Quantitative trait loci involved in the reproductive success of a parasitoid wasp

Abstract

Dissecting the genetic basis of intraspecific variations in life history traits is essential to understand their evolution, notably for potential biocontrol agents. Such variations are observed in the endoparasitoid Cotesia typhae (Hymenoptera: Braconidae), specialized on the pest Sesamia nonagrioides (Lepidoptera: Noctuidae). Previously, we identified two strains of C. typhae that differed significantly for life history traits on an allopatric host population. To investigate the genetic basis underlying these phenotypic differences, we used a quantitative trait locus (QTL) approach based on restriction site‐associated DNA markers. The characteristic of C. typhae reproduction allowed us generating sisters sharing almost the same genetic content, named clonal sibship. Crosses between individuals from the two strains were performed to generate F2 and F8 recombinant CSS. The genotypes of 181 clonal sibships were determined as well as the phenotypes of the corresponding 4,000 females. Informative markers were then used to build a high‐quality genetic map. These 465 markers spanned a total length of 1,300 cM and were organized in 10 linkage groups which corresponded to the number of C. typhae chromosomes. Three QTLs were detected for parasitism success and two for offspring number, while none were identified for sex ratio. The QTLs explained, respectively, 27.7% and 24.5% of the phenotypic variation observed. The gene content of the genomic intervals was investigated based on the genome of C. congregata and revealed 67 interesting candidates, as potentially involved in the studied traits, including components of the venom and of the symbiotic virus (bracovirus) shown to be necessary for parasitism success in related wasps.

Genome-Wide Patterns of Bracovirus Chromosomal Integration into Multiple Host Tissues during Parasitism

“…This assembly was made of only 72 scaffolds and had an N 50 value of 6.81 Mb (see Table S2). It is noteworthy that the assembly nearly reached the chromosome scale with a mean of 7.2 scaffolds per chromosome, since C. typhae has 10 chromosomes per haploid genome ( 34 ).…”

“…Ovipositions were confirmed by visual observations for all of them. During oviposition, C. typhae lays a relatively large number of eggs in its host, generally ranging between 70 and 110 eggs ( 34 ). Larval development typically takes about 14 days under laboratory conditions until wasp larvae emerge from their host and pupate ( 52 ).…”

Spontaneous parthenogenesis in the parasitoid wasp Cotesia typhae: low frequency anomaly or evolving process?

“…The results are only shown for the 4 chromosomes for which a higher number of markers were genotyped. The black segments on the x axis are indicative of the genetic position of all the markers of the genetic map (Benoist et al, 2020a) and the red segments with the dotted lines correspond to the positions of the markers genotyped in this study. The occurrence of homozygous and heterozygous states along the chromosomes is congruent with a mechanism similar to automixis.…”

Quantitative trait locus analysis of parasitoid counteradaptation to symbiont-conferred resistance

“…Using a crossing design that involved the two species N. vitripennis and N. giraulti , Werren et al ( 2016 ) found a QTL that explained 14% of the phenotypic variance in head width-to-head length ratio. In C. congregata , even 27.7 and 24.5% of the phenotypic variance observed in parasitism success and offspring number could be explained by individual QTLs (Benoist et al 2020 ). It is possible that we underestimated the importance of the counteradaptation QTL, despite the size of our mapping population being close to the suggested range of 250–300 for QTL studies in N. vitripennis (Gadau et al 2012 ), because the environmental variance ( V E ) was certainly high.…”

“…We tried to reduce this variation somewhat by using the residuals of a zero-inflated GLM that corrected for some sources of V E , but the effect was limited. A possible improvement would consist in increasing the number of phenotyped sister F3 females to obtain a more accurate measure of their phenotype (Benoist et al 2020 ). Additionally, a better control of the experimental set-up to reduce V E (e.g., equal numbers of aphids available to parasitize) could contribute to a more precise measure of the counteradaptation trait.…”