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A male-killing Wolbachia endosymbiont is concealed by another endosymbiont and a nuclear suppressor
Kelly M Richardson1, Perran A Ross1,2, Brandon S Cooper3
1School of BioSciences, Bio21 Institute, University of Melbourne, Parkville, Victoria, Australia.
Abstract:
Bacteria that live inside the cells of insect hosts (endosymbionts) can alter the reproduction of their hosts, including the killing of male offspring (male killing, MK). MK has only been described in a few insects, but this may reflect challenges in detecting MK rather than its rarity. Here, we identify MK Wolbachia at a low frequency (around 4%) in natural populations of Drosophila pseudotakahashii. MK Wolbachia had a stable density and maternal transmission during laboratory culture, but the MK phenotype which manifested mainly at the larval stage was lost rapidly. MK Wolbachia occurred alongside a second Wolbachia strain expressing a different reproductive manipulation, cytoplasmic incompatibility (CI). A genomic analysis highlighted Wolbachia regions diverged between the 2 strains involving 17 genes, and homologs of the wmk and cif genes implicated in MK and CI were identified in the Wolbachia assembly. Doubly infected males induced CI with uninfected females but not females singly infected with CI-causing Wolbachia. A rapidly spreading dominant nuclear suppressor genetic element affecting MK was identified through backcrossing and subsequent analysis with ddRAD SNPs of the D. pseudotakahashii genome. 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.
Insights
Male killing (MK) bacteria were found in Drosophila pseudotakahashii fruit flies. A nuclear suppressor element and a second Wolbachia strain complicated MK detection and dynamics.
Area of Science:
- Microbial Ecology
- Genetics
- Evolutionary Biology
Background:
- Endosymbiotic bacteria can manipulate insect reproduction, including male killing (MK).
- MK has been rarely described, potentially due to detection challenges.
Purpose of the Study:
- To investigate the presence and dynamics of male killing (MK) Wolbachia in Drosophila pseudotakahashii.
- To characterize the genetic interactions between MK Wolbachia, other Wolbachia strains, and the host genome.
Main Methods:
- Detection of MK Wolbachia in natural populations of Drosophila pseudotakahashii.
- Laboratory culture to assess Wolbachia stability and phenotype expression.
- Genomic analysis of Wolbachia strains and host genome sequencing (ddRAD SNPs).
- Backcrossing experiments to identify host genetic factors influencing MK.
Main Results:
- MK Wolbachia identified at low frequency (4%) in natural populations.
- MK phenotype was unstable and rapidly lost during laboratory culture.
- Co-infection with a second Wolbachia strain causing cytoplasmic incompatibility (CI) was observed.
- Genomic analysis revealed divergence between Wolbachia strains, including homologs for MK and CI.
- A dominant nuclear suppressor element affecting MK was identified in the host genome.
Conclusions:
- Detection of male killing (MK) is complex, influenced by both microbial and host genetic factors.
- The dynamics of MK in natural populations are challenging to study due to rapid phenotype loss and co-infecting microbes.
- Host nuclear genes can significantly impact the expression and detectability of endosymbiont-driven phenotypes like MK.
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