A STABLE EIMERIAN ASSEMBLAGE IN WYOMING GROUND-SQUIRRELS (SPERMOPHILUS ELEGANS ELEGANS) - MAINTAINING VIABILITY OVER WINTER

A Stable assemblage of 3 uncommon (prevalence < 20%) and 3 common (pre valence > 45%) species of Eimeria (Apicomplexa: Eimeriina) is known to infect Wyoming ground squirrels (Spermophilus elegans elegans). Sever al factors may contribute to the prevalence stability including host i mmune response, parasite-parasite interactions, and oocyst survival un der ambient environmental conditions. To determine the effects of vari ous environmental conditions on 3 of these eimerians, oocysts of 1 unc ommon (E. larimerensis) and 2 common (E. beecheyi and E. callospermoph ili) species were placed into 6 treatment groups and sampled monthly o ver winter. Treatments included ambient temperature (sun, shade, and s ubsoil) and constant 8 degrees C temperature (moistened with 2% potass ium dichromate or water, or allowed to desiccate). After 6 mo, oocysts from each treatment were administered to uninfected squirrels (2 squi rrels per treatment group). Although all oocysts examined appeared gro ssly abnormal when examined microscopically, all 12 squirrels develope d patent infections of E. larimerensis and E. callospermophili, and 11 of 12 developed infections of E. beecheyi. All 3 eimerian species mai ntained viability under conditions of severe desiccation, ultraviolet radiation, and repeated freezing and thawing. It is likely that resist ance to harsh environmental conditions plays an important role in the maintenance of this parasite assemblage.