Cowman, Deborah Fay (2005-12). Pesticides and amphibian declines in the Sierra Nevada Mountains, California. Doctoral Dissertation. Thesis uri icon


  • Pacific chorus frog (Pseudacris regilla) hatchlings were translocated and placed in cages in sites (~2,200 m elevation) located in Lassen, Yosemite, and Sequoia National Parks. DDE was found in 97% of Yosemite National Park samples, 84% in Sequoia National Park samples, and 15% of Lassen Volcanic National Park samples in 2001 and 2002. Total endosulfans were detected in 3% of Sequoia samples, 9% of Lassen samples and 24% of Yosemite samples. Both pesticides were detected in tadpoles and metamorphs raised at the three parks regardless of origin. Because the tadpoles were translocated post hatching, this finding indicates that the pesticides, particularly DDE, were accumulated at the site, instead of through deposition in the egg mass. Liver cells from 108 newly metamorphosed frogs were examined with flow cytometry (FCM) techniques for evaluation of chromosome breakage as measured by the half-peak coefficient of variation (HPCV) of the G1 peak. Regardless of origin, experimental groups raised at Lassen, the reference site, had significantly less chromosomal breakage (p=0.04) than metamorphs raised at the other two parks. This is the first documented evidence of DNA damage in juvenile frogs in the Sierra Nevada Mountains. Cholinesterase (ChE) was measured in tadpoles collected at 28 days and in juvenile frogs collected upon metamorphosis. In 2001, ChE activity was significantly higher in animals raised at Lassen (reference site), than at the other two parks, indicating less exposure to cholinesterase-inhibiting pesticides. This trend was not observed in 2002, although Sequoia ChE values were consistently lower than the other two parks. Temperatures were significantly different among the three parks for both years (p<0.0001) and lower temperatures may correlate with lower ChE levels. Survivorship to metamorphosis, days to metamorphosis, snout-vent lengths (SVL), and malformations were evaluated. Animals raised in Sequoia had shorter SVLs, took longer to metamorphose, and had lower survivorship to metamorphosis than in the other two parks (p<0.0001). Effects noted in P. regilla may be magnified in long lived ranid species. These findings may be important in evaluating the overall impact of aerially transported pesticides on declining frog populations in the Sierra Nevada Mountains.

publication date

  • December 2005