Microbiome reduction and endosymbiont gain from a switch in sea urchin life-history

Animal gastrointestinal tracts harbor a microbiome that is integral to host function, yet species from diverse phyla have evolved a reduced digestive system or lost it completely. Whether such changes are associated with alterations in the diversity and/or abundance of the microbiome remains an untested hypothesis in evolutionary symbiosis. Here, using the life-history transition from planktotrophy (feeding) to lecithotrophy (non-feeding) in the sea urchin Heliocidaris, we demonstrate that the lack of a functional gut corresponds with a reduction in microbial community diversity and abundance as well as the association with a diet-specific microbiome. We also determine that the lecithotroph vertically transmits a Rickettsiales that may complement host nutrition through amino acid biosynthesis and influence host reproduction. Our results indicate that the evolutionary loss of a functional gut correlates with a reduction in the microbiome and the association with an endosymbiont. Symbioti...

动物胃肠道寄居着对宿主功能至关重要的微生物组（microbiome），然而来自多个不同门类的物种却演化出了简化的消化系统，甚至完全丧失了该系统。这类演化变化是否与微生物组的多样性和/或丰度改变相关，仍是进化共生研究领域中尚未得到验证的假说。本研究以海胆属（Heliocidaris）物种从浮游营养型（planktotrophy，摄食模式）到卵黄营养型（lecithotrophy，非摄食模式）的生活史转变为研究模型，证实功能性肠道的缺失与微生物群落多样性、丰度的降低，以及与特定饮食相关微生物组的关联减弱存在对应关系。本研究还发现，卵黄营养型海胆可垂直传播立克次体目（Rickettsiales）微生物，该类群可通过氨基酸生物合成途径辅助宿主获取营养，并对宿主繁殖产生影响。本研究结果表明，功能性肠道的演化丢失与微生物组的缩减以及与内共生体的关联存在显著相关性。Symbioti...