Associations between innate immune function and ectoparasites in wild rodent hosts

Area of Science:

• Ecology
• Evolutionary Biology
• Immunology

Background:

• Host immune function is crucial for fitness, with investment influenced by parasitism risk.
• Ectoparasites like ticks, fleas, and mites can significantly impact host health and survival.
• Understanding host-parasite coevolutionary dynamics is key to predicting host-parasite interactions.

Purpose of the Study:

• To investigate the relationship between ectoparasite burden and innate immune function in two rodent species.
• To test the hypothesis that higher tick burdens correlate with enhanced immune function as an evolutionary adaptation.
• To explore potential differences in immune responses related to flea and mite infestations.

Main Methods:

• Sampling of white-footed mice (Peromyscus leucopus) and prairie voles (Microtus ochrogaster) and their ectoparasites.
• Quantification of tick, flea, and mite burdens on individual hosts.
• Measurement of host innate immune function using a bacterial killing assay.

Main Results:

• Peromyscus leucopus exhibited significantly higher bacterial killing ability, correlating with higher tick burdens, compared to Microtus ochrogaster.
• No significant difference in total flea burden was found between species, nor a relationship with immune function.
• Microtus ochrogaster had higher mite burdens, with females carrying more mites than males, but no link to immune function was established.

Conclusions:

• Higher tick burdens in Peromyscus leucopus are associated with enhanced innate immune function, supporting an evolutionary response to parasitism.
• The energetic costs of maintaining high immunity appear to be balanced by benefits in Peromyscus, unlike in Microtus.
• Immune responses to fleas and mites may differ due to host specificity and lack of known vector roles in North American mites.