Direct Parental (DIPA) CRISPR in the jewel wasp, Nasonia vitripennis

While clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 technology has demonstrated remarkable promise as a gene-editing tool, its application in certain insects, such as the jewel wasp, Nasonia vitripennis, has been hindered by a lack of a tractable method for reagent delivery. Direct Parental (DIPA-) CRISPR recently emerged as a facile way to induce gene lesions because it involves adult injection with commercially available Cas9-sgRNA with no helper reagent. However, DIPA-CRISPR has so far been tested in only a few insects. Here, we have assessed the amenability of DIPA-CRISPR in N. vitripennis by targeting two eye pigmentation genes, cinnabar and vermilion, which function in the ommochrome pathway. Successful generation of lesions in both genes demonstrated the functionality of DIPA-CRISPR in N. vitripennis and its potential application to other genes, thereby expanding the range of insects suitable for this method. We varied two parameters, Cas9-sgRNA concentration and injection volume, to determine optimal injection conditions. We found that the larger injection volume coupled with either higher or lower reagent concentration was needed for consistent mutation production. However, DIPA-CRISPR yields an overall low mutation rate in N. vitripennis when compared to other tested insects, a characteristic that may be attributed to a proportionally low vitellogenic import efficiency in the jewel wasp. We discuss different factors that may be considered in determining when DIPA-CRISPR may be preferable over other reagent delivery methods.

Time measurement in insect photoperiodism: external and internal coincidence

The identity and nature of the photoperiodic photoreceptors are now quite well known, as is the nature of the endocrine regulation of the resulting diapauses. The central problem of time measurement-how the photoperiodic clock differentiates long from short days-however, is still obscure, known only from whole-animal experiments and abstract models, although it is clearly a function of the insect circadian system. This review describes some of these experiments in terms of oscillator entrainment and two widely applicable photoperiodic clock models, external and internal coincidence, mainly using data from experiments on flesh flies (Sarcophaga spp) and the parasitic wasp, Nasonia vitripennis.

Epigenetics and seasonal timing in animals: a concise review

Seasonal adaptation in animals is a complex process that involves genetic, epigenetic, and environmental factors. The present review explores recent studies on epigenetic mechanisms implicated in seasonal adaptation in animals. The review is divided into three main sections, each focusing on a different epigenetic mechanism: DNA methylation, histone modifications, and non-coding RNA. Additionally, the review delves into the current understanding of how these epigenetic factors contribute to the regulation of circadian and seasonal cycles. Understanding these molecular mechanisms provides the first step in deciphering the complex interplay between genetics, epigenetics, and the environment in driving seasonal adaptation in animals. By exploring these mechanisms, a better understanding of how animals adapt to changing environmental conditions can be achieved.

Testing for variation in photoperiodic plasticity in a butterfly: Inconsistent effects of circadian genes between geographic scales

The genetic components of the circadian clock have been implicated as involved in photoperiodic regulation of winter diapause across various insect groups, thereby contributing to adaptation to adverse seasonal conditions. So far, the effects of within-population variation in these genes have not been well explored. Here, we present an experimental test of the effects of within-population variation at two circadian genes, timeless and period, on photoperiodic responses in the butterfly Pararge aegeria. While nonsynonymous candidate SNPs in both of these genes have previously shown to be associated with diapause induction on a between-population level, in the present experiment no such effect was found on a within-population level. In trying to reconcile these results, we examine sequence data, revealing considerable, previously unknown protein-level variation at both timeless and period across Scandinavian populations, including variants unique to the population studied here. Hence, we hypothesize that these variants may counteract the previously observed diapause-averting effect of the candidate SNPs, possibly explaining the difference in results between the experiments. Whatever the cause, these results highlight how the effects of candidate SNPs may sometimes vary across genetic backgrounds, which complicates evolutionary interpretations of geographic patterns of genetic variation.

