Shannon entropy to evaluate substitution rate variation among viral nucleotide positions in datasets of viral siRNAs

Next-generation sequencing has opened the door to the reconstruction of viral populations and examination of the composition of mutant spectra in infected cells, tissues, and host organisms. In this chapter we present details on the use of the Shannon entropy method to estimate the site-specific nucleotide relative variability of turnip crinkle virus, a positive (+) stranded RNA plant virus, in a large dataset of short RNAs of Cicer arietinum L., a natural reservoir of the virus. We propose this method as a viral metagenomics tool to provide a more detailed description of the viral quasispecies in infected plant tissue. Viral replicative fitness relates to an optimal composition of variants that provide the molecular basis of virus behavior in the complex environment of natural infections. A complete description of viral quasispecies may have implications in determining fitness landscapes for host-virus coexistence and help to design specific diagnostic protocols and antiviral strategies.