In the mid-1980's until the late 1990's, Lesser Scaup (<i>Aythya affinis</i>)populations in the boreal forest declined and have remained at historical low levels since that time. This has resulted in a population well below conservation goals. Potential causes for this population decline include a reduction in productivity, which could be related to changes in boreal forest habitat, nutritional condition during reproduction, or due to contaminants acquired during migration or wintering. Though several studies have assessed contaminant levels in Lesser Scaup on wintering, staging and migration routes, relatively little data exist from northern boreal forest areas, one of the core breeding habitats of the Lesser Scaup population and where population declines appear to be most severe. To this end,male Lesser Scaup were trapped from sites in the northern boreal forest in 2004 and 2005 to assess trace element contaminant levels. Previous research has shown that trace elements including cadmium and selenium can influence hormonal status in waterfowl. Specifically, a positive relationship between cadmium and corticosterone and a negative correlation between liver selenium and corticosterone have been observed. The purpose of this study was to test the hypothesis that trace element contaminants can influence hormonal status and related physiological functions in male Lesser Scaup, and that interactions between contaminants, physiological variables such as body condition and social status can modify expression of toxic effects. Blood samples were collected from trapped males to assess stress related changes in blood chemistry (corticosterone, testosterone, glucose and thyroxine) and males were then collected for contaminant analysis and assessment of reproductive physiology. The geometric mean levels of kidney cadmium, liver selenium and liver mercury were 9ppm, 4.33 ppm, 1.31 ppm dry weight respectively. Several variables and interactions including pair status, cadmium, selenium, mercury, body condition and body size influenced corticosterone levels. In male Scaup with high cadmium levels, corticosterone was negatively related to liver selenium in birds with good body condition (R2=0.701,n=9, P=0.005) but not in birds with poor body condition (R2=0.033, n=10,P=0.61). Likewise, in birds with high cadmium, a negative association was found between liver mercury and corticosterone in structurally smaller males (R2=0.491,n=10, P=0.024), whereas no such relationship was found in larger males(R2=0.307, n=9, P=0.12). In birds with low cadmium and low mercury, selenium and corticosterone were negatively correlated (R2=0.568, n=10, P=0.012) while no association was found in males with high mercury (R2=0.325, n=10, P=0.085). Unpaired birds had higher corticosterone than in ducks with low cadmium(F1,17=6.70, P=0.023), while there was no difference between groups in ducks with high cadmium. Glucose levels were not influenced by contaminants or other variables in this study (R2=0.551, F21,17=0.99, P=0.51). Thyroxine levels were positively correlated to mercury levels in paired birds (R2=0.485, n=19, P<0.001)but were not related in unpaired birds (R2=0.063, n=20, P=0.28). Thyroxine levels also showed a relationship with date of capture (F1,37=6.77, n=39, P=0.014). Pair status was influenced by body condition and body size (P2 =9.997, df=2, P=0.007)with larger birds being in better condition and larger, while hormone levels and testicular morphology did not appear to influence pair status. Mass of testes (F9,27=0.45, P=0.90) and testosterone concentrations (F10,28=0.31, P=0.10) were not influenced by contaminant levels, body condition or body size. Seminiferous tubule diameter was positively related to testes mass (R2=0.397, n=39, P<0.0001) and negatively related to liver selenium levels (R2=0.123, n=39, P=0.009). To clarify the influence of selenium on corticosterone, captive male Lesser Scaup were fed diets dosed with selenomethionine. Dose groups accumulated different levels of selenium (control group=0.19 ng/ml, 7.5 ppm group=0.74 ng/ml and 15 ppm=1.01 ng/ml) (F2,12=155.12; P<0.001) but this appeared to have no effect on corticosterone levels (Wilks Lambda=0.659, F4,10=1.29, P=0.34) or behavioral patterns (Wilks Lambda=0.659, F4,10=1.294, P=0.34) in captive birds. Results from the field portion of this study support the hypothesis that trace element levels can influence hormonal status in wild Lesser Scaup and that interactions of contaminants and physiological variables can modify expression of toxic effects. Studies such as this one display the complex nature of biological systems and emphasize the importance of considering interactions between different contaminants and other variables to clearly assess their influences on physiology.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-05012007-123520 |
| Date | 01 May 2007 |
| Creators | Pollock, Brady Robert |
| Contributors | Machin, Karen L. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-05012007-123520/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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