Phylogeographic and Ecological Insights Into the Evolutionary History of the Grass- and Sedge-Specializing Deltocephalinae Leafhoppers.

Grass- and sedge-specializing species comprise approximately one-third of the tribes in the Deltocephalinae subfamily, making them an integral part of grassland ecosystems in Mongolia, where grasslands and arid rangelands dominate. However, their evolutionary and ecological dynamics remain poorly understood. We sampled 22 sites across Mongolia and identified 37 species from 16 genera of Deltocephalinae, including 10 new records for Mongolia. These sites were specifically selected to focus on regions with high diversity and abundance of grass- and sedge-specialized Deltocephalinae, based on previous surveys and accessibility for fieldwork. Seventeen of the 22 sites are concentrated in central and eastern Mongolia, representing key habitats rather than a fully random or uniform distribution across the country. Phylogenetic analyses supported the monophyly of grass- and sedge-specializing tribes, and divergence dating placed their split from other Deltocephalinae at ~95.9 Ma, predating the origin of grasses and sedges (76-88 Ma). This suggests early host shifts or ecological flexibility, with subsequent diversification and dispersal coinciding with the expansion of grasslands. Ecological niche modeling revealed that the distribution of grass- and sedge-specializing species contracted during the Last Glacial Maximum, likely due to colder, drier climates and predicts further contraction under future anthropogenic pressures such as overgrazing. This study provides the first comprehensive phylogeographic and ecological analysis of grass- and sedge-specializing leafhoppers in Mongolia, offering new insights into their diversification and interactions with grassland ecosystems.