Department of Ecology and Evolutionary Biology, Yale University, 21 Sachem St., New Haven, CT 06520, USA.
Appl Environ Microbiol. 2011 Dec;77(23):8400-8. doi: 10.1128/AEM.05688-11. Epub 2011 Sep 23.
Vertical transmission of obligate symbionts generates a predictable evolutionary history of symbionts that reflects that of their hosts. In insects, evolutionary associations between symbionts and their hosts have been investigated primarily among species, leaving population-level processes largely unknown. In this study, we investigated the tsetse (Diptera: Glossinidae) bacterial symbiont, Wigglesworthia glossinidia, to determine whether observed codiversification of symbiont and tsetse host species extends to a single host species (Glossina fuscipes fuscipes) in Uganda. To explore symbiont genetic variation in G. f. fuscipes populations, we screened two variable loci (lon and lepA) from the Wigglesworthia glossinidia bacterium in the host species Glossina fuscipes fuscipes (W. g. fuscipes) and examined phylogeographic and demographic characteristics in multiple host populations. Symbiont genetic variation was apparent within and among populations. We identified two distinct symbiont lineages, in northern and southern Uganda. Incongruence length difference (ILD) tests indicated that the two lineages corresponded exactly to northern and southern G. f. fuscipes mitochondrial DNA (mtDNA) haplogroups (P = 1.0). Analysis of molecular variance (AMOVA) confirmed that most variation was partitioned between the northern and southern lineages defined by host mtDNA (85.44%). However, ILD tests rejected finer-scale congruence within the northern and southern populations (P = 0.009). This incongruence was potentially due to incomplete lineage sorting that resulted in novel combinations of symbiont genetic variants and host background. Identifying these novel combinations may have public health significance, since tsetse is the sole vector of sleeping sickness and Wigglesworthia is known to influence host vector competence. Thus, understanding the adaptive value of these host-symbiont combinations may afford opportunities to develop vector control methods.
专性共生体的垂直传播产生了共生体可预测的进化历史，反映了其宿主的进化历史。在昆虫中，共生体与宿主之间的进化关联主要在物种间进行了研究，而种群水平的过程在很大程度上仍不清楚。在这项研究中，我们调查了采采蝇（双翅目： Glossinidae）细菌共生体 Wigglesworthia glossinidia，以确定共生体和采采蝇宿主物种的观察到的共进化是否扩展到乌干达的单个宿主物种（ Glossina fuscipes fuscipes ）。为了探索 G. f. fuscipes 种群中共生体的遗传变异，我们在宿主物种 Glossina fuscipes fuscipes （ W. g. fuscipes ）中筛选了 Wigglesworthia glossinidia 细菌的两个可变基因座（ lon 和 lepA ），并检查了多个宿主种群的系统地理和种群动态特征。共生体的遗传变异在种群内和种群间都很明显。我们在乌干达北部和南部鉴定出两个不同的共生体谱系。不一致长度差异（ILD）检验表明，这两个谱系与北部和南部 G. f. fuscipes 线粒体 DNA （ mtDNA ）单倍群完全对应（ P = 1.0 ）。分子方差分析（ AMOVA ）证实，大多数变异是由宿主 mtDNA 定义的北部和南部谱系之间划分的（ 85.44 ％）。但是，ILD 检验拒绝了北部和南部种群内的更细尺度的一致性（ P = 0.009 ）。这种不一致可能是由于不完全谱系分选导致共生体遗传变异体和宿主背景的新组合所致。鉴定这些新组合可能具有公共卫生意义，因为采采蝇是昏睡病的唯一媒介，而 Wigglesworthia 已知会影响宿主媒介效能。因此，了解这些宿主-共生体组合的适应价值可能为开发媒介控制方法提供机会。
