Toxicity of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in three vertebrate species.

The explosive, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine or high-melting explosive (HMX), has been found in soils in areas used for testing and training by the military. Many of these areas contain habitat for valued wildlife species. In an effort to better understand the environmental consequences from exposure, a reptilian (western fence lizard [Sceloporus occidentalis]), an amphibian (red-backed salamander [Plethodon cinereus]), and a mammalian species (rabbit [Oryctolagus cuniculus]) were exposed to HMX under controlled laboratory conditions. Lizards and rabbits were exposed to HMX by way of corn oil through gavage, and salamanders were exposed to HMX in soil. Two deaths occurred from acute oral exposures to lizards to 5000 mg HMX/kg BW. Histological and gross pathologic assessment suggested gut impaction as a possible cause of death. Salamanders exposed to concentrations of HMX in soil < or = 1970 mg HMX/kg soil for 10 days did not show adverse effects. Rabbits, however, showed neurologic effects manifested as hyperkinetic events with convulsions at > 24 h after oral exposures. An LD(50) for rabbits was calculated as 93 mg/kg (95% confidence interval 76-117). A subacute 14-day testing regime found a lowest observed effect level of 10 mg/kg-d and a no observed adverse effect level of 5 mg/kg-d based on hyperkinesia and seizure incidence, although changes suggesting functional hepatic alterations were also found. These data suggest that physiologic differences between species, particularly in gastrointestinal structure and function, can affect the absorption of HMX and hence lead to marked differences in toxicity from exposure to the same compound.

Effects of atrazine on anuran development are altered by the presence of a nonlethal predator.

Although predator-induced stress is a common biotic factor in aquatic communities that can strongly influence anuran development, there have been no studies to date that examined the interaction between this factor and atrazine, the most widely used pesticide in the United States. The potential synergistic effects of atrazine (0, 20, or 200 microg/L) and predatory stress on the survival, growth, development, and reproductive development of Hyla versicolor (gray treefrog) tadpoles were investigated. Atrazine reduced the proportion of tadpoles reaching metamorphosis; however, this effect was modified by the presence of a nonlethal predator. The combined effects of predatory stress and exposure to 200 microg/L atrazine resulted in the lowest proportion of tadpoles reaching metamorphosis. No treatment effects were observed for mass, snout-urostyle length, or the proportion of metamorphs that were male or female. No macroscopic gonadal anomalies were observed. Many gonads were underdeveloped; however, gonadal development was more advanced in metamorphs exposed to 200 microg/L atrazine. This effect was modified by the presence of a nonlethal predator such that female gonadal development was further accelerated and male gonadal development was retarded by predatory stress. These results indicate that simplified laboratory studies may not accurately reflect the effects of atrazine on anuran development in natural communities.

Predator induced phenotypic plasticity in the pinewoods tree frog, Hyla femoralis: necessary cues and the cost of development.

Predator-induced defenses can result from non-contact cues associated with the presence of a feeding predator; however, the nature of the predator cue has not been determined. We tested the role of two non-contact cues, metabolites of digestion of conspecific prey released by the predator and alarm pheromones released by attacked conspecific prey, in the development of inducible defenses by exposing pinewoods tree frog (Hyla femoralis) tadpoles to non-lethal dragonfly (Anax junius) larvae fed either inside experimental bins or removed from the bins for feeding to eliminate alarm pheromones. The costs associated with the development of the induced morphology were also investigated by providing the tadpoles with two food levels intended to provide adequate or growth limiting resources. The generalized morphological response of H. femoralis tadpoles to predators included the development of bodies and tails that were both deeper and shorter, smaller overall body size, and increased orange tail fin coloration and black tail outline. Metabolites of digestion were sufficient to initiate development of inducible defenses; however, the combination of metabolites and alarm cue resulted in a greater response. Furthermore, growth and development were slowed in tadpoles that expressed the induced morphology; however, this growth cost was insufficient to preclude the development of the induced morphology when food resources were low. These results indicate that two aspects of the indirect predator cue work together to trigger a morphological anti-predator response.