Estimating population size and transmission bottlenecks in maternally transmitted endosymbiotic bacteria
Estimating population size and transmission bottlenecks in maternally transmitted endosymbiotic bacteria
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DOI：
10.1007/s00248-002-0012-9
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发表时间：
2002-08-01
影响因子：
3.6
通讯作者：
Moran, NA
中科院分区：
文献类型：
--
作者：
Mira, A;Moran, NA
许多种类的细菌内共生体是在动物出生前通过母体直接传播到卵子或胚胎而获得的。这种垂直传播造成了数量的减少或“瓶颈”，而这个瓶颈的大小影响了共生谱系的种群结构和进化。我们利用基本的光学和电子显微镜技术估计了蚜虫的细菌共生体Buchnera的传播瓶颈的大小。通过对整个蚜虫腹部、卵和胚胎的连续切片，我们确定了以下参数：(i)布氏虫细胞的平均直径为2.9微米。（ii）在一个水蛭子囊胚中，水蛭的总数约为36,700个，而在一个一龄若虫中，水蛭的总数超过119,000个。（iii）每个细菌细胞的共生体数量在胚胎中约为800个，在一龄若虫中约为3200个。（iv）每个有性卵所携带的布氏蝽总数为：纳索诺布氏蝽850只，沙棘布氏蝽1800只，安氏尿纹蝽8000只以上。(v)雌蜂胚芽次生内共生体总数为12170个，一龄若虫次生内共生体总数为18360个。次生共生体分布在细胞外和细胞内的2000-8000个细菌群中。这些数字与先前基于基因拷贝数对共生体种群大小的少数估计一致。
Many species of bacterial endosymbionts are acquired by animal hosts before birth, through direct transmission from mothers to eggs or embryos. This vertical transmission imposes a reduction in numbers or "bottleneck," and the size of this bottleneck affects the population structure and evolution of symbiotic lineages. We have estimated the size of the transmission bottleneck in Buchnera, the bacterial symbiont of aphids, using basic light and electron microscopy techniques. By serial-sectioning whole aphid abdomens, their eggs, and embryos, we determined the following parameters: (i) The average size of a Buchnera cell is 2.9 mum in diameter. (ii) The total number of Buchnera in an Acyrthosiphon pisum embryo was around 36,700, whereas a first instar nymph contained more than 119,000. (iii) The number of symbionts per bacteriocyte was around 800 in an embryo and 3200 in a first instar nymph. (iv) The total number of Buchnera transmitted to each sexual egg ranged from 850 in Nasonovia to 1800 in A. pisum to more than 8000 in Uroleucon ambrosiae. (v) The total number of secondary endosymbionts in A. pisum was 12,170 for an embryo and 18,360 for a first instar nymph. Secondary symbionts were arranged both extracellularly and in clusters of 2000-8000 bacteria inside bacteriocytes. These numbers are consistent with the few previous estimates of symbiont population sizes based on counts of gene copies.