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

Since 1998, during seasonal migrations throughout the Upper Midwest, U.S., tens of thousands of lesser scaup (Aythya affinis) have died from Cyathocotyle bushiensis (Cb) and Sphaeridiotrema spp. (Ss) (Class: Trematoda) intestinal infections after consuming infected exotic faucet snails (Bithynia tentaculata). Faucet snails serve as the first and second intermediate host for Cb and Ss and lesser scaup serve as the final host. First recorded in the Upper Mississippi River in 2002, faucet snails have been expanding south and to date, have reached Navigation Pool 13. This spread increases the concern that these epizootic events will soon occur in Navigation Pool 19, a critical mid-latitude stopover area for lesser scaup. The consequences of Cb and Ss infections on lesser scaup reproduction and morbidity are unknown. To address these gaps in our knowledge, the effects of sub-lethal trematode infections on the physiological response and body condition of lesser scaup in the Upper Mississippi River System were experimentally assessed. In spring 2019, female lesser scaup (n = 37) were captured from mid-latitude stopover areas (i.e., La Grange Pool of the Illinois River and Navigation Pool 19 of the Mississippi River) and held in captivity for 4 months at Forbes Biological Station, Havana, IL. Faucet snails were collected by hand from Navigation Pool 7 of the Mississippi River and artificially digested to recover infectious Cb and Ss metacercariae to infect birds. A total of 21 captive lesser scaup received a single sub-lethal dose (X̄ = 96 Ss and X̄ = 169 Cb) of metacercariae while 16 birds served as uninfected controls. All birds were euthanized 10 days later. Preliminary analysis of blood and fecal samples collected will explore temporal changes in lesser scaup health along a continuum from initial infection to point of euthanasia; clarifying the role these parasites may play in declining lesser scaup numbers and population health.