Distinct Effects of the Male-Killing Bacteria Wolbachia and Spiroplasma and a Partiti-Like Virus in the Tea Pest Moth, Homona magnanima

Abstract

Male killing, the phenomenon of male death during development, is considered to be one of the advantageous strategies exerted by maternally transmitted microbes. Male killing has attracted interest in the fields of evolutionary biology and ecology for decades; however, little is known about its mechanism and origin. Here, we characterized and compared the effects of three distinct male killers, Wolbachia (Alphaproteobacteria), Spiroplasma (Mollicutes), and Osugoroshi virus (OGV) (Partitiviridae) in the tea pest moth Homona magnanima (Lepidoptera, Tortricidae). Regardless of the genetic sex (male: ZZ; female: ZW), female specific splice variants of the doublesex gene (dsx), a downstream regulator of the sex-determining gene cascade, was expressed in H. magnanima harbored either male-killing Wolbachia or Spiroplasma. However, OGV and non-male-killing Wolbachia did not alter dsx splicing. RNA sequencing and quantitative PCR assays demonstrated that male-killing Wolbachia impaired the hosts dosage compensation system by altering the global gene expression of the Z chromosome (corresponding to Bombyx mori chromosome 1 and 15) in males, whereas Spiroplasma did not affect dosage compensation. In contrast, the partiti-like virus OGVs did not affect sex-determination cascades or dosage compensation systems. Besides, male killers distinctly altered host gene expression and metabolomes associated with physiology, morphology, and diverse metabolic pathways. Moreover, Wolbachia and Spiroplasma infections triggered abnormal apoptosis only in male embryos. These findings suggest that distantly related microbes employ distinct machineries to kill identical host males, which have been acquired through independent evolutionary processes. ImportanceMale-killing caused by diverse microbes has attracted substantial attention. However, it remains unclear how such male killers have evolved similar phenotypes, in part because male-killing mechanisms have been studied using different insect models. Here, by comparing three phylogenetically distinct male killers, Wolbachia, Spiroplasma, and a partiti-like virus, in an identical host, we provide evidence that microbes can affect male viability through distinct machinery, demonstrating distinct evolutionary scenarios for microbes to acquire make-killing ability. These findings provide insight into new directions for studying microbe-host interactions.