The effect of host spatial distribution on patterns of parasitism by Nasonia vitripennis

Patterns of parasitism of Calliphora sp. pupae by Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) are explored under various conditions of host aggregation. Increasing the hosts' spatial aggregation decreased the number of hosts actually parasitised but had no significant effect on the total number of hosts attacked. Increasing host aggregation also resulted in a smaller parasitoid population with a more male biased sex ratio.

---

Résumé Nous avons examiné les effets de différents niveaux d'agrégation des hôtes (pupes de Calliphora) sur l'efficacité parasitaire de Nasonia vitripennis. Une augmentation de l'agrégation des pupes a diminué le nombre d'hôtes parasités bien que le nombre de pupes attaquées ait été peu modifié. Cette différence a été attribuée à un accroissement des interactions comportementales entre les parasitoïdes et à une tendance au superparasitisme plus élevée lors des distributions les plus agrégatives. Plus les hôtes étaient concentrés, moins l'effectif de parasitoïdes achevant leur développement et émergeant était important. La fréquence des males a augmenté avec la concentration des pupes. Nous avons estimé que les facteurs déterminants ont été les interactions comportementales entre femelles et leur aptitude à modifier le taux sexuel de leur descendance immédiate.Nous en avons conclu que N. vitripennis est peut-être mieux adaptée aux populations d'hôtes distribuées au hasard, type de distribution le plus vraisemblable dans les populations naturelles.

     

Bacterial infections associated with the son-killer trait in the parasitoid wasp Nasonia (= Mormoniella) vitripennis (Hymenoptera: Pteromalidae)

The son-killer (sk) trait in the parasitoid wasp, Nasonia vitripennis, causes the production of very female-biased sex ratios through the mortality of males. Some 80% of all male eggs fail to hatch. The trait is both maternally and contagiously transmitted. Here evidence is presented that the trait is associated with systemic and chronic bacterial infections in adult wasps. Infections develop trans-stadially, originating in the midgut of larvae and subsequently spreading to other tissues, including the brain, fat body, muscles, eyes, and hemocytes. Female reproductive tracts often show infections but infections are absent in male reproductive organs; other sex differences occur as well. The bacteria involved are pleomorphic, with straight rods being the most common form.     

Mapping of hybrid incompatibility loci in Nasonia

According to theory, F(2) hybrid breakdown (lethality or sterility) is due to incompatibilities between interacting genes of the different species (i.e., the breaking up of coadapted gene complexes). Detection of such incompatibilities is particularly straightforward in haplodiploid species, because virgin F(1) hybrid females will produce haploid recombinant F(2) males. This feature allows for screening of the complete genome for recessive genetic incompatibilities. Crosses were performed between Nasonia vitripennis (v) and its sibling species N. giraulti (g). First, a linkage map was produced using RAPD markers. RAPD markers showed an overall bias toward vitripennis alleles, a pattern not predicted by the basic two-interactor Dobzhansky-Muller model. Recovery patterns of visible markers were consistent with those of linked RAPD markers. If particular genetic interactions between two loci are causing hybrid lethality, then those genotypes should be underrepresented or absent among adult F(2) males. Four sets of significant incompatibilities were detected by performing pairwise comparisons of markers on different chromosomes. Likely explanations for the observed patterns are maternal effect-zygotic gene incompatibilities or clustering of incompatibility loci. Due to the short generation time, advantages of haplodiploidy, and availability of markers, Nasonia promises to be a productive system for investigating the genetics of hybrid inviability.     

Inheritance of gynandromorphism in the parasitic wasp Nasonia vitripennis

The parasitic wasp Nasonia vitripennis has haplo-diploid sex determination. Males develop from unfertilized eggs and are haploid, whereas females develop from fertilized eggs and are diploid. Females and males can be easily distinguished by their morphology. A strain that produces individuals with both male and female features (gynandromorphs) is studied. We provide data on female/male patterning within and between individuals, on environmental effects influencing the occurrence of gynandromorphism, and on its pattern of inheritance. A clear anterior/posterior pattern of feminization is evident in gynandromorphic individuals that developed from unfertilized haploid eggs. The proportion of gynandromorphic individuals can be increased by exposing the mothers to high temperature and also by exposing embryos at early stages of development. Selection for increased gynandromorph frequency was successful. Backcross and introgression experiments showed that a combination of a nuclear and a heritable cytoplasmic component causes gynandromorphism. Analyses of reciprocal F(2) and F(3) progeny indicate a maternal effect locus (gyn1) that maps to chromosome IV. Coupled with previous studies, our results are consistent with a N. vitripennis sex determination involving a maternal/zygotic balance system and/or maternal imprinting. Genetics and temperature effects suggest a temperature-sensitive mutation of a maternally produced masculinizing product that acts during a critical period in early embryogenesis.     

