Nasonia Species Research Articles

Genetic and genomic architecture of species-specific cuticular hydrocarbon variation in parasitoid wasps.

Cuticular hydrocarbons (CHCs) serve two fundamental functions in insects: protection against desiccation and chemical signalling. How the interaction of genes shapes CHC profiles, which are essential for insect survival, adaptation and reproductive success, is still poorly understood. Here we investigate the genetic and genomic basis of CHC biosynthesis and variation in parasitoid wasps of the genus Nasonia. We mapped 91 quantitative trait loci (QTL) explaining the variation of a total of 43 CHCs in F2 hybrid males from interspecific crosses between three Nasonia species. To identify candidate genes, we localized orthologues of CHC biosynthesis-related genes in the Nasonia genomes. We discovered multiple genomic regions where the location of QTL coincides with the location of CHC biosynthesis-related candidate genes. Most conspicuously, on a region close to the centromere of chromosome 1, multiple CHC biosynthesis-related candidate genes co-localize with several QTL explaining variation in methyl-branched alkanes. The genetic underpinnings behind this compound class are not well understood so far, despite their high potential for encoding chemical information as well as their prevalence in hymenopteran CHC profiles. Our study considerably extends our knowledge on the genetic architecture governing this important compound class, establishing a model for methyl-branched alkane genetics in the Hymenoptera in general.

A re‐assessment of within‐host mating behavior in the Nasonia species complex

AbstractInsects 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.

The generalist parasitoid Nasonia vitripennis shows more behavioural plasticity in host preference than its three specialist sister species

AbstractHost preference is an important behaviour in parasitoid females as they must choose suitable hosts for their offspring. Preference includes location, recognition and acceptance of hosts. Both genetic and environmental factors can affect all those stages. Here, we focus on two factors (rearing history and experience) affecting host preference in the parasitoid wasp genus Nasonia (Hymenoptera: Chalcidoidea: Pteromalidae: Pteromalinae), which harbours both a host generalist (N. vitripennis) and several closely related specialists (N. giraulti, N. longicornis and N. oneida). We tested whether Nasonia females prefer the host that they developed in by rearing them on two different host species (Lucilia sericata and Calliphora vomitoria) for over 10 generations before testing them for their host preference. We then tested whether experience changes host preference by allowing the females to feed and oviposit on either host species before testing their host preference. Only the generalist N. vitripennis showed behavioural plasticity as the effect of rearing history on host preference was overruled by their experience with a different host species. In contrast, the three specialist species were not affected by long‐term rearing history and only shifted their host preference based on experience. In all four known Nasonia species, individual adult experience modulated host recognition, acceptance and preference.

Comparative analysis reveals the expansion of mitochondrial DNA control region containing unusually high G-C tandem repeat arrays in Nasonia vitripennis

Insect mitochondrial DNA (mtDNA) ranges from 14 to 19 kbp, and the size difference is attributed to the AT-rich control region. Jewel wasps have a parasitoid lifestyle, which may affect mitochondria function and evolution. We sequenced, assembled, and annotated mitochondrial genomes in Nasonia and outgroup species. Gene composition and order are conserved within Nasonia, but they differ from other parasitoids by two large inversion events that were not reported before. We observed a much higher substitution rate relative to the nuclear genome and mitochondrial introgression between N. giraulti and N. oneida, which is consistent with previous studies. Most strikingly, N. vitripennis mtDNA has an extremely long control region (7665 bp), containing twenty-nine 217 bp tandem repeats and can fold into a super-cruciform structure. In contrast to tandem repeats commonly found in other mitochondria, these high-copy repeats are highly conserved (98.7% sequence identity), much longer in length (approximately 8 Kb), extremely GC-rich (50.7%), and CpG-rich (percent CpG 19.4% vs. 1.1% in coding region), resulting in a 23 kbp mtDNA beyond the typical size range in insects. These N. vitripennis-specific mitochondrial repeats are not related to any known sequences in insect mitochondria. Their evolutionary origin and functional consequences warrant further investigations.

