Sex Determination Mechanisms in Hymenoptera

Hymenopteran insects display a remarkable array of sex determination systems underpinned by haplodiploidy, in which unfertilised eggs produce haploid males and fertilised eggs produce diploid females. In many species this pattern is controlled by complementary sex determination (CSD), where allelic diversity at one or more sex‐determining loci dictates whether an individual develops as male or female. Under single‐locus CSD (sl‐CSD) heterozygotes become females, hemizygotes become males and homozygotes develop into often sterile diploid males. In multispecies families, multi‐locus CSD (ml‐CSD) reduces the risk of diploid male production by requiring heterozygosity at several loci for female development. Alternative mechanisms include maternal imprinting of sex‐determining genes and non-CSD pathways in which paternal genome elimination or mechanistic modifications of meiosis lead to female development through parthenogenesis (thelytoky). The production of sterile or low-fitness diploid males imposes genetic loads on small or inbred populations and influences the evolution of behaviours such as polyandry, polygyny and kin avoidance. Understanding these mechanisms is central to pollinator conservation, biological control breeding and population management.

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Sex Determination Mechanisms in Hymenoptera publication trend

The graph below shows the total number of articles in sex determination mechanisms in hymenoptera across all publications each year (not limited to Nature Index journals).

Technical terms

Haplodiploidy: A sex determination system in which males develop from unfertilised haploid eggs and females from fertilised diploid eggs.

Single‐locus complementary sex determination (sl‐CSD): A mechanism in which allelic heterozygosity at one sex-determining locus produces females, hemizygotes produce males and homozygotes produce diploid males.

Multi‐locus complementary sex determination (ml‐CSD): A system requiring heterozygosity at several independent sex-determining loci for female development, reducing diploid male production.

Diploid male vortex: A population decline phenomenon in species with CSD, where inbreeding increases diploid male production, reducing effective breeders and accelerating extinction risk.

Gynandromorph: An individual exhibiting both male and female phenotypic traits, often as a mosaic of tissues with different sexual identities.

References

1. Revisiting the hymenopteran diploid male vortex: a review of avoidance mechanisms and incidence. Entomologia Experimentalis et Applicata (2022).
2. Possible Epigenetic Origin of a Recurrent Gynandromorph Pattern in Megachile Wild Bees. Insects (2021).
3. Complementary Sex Determination in the Parasitic Wasp Diachasmimorpha longicaudata. PLOS ONE (2015).