The parasitoid wasp Nasonia: an emerging model system with haploid male genetics

Abstract

Nasonia is a complex of four closely related species of wasps that is rapidly emerging as a model for evolutionary and developmental genetics. It has several features that make it an excellent genetic system, including a short generation time, ease of rearing, interfertile species, visible and molecular markers, and a sequenced genome. The form of sex determination, called "haplodiploidy," makes Nasonia particularly suitable as a genetic tool. Females are diploid and develop from fertilized eggs, whereas males are haploid and develop from unfertilized eggs. This allows geneticists to exploit many of the advantages of haploid genetics in an otherwise complex eukaryotic organism. Nasonia readily inbreeds, permitting production of isogenic lines, and the four species in the genus are interfertile (after removal of the endosymbiont Wolbachia), facilitating movement of genes between the species for efficient positional cloning of quantitative trait loci (QTL). Genome sequencing of the genetic model Nasonia vitripennis and two interfertile species, Nasonia giraulti and Nasonia longicornis, is now completed. This genome project provides a wealth of interspecies polymorphisms (e.g., single nucleotide polymorphisms [SNPs], insertion-deletions [indels], microsatellites) to facilitate positional cloning of genes involved in species differences in behavior, morphology, and development. Advances in the genetics of this system also open a path for improvement of parasitoid insects as agents of pest control.

Figure 1

Nasonia vitripennis male and female engaged in courtship.

Figure 2

Phylogenetic relationships among Nasonia species based on 10 nuclear genes (NJ using Mega 3.1, 5000 reps). Time scale uses divergence Nv-Ng estimates based on earlier calculations (Campbell et al. 1993). The relationships are also highly supported by other gene comparisons. All species (except the outgroup) are inter-fertile when cured of Wolbachia.

Figure 3

Diagram of Nasonia vitripennis pupae. Characteristics used to distinguish males and females (wing size, ovipositor) are highlighted. Pupal wing size is not as reliable for sexing the other species. A, female. B, male.

Figure 4

Crossing Scheme for Haploid Recombinant Males and Clonal Females. Haploid recombinant males can be produced between interfertile species (vitripennis and giraulti) or inbred strains within a species. F3 clonal females are produced when individual haploid recombinant males (all sperm is genetically identical) are crossed to females from an inbred strain (eggs genetically identical). Resulting sets of F3 females have identical recombinant genotypes, and therefore are effectively clonal.

Protocol 5 Figure 1

RNAi injection in Nasonia larvae. A. fourth instar pre-defecation larvae have a slightly contracted gut with gray contents. The posterior end is more tapered than the anterior. B. double-stranded RNA (dsRNA) marked with food coloring is injected posterior of the gut.

Protocol 5 Figure 2

Phenotype of adult wasps from RNAi of cinnabar. Adult wasps on the left were treated as 3^rd instar larvae by injection with doublestranded RNA from the eye color gene cinnabar, whereas those on the right received control injections. As can be seen, a red-eye phenotype results from cinnabar knockdown whereas controls show the wild-type brown eye phenotype.