The for gene as one of the drivers of foraging variations in a parasitic wasp.

Foraging behaviours encompass strategies to locate resources and to exploit them. In many taxa, these behaviours are driven by a major gene called for, but the mechanisms of gene regulation vary between species. In the parasitoid wasp Venturia canescens, sexual and asexual populations coexist in sympatry but differ in life-history traits, physiology and behaviours, which could impact their foraging strategies. Here, we explored the molecular bases underpinning divergence in behaviours by testing two mutually nonexclusive hypotheses: first, the divergence in the for gene correlates with differences in foraging strategies, and second, the latter rely on a divergence in whole-genome expression. Using comparative genomics, we showed that the for gene was conserved across insects considering both sequence and gene model complexity. Polymorphism analysis did not support the occurrence of two allelic variants diverging across the two populations, yet the asexual population exhibited less polymorphism than the sexual population. Sexual and asexual transcriptomes split sharply, with 10.9% differentially expressed genes, but these were not enriched in behaviour-related genes. We showed that the for gene was more highly expressed in asexual female heads than in sexual heads and that those differences correlate with divergence in foraging behaviours in our experiment given that asexuals explored the environment more and exploited more host patches. Overall, these results suggested that fine tuning of for gene expression between populations may have led to distinct foraging behaviours. We hypothesized that reproductive polymorphism and coexistence in sympatry of sexual and asexual populations specialized to different ecological niches via divergent optima on phenotypic traits could imply adaptation through different expression patterns of the for gene and at many other loci throughout the genome.

RNA Viruses Are Prevalent and Active Tenants of the Predatory Mite Phytoseiulus persimilis (Acari: Phytoseiidae).

Many arthropod species harbor a diverse range of viruses. While much is known about pathogenic viruses of some economically important insects and arthropods involved in disease transmission, viruses associated with mites have rarely been studied. The main objective of this study was to characterize the virome of Phytoseiulus persimilis (Phytoseiidae), a predatory mite commercially used worldwide for the biological control of the key pest Tetranychus urticae (Tetranichidae). A combination of de novo transcriptome assembly and virion sequencing, revealed that RNA viruses are highly prevalent and active tenants of commercial populations of P. persimilis, comprising on average 9% of the mite's total mRNA. Seventeen RNA viruses dominated the mite's virome (i.e., were highly transcribed) with over half (n = 10) belonging to the order Picornavirales, + ssRNA viruses that infect a large range of hosts, including arthropods. Screening of the 17 dominant virus sequences in P. persimilis and T. urticae revealed that three viruses (two Picornavirales of the families Iflaviridae and Dicistroviridae, and one unclassified Riboviria) are unique to P. persimilis and three others (two unclassified Picornavirales and one unclassified Riboviria) are present in both mite species. Most of the sequences were related to viruses previously documented in economically important arthropods, while others have rarely been documented before in arthropods. These findings demonstrate that P. persimilis, like many other arthropods, harbors a diverse RNA virome, which might affect the mite's physiology and consequently its efficiency as a biological control agent.

Genomic characterization of viruses associated with the parasitoid Anagyrus vladimiri (Hymenoptera: Encyrtidae).

Knowledge on symbiotic microorganisms of insects has increased dramatically in recent years, yet relatively little data are available regarding non-pathogenic viruses. Here we studied the virome of the parasitoid wasp Anagyrus vladimiri Triapitsyn (Hymenoptera: Encyrtidae), a biocontrol agent of mealybugs. By high-throughput sequencing of viral nucleic acids, we revealed three novel viruses, belonging to the families Reoviridae [provisionally termed AnvRV (Anagyrus vladimiri reovirus)], Iflaviridae (AnvIFV) and Dicistroviridae (AnvDV). Phylogenetic analysis further classified AnvRV in the genus Idnoreovirus, and AnvDV in the genus Triatovirus. The genome of AnvRV comprises 10 distinct genomic segments ranging in length from 1.5 to 4.2 kb, but only two out of the 10 ORFs have a known function. AnvIFV and AnvDV each have one polypeptide ORF, which is typical of iflaviruses but very un-common among dicistroviruses. Five conserved domains were found along both the ORFs of those two viruses. AnvRV was found to be fixed in an A. vladimiri population that was obtained from a mass rearing facility, whereas its prevalence in field-collected A. vladimiri was ~15 %. Similarly, the prevalence of AnvIFV and AnvDV was much higher in the mass rearing population than in the field population. The presence of AnvDV was positively correlated with the presence of Wolbachia in the same individuals. Transmission electron micrographs of females' ovaries revealed clusters and viroplasms of reovirus-like particles in follicle cells, suggesting that AnvRV is vertically transmitted from mother to offspring. AnvRV was not detected in the mealybugs, supporting the assumption that this virus is truly associated with the wasps. The possible effects of these viruses on A. vladimiri's biology, and on biocontrol agents in general, are discussed. Our findings identify RNA viruses as potentially involved in the multitrophic system of mealybugs, their parasitoids and other members of the holobiont.

