The Ecology and Genetics of a Host Shift: Microbotryum as a Model System

Abstract

The need to prevent and cure emerging diseases often precludes their continuing study in situ. We present studies on the process of disease emergence by host shifts using the model system of anther-smut disease (Microbotryum violaceum) on the plant genus Silene (Caryophyllaceae). This system has little direct social impact, and it is readily amenable to experimental manipulation. Our microevolutionary studies have focused on the host shift of Microbotryum from Silene alba (=latifolia; white campion) onto Silene vulgaris (bladder campion) in a population in Virginia. Karyotypic variation shows that the host shift is recent and originates from the disease on sympatric S. alba. Analysis of the spatial pattern of disease shows that the host shift has been contingent on the co-occurrence of the two species at a local scale. Cross-inoculation studies show that families of the new host differ greatly in their susceptibility to the pathogen, indicating the potential for rapid evolution of resistance. Disease expression on the new host is frequently abnormal, suggesting that the pathogen is imperfectly adapted to its new host. In experimental populations, disease transmission within populations of the old host is greater than within populations of the new host. However, there is also a high transmission rate of the disease from the new host back to the old host, suggesting a feedback effect that increases disease prevalence in the community as a whole. Continuing studies of these populations are designed to determine whether this new host-pathogen system is likely to be self-sustaining and to quantify evolutionary changes in both the host and the pathogen.

Similarities among ectoparasite fauna of sigmodontine rodents: phylogenetic and geographical influences

“…The range of parasites that are associated with a particular host species may be influenced by evolution and is primarily influenced by the acquisition and loss of parasite species over time. A host species acquires a parasitic species either by inheritance from ancestral host species (Brooks, 1988) or by exchange with other related or unrelated host species that co-occur in the same geographical area (Antonovics et al 2002;Brooks et al 2006). In contrast, the loss of an associated parasite species can occur through historical 'accidents' (e.g., the abrupt division of a host population in which a founding population becomes isolated and free of a specific parasite species) or by the dispersal of the host species to new environments, which present unfavourable conditions for some parasite species (e.g., the absence of an appropriate intermediate host in the new environment) (Hafner and Page, 1995;Paterson et al 1999).…”

Repetitive DNA in the automictic fungus Microbotryum violaceum

“…Cryptococcus neoformans; Goodwin & Poulter, 2001), and how completely an organism must restrict outcrossing to decrease repetitive element diversity is unknown. Here, I describe repetitive DNA in the genome of Microbotryum violaceum, a highly selfing basidiomycete fungus (Antonovics, Hood & Partain, 2002;Garber & Ruddat, 2002;. The study is based on a genome sampling approach that could also be used to investigate the nuclear content in other organisms where complete genome sequencing is not feasible.…”

Disease in Natural Plant Populations, Communities, and Ecosystems: Insights into Ecological and Evolutionary Processes

“…Finally, research on disease in natural systems can solidify important research questions and approaches that have practical benefit. Antonovics et al (13), for example, illustrated how studies of fungal infection of a roadside weed allowed them to explore fundamental questions about emerging diseases that would be impossible to address in human or agricultural situations.…”

“…In two different studies where the anther-smut pathogen was found to infect previously unknown hosts, disease symptoms on the new host were atypical, suggesting poor adaptation (13,76). Inoculation experiments with the new host revealed considerable variation in susceptibility, suggesting the potential for rapid evolution of host resistance (13).…”

“…In two different studies where the anther-smut pathogen was found to infect previously unknown hosts, disease symptoms on the new host were atypical, suggesting poor adaptation (13,76). Inoculation experiments with the new host revealed considerable variation in susceptibility, suggesting the potential for rapid evolution of host resistance (13). Although one might predict that pathogens would move to genetically related host species, Roy (110) found that geographic proximity of potential hosts was a stronger predictor of host shifts than phylogenetic relationships in a study of rusts on crucifers.…”