Figure 4.

A hypothetical illustration of the evolutionary frameworks at different biological scales. Here, we present a scenario where the existence of three frameworks analyzed in this study–life history theory, evolution of virulence, and generalism–specialism–could be reconciled through application to different scales of virus–host interactions. Life history theory could be applied to the problem of reproduction within a cell versus surviving transmission between cells. The evolution of virulence might apply to virulence traits associated with growth within a host at the organismal scale, and transmission to other (generally conspecific) hosts. Lastly, for the generalism–specialism dichotomy, the purported tradeoff exists between growth fitness within a single species or population and the ability to propagate across different species or populations. This entire model represents a speculative view on tradeoff frame- works whereby they could all operate and have relevance for our efforts to understand the constraints underlying virus evolution.