A Behavior-Manipulating Virus Relative as a Source of Adaptive Genes for Drosophila Parasitoids.

Some species of parasitic wasps have domesticated viral machineries to deliver immunosuppressive factors to their hosts. Up to now, all described cases fall into the Ichneumonoidea superfamily, which only represents around 10% of hymenoptera diversity, raising the question of whether such domestication occurred outside this clade. Furthermore, the biology of the ancestral donor viruses is completely unknown. Since the 1980s, we know that Drosophila parasitoids belonging to the Leptopilina genus, which diverged from the Ichneumonoidea superfamily 225 Ma, do produce immunosuppressive virus-like structure in their reproductive apparatus. However, the viral origin of these structures has been the subject of debate. In this article, we provide genomic and experimental evidence that those structures do derive from an ancestral virus endogenization event. Interestingly, its close relatives induce a behavior manipulation in present-day wasps. Thus, we conclude that virus domestication is more prevalent than previously thought and that behavior manipulation may have been instrumental in the birth of such associations.

Extrinsic and intrinsic constraints interact to drive extra-pair paternities in the Alpine marmot.

To reproduce, animals have to form pairs and large variations in the degree of mate switching are observed. Extrinsic and intrinsic factors can constrain individual's mate switching. Among intrinsic factors, genes involved in pair-bonding, such as Avpr-1a, receive increasing attention. The length of microsatellites present in the regulatory region of Avpr-1a determines the neural densities and distributions of the vasopressin receptors known to impact pair-bonding behaviours. For the first time, we investigated whether and how the genetic makeup at Avpr-1a, an intrinsic factor, and the social context, an extrinsic factor, experienced by wild Alpine marmot (Marmota marmota) females affect the proportion of extra-pair young. This proportion was positively correlated with the length of their Avpr-1a regulatory region but only when the social constraints were relaxed, that is when mature male subordinates were present. When ignoring the interactive effect between the length of their Avpr-1a regulatory region and the social constraints, the genetic makeup at Avpr-1a was not associated with the proportion of extra-pair young. Under natural conditions, the genetic regulation of pair-bonding could be hidden by extrinsic factors constraining mate choice.

Additional heritable virus in the parasitic wasp Leptopilina boulardi: prevalence, transmission and phenotypic effects.

Parasitoid wasps can be found in association with heritable viruses. Although some viruses have been shown to profoundly affect the biology and evolution of parasitoid wasps, the genetic and phenotypic diversity of parasitoid-associated viruses remains largely unexplored. We previously discovered a behaviour-manipulating DNA virus in the parasitoid wasp Leptopilina boulardi. In this species, which lays its eggs inside Drosophila larvae, Leptopilina boulardi filamentous virus (LbFV) forces the females to lay their eggs in already parasitized Drosophila larvae. This behavioural manipulation increases the chances for the horizontal transmission of the virus. Here, we describe in the same parasitoid species another virus, which we propose to call Leptopilina boulardi toti-like virus (LbTV). This double-stranded RNA virus is highly prevalent in insect laboratory lines as well as in parasitoids caught in the field. In some cases, LbTV was found in coinfection with LbFV, but did not affect the behaviour of the wasp. Instead we found that the presence of LbTV correlates with an increase in the number of offspring, mostly due to increased survival of parasitoid larvae. LbTV is vertically transmitted mostly through the maternal lineage even if frequent paternal transmission also occurs. Unlike LbFV, LbTV is not horizontally transmitted. Its genome encodes a putative RNA-dependent RNA polymerase (RdRp) showing similarities with RdRps of Totiviridae. These results underline the high incidence and diversity of inherited viruses in parasitoids as well as their potential impact on the phenotype of their hosts.

