UWEC CERCA 2025

Understanding why some individuals within populations are more prone to harbor parasites (and diseases) than others is an important biological question. Repeated measures on marked individuals over time are required to assess the extent to which individual identity, age, sex, or year of study most strongly shape prevalence in nature. Here, we studied the potential for age and sex to structure parasite prevalence in the California ground squirrel (Otospermophilus beecheyi). This native rodent is common across California and frequently interacts with humans. Its fleas have been studied extensively in the context of bubonic plague, but their endoparasites have not been the subject of systematic study. As part of a long-term study, we collected fleas in 70% ethanol and fecal samples in formalin from live-trapped individual ground squirrels of known ages and sexes in situ for two consecutive years. We microscopically identified parasite prevalence in the lab. We explored individual squirrels’ parasitic profiles for members of two study populations that vary in levels of human disturbance. Our findings offer an in-depth understanding of how identity, age, and sex of hosts influence parasite prevalence in our two study populations but also have implications for understanding zoonotic diseases in human-altered landscapes.