Variable levels of immunity to experimental Eimetia arizonensis infections in natural, seminatural, and laboratory populations of deer mice (Peromyscus maniculatus)
Acquired immunity to parasites may affect both host and parasite population dynamics. Although immunity has been studied experimentally in laboratory-reared hosts, less attention has focused on free-living animals. I examined acquired immunity of free-living deer mice (Peromyscus maniculatus) to naturally occurring and experimental infections of Eimeria arizonensis (Protozoa: Coccidia). In a mark – recapture study, I found evidence of complete immunity to natural infections in only 1 of 3 years and evidence of partial immunity in all years. I subsequently examined partial immunity to experimental infections by giving laboratory-reared, free-living, and enclosure populations of deer mice two or three consecutive E. arizonensis infections. Greater than 90% (13 of 14) of laboratory-reared animals developed immunity after only one exposure, suggesting that E. arizonensis is immunogenic. However, significantly fewer animals living under natural and seminatural conditions developed immunity after one exposure in two of three experiments. These observational and experimental results suggest that immunocompetence of free-living deer mice to E. arizonensis may be variable and may differ with respect to that of laboratory-reared animals.