Chemical Ecology of the Parasitoid Wasp Genus Nasonia (Hymenoptera, Pteromalidae)

The use of chemical cues and signals is essential for communication in insects. Wasps of the genus Nasonia (Hymenoptera, Pteromalidae) are gregarious parasitoids that lay their eggs into puparia of cyclorrhaphous flies. During their life cycle, various kinds of semiochemicals are used: (1) a male abdominal sex pheromone that attracts females and induces site fidelity in males, (2) a female-derived contact sex pheromone eliciting courtship behavior in males, (3) an oral male aphrodisiac eliciting receptivity signaling in females and causing a switch in the females' olfactory preferences, (4) chemicals derived from host habitat and host puparia used in olfactory host finding by female wasps, and (5) chemicals used by females to assess the quality and parasitization status of potential hosts. We review the literature on the chemical ecology of Nasonia spp. following the wasps' life cycle from emergence to oviposition. We depict biosynthetic pathways where available, discuss ecological implications, highlight differences among Nasonia species, summarize insights into their olfactory perception and associative learning abilities, and point out gaps in our understanding of the chemical ecology of these parasitoids to be addressed in future studies.

Detection of very long-chain hydrocarbons by laser mass spectrometry reveals novel species-, sex-, and age-dependent differences in the cuticular profiles of three Nasonia species.

Long-chain cuticular hydrocarbons (CHC) are key components of chemical communication in many insects. The parasitoid jewel wasps from the genus Nasonia use their CHC profile as sex pheromone and for species recognition. The standard analytical tool to analyze CHC is gas chromatography coupled with mass spectrometric detection (GC/MS). This method reliably identifies short- to long-chain alkanes and alkenes, but CHC with more than 40 carbon atoms are usually not detected. Here, we applied two laser mass spectrometry (MS) techniques, namely direct laser desorption/ionization (d)LDI and silver-assisted (Ag-)LDI MS, respectively, to analyze CHC profiles of N. vitripennis, N. giraulti, and N. longicornis directly from the cuticle or extracts. Furthermore, we applied direct analysis in real-time (DART) MS as another orthogonal technique for extracts. The three methods corroborated previous results based on GC/MS, i.e., the production of CHC with carbon numbers between C25 and C40. However, we discovered a novel series of long-chain CHC ranging from C41 to C51/C52. Additionally, several previously unreported singly and doubly unsaturated alkenes in the C31-C39 range were found. Use of principal component analysis (PCA) revealed that the composition of the newly discovered CHC varies significantly between species, sex, and age of the animals. Our study adds to the growing literature on the presence of very long-chain CHC in insects and hints at putative roles in insect communication. Graphical abstract.

Male Sex Pheromone of the Parasitoid Wasp Urolepis rufipes Demonstrates Biosynthetic Switch Between Fatty Acid and Isoprenoid Metabolism Within the Nasonia Group

Sex pheromones play a crucial role in the mate finding process of insects. The information has to be encoded in a species specific manner to avoid fitness costs due tocourtship by or even mismating with closely related species. Hence, sex pheromones typically diversify when new species evolve. Pheromones of closely related species typically vary in their chemical composition, but the compounds they use are often biosynthetically related. The biosynthetic pathways of insect pheromones are variations of conserved pathways that lead to primary and secondary metabolites. A switch from one pathway to another, particularly in species that use the same type of pheromone glands, is the exception. Here we use chemical analyses and behavioral bioassays to examine the male sex pheromone of the parasitoid wasp Urolepis rufipes. The genus Urolepis is most closely related to Nasonia and Trichomalopsis, forming the so-called “Nasonia group”. All Nasonia species and T. sarcophagae, the only Trichomalopsis species studied so far, produce fatty acid-derived hydroxylactones in their rectal vesicle. The pheromones are deposited on the ground and other substrates and attract virgin females. We show that males of U. rufipes produce a sex pheromone in the same gland and use it in the same manner as the other species of the Nasonia group. Structure elucidation and stable isotope labelling experiments revealed, however, that the U. rufipes pheromone is 2,6-dimethyl-7-octene-1,6-diol, a monoterpenoid derived from the mevalonate pathway. This suggests a biosynthetic switch between the fatty acid and isoprenoid metabolism in the Nasonia group.