Effects of polyploidization and their evolutionary implications are revealed by heritable polyploidy in the haplodiploid wasp Nasonia vitripennis

Recurrent polyploidization occurred in the evolutionary history of most Eukaryota. However, how neopolyploid detriment (sterility, gigantism, gene dosage imbalances) has been overcome and even been bridged to evolutionary advantage (gene network diversification, mass radiation, range expansion) is largely unknown, particularly for animals. We used the parasitoid wasp Nasonia vitripennis, a rare insect system with heritable polyploidy, to begin addressing this knowledge gap. In Hymenoptera the sexes have different ploidies (haploid males, diploid females) and neopolyploids (diploid males, triploid females) occur for various species. Although such polyploids are usually sterile, those of N. vitripennis are reproductively capable and can even establish stable polyploid lines. To assess the effects of polyploidization, we compared a long-established polyploid line, the Whiting polyploid line (WPL) and a newly generated transformer knockdown line (tKDL) for fitness traits, absolute gene expression, and cell size and number. WPL polyploids have high male fitness and low female fecundity, while tKDL polyploids have poor male mate competition ability and high fertility. WPL has larger cells and cell number reduction, but the tKDL does not differ in this respect. Expression analyses of two housekeeping genes indicated that gene dosage is linked to sex irrespective of ploidy. Our study suggests that polyploid phenotypic variation may explain why some polyploid lineages thrive and others die out; a commonly proposed but difficult-to-test hypothesis. This documentation of diploid males (tKDL) with impaired competitive mating ability; triploid females with high fitness variation; and hymenopteran sexual dosage compensation (despite the lack of sex chromosomes) all challenges general assumptions on hymenopteran biology. We conclude that polyploidization is dependent on the duplicated genome characteristics and that genomes of different lines are unequally suited to survive diploidization. These results demonstrate the utility of N. vitripennis for delineating mechanisms of animal polyploid evolution, analogous to more advanced polyploid plant models.

Ability of a selfish B chromosome to evade genome elimination in the jewel wasp, Nasonia vitripennis

B chromosomes are non-essential, extra chromosomes that can exhibit transmission-enhancing behaviors, including meiotic drive, mitotic drive, and induction of genome elimination, in plants and animals. A fundamental but poorly understood question is what characteristics allow B chromosomes to exhibit these extraordinary behaviors. The jewel wasp, Nasonia vitripennis, harbors a heterochromatic, paternally transmitted B chromosome known as paternal sex ratio (PSR), which causes complete elimination of the sperm-contributed half of the genome during the first mitotic division of fertilized embryos. This genome elimination event may result from specific, previously observed alterations of the paternal chromatin. Due to the haplo-diploid reproduction of the wasp, genome elimination by PSR causes female-destined embryos to develop as haploid males that transmit PSR. PSR does not undergo self-elimination despite its presence with the paternal chromatin until the elimination event. Here we performed fluorescence microscopic analyses aimed at understanding this unexplained property. Our results show that PSR, like the rest of the genome, participates in the histone-to-protamine transition, arguing that PSR does not avoid this transition to escape self-elimination. In addition, PSR partially escapes the chromatin-altering activity of the intracellular bacterium, Wolbachia, demonstrating that this ability to evade chromatin alteration is not limited to PSR's own activity. Finally, we observed that the rDNA locus and other unidentified heterochromatic regions of the wasp's genome also seem to evade chromatin disruption by PSR, suggesting that PSR's genome-eliminating activity does not affect heterochromatin. Thus, PSR may target an aspect of euchromatin to cause genome elimination.

Circadian Activity and Clock Genes in Pachycrepoideus vindemmiae: Implications for Field Applications and Circadian Clock Mechanisms of Parasitoid Wasps

Despite the importance of circadian rhythms in insect behavior, our understanding of circadian activity and the molecular oscillatory mechanism in parasitoid wasp circadian clocks is limited. In this study, behavioral activities expected to be under the control of the endogenous circadian system were characterized in an ectoparasitoid wasp, Pachycrepoideus vindemmiae. Most adults exhibited emergence between late night and early morning, while mating only occurred during the daytime, with a peak at midday. Oviposition had three peaks in the early morning, late day, or early night and late night. Additionally, we identified eight putative clock genes from P. vindemmiae. The quantitative PCR (qPCR) results indicate that most clock genes showed significant rhythmic expressions. Our comparative analysis of clock genes in P. vindemmiae and 43 other parasitoid wasps revealed that none of the wasps possessed the timeless and cry1 genes commonly found in some other insect species, suggesting that the circadian clock system in parasitoid wasps is distinct from that in other non-Hymenoptera insects such as Drosophila. Thus, this study attempted to build the first hypothetical circadian clock model for a parasitoid wasp, thus generating hypotheses and providing a platform for the future functional characterization of P. vindemmiae clock genes as well as those of other parasitoid wasps. Finally, these findings on P. vindemmiae circadian activity will aid the development of effective field release programs for biological control, which can be tested under field conditions.

