COS 289-4 - Host-switching events affect the evolution of the network of interactions

Abstract: Host-switching events are frequent in nature, influencing the dynamics of parasite communities and affecting the evolution of ecological networks and species diversification. Here, we investigate how host-switching events in a microevolutionary scale alter the structure of host-parasite networks and shape the evolution of these interacting assemblages. We developed a theoretical model for the evolution of parasites incorporating the empirical host phylogenies and analyzed the resulting communities employing network science tools. In the model, parasite individuals can switch hosts under variable probability, which decreases as the host species differentiate. Empirical and simulated networks were characterized by: species richness, nestedness, connectance, and modularity. In our investigation, we first searched for the range of host-switching intensity that resulted in a network of interactions with a topology similar to the current empirical network, i.e., the model reproduced all metrics simultaneously for four of the ten analyzed datasets. In general, as the intensity of host-switching increases, modularity decreases, and connectance increases, both monotonically. In contrast, nestedness and richness present peaks for intermediate values of host-switching intensity. We then examined how the metrics changed over time within this range. For the four communities, at the beginning of the simulation, a unique host interacts with a single parasite, establishing a high connectance. New host species emerge over time, increasing the repertoire of parasites (hosts used) and leading to oscillations on the network structure's metrics and parasite richness. Once all host species in the community emerge, we observe an increase in parasite diversification, high modularity and low connectance and nestedness. When compared to null models the simulated networks over time varied from high to low nestedness and low to high modularity; however, none was nested nor modular at the current time. In conclusion, our study suggests that parasite diversity and the structure of the interaction network are not stationary over evolutionary time. These oscillations seem to be influenced by host speciation events.