Hidden endosymbionts: A male-killer concealed by another endosymbiont and a nuclear suppressor

Abstract

AbstractMaternally transmitted endosymbiotic bacteria that cause male killing (MK) have only been described from a few insects, but this may reflect challenges in their detection rather than a rarity of MK. Here we identify MKWolbachiain populations ofDrosophila pseudotakahashii, present at a low frequency (around 4%) in natural populations and previously undetected due to a different fixedWolbachiastrain in this species expressing a different reproductive manipulation, cytoplasmic incompatibility (CI). The MK phenotype was eliminated after tetracycline treatment that removedWolbachia. Molecular analyses indicated the MK phenotype to be expressed when a secondWolbachiastrain was present alongside the CIWolbachia. A genomic analysis highlightedWolbachiaregions diverged between the strains involving 17 genes and also identified theWolbachiaas representing an outgroup to a clade ofWolbachiainfectingmelanogaster-group species, includingwRi-like andwMel-like strains. Doubly infected males induced CI with uninfected females but not females singly infected with CI-causingWolbachia. The MK phenotype manifested at the larval stage and was transmitted maternally at a high fidelity but with occasional loss of the MKWolbachiastrain. A rapidly spreading dominant nuclear suppressor genetic element affecting MK was identified through backcrossing and subsequent analysis with ddRAD SNPs of theD. pseudotakahashiigenome. These findings highlight the complexity of nuclear and microbial components affecting MK endosymbiont detection and dynamics in populations, and the challenges of making connections between endosymbionts and the host phenotypes affected by them.