Adaptive latitudinal cline of photoperiodic diapause induction in the parasitoid <i>Nasonia vitripennis</i> in Europe

Living in seasonally changing environments requires adaptation to seasonal cycles. Many insects use the change in day length as a reliable cue for upcoming winter and respond to shortened photoperiod through diapause. In this study, we report the clinal variation in photoperiodic diapause induction in populations of the parasitoid wasp Nasonia vitripennis collected along a latitudinal gradient in Europe. In this species, diapause occurs in the larval stage and is maternally induced. Adult Nasonia females were exposed to different photoperiodic cycles and lifetime production of diapausing offspring was scored. Females switched to the production of diapausing offspring after exposure to a threshold number of photoperiodic cycles. A latitudinal cline was found in the proportion of diapausing offspring, the switch point for diapause induction measured as the maternal age at which the female starts to produce diapausing larvae, and the critical photoperiod for diapause induction. Populations at northern latitudes show an earlier switch point, higher proportions of diapausing individuals and longer critical photoperiods. Since the photoperiodic response was measured under the same laboratory conditions, the observed differences between populations most likely reflect genetic differences in sensitivity to photoperiodic cues, resulting from local adaptation to environmental cycles. The observed variability in diapause response combined with the availability of genomic tools for N. vitripennis represent a good opportunity to further investigate the genetic basis of this adaptive trait.

Diploid males support a two-step mechanism of endosymbiont-induced thelytoky in a parasitoid wasp.

BACKGROUND: Haplodiploidy, where females develop from diploid, fertilized eggs and males from haploid, unfertilized eggs, is abundant in some insect lineages. Some species in these lineages reproduce by thelytoky that is caused by infection with endosymbionts: infected females lay haploid eggs that undergo diploidization and develop into females, while males are very rare or absent. It is generally assumed that in thelytokous wasps, endosymbionts merely diploidize the unfertilized eggs, which would then trigger female development. RESULTS: We found that females in the parasitoid wasp Asobara japonica infected with thelytoky-inducing Wolbachia produce 0.7-1.2 % male offspring. Seven to 39 % of these males are diploid, indicating that diploidization and female development can be uncoupled in A. japonica. Wolbachia titer in adults was correlated with their ploidy and sex: diploids carried much higher Wolbachia titers than haploids, and diploid females carried more Wolbachia than diploid males. Data from introgression lines indicated that the development of diploid individuals into males instead of females is not caused by malfunction-mutations in the host genome but that diploid males are most likely produced when the endosymbiont fails to activate the female sex determination pathway. Our data therefore support a two-step mechanism by which endosymbionts induce thelytoky in A. japonica: diploidization of the unfertilized egg is followed by feminization, whereby each step correlates with a threshold of endosymbiont titer during wasp development. CONCLUSIONS: Our new model of endosymbiont-induced thelytoky overthrows the view that certain sex determination mechanisms constrain the evolution of endosymbiont-induced thelytoky in hymenopteran insects. Endosymbionts can cause parthenogenesis through feminization, even in groups in which endosymbiont-diploidized eggs would develop into males following the hosts' sex determination mechanism. In addition, our model broadens our understanding of the mechanisms by which endosymbionts induce thelytoky to enhance their transmission to the next generation. Importantly, it also provides a novel window to study the yet-poorly known haplodiploid sex determination mechanisms in haplodiploid insects

Temperature stress increases hybrid incompatibilities in the parasitic wasp genus <i>Nasonia</i>

Hybrid incompatibilities, measured as mortality and sterility, are caused by the disruption of gene interactions. They are important post-zygotic isolation barriers to species hybridization, and much effort is put into the discovery of the genes underlying these incompatibilities. In hybridization studies of the haplodiploid parasitic wasp genus Nasonia, genic incompatibilities have been shown to affect mortality and sterility. The genomic regions associated with mortality have been found to depend on the cytotype of the hybrids and thus suggest cytonuclear incompatibilities. As environmental conditions can affect gene expression and gene interaction, we here investigate the effect of developmental temperature on sterility and mortality in Nasonia hybrids. Results show that extreme temperatures strongly affect both hybrid sterility (mainly spermatogenic failure) and mortality. Molecular mapping revealed that extreme temperatures increase transmission ratio distortion of parental alleles at incompatible loci, and thus, cryptic incompatible loci surface under temperature stress that remain undiscovered under standard temperatures. Our results underline the sensitivity of hybrid incompatibilities to environmental factors and the effects of unstable epistasis

