The Effects Of Perchlorate Exposure On A Model Vertebrate Species: The Threespine Stickleback

Thesis (Ph.D.) University of Alaska Fairbanks, 2008Few studies have examined the effects of chronic perchlorate exposure during multiple stages of development, and fewer still have analyzed the effects of perchlorate over multiple generations. Perchlorate exposure is known to cause thyrocyte hypertrophy (suggesting glandular stimulation), interference with thyroid hormone synthesis, and ultimately altered levels of circulating thyroid hormones, but whether these effects represent adaptive mechanisms or actual impairment is often debated within the scientific community. My research attempts to clarify whether exposure to environmentally relevant concentrations of perchlorate cause impairment at the organismal level. I examine ecologically significant endpoints to provide an indication if a contaminated population would be able to sustain itself I exposed threespine stickleback fish (Gasterosteus aculeatus) to one of eight perchlorate treatments and compared them to each other and to fish raised in water without detectable levels of perchlorate (<1.1 mug/L). I present patterns for two separate generations (G2,2002 and G2,2003 ) of stickleback that were spawned and raised in control or perchlorate treated water and a third generation (G3,2004) that was not directly exposed to perchlorate but whose parents (G2,2003) were raised from syngamy through sexual maturity in control or perchlorate treated water. When warranted, I make comparisons with their wild-caught ancestors (G 1,2002 and G1,2003) that were exposed to perchlorate as adults for up to 22 days. Exposure of mature adult stickleback to perchlorate had no noticeable effect on survival, behavioral, or reproductive endpoints. However, chronic exposure of their offspring (G2,2002 and G2,2003) to perchlorate impaired nearly every aspect of fitness. Aberrant developmental patterns of somatic characters were primarily associated with growth, reproduction, locomotion, anti-predatory structures, and vision. Impaired stickleback (G 2,2003) that produced offspring in water without detectable levels of perchlorate (<1.1 mug/L) gave rise to offspring (G3,2004) without the suite of abnormalities noted among treated fish. These findings suggest that perchlorate exposure during sensitive developmental periods has negative effects on critical life history characteristics of threespine stickleback, but remediation efforts are likely to restore healthy ecosystems. Effects noted among stickleback provide a useful model to assess effects that are likely to occur among other contaminated fishes and perhaps to other vertebrates

The Effect of Growth Rate, Phosphorus Concentration, and Temperature on N-2 Fixation, Carbon Fixation, and Nitrogen Release in Continuous Cultures of Trichodesmium IMS101

With the use of continuous culture systems, rates of dinitrogen (N2) and carbon (C) fixation and nitrogen (N)- and C-based doubling times were assessed in Trichodesmium IMS101 growing exponentially at steady state dilution rates of 0.10, 0.20, and 0.33 d-1 (doubling times of 10, 5, and 3 d - within the range reported for natural populations). Rates of C fixation, N2 fixation, and N release were examined in replicate culture systems with several techniques. Biomass-specific C uptake varied little with population doubling time, but N2 fixation and N release varied markedly among treatments. Total daily gross N2 fixation rates and estimated N release rates were higher in cultures with higher dilution rates. Cultures grown at lower dilution rates had higher daily C:N2 fixation ratios and lower N release rates. Consistent with other studies, it was estimated that Trichodesmium released about 80-90% of their recently fixed N2 during growth. Turnover of cellular C estimated from carbon fixation was a good estimator of population growth rates in steady state cultures, whereas turnover of cellular N estimated from gross or net N2 fixation was not. Small changes in temperature (24°C vs. 28°C) did not appear to affect gross N2 fixation, whereas inorganic phosphorus (1 vs. 5 μmol L-1) supply had a large effect on N2 fixation. These results suggest that continuous culture systems are excellent for elucidating physiological responses of Trichodesmium under ecologically relevant growth conditions and provide a framework for assessing highly variable field estimates of N2 and C fixation