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.

2-Amino-4,6-dinitrotoluene (2A-DNT) is a metabolite of the explosive 2,4,6-trinitrotoluene (TNT) which is present in the soil at numerous U.S. Army installations as the result of TNT manufacture or training activities. Although many avian species are known to inhabit areas where 2A-DNT has been found in the environment, no published studies of the effects of 2A-DNT exposure in birds are available. In this study, we conducted an evaluation of the oral toxicity of 2A-DNT in a representative ground foraging species of management concern, the northern bobwhite (Colinus virginianus). Subacute (14 days) and subchronic (60 days) oral gavage exposure studies were conducted following determination of the median acute lethal dose (LD50 = 1167 mg/kg). In the subacute study, survival occurred at 50 mg/kg/day. This helped to determine dose groups for the subchronic study: 0, 0.5, 3, 14, and 30 mg 2A-DNT/kg body weight-d in corn oil. The lowest observed adverse effects level (LOAEL) was determined to be 14 mg/kg/day based on mortality, and the no observed adverse effects level (NOAEL) was determined to be 3 mg/kg/day based on lack of effects at this exposure level.

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.