Bayesian inference of ancestral host-parasite interactions under a phylogenetic model of host repertoire evolution

Intimate ecological interactions, such as those between parasites and
their hosts, may persist over long time spans, coupling the evolutionary
histories of the lineages involved. Most methods that reconstruct the
coevolutionary history of such interactions make the simplifying
assumption that parasites have a single host. Many methods also focus on
congruence between host and parasite phylogenies, using cospeciation as
the null model. However, there is an increasing body of evidence
suggesting that the host ranges of parasites are more complex: that host
ranges often include more than one host and evolve via gains and losses of
hosts rather than through cospeciation alone. Here, we develop a Bayesian
approach for inferring coevolutionary history based on a model
accommodating these complexities. Specifically, a parasite is assumed to
have a host repertoire, which includes both potential hosts and one or
more actual hosts. Over time, potential hosts can be
added or lost, and potential hosts can develop into actual hosts or vice
versa. Thus, host colonization is modeled as a two-step process that may
potentially be influenced by host relatedness. We first explore the
statistical behavior of our model by simulating evolution of host-parasite
interactions under a range of parameter values. We then use our approach,
implemented in the program RevBayes, to infer the coevolutionary history
between 34 Nymphalini butterfly species and 25 angiosperm families. Our
analysis suggests that host relatedness among angiosperm families
influences how easily Nymphalini lineages gain new hosts.