Abstracts Biological Sciences

Intestinal helminth infections, distributions, and associations with health parameters of spring-migrating female Lesser Scaup in the upper Midwest

by Jamison Conner England

The continental breeding population of Lesser Scaup (Aythya affinis) reached a record low of 3.2 million in 2006 and has since remained below the goal of 6.3 million set by the North American Waterfowl Management Plan. Although many factors have been identified as possible contributors to the decline, the Spring Condition Hypothesis proposes reduced recruitment resulting from females in reduced condition as the most influential cause. Since 2002, infections with non-native trematodes transmitted by the invasive Faucet Snail (Bithynia tentaculata) have resulted in the deaths of tens of thousands of Lesser Scaup in the upper Midwest, USA during migrations. To determine if parasitic intestinal helminths were associated with reduced body condition and health, I collected 130 apparently healthy female Lesser Scaup and identified and enumerated helminths within their intestinal tracts. I also measured a suite of health parameters to identify associations between intestinal helminth infections and their sub-lethal effects on Lesser Scaup. Forty helminth taxa (20 trematodes, 14 cestodes, 4 nematodes, and 2 acanthocephalans) were identified, including one digenean (Plenosoma minimum) for the first time in Lesser Scaup and in the Midwest. Helminth species diversity and mean total helminth abundance were greatest in northern portions of the study region along the Mississippi River, and mean total helminth abundance was less in 2015 than in 2014. Host age and body size were not associated as factors contributing to helminth assemblage, which may be due in part to physiological changes experienced during migration. The intestinal helminth infracommunities of Lesser Scaup were found to vary across the four regions and two years of the study. Variations in helminth infracommunity structure were likely due to geophysical variation within the study area, prey item (intermediate host) diversity, and weather pattern variations that occurred between years thus affecting migration chronologies and prey abundance. Varying associations were detected between 11 health parameters and seven response variables of differing helminth metrics. Most notably were the relationships observed between helminth species diversity and body fat, albumin, glucose, and percentage of white blood cells that were monocytes. Total trematode abundance was negatively related to the plasma metabolite concentrations of non-esterified fatty acids and albumin. Total nematode abundance showed a strong negative association with plasma bilirubin concentrations. The daily lipid dynamic index, a ratio of blood metabolites used as an index of foraging habitat quality, showed a negative association with total cestode abundance and Sphaeridiotrema spp. intensity. Cestode total abundance was also negatively associated with the heterophil:lymphocyte ratio, an indicator of long-term stress, but displayed a strong, positive relationship with plasma bilirubin concentrations. The introduced trematodes responsible for annual die-offs of Lesser Scaup in the upper Midwest displayed…