Thelytoky and Sex Determination in the Hymenoptera: Mutual Constraints

Abstract

The Hymenoptera show a high propensity for transitions from arrhenotokous reproduction (diploid females develop from fertilized eggs, haploid males from unfertilized eggs) to thelytokous reproduction (diploid females develop from unfertilized eggs). However, the evolution of thelytoky is frequently constrained by the sex determination system. Under the ancestral system, complementary sex determination (CSD), the constraint results from the production of diploid males by thelytokous females. The magnitude of this constraint depends on the cytological mechanism of thelytoky, determining the rate at which thelytokous lines lose heterozygosity and on whether a single locus or multiple loci are involved in CSD. In this review, it is discussed how diploid male production in the case of CSD or other constraints in the case of alternative sex determination systems may impede transitions to thelytoky, but it is also shown that under particular (and presumably rare) circumstances the production of diploid males will promote rather than hamper the evolution of thelytoky. Furthermore, constraints between the evolution of thelytoky and sex determination may be mutual, because once thelytoky has evolved, it can impact on sex determination. Finally, researchers are encouraged to exploit the frequent occurrence of thelytoky as an opportunity to learn more about the mechanisms of sex determination in the Hymenoptera.

The Persistence of Facultative Parthenogenesis in Drosophila albomicans

“…Wolbachia -induced parthenogenesis has been well studied in haplodiploid hymenopterans, thrips, and mites but has not been described in Drosophila [43]. Two lines of evidence suggest that parthenogenesis in D. albomicans is unrelated to Wolbachia .…”

“…Second, by using a pair of universal primers to detect the 16S rRNA gene of Wolbachia [42], our preliminary result showed no sign of infection by Wolbachia in the parthenogenetic D. albomicans strains (Figure S1). Two pre-adapted features make the haplodiploid sex-determination system successful for the transition to obligate parthenogenesis [43]. First, haplodiploid hymenopterans have evolved cytoplasmic organelles called accessory nuclei to facilitate the formation of maternal centrosomes [44], [45].…”

“…In contrast, most unfertilized eggs in parthenogenetic Drosophila fail to develop due to the lack of accessory nuclei to form maternal centrosomes [27], [28]. Second, haploid males have acted as a sieve against recessive deleterious mutations, and therefore, haplodiploid species are more tolerant of inbreeding resulting from the increased homozygosity by gamete duplication than are diploid species such as Drosophila [43], [46].…”

Rapid evolution of symbiont‐mediated resistance compromises biological control of aphids by parasitoids

“…In Lysiphlebus fabarum , thelytoky is under genetic control (Sandrock & Vorburger, ) and known to occur via a mechanism termed central fusion automixis (Belshaw & Quicke, ). Thelytokous lines lose heterozygosity over time and become genetically homogeneous, virtually like clones (Vorburger, ). Asexual parasitoids may thus lack the ability to coevolve with their hosts and adapt to the evolution of increased resistance.…”

“…In Lysiphlebus fabarum, thelytoky is under genetic control and known to occur via a mechanism termed central fusion automixis (Belshaw & Quicke, 2003). Thelytokous lines lose heterozygosity over time and become genetically homogeneous, virtually like clones (Vorburger, 2014).…”