Endoparasitoid lifestyle promotes endogenization and domestication of dsDNA viruses.

The accidental endogenization of viral elements within eukaryotic genomes can occasionally provide significant evolutionary benefits, giving rise to their long-term retention, that is, to viral domestication. For instance, in some endoparasitoid wasps (whose immature stages develop inside their hosts), the membrane-fusion property of double-stranded DNA viruses have been repeatedly domesticated following ancestral endogenizations. The endogenized genes provide female wasps with a delivery tool to inject virulence factors that are essential to the developmental success of their offspring. Because all known cases of viral domestication involve endoparasitic wasps, we hypothesized that this lifestyle, relying on a close interaction between individuals, may have promoted the endogenization and domestication of viruses. By analyzing the composition of 124 Hymenoptera genomes, spread over the diversity of this clade and including free-living, ecto, and endoparasitoid species, we tested this hypothesis. Our analysis first revealed that double-stranded DNA viruses, in comparison with other viral genomic structures (ssDNA, dsRNA, ssRNA), are more often endogenized and domesticated (that is, retained by selection) than expected from their estimated abundance in insect viral communities. Second, our analysis indicates that the rate at which dsDNA viruses are endogenized is higher in endoparasitoids than in ectoparasitoids or free-living hymenopterans, which also translates into more frequent events of domestication. Hence, these results are consistent with the hypothesis that the endoparasitoid lifestyle has facilitated the endogenization of dsDNA viruses, in turn, increasing the opportunities of domestications that now play a central role in the biology of many endoparasitoid lineages.

Molecular detection, penetrance, and transmission of an inherited virus responsible for behavioral manipulation of an insect parasitoid.

For insects, the prevalence of numerous vertically transmitted viruses can be high in their host populations. These viruses often have few, if any, pathological effects on their hosts, and consequently, many of them can remain unnoticed for long periods, despite their potential role in the evolution of the host phenotype. Some females of Leptopilina boulardi, a solitary parasitoid of Drosophila larvae, are infected by an inherited virus (LbFV) that manipulates the behavior of the wasp by increasing its tendency to lay eggs in a host that is already parasitized (superparasitism). This behavioral alteration allows horizontal transmission of the virus within superparasitized Drosophila larvae. Using suppressive subtractive hybridization with infected and uninfected lines, we identified one putative viral sequence. Based on this sequence, we developed a simple PCR test. We tested the correlation between the superparasitism phenotype and PCR amplification of the putative viral marker using several experimental conditions (including horizontal transfers) and several parasitoid genotypes. All of the results revealed that there was a perfect match between the superparasitism phenotype and the amplification profile, which validated use of the molecular marker as a tool to track the presence of the virus and provided the first genomic data for this fascinating virus. The results also show that there was very efficient horizontal and vertical transmission of LbFV, which probably explains its high prevalence in the French populations that we sampled (67 and 70% of infected females). This manipulative virus is likely to play a major role in the ecology and evolution of its parasitoid host.

Origin and neofunctionalization of a Drosophila paternal effect gene essential for zygote viability.