Mapping key amino acid residues for the epimerase efficiency and stereospecificity of the sex pheromone biosynthetic short-chain dehydrogenases/reductases of Nasonia

Males of the parasitic wasp genus Nasonia use blends of chiral hydroxylactones as sex pheromones to attract conspecific females. Whereas all Nasonia species use a mixture of (4R,5S)-5-hydroxy-4-decanolide (RS) and 4-methylquinazoline (MQ) as sex pheromones, Nasonia vitripennis evolved (4R,5R)-5-hydroxy-4-decanolide (RR) as an extra sex pheromone component. We recently identified and functionally characterized three short-chain dehydrogenases/reductases (SDRs) NV10127, NV10128, and NV10129 that are capable of catalyzing the epimerization of RS to RR via (4R)-5-oxo-4-decanolide (ODL) as intermediate. Despite their very high sequence identities of 88–98%, these proteins differ drastically in their ability to epimerize RS to RR and in their stereoselectivity when reducing ODL to RR/RS. Here, in order to unravel the sequence differences underlying these varying functional properties of NV1027, NV10128 and NV10129, we created chimeras of the three enzymes and monitored their catalytic activities in vitro. The results show that a few amino acid changes at the C-termini and active sites of Nasonia vitripennis SDRs lead to substantially altered RS to RR epimerization and ODL-reduction activities. Thus, our study adds to the understanding of pheromone evolution by showing that subtle mutations in key biosynthetic enzymes can result in drastic effects on the composition of chemical signals.

Territoriality and behavioural strategies at the natal host patch differ in two microsympatric Nasonia species

Territoriality occurs in a wide variety of animal taxa. The defence of valuable resources, which in the case of territoriality are bound to a specific location, gives the defender priority of access to these resources. Males often defend areas in which the chance to meet females is high and territoriality frequently includes pheromonal marking. When closely related species co-occur within the same environment, different behavioural strategies frequently evolve to avoid reproductive interference. Males of the gregarious parasitoid wasp Nasonia vitripennis exhibit territorial behaviour on the host from which they emerge. However, descriptions of territorial behaviour have been for the most part anecdotal and quantitative standardized observations in an experimental set-up are lacking. In addition, studies of the behaviour of the other Nasonia species that frequently occur in microsympatry, that is, within the same host individual, have rarely been conducted. We investigated and compared territoriality in two species of Nasonia by extensive video recording of emerging wasps in a microcosm approach. We show that males of N. vitripennis meet the concept of territoriality whereas males of Nasonia giraulti do not. Although N. giraulti females are already mated when emerging from the host and males do not show territoriality, N. giraulti males mark the substrate with their abdominal sex pheromone as often as males of N. vitripennis. For N. vitripennis we further show that, although larger males were more often territorial, experience of being in the territorial position was particularly important for winning territoriality contests. Finally, we investigated differences in the pattern of emergence and dispersal between the two species and discuss how the different behavioural strategies may help them avoid reproductive interference.

Learning-induced gene expression in the heads of two Nasonia species that differ in long-term memory formation.

BackgroundCellular processes underlying memory formation are evolutionary conserved, but natural variation in memory dynamics between animal species or populations is common. The genetic basis of this fascinating phenomenon is poorly understood. Closely related species of Nasonia parasitic wasps differ in long-term memory (LTM) formation: N. vitripennis will form transcription-dependent LTM after a single conditioning trial, whereas the closely-related species N. giraulti will not. Genes that were differentially expressed (DE) after conditioning in N. vitripennis, but not in N. giraulti, were identified as candidate genes that may regulate LTM formation.ResultsRNA was collected from heads of both species before and immediately, 4 or 24 hours after conditioning, with 3 replicates per time point. It was sequenced strand-specifically, which allows distinguishing sense from antisense transcripts and improves the quality of expression analyses. We determined conditioning-induced DE compared to naïve controls for both species. These expression patterns were then analysed with GO enrichment analyses for each species and time point, which demonstrated an enrichment of signalling-related genes immediately after conditioning in N. vitripennis only. Analyses of known LTM genes and genes with an opposing expression pattern between the two species revealed additional candidate genes for the difference in LTM formation. These include genes from various signalling cascades, including several members of the Ras and PI3 kinase signalling pathways, and glutamate receptors. Interestingly, several other known LTM genes were exclusively differentially expressed in N. giraulti, which may indicate an LTM-inhibitory mechanism. Among the DE transcripts were also antisense transcripts. Furthermore, antisense transcripts aligning to a number of known memory genes were detected, which may have a role in regulating these genes.ConclusionThis study is the first to describe and compare expression patterns of both protein-coding and antisense transcripts, at different time points after conditioning, of two closely related animal species that differ in LTM formation. Several candidate genes that may regulate differences in LTM have been identified. This transcriptome analysis is a valuable resource for future in-depth studies to elucidate the role of candidate genes and antisense transcription in natural variation in LTM formation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1355-1) contains supplementary material, which is available to authorized users.

