Seasonal Dynamics, Host Network Structure, and Environmental Drivers of Gamasid Mite Communities on Small Mammals in a Dry–Hot Valley: A Year-Round Monitoring Study

Ectoparasitic gamasid mites on small mammals play crucial roles in transmitting zoonotic pathogens like hantaviruses associated with hemorrhagic fever with renal syndrome (HFRS). To elucidate their community, network structure, and seasonal drivers in xeric habitats, a consecutive 12-month localized survey was conducted in Waxi Village, Binchuan County, a dry–hot valley in Yunnan Province, southwest China, from November 2020 to October 2021. From 1329 captured small mammals (18 species, 89.62% rodents), 12,075 gamasid mites belonging to 33 species were identified. The community exhibited overwhelming dominance by the family Laelapidae (Cr = 99.35%) and genus Laelaps (Cr = 97.37%). Laelaps algericus, L. guizhouensis, and L. nuttalli constituted the dominant mite species (cumulative Cr = 88.96%) and formed a tightly correlated core species cluster. Overall infestation prevalence (PM), mean intensity (MI), and mean abundance (MA) were 46.05%, 19.73 mites/host, and 9.09 mites/host, respectively. The bipartite host–gamasid network revealed a significantly nested architecture (NODFobs = 31.16, Z = 14.03, p < 0.001) with high specialization (H2′ = 0.599), anchored by dominant hosts (Rattus andamanensis, Apodemus chevrieri, and Mus caroli). α-diversity analysis showed that Margalef richness, Shannon–Wiener index, and Gini–Simpson index peaked in autumn (November), while troughs occurred in mid-spring (April) and mid-autumn (October). Non-metric multidimensional scaling (NMDS, stress = 0.0048) and PERMANOVA (R2 = 0.074, p = 0.001) confirmed significant seasonal shifts in community composition. Standard redundancy analysis (RDA) suggested temperature as the primary climatic driver (F = 7.205, p = 0.001; total model explanation = 8.2%). However, partial RDA (pRDA) conditioning on host species identity demonstrated that climatic variables directly accounted for only 0.1% of net variance (F = 0.662, p = 0.521). Our findings indicate that gamasid mite community assembly in this dry–hot valley is characterized by strong species dominance and network nestedness and that seasonal fluctuations are consistent with a host-mediated pattern rather than being directly governed by climate.