Hu Yi, Holway David A, Łukasik Piotr, Chau Linh, Kay Adam D, LeBrun Edward G, Miller Katie A, Sanders Jon G, Suarez Andrew V, Russell Jacob A
Department of Biology, Drexel University, Philadelphia, PA, 19104, USA.
Division of Biological Sciences, University of California-San Diego, La Jolla, CA, 92093, USA.
Mol Ecol. 2017 Mar;26(6):1608-1630. doi: 10.1111/mec.13991. Epub 2017 Jan 27.
The functions and compositions of symbiotic bacterial communities often correlate with host ecology. Yet cause-effect relationships and the order of symbiont vs. host change remain unclear in the face of ancient symbioses and conserved host ecology. Several groups of ants exemplify this challenge, as their low-nitrogen diets and specialized symbioses appear conserved and ancient. To address whether nitrogen-provisioning symbionts might be important in the early stages of ant trophic shifts, we studied bacteria from the Argentine ant, Linepithema humile - an invasive species that has transitioned towards greater consumption of sugar-rich, nitrogen-poor foods in parts of its introduced range. Bacteria were present at low densities in most L. humile workers, and among those yielding quality 16S rRNA amplicon sequencing data, we found just three symbionts to be common and dominant. Two, a Lactobacillus and an Acetobacteraceae species, were shared between native and introduced populations. The other, a Rickettsia, was found only in two introduced supercolonies. Across an eight-year period of trophic reduction in one introduced population, we found no change in symbionts, arguing against a relationship between natural dietary change and microbiome composition. Overall, our findings thus argue against major changes in symbiotic bacteria in association with the invasion and trophic shift of L. humile. In addition, genome content from close relatives of the identified symbionts suggests that just one can synthesize most essential amino acids; this bacterium was only modestly abundant in introduced populations, providing little support for a major role of nitrogen-provisioning symbioses in Argentine ant's dietary shift.
共生细菌群落的功能和组成通常与宿主生态相关。然而，面对古老的共生关系和保守的宿主生态，因果关系以及共生体与宿主变化的顺序仍不明确。几组蚂蚁就是这种挑战的例证，因为它们的低氮饮食和特殊的共生关系似乎是保守且古老的。为了探究提供氮的共生体在蚂蚁营养转变早期是否重要，我们研究了阿根廷蚁Linepithema humile中的细菌，这是一种入侵物种，在其引入范围的部分地区已转向更多地食用富含糖分、氮含量低的食物。在大多数阿根廷蚁工蚁中，细菌密度较低，在那些产生高质量16S rRNA扩增子测序数据的个体中，我们发现只有三种共生体是常见且占主导的。其中两种，一种乳酸杆菌和一种醋杆菌科物种，在本地和引入种群中都有。另一种，一种立克次氏体，仅在两个引入的超级群落中发现。在一个引入种群长达八年的营养减少期内，我们发现共生体没有变化，这表明自然饮食变化与微生物组组成之间不存在关联。总体而言，我们的研究结果表明，与阿根廷蚁的入侵和营养转变相关的共生细菌没有发生重大变化。此外，已鉴定共生体近亲的基因组内容表明，只有一种能合成大多数必需氨基酸；这种细菌在引入种群中的丰度仅为中等，几乎无法支持提供氮的共生关系在阿根廷蚁饮食转变中起主要作用的观点。
