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Systemic Bacterial Infection and Immune Defense Phenotypes in Drosophila Melanogaster
Published on: May 13, 2015
Spiroplasma infection causes either early or late male killing in Drosophila, depending on maternal host age
Daisuke Kageyama1, Hisashi Anbutsu, Masakazu Shimada
1Department of Systems Sciences, University of Tokyo, Tokyo 153-8902, Japan.
Abstract:
Symbiont-induced male-killing phenotypes have been found in a variety of insects. Conventionally, these phenotypes have been divided into two categories according to the timing of action: early male killing at embryonic stages and late male killing at late larval stages. In Drosophila species, endosymbiotic bacteria of the genus Spiroplasma have been known to cause early male killing. Here, we report that a spiroplasma strain normally causing early male killing also induces late male killing depending on the maternal host age: male-specific mortality of larvae and pupae was more frequently observed in the offspring of young females. As the lowest spiroplasma density and occasional male production were also associated with newly emerged females, we proposed the density-dependent hypothesis for the expression of early and late male-killing phenotypes. Our finding suggested that (1) early and late male-killing phenotypes can be caused by the same symbiont and probably by the same mechanism; (2) late male killing may occur as an attenuated expression of early male killing; (3) expression of early and late male-killing phenotypes may be dependent on the symbiont density, and thus, could potentially be affected by the host immunity and regulation; and (4) early male killing and late male killing could be alternative strategies adopted by microbial reproductive manipulators.
Insights
A Spiroplasma strain in Drosophila can cause both early and late male killing. This dual phenotype expression is dependent on symbiont density, influenced by maternal host age, suggesting a density-dependent hypothesis for male-killing strategies.
Area of Science:
- Microbiology
- Genetics
- Evolutionary Biology
Background:
- Male-killing phenotypes, induced by symbionts, are categorized by the stage of action: embryonic (early) or larval (late).
- Endosymbiotic Spiroplasma bacteria in Drosophila are known inducers of early male killing.
Purpose of the Study:
- To investigate if the same Spiroplasma strain can induce both early and late male-killing phenotypes.
- To explore the influence of maternal host age on the expression of male-killing phenotypes.
Main Methods:
- Observation of male-specific mortality in Drosophila offspring across different maternal host ages.
- Quantification of Spiroplasma density in relation to maternal age and male production.
Main Results:
- A Spiroplasma strain, typically causing early male killing, also induced late male killing in offspring from younger females.
- Lower Spiroplasma density and occasional male production were linked to newly emerged females.
- Male-specific mortality was more frequent in offspring of young females, indicating a maternal age-dependent effect.
Conclusions:
- Early and late male-killing phenotypes can originate from the same symbiont, potentially via the same mechanism.
- Late male killing may represent an attenuated form of early male killing.
- The expression of these phenotypes is likely density-dependent, influenced by symbiont load and host factors like immunity.
- Male-killing phenotypes may serve as alternative reproductive strategies for microbial manipulators.
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