BASELINE PHYSIOLOGIC AND HEMATOLOGIC HEALTH IN WILD-CAUGHT MUSKRATS (ONDATRA ZIBETHICUS) FROM A NEAR-PRISTINE ECOSYSTEM IN NORTHERN MINNESOTA.

Muskrat (Ondatra zibethicus) populations show long-term and widespread declines across North America, necessitating research into potential mechanistic explanations, including population health. Previous research established reference hematology values, a proxy of individual health, of muskrats occurring in highly modified ecosystems. However, our knowledge of hematology metrics in muskrat populations occurring in more natural ecosystems is limited. We measured several hematological parameters of wild-caught muskrats (n = 73) in the Greater Voyageurs Ecosystem in northern Minnesota in 2018-2019 to establish baseline muskrat health in a relatively intact, near-pristine ecosystem. Additionally, we measured rectal temperature and heart and respiratory rates and collected whole blood for complete blood cell count assessment. We established baseline physiologic and hematologic reference ranges for the population and describe variations between total white blood cells, nucleated cell differentials, and basic erythron and platelet estimates and demonstrate methods of estimation to be poor proxies for more standardized counting methods. Our results establish a baseline to compare muskrat health assessments for populations affected by landscape change or in decline.

Landscape influence on spatial patterns of meningeal worm and liver fluke infection in white-tailed deer.

Parasites that primarily infect white-tailed deer (Odocoileus virginianus), such as liver flukes (Fascioloides magna) and meningeal worm (Parelaphostrongylus tenuis), can cause morbidity and mortality when incidentally infecting moose (Alces alces). Ecological factors are expected to influence spatial variation in infection risk by affecting the survival of free-living life stages outside the host and the abundance of intermediate gastropod hosts. Here, we investigate how ecology influenced the fine-scale distribution of these parasites in deer in Voyageurs National Park, Minnesota. Deer pellet groups (N = 295) were sampled for the presence of P. tenuis larvae and F. magna eggs. We found that deer were significantly more likely to be infected with P. tenuis in habitats with less upland deciduous forest and more upland mixed conifer forest and shrub, a pattern that mirrored microhabitat differences in gastropod abundances. Deer were also more likely to be infected with F. magna in areas with more marshland, specifically rooted-floating aquatic marshes (RFAMs). The environment played a larger role than deer density in determining spatial patterns of infection for both parasites, highlighting the importance of considering ecological factors on all stages of a parasite's life cycle in order to understand its occurrence within the definitive host.