Evolution and maintenance of microbe-mediated protection under
occasional pathogen infection
Abstract
Every host is colonized by a variety of microbes, some of which can
protect their hosts from pathogen infection. However, pathogen presence
naturally varies over time in nature, such as in the case of seasonal
epidemics. We experimentally coevolved populations of
Caenorhabditis elegans worm hosts with bacteria possessing
protective traits (Enterococcus faecalis), in treatments varying
the infection frequency with pathogenic Staphylococcus aureus
every host generation, alternating host generations, every fifth host
generation or never. We additionally investigated the effect of initial
pathogen presence at the formation of the defensive symbiosis. Our
results show that enhanced microbe-mediated protection evolved during
host-protective microbe coevolution when faced with rare infections by a
pathogen. Initial pathogen presence had no effect on the evolutionary
outcome of microbe-mediated protection. We also found that protection
was only effective at preventing mortality during the time of pathogen
infection. Overall, our results suggest that resident microbes can be a
form of transgenerational immunity against rare pathogen infection.