Ostracod Genetic Variability in Response to Lake Level-Driven Salinity Dynamics in Nam Co, Central Tibetan Plateau,...

Sedimentary ancient DNA metabarcoding has revolutionized the reconstruction of past lake biodiversity, providing insights into species assemblages spanning thousands of years. We apply this approach to investigate ostracod community dynamics and genetic diversity in a two-millennia sedimentary record from Nam Co, the third largest lake on the Tibetan Plateau, where hydrological fluctuations have driven shifts in salinity and habitat conditions. Using stratigraphic sedaDNA analyses, temporal diversity indices, and environmental proxies, we linked ostracod assemblages to lake-level and climatic changes. Species richness peaked between 628 and 765 ce during moister conditions with increased minerogenic influx, and again since the mid-1970s amid recent warming and glacier-melt-driven lake-level rise. In the earliest sedaDNA record (~230 bce), Tonnacypris gyirongensis indicated warm, nutrient-rich, shallow estuarine conditions. Between ∼600 and ∼830 ce, Candona candida and Ilyocypris angulata reflect freshwater, organic-rich littoral habitats. During the Medieval Climate Anomaly (~948-1143 ce) and Little Ice Age (~1600-1678 ce), alternating dominance of Limnocythere sp. and Leucocytherella sinensis primarily signals changes in water level and salinity due to their different ecological tolerances. Genetic data reveal generally low lineage diversity in parthenogenetic taxa, punctuated by transient increases in phylogenetic diversity during moister intervals at the end of the Late Antique Cold Period (490-830 ce), the late Medieval Climate Anomaly period (1250-1400 ce), and recent warming. Sediments spanning the Little Ice Age exhibit stable richness but shifts in dominance patterns, indicating a change in salinity and alkalinity. Since the 1950s, a marked turnover has occurred with declining L. sinensis and rising Limnocythere inopinata, coinciding with reduced monsoon runoff; in contrast, the post-1970s freshening has promoted the resurgence of L. sinensis, alongside minor occurrences of I. angulata and L. inopinata. Our results demonstrate the sensitivity of Tibetan Plateau ostracod communities to hydrological and climatic variability. By integrating sedaDNA with paleoenvironmental proxies, we reveal both community-level and intra-species genetic responses to past climate change, underscoring the power of sedaDNA metabarcoding for paleoecological and evolutionary research.