PDF(Pubmed)
Abstract：
Many insects feeding on nutritionally challenging diets like plant sap, leaves, or wood engage in ancient associations with bacterial symbionts that supplement limiting nutrients or produce digestive or detoxifying enzymes. However, the distribution, function, and evolutionary dynamics of microbial symbionts in insects exploiting other plant tissues or relying on a predacious diet remain poorly understood. Here, we investigated the evolutionary history and function of the intracellular gamma-proteobacterial symbiont \"Candidatus Dasytiphilus stammeri\" in soft-winged flower beetles (Coleoptera, Melyridae, Dasytinae) that transition from saprophagy or carnivory to palynivory (pollen-feeding) between larval and adult stage. Reconstructing the distribution of the symbiont within the Dasytinae phylogeny unraveled not only a long-term coevolution, originating from a single acquisition event with subsequent host-symbiont codiversification, but also several independent symbiont losses. The analysis of 20 different symbiont genomes revealed that their genomes are severely eroded. However, the universally retained shikimate pathway indicates that the core metabolic contribution to their hosts is the provisioning of tyrosine for cuticle sclerotization and melanization. Despite the high degree of similarity in gene content and order across symbiont strains, the capacity to synthesize additional essential amino acids and vitamins and to recycle urea is retained in some but not all symbionts, suggesting ecological differences among host lineages. This report of tyrosine-provisioning symbionts in insects with saprophagous or carnivorous larvae and pollen-feeding adults expands our understanding of tyrosine supplementation as an important symbiont-provided benefit across a broad range of insects with diverse feeding ecologies.
摘要：
许多昆虫以植物汁液等营养挑战性饮食为食，叶子,或木材与细菌共生体有古老的联系，这些细菌共生体补充限制性营养或产生消化或解毒酶。然而,分布,函数,以及利用其他植物组织或依靠饮食的昆虫中微生物共生体的进化动力学仍然知之甚少。这里,我们研究了软翼花甲虫（Melyridae，Dashtinae）在幼虫和成虫阶段之间从食性或食肉性过渡到古生性（花粉摄食）。重建Dashtinae系统发育中共生体的分布揭示了长期的共同进化，源于单一的收购事件，随后的宿主-共生体共同多元化，但也有几个独立的共生体损失。对20种不同共生体基因组的分析表明，它们的基因组受到严重侵蚀。然而,普遍保留的莽草酸途径表明，对其宿主的核心代谢贡献是为角质层硬化和黑化提供酪氨酸。尽管共生体菌株的基因含量和顺序高度相似，合成额外必需氨基酸和维生素以及回收尿素的能力保留在一些但不是所有的共生体中，表明寄主谱系之间的生态差异。这篇关于昆虫与食腐或食肉幼虫和花粉摄食成虫的酪氨酸共生体的报道，扩大了我们对酪氨酸补充剂的理解，这是一种重要的共生体提供的益处，适用于具有多种摄食生态的广泛昆虫。
