacterial challenge, while phenoloxidase activity, an important insect immune trait, and the expression of the immune receptor PGRP were increased in all offspring. This indicates that information leading to enhanced survival upon pathogen exposure is transferred via sperm, and thus potentially constitutes an epigenetic effect, whereas substances transferred with the seminal fluid could have an additional influence on offspring immune traits and immunological alertness.     

Intraspecific competition reduces niche width in experimental populations

Intraspecific competition is believed to drive niche expansion, because otherwise suboptimal resources can provide a refuge from competition for preferred resources. Competitive niche expansion is well supported by empirical observations, experiments, and theory, and is often invoked to explain phenotypic diversification within populations, some forms of speciation, and adaptive radiation. However, some foraging models predict the opposite outcome, and it therefore remains unclear whether competition will promote or inhibit niche expansion. We conducted experiments to test whether competition changes the fitness landscape to favor niche expansion, and if competition indeed drives niche expansion as expected. Using Tribolium castaneum flour beetles fed either wheat (their ancestral resource), corn (a novel resource) or mixtures of both resources, we show that fitness is maximized on a mixed diet. Next, we show that at higher population density, the optimal diet shifts toward greater use of corn, favoring niche expansion. In stark contrast, when beetles were given a choice of resources, we found that competition caused niche contraction onto the ancestral resource. This presents a puzzling mismatch between how competition alters the fitness landscape, versus competition's effects on resource use. We discuss several explanations for this mismatch, highlighting potential reasons why optimality models might be misleading.     

不同地区转Bt基因抗虫水稻稻谷对赤拟谷盗生长发育的影响

为了明确来自湖北武穴、孝感、随州3个不同地区的转cry1Ab/cry1Ac、cry2A、cry1C基因明恢63(分别命名为TT51、T2A-1和T1C-19)对赤拟谷盗Tribolium castaneumHerbst生长发育的影响,在室内以不同的转Bt基因稻谷继代饲养赤拟谷盗6代,结果表明:各处理赤拟谷盗的卵期3～4d,卵孵化率85%～100%,幼虫期22～27d,化蛹率85%～97%,蛹期6～7d,百蛹重0.25～0.31g,性比0.8～1.4,羽化率82%～97%,产卵前期5～7d。不同抗虫转基因水稻对赤拟谷盗各发育历期及生命表参数没有显著的影响,同一转基因事件,没有因为种植地区的不同造成对赤拟谷盗生长发育的差异。3种Bt蛋白在继代饲养的赤拟谷盗幼虫体内检测均呈阳性反应,但积累量很小,继代饲养后,没有发现在赤拟谷盗体内明显的累积。     

Predicted versus expressed adipokinetic hormones, and other small peptides from the corpus cardiacum-corpus allatum: a case study with beetles and moths

This mass spectrometric study confines itself to peptide masses in the range of 500-1500Da. Adipokinetic hormones (AKHs) that are predicted from the genome of the red flour beetle, Tribolium castaneum, and the silk moth, Bombyx mori, are shown to exist as expressed peptides in the corpora cardiaca (CC) of the respective species as evidenced by various mass spectrometric methods. Additionally, some related species were included in this study, such as the tenebrionid beetles Tribolium brevicornis and Tenebrio molitor, as well as the moths Spodoptera frugiperda, Spodoptera littoralis, Mamestra brassicae and Lacanobia oleracea, to investigate whether AKH peptides are structurally conserved in the same genus or family. Interestingly, the AKH peptide of T. brevicornis is identical to that of T. molitor but not to the ones of its close relative T. castaneum. Moreover, other peptides in T. brevicornis, such as various FXPRL amides (=pyrokinins), also match the complement in T. molitor but differ from those in T. castaneum. All the CC of beetles lacked the signal for the mass of the peptide corazonin. All moths have the nonapeptide Manse-AKH expressed in their CC. In addition, whereas the silk moth has the decapeptide Bommo-AKH as a second peptide, all other moths (all noctuids) express the decapeptide Helze-HrTH. In M. brassicae and L. oleracea a novel amidated Gly-extended Manse-AKH is found as a possible third AKH. The noctuid moth species also all express the same FLRF amide-I, corazonin, and a group-specific isoform of a gamma-PGN-(=gamma-SGNP) peptide. In L. oleracea, however, the latter peptide has a novel sequence which is reported for the first time, and the peptide is code-named Lacol-PK.     

Larval RNAi in Drosophila?