DNA methylation plays a crucial role during early <i>Nasonia</i> development

Although the role of DNA methylation in insect development is still poorly understood, the number and role of DNA methyltransferases in insects vary strongly between species. DNA methylation appears to be widely present among the social hymenoptera and functional studies in Apis have suggested a crucial role for de novo methylation in a wide variety of developmental processes. The sequencing of three parasitoid Nasonia genomes revealed the presence of three Dnmt1 (Dnmt1a, Dnmt1b and Dnmt1c) genes and one Dnmt2 and Dnmt3 gene, suggesting a role of DNA methylation in Nasonia development. In the present study we show that in Nasonia vitripennis all Dnmt1 messenger RNAs (mRNAs) and Dnmt3 mRNA are maternally provided to the embryo and, of these, Dnmt1a is essential during early embryogenesis. Lowering of maternal Dnmt1a mRNA results in embryonic lethality during the onset of gastrulation. This dependence on maternal Dnmt1a during embryogenesis in an organismal group outside the vertebrates, suggests evolutionary conservation of the function of Dnmt1 during embryogenesis.</p

Quantitative Trait Locus Analysis of Mating Behavior and Male Sex Pheromones in Nasonia Wasps.

A major focus in speciation genetics is to identify the chromosomal regions and genes that reduce hybridization and gene flow. We investigated the genetic architecture of mating behavior in the parasitoid wasp species pair Nasonia giraulti and Nasonia oneida that exhibit strong prezygotic isolation. Behavioral analysis showed that N. oneida females had consistently higher latency times and broke off the mating sequence more often in the mounting stage when confronted with N. giraulti males compared with males of their own species. N. oneida males produce a lower quantity of the long-range male sex pheromone, (4R,5S)-5-hydroxy-4-decanolide (RS-HDL). Crosses between the two species yielded hybrid males with various pheromone quantities and these males were used in mating trials with females of either species to measure female mate discrimination rates. A quantitative trait locus (QTL) analysis involving 475 recombinant hybrid males (F2), 2148 reciprocally backcrossed females (F3), and a linkage map of 52 equally spaced neutral single nucleotide polymorphism (SNP) markers plus SNPs in 40 candidate mating behavior genes revealed four QTL for male pheromone amount depending on partner species. Our results demonstrate that the RS-HDL pheromone plays a role in the mating system of N. giraulti and N. oneida, but also that additional communication cues are involved in mate choice. No QTL were found for female mate discrimination which points at a polygenic architecture of female choice with strong environmental influences

Microfluidic chip for culturing intestinal epithelial cell layers: Characterization and comparison of drug transport between dynamic and static models

Dynamic flow in vitro models are currently widely explored for their applicability in drug development research. The application of gut-on-chip models in toxicology is lagging behind. Here we report the application of a gut-on-chip model for biokinetic studies and compare the observed biokinetics of reference compounds with those obtained using a conventional static in vitro model. Intestinal epithelial Caco-2 cells were cultured on a porous membrane assembled between two glass flow chambers for the dynamic model, or on a porous membrane in a Transwell model. Confocal microscopy, lucifer yellow translocation, and alkaline phosphatase activity evaluation revealed that cells cultured in the gut-on-chip model formed tight, differentiated, polarized monolayers like in the static cultures. In the dynamic gut-on-chip model the transport of the high permeability compounds antipyrine, ketoprofen and digoxin was lower (i.e. 4.2-, 2.7- and 1.9-fold respectively) compared to the transport in the static Transwell model. The transport of the low permeability compound, amoxicillin, was similar in both the dynamic and static in vitro model. The obtained transport values of the compounds are in line with the compound Biopharmaceuticals Classification System. It is concluded that the gut-on-chip provides an adequate model for transport studies of chemicals

