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Amphibian declines have been occurring for decades, and some of these declines are attributed to environmental contaminants. In this experiment, we examined the effects of ecologically-relevant concentrations of a common organophosphate insecticide, malathion, on developing Xenopus laevis tadpoles. Two-week-old Xenopus laevis tadpoles were divided into four experimental groups, each with a sample size of ten tadpoles: control (water), 1.0 ng/L malathion, 1.0 μg/L malathion, and 1.0 mg/L malathion. During their 30-day exposure to malathion, tadpoles in the 1.0 mg/L malathion displayed bent tails (p<0.001), unusual swimming behavior, and a higher mortality rate (p<0.001) when compared to the control group. Future experiments should examine the exact etiology of malathion-induced bent tails in Xenopus laevis.
Bromus tectorum L. (Cheatgrass, Downy brome) is an invasive grass that has recently proliferated within the Gunnison Basin, Colorado. This study examined variation in germination in response to temperature, storage duration, and habitat. Four populations within the Gunnison Basin were sampled. Seeds were kept in dry storage for 0, 4, 8, 12, and 16 weeks and then incubated at four different temperature regimes. Seeds in storage for zero weeks had low percent germination, while seeds in storage for 16 weeks had high percent germination. The optimal temperature for germination was room temperature, while the least favorable temperature regime was 5:10 °C. Within these general patterns, significant differences were found among populations in percent germination, but the differences decreased as seeds after-ripened. Seeds that were chilled prior to germination tests at the 5:10 °C temperature regime showed enhanced germination compared to seeds that were not chilled. Similar to what has been found in other studies, delayed germination at high temperatures may be an adaptation to avoid early summer germination. However, in contrast to previous reports, significant lower percent germination of high elevation populations at low temperatures may reflect adaptation to more variable summer temperatures experienced by Gunnison Basin populations of B. tectorum.
Laser technology and use is rapidly expanding in medical, industrial, commercial, and military applications. As a result, the likelihood of inadvertent ocular exposure has also increased. Risks may be especially acute for military personnel when employment occurs under less than ideal circumstances. The ocular tissue layer most susceptible to laser damage is the retinal pigmented epithelium (RPE) due to the highly absorptive nature of its melanin-containing pigment granules. We enucleated pig eyes and exposed the RPE layer to 3 ns pulsed laser-light using a ND:YAG laser. Changes in cellular ultrastructure were observed in 48 h post exposure by transmission electron microscopy. Pigment granules of laser-treated cells showed decreased pigment content and loss of elliptical shape but were otherwise normal and bounded by discrete membranes. Pigment granules appeared striated and in various stages of maturity suggesting capacity for melanin regeneration after laser damage. Thermal denaturation and photomechanical disruption caused by microbubble formation are discussed as possible damage mechanisms.
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