Asymmetric Assortative Mating Behaviour Reflects Incomplete Pre‐zygotic Isolation in the Nasonia Species Complex

AbstractPreference of con‐ over heterospecific mates leading to assortative mating can substantially contribute to pre‐zygotic reproductive isolation and prevent fitness losses if post‐zygotic hybridization barriers already exist. The jewel wasp genus Nasonia displays quite strong and well‐studied post‐zygotic reproductive isolation due to a ubiquitous Wolbachia infection causing cytoplasmic incompatibility between different species. Pre‐zygotic isolation, however, has received far less research attention in this model organism, especially concerning the mechanisms and criteria of mate choice. In the present study, we analysed mate rejection and mate acceptance rates in cross‐comparisons between all four Nasonia species. We put emphasis on observing which sex is more likely to interrupt interspecific matings and how discriminatory behaviour varies across the different species in all possible combinations. We found an asymmetric distribution of assortative mating among the four Nasonia species that appears to be highly influenced by the respective combinations of sex and species. Females appeared to be the main discriminators against heterospecific mating partners, but interestingly, we could also detect mate discrimination and rejection behaviour in males, a widely neglected factor in research on mating behaviour in general and on Nasonia in particular. Moreover, the asymmetry in the assortative mating behaviour was partially reflective of sym‐ or allopatric distributions of natural Nasonia populations.

Natural variation in long-term memory formation among Nasonia parasitic wasp species

Closely related species of parasitic wasps can differ substantially in memory dynamics. In this study we demonstrate differences in the number of conditioning trials required to form long-term memory between the closely related parasitic wasp species Nasonia vitripennis and Nasonia giraulti (Hymenoptera: Pteromalidae). A single conditioning trial, in which a female wasp associates an odour with the reward of finding a host, results in the formation of transcription-dependent long-term memory in N. vitripennis, whereas N. giraulti requires spaced training to do so. Memory formation does not depend on the type of reward: oviposition, which was hypothesized to be a ‘larger’ reward results in similar memory retention as host feeding in both Nasonia species. There are several genetic and genomic tools available for Nasonia species to identify genetic mechanisms that underlie the observed variation in the number of trials required to form long-term memory.

Pheromone Diversification and Age-Dependent Behavioural Plasticity Decrease Interspecific Mating Costs in Nasonia

Interspecific mating can cause severe fitness costs due to the fact that hybrids are often non-viable or less fit. Thus, theory predicts the selection of traits that lessen reproductive interactions between closely related sympatric species. Males of the parasitic wasp Nasonia vitripennis differ from all other Nasonia species by an additional sex pheromone component, but the ecological selective forces underlying this pheromone diversification are unknown. Here we present data from lab experiments suggesting that costly interspecific sexual interactions with the sympatric species N. giraulti might have been responsible for the pheromone evolution and some courtship-related behavioural adaptations in N. vitripennis. Most N. giraulti females are inseminated already within the host, but N. giraulti males still invest in costly sex pheromones after emergence. Furthermore, they do not discriminate between N. vitripennis females and conspecifics during courtship. Therefore, N. vitripennis females, most of which emerge as virgins, face the risk of mating with N. giraulti resulting in costly all-male broods due to Wolbachia-induced cytoplasmic incompatibility. As a counter adaptation, young N. vitripennis females discriminate against N. giraulti males using the more complex conspecific sex pheromone and reject most of them during courtship. With increasing age, however, N. vitripennis females become less choosy, but often compensate mating errors by re-mating with a conspecific. By doing so, they can principally avoid suboptimal offspring sex ratios, but a microcosm experiment suggests that under more natural conditions N. vitripennis females cannot completely avoid fitness costs due to heterospecific mating. Our study provides support for the hypothesis that communication interference of closely related sympatric species using similar sexual signals can generate selective pressures that lead to their divergence.

Cuticular hydrocarbon divergence in the jewel wasp Nasonia: evolutionary shifts in chemical communication channels?

