Why put all your eggs in one basket? Evolutionary perspectives on the origins of monogenic reproduction

Abstract

Sexual reproduction is ubiquitous in eukaryotes, but the mechanisms by which sex is determined are diverse and undergo rapid turnovers in short evolutionary timescales. Usually, an embryo’s sex is fated at the moment of fertilisation, but in rare instances it is the maternal genotype that determines the offspring’s sex. These systems are often characterised by mothers producing single-sex broods, a phenomenon known as monogeny. Monogenic reproduction is well documented in Hymenoptera (ants, bees and wasps), where it is associated with a eusocial lifestyle. However, it is also known to occur in three families in Diptera (true flies): Sciaridae, Cecidomyiidae and Calliphoridae. Here we review current knowledge of monogenic reproduction in these dipteran clades. We discuss how this strange reproductive strategy might evolve, and we consider the potential contributions of inbreeding, sex ratio distorters, and polygenic control of the sex ratio. Finally, we provide suggestions on future work to elucidate the origins of this unusual reproductive strategy. We propose that studying these systems will contribute to our understanding of the evolution and turnover of sex determination systems.

Effective population size of X chromosomes and haplodiploids under cyclical parthenogenesis

“…Whilst we have focused on broad similarities across these life cycles, it is worth emphasizing the diversity in life cycle structures amongst these groups. For example, in the best studied of the cynipid wasps there are two distinct types of female – gynandromorphs and andromorphs – which exclusively produce either sons or daughters, a type of split sex ratio system, although distinct from that seen in other Hymenoptera or Diptera (Stone et al 2002; Meunier et al 2008; Baird et al 2023). Differences in the proportions of these morphs, or differences in reproductive skew between them, will further reduce the effective population size.…”