show Abstracthide AbstractAlphaviruses are mosquito-borne viruses that cause significant human disease ranging from fever and joint pain to chronic debilitating arthritis and severe neurological disease. Mayaro virus (MAYV) is an alphavirus that causes severe arthritis in South America and the Caribbean, but has the potential to spread into new areas similar to the closely related, chikungunya virus (CHIKV). The goal of these studies was to assess the potential for MAYV to adapt to a widely distributed urban mosquito vector, Aedes aegypti using complemntary experimental evolution approaches. We found a mutation with the receptor-binding protein, E2, that resulted in increased viral replication in mosquito cells and greater transmission in live mosquitoes. Importantly, this mutation also reduced the fitness of the virus in human cells, suggesting this mutation is unlikely to enable spread of MAYV without additional mutations.