The evolution and maintenance of intraspecific communication channels constitute a key feature of chemical signalling and sexual communication. However, how divergent chemical communication channels evolve while maintaining their integrity for both sender and receiver is poorly understood. In this study, we compare male and female cuticular hydrocarbon (CHC) profiles in the jewel wasp genus Nasonia, analyse their chemical divergence and investigate their role as species-specific sexual signalling cues. Males and females of all four Nasonia species showed unique, nonoverlapping CHC profiles unambiguously separating them. Surprisingly, male and female phylogenies based on the chemical distances between their CHC profiles differed dramatically, where only male CHC divergence parallels the molecular phylogeny of Nasonia. In particular, N.giraulti female CHC profiles were the most divergent from all other species and very different from its most closely related sibling species N.oneida. Furthermore, although our behavioural assays indicate that female CHC profiles can generally be perceived as sexual cues attracting males in Nasonia, this function has apparently been lost in the highly divergent female N.giraulti CHC profiles. Curiously, N.giraulti males are still attracted to heterospecific, but not to conspecific female CHC profiles. We suggest that this striking discrepancy has been caused by an extensive evolutionary shift in female N.giraulti CHC profiles, which are no longer used as conspecific recognition cues. Our study constitutes the first report of an apparent abandonment of a sexual recognition cue that the receiver did not adapt to.

Circadian Rhythms Differ between Sexes and Closely Related Species of Nasonia Wasps

Activity rhythms in 24 h light-dark cycles, constant darkness, and constant light conditions were analyzed in four different Nasonia species for each sex separately. Besides similarities, clear differences are evident among and within Nasonia species as well as between sexes. In all species, activity in a light-dark cycle is concentrated in the photophase, typical for diurnal organisms. Contrary to most diurnal insect species so far studied, Nasonia follows Aschoff's rule by displaying long (>24 h) internal rhythms in constant darkness but short (<24 h) in constant light. In constant light, N. vitripennis males display robust circadian activity rhythms, whereas females are usually arrhythmic. In contrast to other Nasonia species, N. longicornis males display anticipatory activity, i.e. activity shortly before light-on in a light-dark cycle. As expected, N. oneida shows activity patterns similar to those of N. giraulti but with important differences in key circadian parameters. Differences in circadian activity patterns and parameters between species may reflect synchronization of specific life-history traits to environmental conditions. Scheduling mating or dispersion to a specific time of the day could be a strategy to avoid interspecific hybridization in Nasonia species that live in sympatry.

Fine-Scale Mapping of the Nasonia Genome to Chromosomes Using a High-Density Genotyping Microarray

Nasonia, a genus of four closely related parasitoid insect species, is a model system for genetic research. Their haplodiploid genetics (haploid males and diploid females) and interfertile species are advantageous for the genetic analysis of complex traits and the genetic basis of species differences. A fine-scale genomic map is an important tool for advancing genetic studies in this system. We developed and used a hybrid genotyping microarray to generate a high-resolution genetic map that covers 79% of the sequenced genome of Nasonia vitripennis. The microarray is based on differential hybridization of species-specific oligos between N. vitripennis and Nasonia giraulti at more than 20,000 markers spanning the Nasonia genome. The map places 729 scaffolds onto the five linkage groups of Nasonia, including locating many smaller scaffolds that would be difficult to map by other means. The microarray was used to characterize 26 segmental introgression lines containing chromosomal regions from one species in the genetic background of another. These segmental introgression lines have been used for rapid screening and mapping of quantitative trait loci involved in species differences. Finally, the microarray is extended to bulk-segregant analysis and genotyping of other Nasonia species combinations. These resources should further expand the usefulness of Nasonia for studies of the genetic basis and architecture of complex traits and speciation.

High-throughput olfactory conditioning and memory retention test show variation in Nasonia parasitic wasps.

Most of our knowledge on learning and memory formation results from extensive studies on a small number of animal species. Although features and cellular pathways of learning and memory are highly similar in this diverse group of species, there are also subtle differences. Closely related species of parasitic wasps display substantial variation in memory dynamics and can be instrumental to understanding both the adaptive benefit of and mechanisms underlying this variation. Parasitic wasps of the genus Nasonia offer excellent opportunities for multidisciplinary research on this topic. Genetic and genomic resources available for Nasonia are unrivaled among parasitic wasps, providing tools for genetic dissection of mechanisms that cause differences in learning. This study presents a robust, high-throughput method for olfactory conditioning of Nasonia using a host encounter as reward. A T-maze olfactometer facilitates high-throughput memory retention testing and employs standardized odors of equal detectability, as quantified by electroantennogram recordings. Using this setup, differences in memory retention between Nasonia species were shown. In both Nasonia vitripennis and Nasonia longicornis, memory was observed up to at least 5 days after a single conditioning trial, whereas Nasonia giraulti lost its memory after 2 days. This difference in learning may be an adaptation to species-specific differences in ecological factors, for example, host preference. The high-throughput methods for conditioning and memory retention testing are essential tools to study both ultimate and proximate factors that cause variation in learning and memory formation in Nasonia and other parasitic wasp species.

