Dr. Burch will use the bacteriophage phiX174 and its alternative hosts, E. coli and S. typhimurium, to investigate the impact of host limitation on the evolution of host range in this virus. By manipulating host limitation, she will test the hypothesis that the benefits of host range expansion outweigh the costs when hosts are limited, and that the costs of host range expansion outweigh the benefits when hosts are abundant.
The advantages of host range expansion for parasites include reduced competition for hosts, reduced time spent searching for hosts, and increased probability of transmission to a suitable host. However, parasites are most often observed to specialize on a limited number of hosts. This specialization may be explained by a variety of costs associated with broad host range, including a possible trade-off between fitness on one host and fitness on alternative hosts. Experimental studies of host range have tended to concentrate on the potential costs of expanded host range rather than the potential benefits. In contrast, Dr. Burch will study the evolution of host range by presenting the bacteriophage phiX174 with ecological conditions in which the benefits of expanded host range differ. Studies of this nature may help identify ecological conditions that favor acquisition of new hosts, as in the recent movement of HIV into humans from chimpanzees.
