The chemical basis of mate recognition in two parasitoid wasp species of the genus Nasonia

To recognize one's mate is essential for all sexually reproducing animals. In insects, mate recognition is often based on chemical cues such as hydrocarbons which are distributed over the insect's cuticle. In the parasitoid wasp genus Nasonia (Hymenoptera: Pteromalidae), interspecific mating possibly occurs in microsympatry between Nasonia vitripennis Walker and Nasonia giraulti Darling despite post-zygotic isolation mechanisms preventing hybridization. Males of N. vitripennis are known to equally court con- and heterospecific females, which they recognize by means of cuticular hydrocarbons. A recent study surprisingly showed that this might not be the case in N. giraulti, leaving open how males of this species achieve the recognition of mating partners. In this study, we investigated chemical mate recognition in N. giraulti in more detail and compared observed behaviors with behaviors of N. vitripennis by conducting experiments with both species concurrently and under the same experimental conditions. We disentangled the role of female-derived non-polar cuticular lipids – i.e., cuticular hydrocarbons – and more polar cuticular lipids in the ability of males to recognize con- and heterospecific females. In addition, we tested whether females of the two species discriminate similarly between con- and heterospecific males. We demonstrate that, in contrast to N. vitripennis, males of N. giraulti prefer live conspecific females over heterospecific ones. Furthermore, in contrast to N. vitripennis, mate recognition in N. giraulti males is not based on cuticular hydrocarbons, but rather involves other chemical messengers, presumably more polar cuticular lipids. In both species, discrimination against heterospecific males decreases with female age

Validating the demethylating effects of 5-aza-2'-deoxycytidine in insects requires a whole-genome approach (A reply to Ellers et al.)

This work was initiated as part of Natural Environment Research Council grant NE/J024481/1.We previously demonstrated that treatment with the demethylating agent 5-aza-2′-deoxycytidine (5-azadC) alters the offspring sex ratios produced by females of the parasitoid wasp Nasonia vitripennis (Cook et al. 2015). Females allocate offspring sex ratio in line with Local Mate Competition theory, producing more or less female-biased sex ratios as the number of other females laying eggs on a patch varies, thereby reducing competition amongst their sons for mates. Interestingly, treatment with 5-aza-dC did not ablate the facultative sex allocation response. Instead, sex ratios became less female-biased, a shift in the direction of the optimum sex ratio for paternally-inherited alleles according to genomic conflict theory. This was the first (albeit indirect) experimental evidence for genomic conflict over sex allocation. Ellers et al. (2019) have since assayed the effects of 5-aza-dC on DNA methylation in ten Nasonia genes, finding no evidence of demethylation in these 10 genes, from which they conclude that 5-aza-dC has no demethylating capability in Nasonia vitripennis. Quantifying the efficacy of 5-aza-dC in terms of demethylation is indeed crucial to in-depth interpretation of studies using 5-aza-dC to link phenotypes to epigenetic regulation. Here, we outline the mode of action of 5-aza-dC and demonstrate that determining the efficacy of 5-aza-dC in insect systems requires a whole-genome approach.PostprintPeer reviewe

Seasonal morphotypes of <i>Drosophila suzukii</i> differ in key life-history traits during and after a prolonged period of cold exposure

Seasonal polyphenism in Drosophila suzukii manifests itself in two discrete adult morphotypes, the “winter morph” (WM) and the “summer morph” (SM). These morphotypes are known to differ in thermal stress tolerance, and they co-occur during parts of the year. In this study, we aimed to estimate morph-specific survival and fecundity in laboratory settings simulating field conditions. We specifically analyzed how WM and SM D. suzukii differed in mortality and reproduction during and after a period of cold exposure resembling winter and spring conditions in temperate climates. The median lifespan of D. suzukii varied around 5 months for the WM flies and around 7 months for the SM flies. WM flies showed higher survival during the cold-exposure period compared with SM flies, and especially SM males suffered high mortality under these conditions. In contrast, SM flies had lower mortality rates than WM flies under spring-like conditions. Intriguingly, reproductive status (virgin or mated) did not impact the fly survival, either during the cold exposure or during spring-like conditions. Even though the reproductive potential of WM flies was greatly reduced compared with SM flies, both WM and SM females that had mated before the cold exposure were able to continuously produce viable offspring for 5 months under spring-like conditions. Finally, the fertility of the overwintered WM males was almost zero, while the surviving SM males did not suffer reduced fertility. Combined with other studies on D. suzukii monitoring and overwintering behavior, these results suggest that overwintered flies of both morphotypes could live long enough to infest the first commercial crops of the season. The high mortality of SM males and the low fertility of WM males after prolonged cold exposure also highlight the necessity for females to store sperm over winter to be able to start reproducing early in the following spring.</p

