Genome size evolution in grasshoppers (Orthoptera: Caelifera: Acrididae)

Grasshoppers (Orthoptera: Acrididae) are known for their significantly enlarged genome compared to other insects. However, our understanding of the evolutionary dynamics of genome size (GS) with this family is still limited. This study measured the GS of 62 grasshopper species using flow cytometry and assembled 10 new mitochondrial genomes for comparative phylogenetic analyses. An expanded species sampling discovered several grasshopper species with giant GS surpassing the previous insect record. We then applied recently developed methods to test more complicated, heterogeneous evolutionary models. We found that grasshopper GS has a strong phylogenetic signal and does not correlate with species' body size or flight ability. These results support the neutral or near-neutral hypotheses of GS evolution. However, GS had accelerated rates of evolution on some grasshopper lineages, suggesting heterogeneity in its evolutionary dynamics. Ancestral state reconstruction indicates that the large genome evolved before the origin of the Acrididae family. Future studies with more species measurements will help assess the frequency of macroevolutionary shifts and identify possible mechanisms for these shifts in grasshopper GS evolution.