Abstract
We studied the sex determination in Diachasmimorpha longicaudata, a parasitoid braconid wasp widely used as biological control agent of fruit pest tephritid flies. We tested the complementary sex determination hypothesis (CSD) known in at least 60 species of Hymenoptera. According to CSD, male or female development depends on the allelic composition of one sex locus (single-locus CSD) or multiple sex loci (multiple-locus CSD). Hemizygote individuals are normal haploid males, and heterozygotes for at least one sex locus are normal diploid females, but homozygotes for all the sex loci are diploid males. In order to force the occurrence of diploid males in D. longicaudata, we established highly inbred lines and examined their offspring using chromosome counting, flow cytometry, and sex ratio analysis. We found that when mother-son crosses were studied, this wasp produced about 20% of diploid males out of the total male progeny. Our results suggest that this parasitoid may represent the second genus with multiple-locus CSD in Hymenoptera. Knowledge about the sex determination system in D. longicaudata is relevant for the improvement of mass rearing protocols of this species. This information also provides the necessary background for further investigations on the underlying molecular mechanisms of sex determination in this species, and a better insight into the evolution of this pathway in Hymenoptera in particular and insects in general.
Highlights
Sex determination refers to the developmental program which commits an individual to female or male path [1]
The parasitoid Diachasmimorpha longicaudata and its host, the fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), were obtained from the experimental rearing facility established at the Instituto de Genética, INTA, Hurlingham, Buenos Aires, Argentina [25]
The experiments of sex ratio with inbred lines showed an increase in the proportion of males across inbreeding generations
Summary
Sex determination refers to the developmental program which commits an individual to female or male path [1]. In Hymenoptera, the sex is determined by haplodiploidy (reviewed in [2, 3]) Even though this mechanism does not rely on the presence of sex chromosomes, males and females differ in their chromosome constitution [4]. Diploid males were described in 83 species [6], showing that sex determination in Hymenoptera is a more complex process. These males are typically found in situations where genetic diversity drastically decreases, as in inbred populations [7]. They can be viable or unviable, fertile or sterile [4, 7]. Diploid males impose a genetic load on the population, bias the sex ratio in favour of males, and reduce the females’ reproductive potential as diploid males originate from fertilised eggs [4, 8]
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