RNA interference (RNAi) has become a common method of gene knockdown in many model systems. To trigger an RNAi response, double-stranded RNA (dsRNA) must enter the cell. In some organisms such as Caenorhabditis elegans, cells can take up dsRNA from the extracellular environment via a cellular uptake mechanism termed systemic RNAi. However, in the fruit fly Drosophila melanogaster, it is widely believed that cells are unable to take up dsRNA, although there is little published data to support this claim. In this study, we set out to determine whether this perception has a factual basis. We took advantage of traditional Gal4/upstream activation sequence (UAS) transgenic flies as well as the mosaic analysis with a repressible cell marker (MARCM) system to show that extracellular injection of dsRNA into Drosophila larvae cannot trigger RNAi in most Drosophila tissues (with the exception of hemocytes). Our results show that this is not due to a lack of RNAi machinery in these tissues as overexpression of dsRNA inside the cells using hairpin RNAs efficiently induces an RNAi response in the same tissues. These results suggest that, while most Drosophila tissues indeed lack the ability to uptake dsRNA from the surrounding environment, hemocytes can initiate RNAi in response to extracellular dsRNA. We also examined another insect, the red flour beetle Tribolium castaneum, which has been shown to exhibit a robust systemic RNAi response. We show that virtually all Tribolium tissues can respond to extracellular dsRNA, which is strikingly different from the situation in Drosophila. Our data provide specific information about the tissues amenable to RNAi in two different insects, which may help us understand the molecular basis of systemic RNAi.     

TGFβ signaling in Tribolium: vertebrate-like components in a beetle

The cytokines of the TGFβ superfamily are highly conserved in evolution and elicit a diverse range of cellular responses in all metazoa. In Drosophila, the signaling pathways of the two TGFβ subfamilies, Activins and Bone Morphogenetic Proteins (BMPs), have been well studied. To address the question of whether the findings from Drosophila are representative of insects in general, we analyzed the components of TGFβ-signaling present in the genome of the beetle Tribolium castaneum. We were able to identify orthologs of the BMPs Decapentaplegic and Glass bottom boat, of the Activins Activinβ and Dawdle, as well as orthologs of the less well-known ligands Myoglianin and Maverick, together with orthologs of all TGFβ receptors and cytoplasmic signal transducers present in Drosophila. This indicates that the diversity of TGFβ signaling components is generally well conserved between Drosophila and Tribolium. However, the genome of the beetle—and of the bee Apis mellifera—lacks an ortholog of the Drosophila BMP Screw but does contain a vertebrate-like BMP10 homolog which is not found in Drosophila. Concerning BMP inhibitors, Tribolium displays an even more vertebrate-like ensemble of components. We found two orthologs of the vertebrate DAN family, Dan and Gremlin, and show embryonic expression of a vertebrate-like BAMBI ortholog, all of which are absent in Drosophila. This suggests that Tribolium might have retained a more ancestral composition of TGFβ signaling components and that TGFβ signaling underwent considerable change in the Drosophila lineage. Tribolium is an excellent model to study the function of these ancestral signaling components in insects. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The influence of the ability to disperse on generation length and population size in the flour beetle, Tribolium castaneum

Abstract.

• 1 In Tribolium castaneum Herbst, in which dispersal is genetically determined, it is possible to select for strains that are characterized by high and low dispersal, High dispersal (HD) beetles are better adapted than low dispersal (LD) beetles for colonization, as can be seen from differences that exist between the two groups with regard to several life-history parameters.
• 2 Comparisons were made between the dynamics of seventy-two HD and seventy-two LD populations. Generation length in HD populations was significantly shorter than in LD populations. After 9¹/₂ weeks, in open treatments (from which dispersal away from the set was allowed), HD populations had more beetles than LD populations, whereas in closed treatments (from which dispersal away from the set was not allowed) the opposite was true.
• 3 These findings may explain the maintenance of the genetic variability of dispersal behaviour in natural populations of T.castmeurn.

     

Maternal effect of a hybrid inviability gene in Tribolium castaneum

The Tribolium castaneum hybrid inviability gene, H, was selectively introgressed into a genetic background lacking H through serial paternal backcrosses. This revealed a poor viability phenotype (partial paralysis and poor control of the limbs, referred to as tremor) not present in the parent strains. Tremor cosegregated with H, but was expressed only when transmitted paternally and only when H was not also present maternally. The inferred maternal, self‐suppressive effect of H may explain nonreciprocal incompatibilty previously observed between H and H‐incompatible strains. This revised version was published online in July 2006 with corrections to the Cover Date.