Abstract
The haplodiploid sex determining mechanism in Hymenoptera (males are haploid, females are diploid) has played an important role in the evolution of this insect order. In Hymenoptera sex is usually determined by a single locus, heterozygotes are female and hemizygotes are male. Under inbreeding, homozygous diploid and sterile males occur which form a genetic burden for a population. We review life history and genetical traits that may overcome the disadvantages of single locus complementary sex determination (sl-CSD). Behavioural adaptations to avoid matings between relatives include active dispersal from natal patches and mating preferences for non-relatives. In non-social species, temporal and spatial segregation of male and female offspring reduces the burden of sl-CSD. In social species, diploid males are produced at the expense of workers and female reproductives. In some social species, diploid males and diploid male producing queens are killed by workers. Diploid male production may have played a role in the evolution or maintenance of polygyny (multiple queens) and polyandry (multiple mating). Some forms of thelytoky (parthenogenetic female production) increase homozygosity and are therefore incompatible with sl-CSD. We discuss a number of hypothetical adaptations to sl-CSD which should be considered in future studies of this insect order.
Highlights
The insect order Hymenoptera comprises over 200,000 species of ants, bees, wasps and sawflies
Wolbachia effects on sex determination A theoretical possibility of how Wolbachia induced thelytoky could evolve in single locus complementary sex determination (sl-CSD) species is if the Wolbachia bacteria could overrule the hosts sex determining process, e.g. by making a product that turns diploid homozygous males into females
Whatever the mechanism may be, this study shows that selection could potentially act to restore diploid male fertility by changes in the meiotic mechanism of spermatogenesis or in chromosome processing during the first mitotic division of the fertilised egg
Summary
The insect order Hymenoptera comprises over 200,000 species of ants, bees, wasps and sawflies. Wolbachia effects on sex determination A theoretical possibility of how Wolbachia induced thelytoky could evolve in sl-CSD species is if the Wolbachia bacteria could overrule the hosts sex determining process, e.g. by making a product that turns diploid homozygous males into females. Whatever the mechanism may be, this study shows that selection could potentially act to restore diploid male fertility by changes in the meiotic mechanism of spermatogenesis or in chromosome processing during the first mitotic division of the fertilised egg. Matched genome inactivation Paternal genome loss (PGL) exists in a number of mites and insects, including cynipid wasps, coccids and the fungal gnat Sciara [2], and has been reported from the autoparasitoid Encarsia pergandiella [115]. Recognition of paternally and maternally inherited chromosome complements has been well documented, e.g. in the case of the Paternal Sex Ratio (PSR) chromosome [116], but the exact mechanisms are typically not known and neither are the conditions under which it evolved
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