Survival, Immune System, Oxidative Stress and Body Condition

Principal Investigator:
Caroline Brady, M.Sc. Graduate

Supervisors:
Dr. Scott Petrie, Long Point Waterfowl 
Executive Director
Dr. Robert Bailey, University of Western Ontario

 

The combined continental Greater and Lesser scaup population declined between the mid-1980s and late 1990s, and is still 33% below the long-term average.  The contaminant hypothesis, one of several hypotheses proposed to explain the decline and lack of recovery, suggests scaup are acquiring levels of trace metals and/or other contaminants that subsequently impact survival or reproduction.  Elevated contaminant burdens can cause increased mortality, impaired reproduction, suppressed immune function, oxidative stress, and reduced body condition in waterfowl.

Liver concentrations of many trace elements, and organic compounds have been measured in free-ranging scaup collected at various locations throughout the year. Selenium (Se) is the only contaminant that was consistently observed at
concentrations of potential concern in staging and wintering scaup.  Se is a semi-metallic trace element that is required by birds in low concentrations but can become toxic at slightly elevated concentrations.  In captive mallards (Anas platyrhynchos), liver Se concentrations >10 mg/kg (dw) can cause reproductive impairment; concentrations > 33 mg/kg can cause sub-lethal effects such as decreased body weight, and histopathological lesions, but it is unclear what dietary Se dose results in liver levels of >10 mg/kg, and >33mg/kg in scaup.

The Lower Great Lakes (LGL) region has historically been used by large numbers of staging and wintering scaup; these birds primarily ate native bivalves and gastropods.  However, non-native Zebra (Dreissena polymorpha) and Quagga (D. bugensis) mussels (hereafter dreissenid mussels) have established and reached substantial densities on the LGL.  With this readily available food source, scaup began incorporating large quantities of dreissenid mussels into their diets.  Unlike native bivalves, dreissenid mussels can filter large quantities of water, thus accumulating water- and pelagic-based contaminants, including Se, which becomes available for food chain transfer to molluscivorous waterfowl such as scaup.  If Se is contributing to the lack of recovery of the scaup population, it may be doing so by interacting with natural stressors, such as weather, disease and disturbance, in such ways to reduce adult health and survival.

Long-term exposure to Se warrants concern because elevated Se burdens in aquatic birds has been associated with negative reproductive and physiological effects, such as reduced breeding propensity, delayed egg initiation, embryotoxicity, reduced offspring survival, hepatic lesions, abnormal feather loss, and emaciation.  Although long-term effects of elevated Se are currently unknown in scaup, it is plausible that scaup that stage and winter on the LGL (4-6 month duration) are being adversely impacted.

Although several captive Se-dosing studies have assessed the reproductive impacts on waterfowl, few have examined wintering survival.  Therefore, the purpose of this study is to investigate the effect of Se-dosing on staging and wintering captive Lesser Scaup using a number of indicators of health (e.g., immune function, stress response and body condition) in relation to liver Se levels.  This study will also determine survival rates of birds fed a diet of Se enriched food at two dosages (low: 11.5 mg/kg and high:23 mg/kg) in comparison to a control and determine if it is physiologically possible for Lesser Scaup to survive above the 33 mg/kg hepatic Se threshold.

Hypotheses and Predictions

Primary Prediction: Survival and health of captive, wild-strain Lesser Scaup are differentially affected by accumulation and chronic exposure to Se (via dietary intake) during a six-month wintering period in Southern Ontario.

Hypothesis 1: Hepatic Se levels of Lesser Scaup are affected by the dietary Se dose, and duration of exposure.

Prediction 1a:  Birds fed a control diet will have background hepatic Se levels (<10 mg/kg), birds in the fed the low dose diet (11.5 mg/kg) will exhibit elevated hepatic Se levels (>10-32mg/kg), and birds fed the high dose diet (23 mg/kg) will have sub-lethal hepatic Se levels (>33mg/kg); hepatic Se concentrations will increase over time in both high and low dose groups.

Hypothesis 2: Hepatic Se levels and duration of Se exposure throughout winter affect survival of Lesser Scaup.

Prediction 2a: Birds with elevated and sub-lethal hepatic Se burdens will exhibit lower survival than birds with background hepatic Se levels.

Prediction 2b: Cohort-specific (week 8, 16, 24) survival estimates within control groups will be higher than birds with sub-lethal hepatic Se levels; survival of birds with elevated hepatic Se levels will be intermediate to birds with sub-lethal hepatic levels and control birds throughout winter.

Prediction 2c: Survival estimates of control groups will not differ throughout winter (i.e., among week 8, 16, and 24 cohorts), but will decrease over time in birds with both elevated and sub-lethal hepatic Se levels.

Hypothesis 3: Immune function response and the condition (size/mass) of immune system organs (i.e., thymus, bursa of fabricus and spleen) of Lesser Scaup are affected by hepatic Se levels, and duration of exposure to Se throughout winter.

Prediction 3a: Individuals with sub-lethal hepatic Se levels will have a lower immune response (i.e., less swelling response to the phytohemagglutinin skin test, and fewer immunoglobulin (Ig) M (primary antibody), and IgG (secondary response) antibodies produced in reaction to the sheep red blood cell injection) and will exhibit smaller/lighter organs as compared to birds in the control group; immune function response and organ size/mass of birds with elevated hepatic Se levels will be intermediate to birds with sub-lethal hepatic levels and control birds throughout winter.

Hypothesis 4: Oxidative stress in liver tissues of Lesser Scaup are affected by hepatic Se level and duration of exposure to Se throughout winter.

Prediction 4a: Scaup with sub-lethal hepatic Se levels will have lower liver glutathione reserves, and increased lipid peroxidation; birds with elevated hepatic Se levels will be intermediate to birds with sub-lethal hepatic Se levels and the control birds.

Hypothesis 5: Body condition (fat, protein, and mineral) of Lesser Scaup will be affected by hepatic Se levels and duration of exposure to Se throughout winter.

Prediction 5a: Birds with sub-lethal hepatic Se levels will weigh less and have lower total fat, total protein, and mineral content than birds with elevated hepatic Se levels and control birds.

Hypothesis 6: Organ weights of Lesser Scaup will be affected by hepatic Se level and duration of exposure to Se throughout winter.

Prediction 6a: Birds with sub-lethal hepatic Se levels will have lighter (i.e.,spleen and pancreas), and heavier (i.e., liver, heart, and kidneys) organs than birds with elevated hepatic Se levels and control birds.


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