Treatment of resistant Raynaud's phenomenon with single-port thoracoscopic sympathicotomy:a novel minimally invasive endoscopic technique

OBJECTIVE: To assess the minimally invasive single-port thoracoscopic sympathicotomy feasibility and efficacy in patients with treatment-resistant RP. METHODS: Single-port thoracoscopic sympathicotomy was performed unilaterally on the left side in eight patients with RP (six males, two females, with a median age of 45.2 years). Five patients had primary and three had secondary RP. Perfusion effects in the hands were assessed at baseline and after 1 month by using a cooling and recovery procedure, and by using laser speckle contrast analysis. Number and duration of RP attacks were reported over a 2-week period. RESULTS: Patient satisfaction was 100% after surgery. After surgery, a unilateral improvement in perfusion was observed in the left hand compared with the right hand, with cooling and recovery (P = 0.008) and with laser speckle contrast analysis (P = 0.023). In addition, the number and duration of the attacks in the left hand decreased compared with the right hand (both P = 0.028). No serious adverse events occurred in a follow-up period of at least 10 months. CONCLUSION: Single-port thoracoscopic sympathicotomy is feasible and can be effective in improving hand perfusion in patients with RP. However, long-term efficacy needs to be established. CLINICAL TRIAL REGISTRATION NUMBER: NCT02680509

Skin and liver diseases induced in flounder (Platichthys flesus) after long-term exposure to contaminated sediments in large-scale mesocosms.

Disease development in flounder (Platichthys flesus) was studied over a period of 3 years in three large mesocosms (40 m x 40 m x 3 m). Two of the mesocosms contained clean sand and the third, sharing a common water circulation with one of the clean-sand mesocosms, was stocked with contaminated dredged spoil. In this way, one of the clean-sand mesocosms was indirectly polluted via the water phase, and analysis of contaminant concentrations in sediments and flounder tissues showed that it had a status intermediate between the other two. Random samples of the flounder populations from the indirectly polluted and reference mesocosms were examined every 2 months for epidermal diseases (lymphocystis, skin ulcers, fin rot) and then released. In addition, every 6 months, random samples of fish from all three mesocosms were sacrificed for histological and chemical investigation. With regard to the development of epidermal disease, the results showed little difference between the reference mesocosm and the indirectly polluted mesocosm, with the exception that lymphocystis was significantly elevated in the indirectly polluted mesocosm. Although pollution may be a risk factor in the etiology of this disease, such a relationship would probably be obscured under field conditions due to variation arising from other factors. Histopathological analysis of the livers revealed in total four cases of hepatocellular adenoma (1.5% of sampled population) in fish from the polluted mesocosms, the first occurring after 2.5 years of exposure in fish from the indirectly polluted mesocosm. Furthermore, several other liver lesions, including foci of cellular alteration and hydropic vacuolated lesions, developed during the course of the experiment before tumor formation was apparent. Prevalences of these conditions were very much lower in the reference mesocosm than in the two polluted mesocosms. Densities of melanomacrophage centers in the liver showed a similar trend. The findings clearly indicate that long-term exposure to chemically contaminated dredged spoil can induce liver neoplasia and other liver lesions in flounder at contaminant levels comparable to those found in the natural environment

Innovaties in het kwadraat : samen voor extra resultaat : eindrapportage

De Kader Richtlijn Water (KRW) richt zich op de verbetering van de ecologische en chemische waterkwaliteit. Eén van de knelpunten die het halen van de KRW-doelen in de weg staat is de milieubelasting van nutriënten en gewasbeschermingsmiddelen uit intensieve plantaardige teelten. Doel van het project Innovaties in het Kwadraat was een bijdrage te leveren aan het verminderen van de emissie naar het oppervlaktewater van gewasbeschermingsmiddelen en nutriënten vanuit drie belangrijke teelten met relatief veel normoverschrijdingen: peer, aardbei en prei