No patrigenes required for femaleness in the haplodiploid wasp Nasonia vitripennis

Abstract

The parasitoid wasp Nasonia vitripennis is an emerging model organism for developmental and behavioral genetics. It reproduces by haplodiploidy; males typically develop parthenogenetically from haploid eggs and females from fertilized diploid eggs. A polyploid mutant strain is available in which females are triploid and lay haploid and diploid eggs that normally develop into males when unfertilized. In contrast to previous reports, approximately 2% of triploid females were found to occasionally produce daughters as well as gynandromorphs from diploid unfertilized eggs. Daughter production increased with age and differed among familial lineages. This is the first report of parthenogenetic female development in Nasonia. The results show that a paternally provided genome is not required for femaleness and call for modifications of existing models of sex determination in Nasonia.

Figure 1.

The polyploid mutant strain of Nasonia. oyster (pink eyes) and scarlet (red eyes) are recessive complementing eye-color mutations that occur at a single segregation unit (“R-locus”) in which no recombination occurs. Virgin triploid oy +/+ st/+ st females are designated as the parental generation in the experiments. They lay haploid oy + and + st eggs as well as diploid oy +/+ st and + st/+ st eggs, which typically develop into males. Diploid oy +/+ st males can be distinguished by their purple (wild type) eyes and produce fertile diploid sperm. They are crossed with + st/+ st females of a standard stock, resulting in triploid females again.

Figure 2.

The distinction between females and males in N. vitripennis. (A) Females have dark-brown antennae and legs, large wings, and an ovipositor. (B) Males have yellow antennae and legs, short wings, and no ovipositor. (C and D) Gynandromorphs have features of both sexes. Black arrows indicate femaleness; red arrows, maleness.