Effects of single and combined embryonic exposures to herbicide and conspecific chemical alarm cues on hatching and larval traits in the common frog (Rana temporaria).

Recent studies indicate that amphibian embryos can exhibit hatching plasticity in response to chemical cues indicative of a predation risk. However, data are lacking concerning the possible impacts of waterborne contaminants on such a process. To investigate this impact, we raised eggs of the common frog (Rana temporaria) until hatching in water contaminated with sublethal concentrations (0.01, 0.1, and 1 mg/L) of amitrole, a widely used triazole herbicide, either with or without the presence of chemical alarm cues from crushed conspecific tadpoles. Embryonic exposure to conspecific alarm cues resulted in a delay in hatching, reduced growth, and decreased larval activity, regardless of the amitrole concentration present during the incubation. Conspecific cues also induced morphological changes, but only in individuals incubated in water contaminated with the highest amitrole concentration. The herbicide impacts on hatching time were restricted to embryos incubated in the presence of conspecific cues, with individuals exposed to 0.1 and 1 mg/L showing an extended embryonic period compared to controls in uncontaminated water. Whether tested alone or in combination with conspecific cues, amitrole also induced slight morphological changes but did not affect larval growth or behavioral activity. Thus, depending on the trait considered, both chemical stressors exhibited either single or interactive effects. Furthermore, our data indicate that a stressing factor without apparent impact when tested alone could exert effects when combined with another stressor. Such results highlight the importance of considering multiple environmental factors and biological traits when examining stress-induced phenotypic variability.

Waterborne amitrole affects the predator-prey relationship between common frog tadpoles (Rana temporaria) and larval spotted salamander (Salamandra salamandra).

Within their aquatic habitats, larval amphibians are often subjected to multiple natural and anthropic stressors. Among these, predation and waterborne pollution represent two types of stressing factor that frequently co-occur. In this connection, the present laboratory study was designed to investigate the effects of amitrole, a commonly used triazole herbicide, on the predator-prey relationship between common frog tadpoles (Rana temporaria) and larval spotted salamander (Salamandra salamandra). Tadpoles were exposed for 3 days to 0, 0.01, 0.1, 1, and 10 mg/L amitrole, either in the absence or in the presence of larval salamanders. Tadpole behavior (refuge use, movements) was monitored every day, and the predation efficiency was assessed at the end of the experiment by counting the number of surviving tadpoles. In the absence of the predator, amitrole-exposed tadpoles (at 0.01, 0.1, and 1 mg/L) increased their refuge use and decreased their rate of movements. In the presence of the predator, amitrole contamination did not affect tadpole behavior, except on the first day, where tadpoles exposed to 10 mg/L were found to be significantly more active than unexposed control tadpoles. Throughout the experiment, control tadpoles were the only group to show significant reductions of activity and visibility in response to the predator's presence. In contrast, tadpoles exposed to 0.01 and 0.1 mg/L amitrole increased their refuge use in response to the predator, whereas their rate of movements remained unaffected. Furthermore, exposures of tadpoles to the two highest amitrole concentrations (1 and 10 mg/L) resulted in the loss of both behavioral responses to the predator's presence. Interestingly, the lack of antipredator behavior in amitrole-exposed tadpoles did not enhance their vulnerability to predation by the larval salamander. Moreover, tadpoles exposed to the two highest herbicide concentrations showed a better survival than unexposed controls, indicating that amitrole contamination also had detrimental effects on the predatory behavior of the larval salamander. These findings emphasize the need to consider the effects of contaminants on both predator and prey before drawing conclusions about the possible consequences of prey behavioral modifications on the predation risk.

Biochemical and behavioral effects of carbofuran in goldfish (Carassius auratus).

The effects of concentration (5, 50, and 500 microg/L) and duration (24, 48 h) of exposure to carbofuran, a carbamate insecticide, were assessed on brain catecholamine (norepinephrine [NE] and dopamine), plasma glucose, and hepatic glycogen contents and behavioral activities of goldfish (Carassius auratus). After 24 h of exposure to 50 and 500 microg/L, the level of NE was increased in the olfactory bulbs. The same effect was observed after a 48-h exposure to 500 and 50 microg/L in the telencephalic hemispheres and in the hypothalamus, respectively. An increase in the level of dopamine was also found in hypothalamus after 48 h of exposure to 500 microg/L carbofuran. Plasma glucose increased in concentration after both periods of exposure to carbofuran at 50 and 500 microg/L. Hepatic glycogen concentration decreased after a 48-h exposure to the highest concentration. Behavioral endpoints related to swimming pattern and social interactions were affected after a 24-h exposure to the lowest concentration tested (5 microg/L). The relative sensitivities of these different types of responses to exposure to carbofuran are discussed in light of data on the neurotoxic effects of carbamate and organophosphate insecticides in fish.