Genomics of sex allocation in the parasitoid wasp Nasonia vitripennis

This research was funded by the Netherlands Genomics Initiative (Zenith 93511041) and the by the Natural Environment Research Council (NE/J024481/1).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.Publisher PDFPeer reviewe

Chemical and population genetic analysis show no evidence of ecotype formation in a European population of the parasitoid wasp Nasonia vitripennis

Ecotypes, subpopulations or strains of a single species locally adapted to divergent ecological conditions within the same habitat are often considered to be the first steps in sympatric speciation. It has been suggested that two ecotypes are distinguishable in Nasonia vitripennis, a prominent model organism for parasitic Hymenoptera, with one ecotype parasitizing fly pupae in bird nests, and the other one parasitizing fly pupae on carrion. This differentiation into two ecotypes has been hypothesized to indicate incipient sympatric speciation in populations of this globally distributed species. In the present study, we investigated the differentiation into these two distinct ecotypes focusing on chemical profiles and the population genetic divergence in a wild N. vitripennis population from the Netherlands. Isofemale lines were obtained from bird nest boxes and from deer carrion, respectively, representing both microhabitats. To test for phenotypic differentiation, we determined the surface cuticular hydrocarbon (CHC) profiles from wasps of both host patches. Using a panel of 14 microsatellites, we concordantly determined the population genetic structure and tested for genetic differentiation between foundresses obtained from both microhabitats. Both the phenotypic as well as the genetic datasets show no evidence for any kind of separation based on the postulated two ecotypes, but rather suggest free interbreeding with no gene flow interruption between the two distinct host patches. Our findings challenge previous assumptions on clearly distinguishable ecotypes in N. vitripennis, and demonstrate how a chemical ecological assessment coupled with population genetics can be instrumental in re-evaluating the potential of ecological differentiation and incipient speciation mechanisms in parasitoid wasps

THE FIRST VATICAN COUNCIL IN THE ZAGREB PRESS

U članku se donose informacije o pripremama i radu Prvoga vatikanskog koncila kako ih je prenosio zagrebački tisak. Istražuje se pisanje triju zagrebačkih tiskovina: Narodnih novina, Agramer Zeitunga i Zagrebačkoga katoličkog lista. Na osnovi vijesti iz navedenih izvora izlaže se početak, djelovanje i rad Prvoga vatikanskog koncila sve od njegova sazivanja 29. lipnja 1869. pa do prekida 1. rujna 1870., nakon čega je uslijedila okupacija Rima, što je učinila Kraljevina Italija, i prekid postojanja Papinske Države. Posebna pozornost posvećuje se koncilskom zasjedanjima na kojima je najaktualnija bila tema o papinoj nepogrešivosti. Na kraju rada u zaključnim razmatranjima donosi se analiza pisanja zagrebačkog tiska, iščitava se njihov stav o radu Koncila i proglašenoj dogmi, uočava se važnost tiska i javnosti u odnosu na zasjedanje Koncila. Opća konstatacija je da zagrebačke tiskovine nisu blagonaklono gledale na proglašenje dogme o papinoj nepogrešivosti, već su slijedile politiku vlastite države i stavove većine domaćeg episkopata.This article reveals information about preparations and work of the First Vatican Council as it was reported in the contemporary Zagreb press. Authors investigate writings in three newspapers from Zagreb: Narodne novine [National newspapers], Agramer Zeintug [Zagreb Newspapers] and Zagrebački katolički list [Zagreb Catholic Newspapers]. On the basis of the articles and information published in these newspapers, authors reconstruct opening and work of the First Vatican Council from its convocation (29th June 1869) until its downtime on 1st September 1870, which was followed by Italian occupation of Rome and abolishment of the Papal state. Authors give special attention to the Council’s sessions in which the most important topic was thesis about the papal impeccability. In the conclusion authors deliver an analysis of the texts published in the Zagreb press concerning the Council, in which they reveal press’ attitude and opinions about the work of the Council and the decreed dogma. Finally, authors have deduced that the press was quite important in making of the public opinion about the Council. Namely, it is quite clear that Zagreb press did not welcome decree of dogma on the papal impeccability, and in this manner press followed state policy and views of the majority of the local episcopacy

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

A re‐assessment of within‐host mating behavior in the <i>Nasonia</i> species complex