Circadian clock genes and photoperiodic diapause in the moth Sesamia nonagrioides

Insects, like most organisms, have an internal circadian clock that oscillates with a daily rhythmicity, and a timing mechanism (photoperiodic clock) that mediates seasonal events, including diapause. It has been argued that there is a connection between the two clocks. The Mediterranean corn stalk borer moth, Sesamia nonagrioides, undergoes facultative diapause governed by photoperiod. To obtain clues to the link between the molecular mechanism of circadian and photoperiod clocks, we cloned and investigated the expression profiles of the clock genes Snper, Sntim, Sncyc and Sncry1 in the aforementioned moth species. Our previous results suggested that these genes might be implicated in the regulation of the diapause programming in S. nonagrioides. Here we studied the expression patterns of these four clock genes in larvae reared under abnormal non-24 h light-dark cycles (L10:D62 and L10:D14:L10:D62) in order to assess whether disruption of circadian clock would have any effect in the photoperiodic regulation of diapause. In the L10:D14:L10:D62 cycle abnormal expression patterns of the Sntim/Sncry1 and Snper/Sncyc, pairs were found, compared to normal 24 h light-dark photoperiods suggesting that individual clock genes are acting independently in the molecular diapause program of S. nonagrioides. Photoperiod therefore appears to be the crucial signal for the regulation of these four genes.

Circadian rhythm entrainment of the jewel wasp, Nasonia vitripennis, by antagonistic interactions of multiple spectral inputs

Circadian light entrainment in some insects is regulated by blue-light-sensitive cryptochrome (CRY) protein that is expressed in the clock neurons, but this is not the case in hymenopterans. The hymenopteran clock does contain CRY, but it appears to be light-insensitive. Therefore, we investigated the role of retinal photoreceptors in the photic entrainment of the jewel wasp Nasonia vitripennis. Application of monochromatic light stimuli at different light intensities caused phase shifts in the wasp's circadian activity from which an action spectrum with three distinct peaks was derived. Electrophysiological recordings from the compound eyes and ocelli revealed the presence of three photoreceptor classes, with peak sensitivities at 340 nm (ultraviolet), 450 nm (blue) and 530 nm (green). An additional photoreceptor class in the ocelli with sensitivity maximum at 560-580 nm (red) was found. Whereas a simple sum of photoreceptor spectral sensitivities could not explain the action spectrum of the circadian phase shifts, modelling of the action spectrum indicates antagonistic interactions between pairs of spectral photoreceptors, residing in the compound eyes and the ocelli. Our findings imply that the photic entrainment mechanism in N. vitripennis encompasses the neural pathways for measuring the absolute luminance as well as the circuits mediating colour opponency.

Nasonia-microbiome associations: a model for evolutionary hologenomics research

In recent years, with the development of microbial research technologies, microbiota research has received widespread attention. The parasitoid wasp genus Nasonia is a good model organism for studying insect behavior, development, evolutionary genetics, speciation, and symbiosis. This review describes key advances and progress in the field of the Nasonia-microbiome interactions. We provide an overview of the advantages of Nasonia as a model organism for microbiome studies, list research methods to study the Nasonia microbiome, and discuss recent discoveries in Nasonia microbiome research. This summary of the complexities of Nasonia-microbiome relationships will help to contribute to a better understanding of the interactions between animals and their microbiomes and establish a clear research direction for Nasonia-microbiome interactions in the future.

