Population dynamics of male-killing and non-male-killing spiroplasmas in Drosophila melanogaster
Population dynamics of male-killing and non-male-killing spiroplasmas in Drosophila melanogaster
复制标题
DOI：
10.1128/aem.69.3.1428-1434.2003
复制
发表时间：
2003-03-01
影响因子：
4.4
通讯作者：
Fukatsu, T
中科院分区：
文献类型：
--
作者：
Anbutsu, H;Fukatsu, T
内共生细菌螺旋体属(Spirodium spp.)通过雌性寄主垂直传播，已知会导致昆虫雄性后代选择性死亡。一种名为NSRO的螺旋体能在果蝇物种中引起雄性死亡，并且已经分离出一种非雄性杀死NSRO的变种，命名为NSRO-A。目前还不知道为什么NSRO-A不会杀死雄性。利用定量聚合酶链式反应技术，对实验寄主黑腹果蝇整个发育过程中NSRO和NSRO-A的种群动态进行了研究。在寄主发育早期，NSRO的滴度在1龄和2龄显著高于NSRO-A，而在卵、3龄和蛹阶段，两者的滴度几乎相同。在成虫出现时，两种螺旋体的滴度相似，约为2×10(8)Dna A拷贝当量。然而，在整个宿主老化过程中，这两种螺旋体呈现出明显不同的种群增长模式。NSRO的滴度在3周内呈指数增长，达到峰值约为每只昆虫4×10(9)DNAA拷贝当量，然后下降。相反，NSRO-A的效价在整个生命周期的成虫部分几乎是恒定的。因此，在成年雌性中，除了羽化后的一小段时间外，NSRO的滴度显著高于NSRO-A的滴度。虽然感染NSRO的成年雌性几乎100%杀死雄性，但在NSRO效价与NSRO-A一样低的情况下，一些雄性后代在羽化后4天内就会产生。基于这些结果，我们提出了螺旋体对男性致死表达的阈值密度假说。通过寄主世代垂直传播的瓶颈程度估计NSRO为5×10(-5)，NSRO-A为3×10(-4)。
The endosymbiotic bacteria Spiroplasma spp. are vertically transmitted through female hosts and are known to cause selective death of male offspring in insects. One strain of spiroplasma, NSRO, causes male killing in Drosophila species, and a non-male-killing variant of NSRO, designated NSRO-A, has been isolated. It is not known why NSRO-A does not kill males. In an attempt to understand the mechanism of male killing, we investigated the population dynamics of NSRO and NSRO-A throughout the developmental course of the laboratory host Drosophild melanogaster by using a quantitative PCR technique. In the early development of the host insect, the titers of NSRO were significantly higher than those of NSRO-A at the first- and second-instar stages, whereas at the egg, third-instar, and pupal stages, the titers of the two spiroplasmas were almost the same. Upon adult emergence, the titers of the two spiroplasmas were similar, around 2 X 10(8) dnaA copy equivalents. However, throughout host aging, the two spiroplasmas showed strikingly different population growth patterns. The titers of NSRO increased exponentially for 3 weeks, attained a peak value of around 4 X 10(9) dnaA copy equivalents per insect, and then decreased. In contrast, the titers of NSRO-A were almost constant throughout the adult portion of the life cycle. In adult females, consequently, the titer of NSRO was significantly higher than the titer of NSRO-A except for a short period just after emergence. Although infection of adult females with NSRO resulted in almost 100% male killing, production of some male offspring was observed within 4 days after emergence when the titers of NSRO were as low as those of NSRO-A. Based on these results, we proposed a threshold density hypothesis for the expression of male killing caused by the spiroplasma. The extents of the bottleneck in the vertical transmission through host generations were estimated to be 5 x 10(-5) for NSRO and 3 x 10(-4) for NSRO-A.