Data from: Low temperature reveals genetic variability against male-killing Spiroplasma in Drosophila melanogaster natural populations

Spiroplasma endosymbionts are maternally inherited microorganisms which infect many arthropod species. In some Drosophila species, it acts as a reproductive manipulator, spreading in populations by killing the sons of infected mothers. Distinct Drosophila melanogaster populations from Brazil exhibit variable male-killing Spiroplasma prevalences. In this study, we investigated the presence of variability for the male-killing phenotype among Drosophila and/or Spiroplasma strains and verified if it correlates with the endosymbiont prevalence in natural populations. For that, we analyzed the male-killing expression when Spiroplasma strains from different populations were transferred to a standard D. melanogaster line (Canton-S) and when a common Spiroplasma strain was transferred to different wild-caught D. melanogaster lines, both at optimal and challenging temperatures for the bacteria. No variation was observed in the male-killing phenotype induced by different Spiroplasma strains. No phenotypic variability among fly lines was detected at optimal temperature (23 °C), as well. Conversely, significant variation in the male-killing expression was revealed among D. melanogaster lines at 18.5 °C, probably caused by imperfect transmission of the endosymbiont. Distinct lines differed in their average sex ratios as well as in the pattern of male-killing expression as the infected females aged. Greater variation occurred among lines from one locality, although there was no clear correlation between the male-killing intensity and the endosymbiont prevalence in each population. Imperfect transmission or male killing may also occur in the field, thus helping to explain the low or intermediate prevalences reported in nature. We discuss the implications of our results for the dynamics of male-killing Spiroplasma in natural populations.

螺原体（Spiroplasma）内共生体是一类母系遗传的微生物，可侵染多种节肢动物物种。在部分果蝇（Drosophila）物种中，这类共生体作为生殖调控因子，通过杀死受感染母代的雄性子代实现在种群中的传播。来自巴西的不同黑腹果蝇（Drosophila melanogaster）种群中，螺原体的雄性致死感染率存在差异。本研究旨在探究果蝇菌株和/或螺原体菌株间的雄性致死表型变异情况，并验证该变异是否与自然种群中内共生体的感染率相关。为此，我们设置两组实验分析雄性致死表达情况：一是将不同种群来源的螺原体菌株接种至标准化黑腹果蝇品系（Canton-S）中；二是将通用螺原体菌株接种至不同野生捕获的黑腹果蝇品系中，实验分别在适合该细菌生长的最适温度与胁迫温度下开展。不同螺原体菌株诱导的雄性致死表型未出现明显变异。在最适温度（23℃）下，不同果蝇品系间也未检测到表型变异。与之相反，在18.5℃条件下，黑腹果蝇品系间的雄性致死表达水平存在显著差异，该现象可能由内共生体的不完全传播所致。不同品系的平均性别比例以及受感染雌蝇衰老过程中的雄性致死表达模式均存在差异。同一采集地点的果蝇品系间变异程度更高，不过各野生种群中雄性致死强度与内共生体感染率之间并未呈现明确的相关性。野外环境中同样可能存在不完全传播或雄性致死现象，这有助于解释自然界中报道的低感染率或中等感染率情况。本研究最后讨论了实验结果对自然种群中雄性致死螺原体种群动态研究的启示。