Molecular Mechanisms of Winter Survival

Winter provides many challenges for insects, including direct injury to tissues and energy drain due to low food availability. As a result, the geographic distribution of many species is tightly coupled to their ability to survive winter. In this review, we summarize molecular processes associated with winter survival, with a particular focus on coping with cold injury and energetic challenges. Anticipatory processes such as cold acclimation and diapause cause wholesale transcriptional reorganization that increases cold resistance and promotes cryoprotectant production and energy storage. Molecular responses to low temperature are also dynamic and include signaling events during and after a cold stressor to prevent and repair cold injury. In addition, we highlight mechanisms that are subject to selection as insects evolve to variable winter conditions. Based on current knowledge, despite common threads, molecular mechanisms of winter survival vary considerably across species, and taxonomic biases must be addressed to fully appreciate the mechanistic basis of winter survival across the insect phylogeny.

Seasonal Adaptation: Geographic Photoperiod-Temperature Patterns Explain Genetic Variation in the Common Vole Tsh Receptor

The vertebrate photoperiodic neuroendocrine system uses the photoperiod as a proxy to time the annual rhythms in reproduction. The thyrotropin receptor (TSHR) is a key protein in the mammalian seasonal reproduction pathway. Its abundance and function can tune sensitivity to the photoperiod. To investigate seasonal adaptation in mammals, the hinge region and the first part of the transmembrane domain of the Tshr gene were sequenced for 278 common vole (Microtus arvalis) specimens from 15 localities in Western Europe and 28 localities in Eastern Europe. Forty-nine single nucleotide polymorphisms (SNPs; twenty-two intronic and twenty-seven exonic) were found, with a weak or lack of correlation with pairwise geographical distance, latitude, longitude, and altitude. By applying a temperature threshold to the local photoperiod-temperature ellipsoid, we obtained a predicted critical photoperiod (pCPP) as a proxy for the spring onset of local primary food production (grass). The obtained pCPP explains the distribution of the genetic variation in Tshr in Western Europe through highly significant correlations with five intronic and seven exonic SNPs. The relationship between pCPP and SNPs was lacking in Eastern Europe. Thus, Tshr, which plays a pivotal role in the sensitivity of the mammalian photoperiodic neuroendocrine system, was targeted by natural selection in Western European vole populations, resulting in the optimized timing of seasonal reproduction.

Characterizing the relative abundance of circadian transcription factors in diapausing and nondiapausing Northern house mosquitoes

The Northern house mosquito (Culex pipiens) is a major vector of West Nile virus. To survive harsh conditions in winter adult females of Cx. pipiens enter a state of arrested reproductive development called diapause. Diapause is triggered by the short daylengths of late summer and early fall. The methods by which Cx. pipiens measures daylength are still unknown. However, it is suspected that clock genes, which provide information on daylength, may also regulate diapause. The proteins produced by these genes often cycle in abundance throughout the day in diapausing and nondiapausing insects. Two clock genes suspected to control diapause are cycle (cyc) and Par domain protein1 (Pdp1) as they encode circadian transcription factors that may regulate genes that are involved in diapause. Using Western blotting we measured the relative protein abundance of CYC and PDP1 throughout the day in the whole bodies and the heads of Cx. pipiens reared under either long-day, diapause-averting conditions or short-day, diapause-inducing conditions. We found that in whole bodies there was no significant oscillation of CYC or PDP1 abundance in both long day and short day-reared mosquitoes. In the heads of long day-reared mosquitoes both CYC and PDP1 cycled. In contrast, only PDP1 abundance showed diel differences in abundance in the heads of short day-reared mosquitoes. These data bring us one step closer to understanding the role that CYC and PDP1 may play in regulating diapause and other biological processes.

Juvenile hormone as a causal factor for maternal regulation of diapause in a wasp

