Beyond Urbanization: Haemogregarine Infection Dynamics in Freshwater Turtles Across Anthropogenic Landscapes

Parasites are increasingly recognized as indicators of ecosystem condition, in part, because the relative complexity of their life cycles relies on ecosystem stability over time. Haemogregarine infections in freshwater turtles are rarely reported as an assessment of freshwater ecosystems, despite these parasites being nearly ubiquitous and sensitive to environmental context. This study investigated haemogregarine infection prevalence and relative abundance of haemogregarine DNA in blood samples from multiple turtle species and across several aquatic ecosystems in Texas and New Mexico, USA. We evaluated associations with host species, river system, anthropogenically modified flow condition, and urbanization context from quantitative PCR results and statistical modeling. Host species was the most consistent predictor of infection patterns, with Trachemys scripta elegans exhibiting the highest observed infection prevalence and relative parasite DNA abundance, whereas Pseudemys gorzugi exhibited the lowest values. After accounting for host species, infection prevalence differed among river systems, and turtles from anthropogenically created low-flow or flow-modified habitats had lower infection odds than those from flowing habitats. Although observed infection prevalence was higher at sites classified as urban, this association was reversed after accounting for host species composition and flow condition, highlighting substantial confounding caused by uneven species representation across environments. Among qPCR-positive individuals, host species remained significantly associated with relative parasite DNA abundance, whereas flow condition and urban status provided only a slight reduction in unexplained variation. Relative carapace length was associated with infection prevalence among adults, whereas sex and standardized body mass were not. The results indicate that host species and environmental context contribute differently to haemogregarine infection dynamics and emphasize the importance of accounting for host-community composition when evaluating environmental effects.