Abstract
As natural reservoirs for diverse viruses, mammals harbor complex and highly diverse viral communities. The Qinghai-Tibet Plateau, recognized as the "Third Pole" of Earth, exerts substantial evolutionary pressure on virions through its extreme environmental conditions characterized by high altitude, hypoxia, intense ultraviolet radiation, and dramatic diurnal temperature variation. Circular Rep-encoding single-stranded DNA (CRESS-DNA) viruses represent a ubiquitous group of small viruses that play crucial roles in maintaining global ecological equilibrium. Through viral metagenomic analysis of 741 fresh fecal samples collected from six wild herbivorous mammal species across three geographical regions of the Qinghai-Tibet Plateau, we systematically characterized their virome composition, revealing distinct interspecies variations in viral community structure. Focusing on CRESS-DNA viruses, we identified 180 complete viral sequences containing intact replication-associated protein (Rep) genes, including: Circoviridae (2 sequences, 1 novel), Genomoviridae (48 sequences, 38 novel), Smacoviridae (106 sequences, 103 novel), and Unclassified CRESS-DNA viruses (24 sequences, 20 novel), collectively representing an 86% discovery rate of novel viral virus. These viral sequences exhibited remarkable genetic divergence, with the majority (73%) failing to cluster within established taxonomic units, suggesting the plateau may constitute an evolutionary hotspot for novel CRESS-DNA viruses. Our findings not only expand current understanding of CRESS-DNA viral diversity but also indicate potential long-term symbiotic virus-host relationships rather than purely pathogenic interactions in this extreme ecosystem. Notably, high viral detection rates in species such as the Pseudois nayaur suggest their potential role as key transmission vectors. These discoveries provide novel insights into virus-host coevolution mechanisms under extreme environmental conditions and establish a scientific foundation for early warning systems of viral transmission risks in high-altitude ecosystems.
