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

Abstract

Few 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.