Evaluating the Physiological Response of Sub-lethal Infections of Sphaeridiotrema spp. and Cyathocotyle bushiensis trematodes in Captive Lesser Scaup (Aythya affinis)

Since 2000, thousands of lesser scaup (Aythya affinis) die annually during migration through the Upper Midwest, USA from Cyathocotyle bushiensis (Cb) and Sphaeridiotrema spp. (Ss) intestinal infections after consuming infected exotic faucet snails (Bithynia tentaculata). Faucet snails have since reached Pool 13 of the Mississippi River raising concern of further spread to Pool 19, a critical mid-latitude stopover area for lesser scaup. Although not all trematodiasis infections result in mortality, we hypothesize that sub-lethal infection may affect subsequent migration and fitness through decreased body condition, indexed by a wide range of blood metabolites (e.g., triglycerides, glucose, albumin), white blood cells (WBCs), and total body measures (e.g., weight and temperature). We experimentally tested these physiological parameters in captivity with wild-caught and captive-reared lesser scaup. In July 2019, 21 wild-caught females received a single sub-lethal dose (x¯ = 96 Ss and x¯ = 169 Cb) of metacercariae while 16 individuals served as controls. In December 2019, 16 male and female captive-reared lesser scaup received a single sub-lethal dose (x¯ = 293 Ss and x¯ = 124 Cb) of metacercariae while 8 individuals served as controls. We collected blood, feces, body temperature, and weight from all individuals prior to dosing (i.e., day 0), on day 5, and on day 10 when all birds were euthanized and necropsied. Preliminary results suggest that infected individuals had decreased blood biochemical concentrations of triglycerides, blood urea nitrogen, bilirubin, albumin, PCV, and overall decreased body condition, but increased concentrations of non-esterified fatty acids, eosinophils, basophils, and WBCs as well as elevated body temperature. We witnessed mixed results between trials in ß-hydroxybutyrate and glucose concentrations. Infected individuals experienced a predicted physiological reaction to the treatment, but those in better body condition (i.e., captive-reared birds) experienced a less severe reaction.