Effects of the parasite Eimeria arizonensis on survival of deer mice (Peromyscus maniculatus)

Few experimental studies have documented the negative effect of parasites on fitness of hosts under natural or seminatural conditions. We studied the effect of Ei,nel-ia arizonensis (Protozoa) on recruitment, winter survival, and change in body mass in deer mice (Peromyscus maniculatus). In field observations, the presence of E. arizonensis was negatively related to recruitment in females and to over-winter survival in males. Experimental manipulation of E. arizonensis in large field enclosures also showed that infection negatively affected over-winter survival of males, There was no relationship between the body mass of deer mice and the presence of either natural or experimental infection. Thus, the mechanism through which E. arizonensis affects survival remains unclear.