Ecological opportunity as a driving force of radiation events and time-dependent evolutionary rates in papillomaviruses

Papillomaviruses (PVs) have a wide host range, infecting mammals, birds, turtles, and snakes. The recent discovery of PVs in different fish species allows for a more complete reconstruction of the evolutionary history of this viral family. In this study we perform phylogenetic dating to analyse evolutionary events that occurred during PV evolution, as well as to estimate speciation and evolutionary rates. We have used four different data sets to explore and correct for potential biases that particular taxa combinations may introduce during molecular time inference. When considering the evolution of substitution rates we observed that short-term rate estimates are much higher than long-term rate estimates, also known as the time-dependent rate phenomenon. When considering the evolution of viral branching events (as a proxy for speciation rates), we show that these have not been constant through time, suggesting the occurrence of distinct evolutionary events such as adaptive radiations and/or changes in the available host niches. In a joint analysis with host speciation rates, we identified at least four different evolutionary periods, suggesting that the evolution of PVs has been multiphasic, and thus refining the previously suggested biphasic evolutionary scenario. Thanks to the discovery of novel PVs in basal hosts and to the implementation of a time-dependent rate model for molecular dating, our results provide new insights into the evolutionary history of PVs. In this updated evolutionary scenario, ecological opportunity appears as one main driving force for the different radiation and key-innovation events we observe.