Comparative Analyses of DNA Methylation and Sequence Evolution Using Nasonia Genomes

The functional and evolutionary significance of DNA methylation in insect genomes remains to be resolved. Nasonia is well situated for comparative analyses of DNA methylation and genome evolution, since the genomes of a moderately distant outgroup species as well as closely related sibling species are available. Using direct sequencing of bisulfite-converted DNA, we uncovered a substantial level of DNA methylation in 17 of 18 Nasonia vitripennis genes and a strong correlation between methylation level and CpG depletion. Notably, in the sex-determining locus transformer, the exon that is alternatively spliced between the sexes is heavily methylated in both males and females, whereas other exons are only sparsely methylated. Orthologous genes of the honeybee and Nasonia show highly similar relative levels of CpG depletion, despite ~190 My divergence. Densely and sparsely methylated genes in these species also exhibit similar functional enrichments. We found that the degree of CpG depletion is negatively correlated with substitution rates between closely related Nasonia species for synonymous, nonsynonymous, and intron sites. This suggests that mutation rates increase with decreasing levels of germ line methylation. Thus, DNA methylation is prevalent in the Nasonia genome, may participate in regulatory processes such as sex determination and alternative splicing, and is correlated with several aspects of genome and sequence evolution.

Behavioral and genetic characteristics of a new species of Nasonia.

Nasonia (Hymenoptera: Pteromalidae) is a genus of parasitoid wasps, which is fast emerging as a model system for evolutionary, genetic, developmental and host-endosymbiont interaction studies. In this study, we report a new species, Nasonia oneida, distinguish its behavioral, genetic and morphological features, and characterize its pre-mating and post-mating isolation with the other Nasonia species. Phylogenetic analyses indicate that N. oneida is the sister species to Nasonia giraulti with its own uniquely distinct cuticular hydrocarbon profiles, behavioral characteristics and subtle morphological differences. An important characteristic of N. oneida is the strong mate discrimination shown by the females against all the other Nasonia species. A genetic analysis of this phenotype by interspecies hybridization indicates that this strong discriminating phenotype is recessive. A formal species description of N. oneida Raychoudhury & Desjardins is also provided.

Contrasting patterns of selective constraints in nuclear-encoded genes of the oxidative phosphorylation pathway in holometabolous insects and their possible role in hybrid breakdown in Nasonia

The principal energy generating system in animals is the oxidative phosphorylation (OXPHOS) pathway, which depends on the tight interaction of nuclear and mitochondrial encoded genes to function properly. Mitochondrial genes accumulate substitutions more quickly than nuclear genes, yet the impact of selection on mitochondrial genes is significantly reduced relative to nuclear genes due to the non-recombining nature of the mitochondrial genome and its predicted smaller effective population size. It has therefore been hypothesized that the nuclear encoded genes of the OXPHOS pathway are under strong selective pressure to compensate for the accumulation of deleterious nucleotide substitutions in mitochondrial encoded OXPHOS genes; a process known as compensatory co-adaptation. We evaluated this hypothesis by analyzing nuclear encoded OXPHOS genes for signatures of positive selection as well as evolutionary constraints at amino acid sites. We considered OXPHOS genes of six holometabolous insects and their orthologs from three Nasonia parasitoid wasps; hybrids of which suffer from an increased mortality rate caused by cytonuclear genic incompatibilities. Although nuclear OXPHOS genes are typically highly conserved, we found significant evidence for elevated amino acid divergence in four of the 59 studied nuclear encoded OXPHOS genes. We also found that three of these four genes, as well as six other OXPHOS genes, contain amino acid substitutions between Nasonia species at evolutionarily constrained sites. It is possible that these genes account for the reported incompatibility in Nasonia hybrids and their characterization may lead to a better understanding of the role of positive selection in the genetics of speciation.