Botfly infections impair the aerobic performance and survival of montane populations of deer mice, Peromyscus maniculatus rufinus

1. Elevations >2000 m represent consistently harsh environments for small endotherms because of abiotic stressors such as cold temperatures and hypoxia.
2. These environmental stressors may limit the ability of populations living at these elevations to respond to biotic selection pressures — such as parasites or pathogens — that in other environmental contexts would impose only minimal energetic- and fitness-related costs.
3. We studied deer mice (Peromyscus maniculatus rufinus) living along two elevational transects (2300 – 4400 m) in the Colorado Rockies and found that infection prevalence by botfly larvae (Cuterebridae) declined at higher elevations. We found no evidence of infections at elevations > 2400 m, but that 33.6% of all deer mice, and 52.2% of adults, were infected at elevations < 2400 m.
4. Botfly infections were associated with reductions in hematocrit levels of 23%, hemoglobin concentrations of 27%, and cold-induced VO2max measures of 19% compared to uninfect...