New Insights Into the Evolution of Immune Adaptors in Murid Rodents

The evolutionary dynamics of immune adaptors in wildlife remain poorly understood, despite their critical role in host-pathogen interactions. In this study, we investigated the molecular evolution of five TIR domain-containing adaptors (MAL, MyD88, SARM, TRAM, and TRIF) in murid rodents across both interspecific and population levels to provide an integrative view of their evolutionary trajectories. Our analyses demonstrate that these adaptors are predominantly under purifying selection in murids, yet contain specific positively selected sites in MAL and MyD88, indicating localized adaptive fine-tuning. These positively selected amino acid sites exhibited substantial genetic divergence among murid species. Within populations, we observed reduced genetic diversity in the adaptor genes compared with noncoding regions across the whole genome in both Rattus tanezumi and Rattus norvegicus, and no significant signals of recent positive or negative selection were detected in either species. Notably, we identified identical or nearly identical allelic variants between these two rat species across all five adaptor genes. Collectively, this study delineates the evolution of immune adaptors in murids across both deep and recent timescales, advancing our understanding of adaptive evolution in multilevel immune systems.