丽蝇蛹集金小蜂几丁质酶基因鉴定与表达分析

几丁质酶是降解几丁质的糖苷水解酶,参与昆虫蜕皮、器官发育、免疫等重要生理过程。目前,寄生蜂等膜翅目昆虫中几丁质酶的鉴定以及功能研究仍较少。本研究基于生物信息学分析,在丽蝇蛹集金小蜂Nasonia vitripennis基因组中鉴定到14个几丁质酶基因,氨基酸个数介于312~2 682之间。系统进化分析表明丽蝇蛹集金小蜂几丁质酶分为9个亚家族,其中Group Ⅳ、Ⅶ亚家族可能通过基因串联复制而发生基因家族扩增。qRT-PCR分析结果表明几丁质酶基因的表达具有多样性,其中NvCht1、NvCht5、NvCht6、NvCht7 4个基因在1.5 d幼虫表达量最高,NvCht3在5 d幼虫表达量最高,NvCht8在幼虫期高表达。此外,幼虫组织中的表达分析结果表明NvCht4、NvCht5、NvCht10、NvCht12在表皮中高表达,NvCht7、NvCht8、NvCht13在肠道中高表达,NvCht9在脂肪体和表皮中高表达,NvCht11在唾液腺中高表达。本研究为寄生蜂几丁质酶的进化分析以及功能研究提供理论基础。     

Reciprocal inheritance of centrosomes in the parthenogenetic hymenopteran Nasonia vitripennis

Background: In the majority of animals, the centrosome-the microtubule-organizing center of the cell-is assembled from components of both the sperm and the egg. How the males of the insect order Hymenoptera acquire centrosomes is a mystery, as they originate from virgin birth.Results: To address this issue, we observed centrosome, spindle and nuclear behavior in real time during early development in the parthenogenetic hymenopteran Nasonia vitripennis. Female meiosis was identical in unfertilized eggs. Centrosomes were assembled before the first mitotic division but were inherited differently in unfertilized and fertilized eggs. In both, large numbers of asters appeared at the cortex of the egg after completion of meiosis. In unfertilized eggs, the asters migrated inwards and two of them became stably associated with the female pronucleus and the remaining cytoplasmic asters rapidly disappeared. In fertilized eggs, the Nasonia sperm brought in paternally derived centrosomes, similar to Drosophila melanogaster. At pronuclear fusion, the diploid zygotic nucleus was associated only with paternally derived centrosomes. None of the cytoplasmic asters associated with the zygotic nucleus and, as in unfertilized eggs, they rapidly degenerated.Conclusions: Selection and migration of the female pronucleus is independent of the sperm and its aster. Unfertilized male eggs inherit maternal centrosomes whereas fertilized female eggs inherit paternal centrosomes. This is the first system described in which centrosomes are reciprocally inherited. The results suggest the existence of a previously undescribed mechanism for regulating centrosome number in the early embryo.     

The quantitative genetic basis of polyandry in the parasitoid wasp, Nasonia vitripennis

Understanding the evolution of female multiple mating (polyandry) is crucial for understanding sexual selection and sexual conflict. Despite this interest, little is known about its genetic basis or whether genetics influences the evolutionary origin or maintenance of polyandry. Here, we explore the quantitative genetic basis of polyandry in the parasitoid wasp Nasonia vitripennis, a species in which female re-mating has been observed to evolve in the laboratory. We performed a quantitative genetic experiment on a recently collected population of wasps. We found low heritabilities of female polyandry (re-mating frequency after 18 h), low heritability of courtship duration and a slightly higher heritability of copulation duration. However, the coefficients of additive genetic variance for these traits were all reasonably large (CV(A)>7.0). We also found considerable dam effects for all traits after controlling for common environment, suggesting either dominance or maternal effects. Our work adds to the evidence that nonadditive genetic effects may influence the evolution of mating behaviour in Nasonia vitripennis, and the evolution of polyandry more generally.     

Sexual selection on male development time in the parasitoid wasp Nasonia vitripennis

Mating systems are shaped by a species' ecology, which sets the stage for sexual selection. Males of the gregarious parasitoid wasp Nasonia vitripennis compete to mate virgin females at the natal site, before females disperse. Males could increase their fitness by being larger and monopolizing female emergence sites or by emerging earlier pre-empting access to females. We consider sexual selection on male body size and development time in Nasonia, and a potential trade-off between the two traits. We explored sex-specific patterns of larval and pupal development, finding that smaller wasps developed slower than their host-mates. Using competition experiments between brothers, we found that earlier eclosing males mated more females independently of absolute and relative body size. Our data explain the lack of relationship between fitness and body size in male Nasonia and reinforce the importance of protandry in mating systems where access to mates is time-limited.     

