Rare biosphere exploration using high-throughput sequencing: research progress and perspectives

Identification of rare species and mapping their distributions is crucial for understanding natural species distributions and causes and consequences of accelerating species declines. However, detection of rare species in both terrestrial and especially aquatic communities typically dominated by numerous microscopic species (i.e. rare biosphere) represents a formidable technical challenge. Rapid advances in high-throughput sequencing (HTS) technologies have revolutionized biodiversity studies in the rare biosphere, and also stimulated associated debates. Here we summarize research progress, discuss debates and problems, and propose possible solutions and future studies to address these issues. In addition, we provide take-home messages for experimental design and data interpretation when utilizing HTS techniques for rare biosphere exploration in ecology and conservation biology.