Climate heterogeneity, season variation, and sexual dimorphism modulate the association between MHC II diversity and parasite variation in striped hamster.

Parasite-mediated selection is widely believed to play a crucial role in maintaining the diversity of the major histocompatibility complex (MHC) genes, which is thought to be maintained through heterozygote advantage, rare-allele advantage, and fluctuating selection. However, the relationship between parasite pressure and MHC diversity has yielded inconsistent findings. These inconsistencies may arise from the influence of environmental factors and individual variations in traits on host-parasite interactions. To address these issues, our study extensively investigated populations of striped hamsters inhabiting regions characterized by environmental heterogeneity. The primary objective was to examine the universality of parasite-mediated selection mechanisms. Our observations revealed the presence of multiple parasite infections, accompanied by spatial and temporal variations in parasite communities and infection patterns among individual hamsters. Specifically, the temperature was found to influence all four parasite indices, while the presence of gamasid mites and parasite richness decreased with increasing precipitation. We also noted significant seasonal variation in parasite dynamics. Moreover, a significant sexual dimorphism was observed with males exhibiting a considerably higher parasite burden compared to their female counterparts. Lastly, we identified the maintenance of MHC polymorphism in striped hamsters as being driven by the heterozygote advantage and fluctuating selection mechanisms. This study underscores the significance of ecological processes in comprehending host-parasite systems and highlights the necessity of considering environmental factors and individual traits when elucidating the mechanisms underlying MHC diversity mediated by parasites.