Most temperate multivoltine insects enter diapause, a hormonally controlled developmental suspension, in response to seasonal photoperiodic and/or thermal cues. Some insect species exhibit maternal regulation of diapause in which developmental trajectories of the offspring are determined by mothers in response to environmental cues that the mother received. Although maternally regulated diapause is common among insects, the maternal endocrinological mechanisms are largely veiled. To approach this issue, we used the jewel wasp Nasonia vitripennis, which produces non-diapause-destined offspring under long days and diapause-destined offspring under short days or low temperatures. Comparative transcriptomics of these wasps revealed possible involvement of the juvenile hormone (JH) biosynthetic cascade in maternal diapause regulation. The expression of juvenile hormone acid O-methyltransferase (jhamt) was typically downregulated in short-day wasps, and this was reflected by a reduction in haemolymph JH concentrations. RNAi targeted at jhamt reduced haemolymph JH concentration and induced wasps to produce diapause-destined offspring even under long days. In addition, topical application of JH suppressed the production of diapause-destined offspring under short days or low temperatures. These results indicate that diapause in N. vitripennis is determined by maternal jhamt expression and haemolymph JH concentration in response to day length. We therefore report a novel role for JH in insect seasonality.

Local adaptation of life cycles in a butterfly is associated with variation in several circadian clock genes

Many insects exhibit geographical variation in voltinism, the number of generations produced per year. This includes high-latitude species in previously glaciated areas, meaning that divergent selection on life cycle traits has taken place during or shortly after recent colonization. Here, we use a population genomics approach to compare a set of nine Scandinavian populations of the butterfly Pararge aegeria that differ in life cycle traits (diapause thresholds and voltinism) along both north-south and east-west clines. Using a de novo-assembled genome, we reconstruct colonization histories and demographic relationships. Based on the inferred population structure, we then scan the genome for candidate loci showing signs of divergent selection potentially associated with population differences in life cycle traits. The identified candidate genes include a number of components of the insect circadian clock (timeless, timeless2, period, cryptochrome and clockwork orange). Most notably, the gene timeless, which has previously been experimentally linked to life cycle regulation in P. aegeria, is here found to contain a novel 97-amino acid deletion unique to, and fixed in, a single population. These results add to a growing body of research framing circadian gene variation as a potential mechanism for generating local adaptation of life cycles.

Photoperiodic Response in the Pars Intercerebralis Neurons, Including Plast-MIP Neurons, in the Brown-Winged Green Bug, Plautia stali

Many insects in temperate regions avoid environmental adversity for reproduction, and thus enter reproductive diapause according to photoperiod. This reproductive diapause is induced by inhibition of juvenile hormone biosynthesis in the corpus allatum. Some neuropeptides that have an effect on juvenile hormone biosynthesis have been detected in insect brains. Thus, the reproductive diapause may be photoperiodically regulated by these juvenile hormones-controlling neuropeptides. However, there is limited understanding of how the neurons expressing these neuropeptides respond to the photoperiod and control the peptide release accordingly. Here, we performed electrophysiological analyses in the pars intercerebralis (PI) of Plautia stali, where juvenile hormone inhibitory neuropeptides, Plautia stali myoinhibitory peptides (Plast-MIPs) are expressed. We found that the large neurons in the PI showed very high firing activity under diapause-inducing short day conditions. Neurotracer staining revealed that all recorded neurons projected to the nervus corporis cardiaci 1, which is known to be connected to the corpus cardiacum-corpus allatum complex. Finally, we determined how many of the large PI cells expressed Plast-MIP by single cell reverse transcription PCR. About half of large PI neurons coexpressed Plast-Mip and other neuropeptides, Diuretic hormone 44 and insulin-like peptide 1. The remaining cells only expressed Diuretic hormone 44 and insulin-like peptide 1. The present results suggested that large PI neurons, including Plast-MIP neurons, have enhanced activity under short day conditions, which may increase Plast-MIP release to the corpus cardiacum-corpus allatum complex and thus contribute to reproductive diapause.

Oviposition-promoting pars intercerebralis neurons show period-dependent photoperiodic changes in their firing activity in the bean bug

