Jekyll or Hyde? The genome (and more) of Nesidiocoris tenuis, a zoophytophagous predatory bug that is both a biological control agent and a pest.

Nesidiocoris tenuis (Reuter) is an efficient predatory biological control agent used throughout the Mediterranean Basin in tomato crops but regarded as a pest in northern European countries. From the family Miridae, it is an economically important insect yet very little is known in terms of genetic information and no genomic or transcriptomic studies have been published. Here, we use a linked-read sequencing strategy on a single female N. tenuis. From this, we assembled the 355 Mbp genome and delivered an ab initio, homology-based and evidence-based annotation. Along the way, the bacterial "contamination" was removed from the assembly. In addition, bacterial lateral gene transfer (LGT) candidates were detected in the N. tenuis genome. The complete gene set is composed of 24 688 genes; the associated proteins were compared to other hemipterans (Cimex lectularis, Halyomorpha halys and Acyrthosiphon pisum). We visualized the genome using various cytogenetic techniques, such as karyotyping, CGH and GISH, indicating a karyotype of 2n = 32. Additional analyses include the localization of 18S rDNA and unique satellite probes as well as pooled sequencing to assess nucleotide diversity and neutrality of the commercial population. This is one of the first mirid genomes to be released and the first of a mirid biological control agent.

Genetics of decayed sexual traits in a parasitoid wasp with endosymbiont-induced asexuality.

Trait decay may occur when selective pressures shift, owing to changes in environment or life style, rendering formerly adaptive traits non-functional or even maladaptive. It remains largely unknown if such decay would stem from multiple mutations with small effects or rather involve few loci with major phenotypic effects. Here, we investigate the decay of female sexual traits, and the genetic causes thereof, in a transition from haplodiploid sexual reproduction to endosymbiont-induced asexual reproduction in the parasitoid wasp Asobara japonica. We take advantage of the fact that asexual females cured of their endosymbionts produce sons instead of daughters, and that these sons can be crossed with sexual females. By combining behavioral experiments with crosses designed to introgress alleles from the asexual into the sexual genome, we found that sexual attractiveness, mating, egg fertilization and plastic adjustment of offspring sex ratio (in response to variation in local mate competition) are decayed in asexual A. japonica females. Furthermore, introgression experiments revealed that the propensity for cured asexual females to produce only sons (because of decayed sexual attractiveness, mating behavior and/or egg fertilization) is likely caused by recessive genetic effects at a single locus. Recessive effects were also found to cause decay of plastic sex-ratio adjustment under variable levels of local mate competition. Our results suggest that few recessive mutations drive decay of female sexual traits, at least in asexual species deriving from haplodiploid sexual ancestors.

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 distribution of microsatellites in the Nasonia parasitoid wasp genome.

Microsatellites are important molecular markers used in numerous genetic contexts. Despite this widespread use, the evolutionary processes governing microsatellite distribution and diversity remain controversial. Here, we present results on the distribution of microsatellites of three species in the parasitic wasp genus Nasonia generated by an in silico data-mining approach. Our results show that the overall microsatellite density in Nasonia is comparable to that of the honey bee, but much higher than in eight non-Hymenopteran arthropods. Across the Nasonia vitripennis genome, microsatellite density varied both within and amongst chromosomes. In contrast to other taxa, dinucleotides are the most abundant repeat type in all four species of Hymenoptera studied. Whether the differences between the Hymenoptera and other taxa are of functional significance remains to be determined.

A comparison of recombination frequencies in intraspecific versus interspecific mapping populations of Nasonia.

We present the first intraspecific linkage map for Nasonia vitripennis based on molecular markers. The map consists of 36 new microsatellite markers, extracted from the Nasonia genome sequence, and spans 515 cM. The five inferred linkage groups correspond to the five chromosomes of Nasonia. Comparison of recombination frequencies of the marker intervals spread over the whole genome (N=33 marker intervals) between the intraspecific N. vitripennis map and an interspecific N. vitripennis x N. giraulti map revealed a slightly higher (1.8%) recombination frequency in the intraspecific cross. We further considered an N. vitripennis x N. longicornis map with 29 microsatellite markers spanning 430 cM. Recombination frequencies in the two interspecific crosses differed neither between reciprocal crosses nor between mapping populations of embryos and adults. No major chromosomal rearrangements were found for the analyzed genomic segments. The observed differential F(2) hybrid male mortality has no significant effect on the genome-wide recombination frequency in Nasonia. We conclude that interspecific crosses between the different Nasonia species, a hallmark of Nasonia genetics, are generally suitable for mapping quantitative and qualitative trait loci for species differences.

Sexual functionality of Leptopilina clavipes (Hymenoptera: Figitidae) after reversing Wolbachia-induced parthenogenesis.

Females infected with parthenogenesis-inducing Wolbachia bacteria can be cured from their infection by antibiotic treatment, resulting in male production. In most cases, however, these males are either sexually not fully functional, or infected females have lost the ability to reproduce sexually. We studied the decay of sexual function in males and females of the parasitoid Leptopilina clavipes. In western Europe, infected and uninfected populations occur allopatrically, allowing for an investigation of both male and female sexual function. This was made by comparing females and males induced from different parthenogenetic populations with those from naturally occurring uninfected populations. Our results indicate that although males show a decay of sexual function, they are still able to fertilize uninfected females. Infected females, however, do not fertilize their eggs after mating with males from uninfected populations. The absence of genomic incompatibilities suggests that these effects are due to the difference in mode of reproduction.