Biodiversity among viral populations. Pyrosequencing data sets from each individual were clustered at 0% (unique) to 10% genetic distances and displayed as rarefaction curves. Y-axis, number of OTU (number of sequence clusters); x-axis, percent of total pyrosequences (sequences sampled ÷ total number of sequences x 100%). Colors of curves indicate the level of clustering: yellow, 0%; black, 1%; blue, 2%; green, 3%; cyan, 4%; purple, 5%; red, 10%. Numbers of OTU at the end of curves at 0% distance represent biodiversity calculated from rarefaction curve at the sequence depth (100% of pyrosequences). Small red boxes indicate approximate sequence depth achieved by conventional clonal sequences.