Animals show photoperiodic responses in physiology and behavior to adapt to seasonal changes. Recent genetic analyses have demonstrated the significance of circadian clock genes in these responses. However, the importance of clock genes in photoperiodic responses at the cellular level and the physiological roles of the cellular responses are poorly understood. The bean bug Riptortus pedestris shows a clear photoperiodic response in its reproduction. In the bug, the pars intercerebralis (PI) is an important brain region for promoting oviposition. Here, we analyzed the role of the photoperiodic neuronal response and its relationship with clock genes, focusing on PI neurons. Large PI neurons exhibited photoperiodic firing changes, and high firing activities were primarily found under photoperiodic conditions suitable for oviposition. RNA interference-mediated knockdown of the clock gene period abolished the photoperiodic response in PI neurons, as well as the response in ovarian development. To clarify whether the photoperiodic response in the PI was dependent on ovarian development, we performed an ovariectomy experiment. Ovariectomy did not have significant effects on the firing activity of PI neurons. Finally, we identified the output molecules of the PI neurons and analyzed the relevance of the output signals in oviposition. PI neurons express multiple neuropeptides-insulin-like peptides and diuretic hormone 44-and RNA interference of these neuropeptides reduced oviposition. Our results suggest that oviposition-promoting peptidergic neurons in the PI exhibit a circadian clock-dependent photoperiodic firing response, which contributes to the photoperiodic promotion of oviposition.

Courtship rhythm in Nasonia vitripennis is affected by the clock gene period

The clock gene period (per) is a regulator of circadian rhythms but may also play a role in the regulation of ultradian rhythms, such as insect courtship. Males of the parasitoid wasp Nasonia vitripennis court females by performing series of head movements (‘head-nods’) and wing vibrations within repeated cycles. The pattern of cycle duration and head-nod number is species-specific and has a genetic basis. In this study, the possible involvement of per in regulating Nasonia courtship rhythms was investigated in a southern and northern European strain that differ in number and timing of courtship components. Knockdown of per via RNA interference (RNAi) resulted in a shortening of the circadian free running period (tau) in constant darkness (DD), and increased both the cycle duration and the number of head-nods per cycle in both strains. These results point at a role of per in the regulation of ultradian rhythms and male courtship behaviour of N. vitripennis and may contribute to resolving the controversy about the role of per in insect courtship behaviour.

A chimeric gene paternally instructs female sex determination in the haplodiploid wasp Nasonia

Various primary signals direct insect sex determination. In hymenopteran insects, the presence of a paternal genome is needed to initiate female development. When absent, uniparental haploid males develop. We molecularly and functionally identified the instructor sex-determination gene, wasp overruler of masculinization (wom), of the haplodiploid wasp Nasonia vitripennis This gene contains a P53-like domain coding region and arose by gene duplication and genomic rearrangements. Maternal silencing of wom results in male development of haploid embryos. Upon fertilization, early zygotic transcription from the paternal wom allele is initiated, followed by a timely zygotic expression of transformer (tra), leading to female development. Wom is an instructor gene with a parent-of-origin effect in sex determination.

Germline mutagenesis of Nasonia vitripennis through ovarian delivery of CRISPR-Cas9 ribonucleoprotein

CRISPR/Cas9 gene editing is a powerful technology to study the genetics of rising model organisms, such as the jewel wasp Nasonia vitripennis. However, current methods involving embryonic microinjection of CRISPR reagents are challenging. Delivery of Cas9 ribonucleoprotein into female ovaries is an alternative that has only been explored in a small handful of insects, such as mosquitoes, whiteflies and beetles. Here, we developed a simple protocol for germline gene editing by injecting Cas9 ribonucleoprotein in adult N. vitripennis females using either ReMOT control (Receptor-Mediated Ovary Transduction of Cargo) or BAPC (Branched Amphiphilic Peptide Capsules) as ovary delivery methods. For ReMOT Control we used the Drosophila melanogaster-derived peptide 'P2C' fused to EGFP to visualize the ovary delivery, and fused to Cas9 protein for gene editing of the cinnabar gene using saponin as an endosomal escape reagent. For BAPC we optimized the concentrations of protein, sgRNA and the transfection reagent. We demonstrate delivery of protein cargo such as EGFP and Cas9 into developing oocytes via P2C peptide and BAPC. Additionally, somatic and germline gene editing were demonstrated. This approach will greatly facilitate CRISPR-applied genetic manipulation in this and other rising model organisms.

