Sex Determination in Insects: Variations on a Common Theme

Abstract

Recent studies in a representative selection of holometabolous insects suggest that, despite diversity at the instructive level, the signal-relaying part of the sex-determining pathway is remarkably well conserved. In principle, it is composed of the transformer gene (tra), which acts as a common binary switch that transduces the selected sexual fate, female when ON, male when OFF, to the downstream effector doublesex(dsx) that controls overt sexual differentiation. An interesting recurrent feature is that tra is switched ON in the early zygote by maternally provisioned tra activity. Different male-determining signals evolved, which prevent maternal activation of zygotic tra to allow for male development. In some species, where lack of maternal activation leaves tra in the OFF state, novel female-determining signals were deployed to activate zygotic tra. It appears that both the instructive end of the pathway upstream of tra as well as the executive end downstream of dsx are primary targets of evolutionary divergence, while the transduction part seems less prone to changes. We propose that this is a feature shared with many other signaling cascades that regulate developmental fates.

Caste development and evolution in ants: it's all about size

“…This theory constitutes an hourglass model, in which a large number of evolutionarily labile caste determination factors influence a conserved set of caste differentiation factors, which then produce diverse and evolutionarily labile caste morphologies (Fig. 4; Akhshabi and Dovrolis, 2011;Bopp et al, 2014;Wagner, 2014). This is reminiscent of sex development in insects, in which sex determination and sex morphology are highly variable, but sex differentiation results from conserved roles of the genes doublesex and transformer (Fig.…”

“…This is reminiscent of sex development in insects, in which sex determination and sex morphology are highly variable, but sex differentiation results from conserved roles of the genes doublesex and transformer (Fig. 4; Akhshabi and Dovrolis, 2011;Bopp et al, 2014;Wagner, 2014). Caste development and sex development share many similarities, with variation in environmental (e.g.…”

“…temperature and nutrition) or genetic (e.g. sex chromosomes and genetic caste determination) factors leading to development of alternative phenotypic states (Brian, 1979;Anderson et al, 2008;Schwander et al, 2010;Bopp et al, 2014;Klein et al, 2016). However, caste development is more frequently mediated by environmental factors, whereas sex development is more frequently mediated by genetic factors.…”

“…Here, we attempt to unify the literature on ant caste development and evolution with a single theoretical framework, drawing on recent advances in evolutionary developmental biology (Carroll et al, 2001;West-Eberhard, 2003;Hartfelder and Emlen, 2012;Bopp et al, 2014;Wagner, 2014;Londe et al, 2015;Xu et al, 2015). We propose that ants possess a developmental spectrum of phenotypes, with increasing body size associated with increasingly queen-like traits (Fig.…”

Similar but not the same: insights into the evolutionary history of paralogous sex-determining genes of the dwarf honey bee Apis florea

“…Furthermore, these primary signals seem to be rapidly evolving, as they derive from different origins such as from gene duplication or allelic variation (Bopp et al, 2014). Among closely related species like Apis and Bombus, gene duplication of fem occurred independently (Koch et al 2014) and likely led to different functions.…”