BACKGROUND: Although evolutionary novelty by gene duplication is well established, the origin and maintenance of essential genes that provide entirely new functions (neofunctionalization) is still largely unknown. Drosophila is a good model for the search of genes that are young enough to allow deciphering the molecular details of their evolutionary history. Recent years have seen increased interest in genes specifically required for male fertility because they often evolve rapidly. A special class of genes affecting male fertility, the paternal effect genes, have also become a focus of study to geneticists and reproductive biologists interested in fertilization and sperm-egg interactions. RESULTS: Using molecular genetics and the annotated Drosophila melanogaster genome, we identified CG14251 as the Drosophila paternal effect gene, ms(3)K81 (K81). This assignment was subsequently confirmed by P-element rescue of K81. A search for orthologous K81 sequences revealed that the distribution of K81 is surprisingly restricted to the 9 species comprising the melanogaster subgroup. Phylogenetic analyses indicate that K81 arose through duplication, most likely retroposition, of a ubiquitously expressed gene before the radiation of the melanogaster subgroup, followed by a period of rapid divergence and acquisition of a critical male germline-specific function. Interestingly, K81 has adopted the expression profile of a flanking gene suggesting that transcriptional coregulation may have been important in the neofunctionalization of K81. CONCLUSION: We present a detailed case history of the origin and evolution of a new essential gene and, in so doing, provide the first molecular identification of a Drosophila paternal effect gene, ms(3)K81 (K81).

Genome Sequencing of the Behavior Manipulating Virus LbFV Reveals a Possible New Virus Family.

Parasites are sometimes able to manipulate the behavior of their hosts. However, the molecular cues underlying this phenomenon are poorly documented. We previously reported that the parasitoid wasp Leptopilina boulardi which develops from Drosophila larvae is often infected by an inherited DNA virus. In addition to being maternally transmitted, the virus benefits from horizontal transmission in superparasitized larvae (Drosophila that have been parasitized several times). Interestingly, the virus forces infected females to lay eggs in already parasitized larvae, thus increasing the chance of being horizontally transmitted. In a first step towards the identification of virus genes responsible for the behavioral manipulation, we present here the genome sequence of the virus, called LbFV. The sequencing revealed that its genome contains an homologous repeat sequence (hrs) found in eight regions in the genome. The presence of this hrs may explain the genomic plasticity that we observed for this genome. The genome of LbFV encodes 108 ORFs, most of them having no homologs in public databases. The virus is however related to Hytrosaviridae, although distantly. LbFV may thus represent a member of a new virus family. Several genes of LbFV were captured from eukaryotes, including two anti-apoptotic genes. More surprisingly, we found that LbFV captured from an ancestral wasp a protein with a Jumonji domain. This gene was afterwards duplicated in the virus genome. We hypothesized that this gene may be involved in manipulating the expression of wasp genes, and possibly in manipulating its behavior.

Worldwide distribution of transposable element copy number in natural populations of Drosophila simulans.

Transposable elements (TEs), which promote various kinds of mutations, constitute a large fraction of the genome. How they invade natural populations and species is therefore of fundamental importance for understanding the dynamics of genetic diversity and genome composition. On the basis of 85 samples of natural populations of Drosophila simulans, we report the distributions of the genome insertion site numbers of nine TEs that were chosen because they have a low average number of sites. Most populations were found to have 0-3 insertion sites, but some of them had a significantly higher number of sites for a given TE. The populations located in regions outside Africa had the highest number of sites for all elements except HMS Beagle and Coral, suggesting a recent increase in the activity of some TEs associated with the colonization patterns of Drosophila simulans. The element Tirant had a very distinctive pattern of distribution: it was identified mainly in populations from East Africa and some islands in the Indian Ocean, and its insertion site number was low in all these populations. The data suggest that the genome of the entire species of Drosophila simulans may be being invaded by TEs from populations in which they are present in high copy number.

Evolution of genome size in Drosophila. is the invader's genome being invaded by transposable elements?

Genome size varies considerably between species, and transposable elements (TEs) are known to play an important role in this variability. However, it is far from clear whether TEs are involved in genome size differences between populations within a given species. We show here that in Drosophila melanogaster and Drosophila simulans the size of the genome varies among populations and is correlated with the TE copy number on the chromosome arms. The TEs embedded within the heterochromatin do not seem to be involved directly in this phenomenon, although they may contribute to differences in genome size. Furthermore, genome size and TE content variations parallel the worldwide colonization of D. melanogaster species. No such relationship exists for the more recently dispersed D. simulans species, which indicates that a quantitative increase in the TEs in local populations and fly migration are sufficient to account for the increase in genome size, with no need for an adaptation hypothesis.