Model and Non-model Insects in Chronobiology

The fruit fly Drosophila melanogaster is an established model organism in chronobiology, because genetic manipulation and breeding in the laboratory are easy. The circadian clock neuroanatomy in D. melanogaster is one of the best-known clock networks in insects and basic circadian behavior has been characterized in detail in this insect. Another model in chronobiology is the honey bee Apis mellifera, of which diurnal foraging behavior has been described already in the early twentieth century. A. mellifera hallmarks the research on the interplay between the clock and sociality and complex behaviors like sun compass navigation and time-place-learning. Nevertheless, there are aspects of clock structure and function, like for example the role of the clock in photoperiodism and diapause, which can be only insufficiently investigated in these two models. Unlike high-latitude flies such as Chymomyza costata or D. ezoana, cosmopolitan D. melanogaster flies do not display a photoperiodic diapause. Similarly, A. mellifera bees do not go into "real" diapause, but most solitary bee species exhibit an obligatory diapause. Furthermore, sociality evolved in different Hymenoptera independently, wherefore it might be misleading to study the social clock only in one social insect. Consequently, additional research on non-model insects is required to understand the circadian clock in Diptera and Hymenoptera. In this review, we introduce the two chronobiology model insects D. melanogaster and A. mellifera, compare them with other insects and show their advantages and limitations as general models for insect circadian clocks.

Functional analysis of Pdp1 and vrille in the circadian system of a cricket

Circadian rhythms are generated by a circadian clock for which oscillations are based on the rhythmic expression of the so-called clock genes. The present study investigated the role of Gryllus bimaculatus vrille (Gb'vri) and Par domain protein 1 (Gb'Pdp1) in the circadian clock of the cricket Gryllus bimaculatus. Structural analysis of Gb'vri and Gb'Pdp1 cDNAs revealed that they are a member of the bZIP transcription factors. Under light/dark cycles (LD) both genes were rhythmically expressed in the clock tissue, the optic lobes, whereas the rhythm diminished under constant darkness (DD). Gb'vri and Gb'Pdp1 mRNA levels were significantly reduced by RNA interference (RNAi) of Gb'Clk and Gb'cyc, suggesting they are controlled by Gb'CLK/Gb'CYC. RNAi of Gb'vri and Gb'Pdp1 had little effect on locomotor rhythms, although their effects became visible when treated together with Gb'cyc^RNAi. The average free-running period of Gb'vri^RNAi/Gb'cyc^RNAi crickets was significantly shorter than that of Gb'cyc^RNAi crickets. A similar period shortening was observed also when treated with Gb'Pdp1^RNAi/Gb'cyc^RNAi. Some Gb'Pdp1^RNAi/Gb'cyc^RNAi crickets showed rhythm splitting into two free-running components with different periods. Gb'vri^RNAi and Gb'Pdp1^RNAi treatments significantly altered the expression of Gb'Clk, Gb'cyc, and Gb'tim in LD. These results suggest that Gb'vri and Gb'Pdp1 play important roles in cricket circadian clocks.

Regulation of Sulfate Uptake and Assimilation in Barley (Hordeum vulgare) as Affected by Rhizospheric and Atmospheric Sulfur Nutrition

To study the regulation of sulfate metabolism in barley (Hordeum vulgare), seedlings were exposed to atmospheric hydrogen sulfide (H₂S) in the presence and absence of a sulfate supply. Sulfate deprivation reduced shoot and root biomass production by 60% and 70%, respectively, and it affected the plant’s mineral nutrient composition. It resulted in a 5.7- and 2.9-fold increased shoot and root molybdenum content, respectively, and a decreased content of several other mineral nutrients. Particularly, it decreased shoot and root total sulfur contents by 60% and 70%, respectively. These decreases could be ascribed to decreased sulfate contents. Sulfate deficiency was additionally characterized by significantly lowered cysteine, glutathione and soluble protein levels, enhanced dry matter, nitrate and free amino acid contents, an increased APS reductase (APR) activity and an increased expression and activity of the root sulfate uptake transporters. When sulfate-deprived barley was exposed to 0.6 µL L⁻¹ atmospheric H₂S, the decrease in biomass production and the development of other sulfur deficiency symptoms were alleviated. Clearly, barley could use H₂S, absorbed by the foliage, as a sulfur source for growth. H₂S fumigation of both sulfate-deprived and sulfate-sufficient plants downregulated APR activity as well as the expression and activity of the sulfate uptake transporters. Evidently, barley switched from rhizospheric sulfate to atmospheric H₂S as sulfur source. Though this indicates that sulfate utilization in barley is controlled by signals originating in the shoot, the signal transduction pathway involved in the shoot-to-root regulation must be further elucidated.

