Insect Sex Determination Manipulated by Their Endosymbionts: Incidences, Mechanisms and Implications

Abstract

The sex-determining systems of arthropods are surprisingly diverse. Some species have male or female heterogametic sex chromosomes while other species do not have sex chromosomes. Most species are diploids but some species, including wasps, ants, thrips and mites, are haplodiploids (n in males; 2n in females). Many of the sexual aberrations, such as sexual mosaics, sex-specific lethality and conversion of sexuality, can be explained by developmental defects including double fertilization of a binucleate egg, loss of a sex chromosome or perturbation of sex-determining gene expression, which occur accidentally or are induced by certain environmental conditions. However, recent studies have revealed that such sexual aberrations can be caused by various groups of vertically-transmitted endosymbiotic microbes such as bacteria of the genera Wolbachia, Rickettsia, Arsenophonus, Spiroplasma and Cardinium, as well as microsporidian protists. In this review, we first summarize the accumulated data on endosymbiont-induced sexual aberrations, and then discuss how such endosymbionts affect the developmental system of their hosts and what kinds of ecological and evolutionary effects these endosymbionts have on their host populations.

<p align="center"><strong>A review of prevalence and phylogeny of the bacterial symbiont <em>Cardinium</em> in mites (subclass: Acari)</strong></p>

“…Cardinium can manipulate the reproduction of their hosts through various strategies, including parthenogenesis (Zchori-Fein et al 2001), feminization (Weeks et al 2001;Zchori-Fein et al 2004;Giorgini et al 2009), cytoplasmic incompatibility (CI) (Hunter et al 2003;Gotoh et al 2007;Ros & Breeuwer 2009) and altered fecundity (Weeks & Stouthamer 2004). These manipulations play significant roles in the host ecology and evolution Kageyama et al 2012). Thus, Cardinium and other symbionts have received intensive attention.…”

Incomplete offspring sex bias in Australian populations of the butterfly Eurema hecabe

“…Kern et al, 2015). Heuristically, our data are novel for the study of arthropod sex distortion (as summarized comprehensively by Werren, 2008;Cordaux et al, 2011;Kageyama et al, 2012). The mechanisms and consequences of complete sex biases are well-documented, including their ability to drive females to near-fixation frequencies in lepidopteran populations (Charlat et al, 2005).…”

“…At the group level, treated dams overproduced sons to a degree equivalent to the overproduction of daughters by untreated cousins. This implicates a causal role for intracellular bacteria, as opposed to protozoans, viruses or fungi (Kageyama et al, 2012). It also discounts causality based purely upon nuclear agents such as meiotic drivers (without excluding their interactive role; sensu.…”

“…This would explain why molecular assays proved universally positive, while simultaneously obscuring the actual incidence of wCI itself (if present) based on wsp PCR/sequencing. Beyond wCI, the candidates for sex bias range from novel strains of Wolbachia to additional sex distorters such as Spiroplasma, Cardinium, Rickettsia and Flavobacteria (Kageyama et al, 2012). More detailed molecular investigation will be necessary to assess the full complement and potential role of bacterial agents in Australian E. hecabe, and to further explore the possibility of lateral gene transfer.…”

“…Either case would present opportunities to examine the broader biogeographic and/or coevolutionary context of host-symbiont interaction. Of course, sex distortion could arise from any number of variants on these scenarios, or entirely different scenarios involving novel Wolbachia strains, other symbionts and microorganisms (Kageyama et al, 2012), or nuclear factors such as epistasis and meiotic drive Weeks et al, 2002).…”