Insects have a wide variety of mating systems. For parasitic wasps, mating sites are often confined to where their hosts occur and this mutual interaction therefore greatly affects the evolution of alternative mating strategies. Parasitoids of the genus Nasonia (Hymenoptera: Pteromalidae) – comprising the species Nasonia vitripennis (Walker), Nasonia longicornis Darling, Nasonia giraulti Darling, and Nasonia oneida Raychouhury & Desjardins – parasitize blowfly pupae and typically mate immediately after emergence of the females from the host puparium. However, in one Nasonia species, N. giraulti, mating predominantly occurs within the host. Here, we re-assess within-host mating (WHM) rates within the Nasonia genus, using laboratory lines and field-collected hosts, including N. oneida for which no data were available yet. We confirm that WHM rates are low in N. vitripennis and N. longicornis, but high in N. giraulti. WHM is rare in N. oneida, despite its sympatry and close phylogenetic relationship with N. giraulti. Multiparasitization experiments with N. vitripennis and N. giraulti resulted in lower WHM proportions of N. giraulti. To evaluate whether this was due to an exit hole in the host pupa created by N. vitripennis males – where an exit hole may result in emergence of N. giraulti females and possibly males prior to mating – we artificially created exit holes in the host parasitized by N. giraulti only. This also yielded a lower WHM proportion. Progeny analysis of interspecific crosses of N. longicornis and N. oneida with N. giraulti, generating hybrid female but non-hybrid male offspring, revealed that WHM is largely determined by the maternal species and, hence, by the species to which the male offspring belong. We conclude that WHM is predominantly a male-mediated trait in N. giraulti, resulting from males refraining from making exit holes and mating with females inside the host. We discuss how these findings can be used to evaluate whether WHM contributes to preventing species hybridization

Recombination and its impact on the genome of the haplodiploid parasitoid wasp Nasonia

Homologous meiotic recombination occurs in most sexually reproducing organisms, yet its evolutionary advantages are elusive. Previous research explored recombination in the honeybee, a eusocial hymenopteran with an exceptionally high genome-wide recombination rate. A comparable study in a non-social member of the Hymenoptera that would disentangle the impact of sociality from Hymenoptera-specific features such as haplodiploidy on the evolution of the high genome-wide recombination rate in social Hymenoptera is missing. Utilizing single-nucleotide polymorphisms (SNPs) between two Nasonia parasitoid wasp genomes, we developed a SNP genotyping microarray to infer a high-density linkage map for Nasonia. The map comprises 1,255 markers with an average distance of 0.3 cM. The mapped markers enabled us to arrange 265 scaffolds of the Nasonia genome assembly 1.0 on the linkage map, representing 63.6% of the assembled N. vitripennis genome. We estimated a genome-wide recombination rate of 1.4-1.5 cM/Mb for Nasonia, which is less than one tenth of the rate reported for the honeybee. The local recombination rate in Nasonia is positively correlated with the distance to the center of the linkage groups, GC content, and the proportion of simple repeats. In contrast to the honeybee genome, gene density in the parasitoid wasp genome is positively associated with the recombination rate; regions of low recombination are characterized by fewer genes with larger introns and by a greater distance between genes. Finally, we found that genes in regions of the genome with a low recombination frequency tend to have a higher ratio of non-synonymous to synonymous substitutions, likely due to the accumulation of slightly deleterious non-synonymous substitutions. These findings are consistent with the hypothesis that recombination reduces interference between linked sites and thereby facilitates adaptive evolution and the purging of deleterious mutations. Our results imply that the genomes of haplodiploid and of diploid higher eukaryotes do not differ systematically in their recombination rates and associated parameters.Publisher PDFPeer reviewe

Overwintered <i>Drosophila suzukii</i> are the main source for infestations of the first fruit crops of the season

The mechanisms allowing the widespread invasive pest Drosophila suzukii to survive from early spring until the availability of the first fruit crops are still unclear. Seasonal biology and population dynamics of D. suzukii were investigated in order to better understand the contribution of the early spring hosts to the infestation of the first fruit crops of the season. We identified hosts available to D. suzukii in early spring and assessed their suitability for the pest oviposition and reproductive success under field and laboratory conditions. The natural infestation rate of one of these hosts, Aucuba japonica, was assessed over springtime and the morphology of the flies that emerged from infested A. japonica fruits was characterized under field conditions. Then, these findings were correlated with long-term monitoring data on seasonal reproductive biology and morphology of the pest, using a cumulative degree-days (DD) analysis. Field sampling revealed that overwintered D. suzukii females were physiologically able to lay eggs at 87 DD which coincided with the detection of the first infested early spring hosts. The latter were continuously and increasingly infested by D. suzukii eggs in nature from early spring until the end of May, in particular Aucuba japonica. Individuals emerged from most of these hosts were characterized by a poor fitness and a rather low success of emergence. In the field, only few summer morphs emerged from naturally infested A. japonica fruits around the end of May-beginning of June. However, field monitoring in orchards revealed that D. suzukii individuals consisted solely of winter morphs until mid-June. These observations indicate that overwintered D. suzukii females are the predominant source for the infestations in the first available fruit crops of the season. We discuss these findings in the context of possible pest control strategies