Genomics of sex allocation in the parasitoid wasp Nasonia vitripennis

BACKGROUND

Whilst adaptive facultative sex allocation has been widely studied at the phenotypic level across a broad range of organisms, we still know remarkably little about its genetic architecture. Here, we explore the genome-wide basis of sex ratio variation in the parasitoid wasp Nasonia vitripennis, perhaps the best studied organism in terms of sex allocation, and well known for its response to local mate competition.

RESULTS

We performed a genome-wide association study (GWAS) for single foundress sex ratios using iso-female lines derived from the recently developed outbred N. vitripennis laboratory strain HVRx. The iso-female lines capture a sample of the genetic variation in HVRx and we present them as the first iteration of the Nasonia vitripennis Genome Reference Panel (NVGRP 1.0). This panel provides an assessment of the standing genetic variation for sex ratio in the study population. Using the NVGRP, we discovered a cluster of 18 linked SNPs, encompassing 9 annotated loci associated with sex ratio variation. Furthermore, we found evidence that sex ratio has a shared genetic basis with clutch size on three different chromosomes.

CONCLUSIONS

Our approach provides a thorough description of the quantitative genetic basis of sex ratio variation in Nasonia at the genome level and reveals a number of inter-related candidate loci underlying sex allocation regulation.

Genome elimination mediated by gene expression from a selfish chromosome

Numerous plants and animals harbor selfish B chromosomes that "drive" or transmit themselves at super-Mendelian frequencies, despite long-term fitness costs to the organism. Currently, it is unknown how B chromosome drive is mediated, and whether B-gene expression plays a role. We used modern sequencing technologies to analyze the fine-scale sequence composition and expression of paternal sex ratio (PSR), a B chromosome in the jewel wasp Nasonia vitripennis. PSR causes female-to-male conversion by destroying the sperm's hereditary material in young embryos to drive. Using RNA interference, we demonstrate that testis-specific expression of a PSR-linked gene, named haploidizer, facilitates this genome elimination-and-sex conversion effect. haploidizer encodes a putative protein with a DNA binding domain, suggesting a functional link with the sperm-derived chromatin.

Evolutionary and functional genetics of insect diapause: a call for greater integration

Diapause in response to seasonality is an important model for rapid evolutionary adaptation that is highly genetically variable, and experiences strong natural selection. Forward genetic methods using various genomic and transcriptomic approaches have begun to characterize the genetic architecture and candidate genes underlying diapause evolution. Largely in parallel, reverse genetic studies have identified functional roles for candidate genes that may or may not be genetically variable. We illustrate the disconnect between the evolutionary and physiological literature using a suite of studies of the role of the circadian clock in diapause regulation. These extensive studies in two different disciplines provide excellent opportunities for integration, which should facilitate rapid progress in understanding both the regulation and evolution of diapause.

Latitudinal Variation in Circadian Rhythmicity in Nasonia vitripennis

Many physiological processes of living organisms show circadian rhythms, governed by an endogenous clock. This clock has a genetic basis and is entrained by external cues, such as light and temperature. Other physiological processes exhibit seasonal rhythms, that are also responsive to light and temperature. We previously reported a natural latitudinal cline of photoperiodic diapause induction in the parasitic wasp Nasonia vitripennis in Europe and a correlated haplotype frequency for the circadian clock gene period (per). To evaluate if this correlation is reflected in circadian behaviour, we investigated the circadian locomotor activity of seven populations from the cline. We found that the proportion of rhythmic males was higher than females in constant darkness, and that mating decreased rhythmicity of both sexes. Only for virgin females, the free running period (τ) increased weakly with latitude. Wasps from the most southern locality had an overall shorter free running rhythm and earlier onset, peak, and offset of activity during the 24 h period, than wasps from the northernmost locality. We evaluated this variation in rhythmicity as a function of period haplotype frequencies in the populations and discussed its functional significance in the context of local adaptation.