Negative Effects of Low Temperatures on the Vertical Transmission and Infection Density of a Spiroplasma Endosymbiont in Drosophila hydei
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- Osaka, R., Nomura, M., Watada, M. et al. Curr Microbiol (2008) 57: 335. doi:10.1007/s00284-008-9199-4
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Maternally transmitted endosymbionts of the genus Spiroplasma infecting several species of Drosophila are known to cause selective death of male offspring (male killing). The male-killing trait is considered to be advantageous for maternally transmitted endosymbionts. However, a non-male-killing spiroplasma is present in Japanese populations of Drosophila hydei at high frequencies (23–66%). This spiroplasma is phylogenetically closely related to the male-killing spiroplasma infecting other Drosophila species. It is unknown why this spiroplasma is maintained in its host populations despite its inability to cause male killing. We examined the susceptibilities of the spiroplasma in D. hydei to four different temperatures (28, 25, 18, and 15°C). Diagnostic PCR revealed that vertical transmission of the spiroplasma was nearly perfect at 28 and 25°C, partially suppressed at 18°C, and completely blocked at 15°C. Furthermore, quantitative PCR demonstrated that offspring treated at 18°C exhibited dramatically lower densities of spiroplasma (i.e., approximately one-tenth) compared to offspring treated at 28 and 25°C. Considering the low temperatures during winter in Japan, some unknown advantageous effects of the spiroplasma that compensate for the failure of vertical transmission are suggested to act in natural populations of D. hydei.