Characterization of a hymenoptaecin-like antimicrobial peptide in the parasitic wasp Nasonia vitripennis

Hymenoptaecin is a Hymenoptera insect-specific, glycine-rich antimicrobial peptide (AMP) found in non-parasitic bees. Here, we describe a unique hymenoptaecin-like gene (named nahymenoptaecin-1) in the parasitic wasp Nasonia vitripennis, which codes for a larger protein precursor with a carboxyl-terminal hymenoptaecin-like domain (HLD) similar to the bee hymenoptaecin. We recombinantly produced its full-length bioactive form as well as 1–33 and 34–98 fragments (named HLD-n and HLD-c, respectively). Recombinant HLD exhibited activity against Gram-negative and Gram-positive bacteria at micromolar concentrations. Compared to the full-length peptide, HLD-c possessed similar potency in inhibiting the growth of Stenotrophomonus but had a narrower antibacterial spectrum, whereas HLD-n only displayed weak effect on Stenotrophomonus, suggesting that HLD-n is a crucial determinant for bacterial target selectivity while HLD-c represents its active unit for the whole molecule. Circular dichroism analysis combined with ab initio structure prediction by Robetta indicated that HLD-n adopts a random coil conformation whereas glycine-rich HLD-c forms a loose β-sheet structure. Relative to bee hymenoptaecin, the upstream region of HLD contains two accurately repeated proline-rich AMP-like peptides instead of an acidic propeptide. Such difference could be a consequence of exon shuffling of autonomous modules after speciation.     

Regulation and function of tailless in the long germ wasp Nasonia vitripennis

In the long germ insect Drosophila, the gene tailless acts to pattern the terminal regions of the embryo. Loss of function of this gene results in the deletion of the anterior and posterior terminal structures and the eighth abdominal segment. Drosophila tailless is activated by the maternal terminal system through Torso signaling at both poles of the embryo, with additional activation by Bicoid at the anterior. Here, we describe the expression and function of tailless in a long germ Hymenoptera, the wasp Nasonia vitripennis. Despite the morphological similarities in the mode of development of these two insects, we find major differences in the regulation and function of tailless between Nasonia and Drosophila. In contrast to the fly, Nasonia tll appears to rely on otd for its activation at both poles. In addition, the anterior domain of Nasonia tll appears to have little or no segmental patterning function, while the posterior tll domain has a much more extensive patterning role than its Drosophila counterpart.     

The quantitative genetic basis of sex ratio variation in Nasonia vitripennis: a QTL study

Our understanding of how natural selection should shape sex allocation is perhaps more developed than for any other trait. However, this understanding is not matched by our knowledge of the genetic basis of sex allocation. Here, we examine the genetic basis of sex ratio variation in the parasitoid wasp Nasonia vitripennis, a species well known for its response to local mate competition (LMC). We identified a quantitative trait locus (QTL) for sex ratio on chromosome 2 and three weaker QTL on chromosomes 3 and 5. We tested predictions that genes associated with sex ratio should be pleiotropic for other traits by seeing if sex ratio QTL co-occurred with clutch size QTL. We found one clutch size QTL on chromosome 1, and six weaker QTL across chromosomes 2, 3 and 5, with some overlap to regions associated with sex ratio. The results suggest rather limited scope for pleiotropy between these traits.     

The paternal sex ratio chromosome induces chromosome loss independently of Wolbachia in the wasp Nasonia vitripennis

 The paternal sex ratio chromosome (PSR) is a paternally-inherited supernumerary chromosome found in some males of Nasonia vitripennis. PSR induces the loss of N. vitripennis’s paternal autosomes in early fertilized embryos. Previous examinations have not directly addressed the complication of PSR’s co-occurrence with Wolbachia. Wolbachia is the name assigned to a group of cytoplasmic bacteria which induce numerous reproductive alterations in their hosts. In Nasonia, Wolbachia cause cytoplasmic incompatibility (CI) which also results in paternal chromosome loss. Here we address the question of whether PSR’s function (i.e. PSR’s transmission and/or ability to induce chromosome loss) depends upon or interacts with Wolbachia. A strain of PSR males is artificially cleared of Wolbachia. Test crosses and cytological observations of this strain demonstrate that PSR’s transmission and ability to induce chromosome loss is not dependent upon Wolbachia. Comparisons suggest an absence of interactions between PSR and Wolbachia when they co-occur. Fluorescent and confocal microscopy are used to examine and compare early embryos. Observations demonstrate that microtubule interactions with chromatin do not appear to cause the initial loss of the paternal chromosomes. Cytological observations presented here also differ from previous reports of PSR- and Wolbachia-induced chromosome loss. Received: 3 May 1996 / Accepted: 24 June 1996