Decades of Enclosure Protection Exert Composite Effects on Grassland Grasshopper Communities

Grasshoppers serve as crucial indicator taxa for assessing the health of grassland ecosystems. While numerous studies have investigated the effects of enclosure protection or overgrazing on grasshopper diversity, it remains unclear whether grasshoppers exhibit phenotypic plasticity and genetic adaptation under different habitat pressures-particularly for species with limited dispersal capacity. This study systematically investigated the effects of 20-40 years' enclosure protection on grasshopper community diversity compared to overgrazing. Furthermore, using the low-mobility grasshopper Chorthippus fallax as a model, we compared egg development rates between the two management regimes and elucidated the underlying genetic structure and differentiation patterns. The results revealed that enclosure protection significantly reshaped grasshopper community structure and led to species-specific population dynamics, despite not altering the Shannon-Wiener index or species richness. Eggs of C. fallax from exclosure-protected sites exhibited a significantly longer development duration than those from overgrazed sites (26.34 vs. 25.74 days; p < 0.05). Population genetic analyses revealed no obvious genetic structure or differentiation between the two groups (F_ST < 0.05). A total of 389 candidate outlier loci potentially associated with environmental adaptation were identified using both BayeScan and F_ST-based methods. Subsequent evolutionary simulations demonstrated that strong genetic differentiation at these loci between the two populations could emerge within approximately 162 ± 19 years under the assumed conditions (F_ST = 0.25; s = 0.05). This study not only reveals the phenotypic and genetic responses of grasshoppers to enclosure protection but also provides a scientific basis for designing sustainable grassland management strategies.