Center for the Study of Biological Complexity, Virginia Commonwealth University, 1000 W. Cary St., Suite 111, Richmond, VA, 23284-2030, USA.
Illinois Natural History Survey, Prairie Research Institute, University of Illinois, Champaign, IL, USA.
BMC Ecol Evol. 2021 Jun 2;21(1):108. doi: 10.1186/s12862-021-01840-7.
Feather feeding lice are abundant and diverse ectoparasites that complete their entire life cycle on an avian host. The principal or sole source of nutrition for these lice is feathers. Feathers appear to lack four amino acids that the lice would require to complete development and reproduce. Several insect groups have acquired heritable and intracellular bacteria that can synthesize metabolites absent in an insect's diet, allowing insects to feed exclusively on nutrient-poor resources. Multiple species of feather feeding lice have been shown to harbor heritable and intracellular bacteria. We expected that these bacteria augment the louse's diet with amino acids and facilitated the evolution of these diverse and specialized parasites. Heritable symbionts of insects often have small genomes that contain a minimal set of genes needed to maintain essential cell functions and synthesize metabolites absent in the host insect's diet. Therefore, we expected the genome of a bacterial endosymbiont in feather lice would be small, but encode pathways for biosynthesis of amino acids.
We sequenced the genome of a bacterial symbiont from a feather feeding louse (Columbicola wolffhuegeli) that parasitizes the Pied Imperial Pigeon (Ducula bicolor) and used its genome to predict metabolism of amino acids based on the presence or absence of genes. We found that this bacterial symbiont has a small genome, similar to the genomes of heritable symbionts described in other insect groups. However, we failed to identify many of the genes that we expected would support metabolism of amino acids in the symbiont genome. We also evaluated other gene pathways and features of the highly reduced genome of this symbiotic bacterium.
Based on the data collected in this study, it does not appear that this bacterial symbiont can synthesize amino acids needed to complement the diet of a feather feeding louse. Our results raise additional questions about the biology of feather chewing lice and the roles of symbiotic bacteria in evolution of diverse avian parasites.
羽虱是丰富多样的外寄生虫，它们在鸟类宿主上完成整个生命周期。这些虱子的主要或唯一营养来源是羽毛。羽毛似乎缺乏虱子完成发育和繁殖所需的四种氨基酸。有几个昆虫群体已经获得了可遗传的和细胞内的细菌，这些细菌可以合成昆虫饮食中缺少的代谢物，使昆虫能够专门以营养贫乏的资源为食。已经证明，多种羽虱都携带有可遗传的和细胞内的细菌。我们预计这些细菌会用氨基酸来补充虱子的饮食，并促进这些多样化和专门化寄生虫的进化。昆虫的可遗传共生体通常具有包含维持必要细胞功能和合成宿主昆虫饮食中缺少的代谢物所需的最小基因集的小基因组。因此，我们预计羽虱内共生细菌的基因组较小，但会编码合成氨基酸的途径。
我们对寄生在 Pied Imperial Pigeon（Ducula bicolor）身上的羽虱（Columbicola wolffhuegeli）的一种细菌共生体进行了基因组测序，并利用其基因组预测了根据基因的存在或缺失，氨基酸的代谢情况。我们发现，这种细菌共生体的基因组较小，与其他昆虫群中描述的可遗传共生体的基因组相似。然而，我们未能识别出许多我们预计在共生体基因组中支持氨基酸代谢的基因。我们还评估了该共生细菌高度简化基因组的其他基因途径和特征。
根据本研究收集的数据，这种细菌共生体似乎不能合成补充羽虱饮食所需的氨基酸。我们的结果提出了关于羽虱生物学和共生细菌在多样化鸟类寄生虫进化中的作用的更多问题。
