The influence of toxic stress on the integrity of individuals and populations of amphibians is insufficiently studied. We examined the impact of persistent organocholorines on a long-lived aquatic salamander, the mudpuppy (Necturus maculosus) through the comparison of populations along pollution gradients in the St. Lawrence and Ottawa River system (Quebec and Ontario) sampled during the winter (1992-1993). The mudpuppies were found to accumulate polychlorinated biphenyls (PCBs) and organochlorine pesticides in ovarian tissues at concentrations apt to cause reproductive and developmental dysfunction (max levels: total PCBs=58.3 mg/kg wwt, DDE=1.66 mg/kg wwt) but among sites differences in the circulating levels of sexual steroids, fecundity, egg diameters and gonado-somatic index (GSI) of vitellogenic females were not detected. However, high prevalence of limb deformities revealed by X-ray analyses, were observed in adults at the contaminated sites (max level: 58.3%), where individuals were significantly more at risk to develop limb defects relative to reference sites (8.8-8.9%). The frequencies of terata, including oligodactyly and polydactyly were positively correlated with the concentrations of embryotoxic and teratogenic chemicals in gonads such as certain congeners of PCBs. Although other causal agents such as pathogens (e.g. larval stage of trematodes) cannot be discarded, contaminants are potentially involved. Actually, these defects could originate from the interference of pollutants with the regeneration of injured limbs or from a toxic impact during critical larval development. High frequency of minor defects in adults might signal that severe malformations compromising the survival are prevalent at earlier stages. We found an ageing of the population at the most polluted site, suggesting a decrease in recruitment which supports the hypothesis of toxic stress during early development. Possible toxic impact on the functional integrity of the corticosterone producing axis, which is closely involved in the stress response, was also investigated. Results suggest that the ability to elevate corticosterone promptly in response to stimulation by corticotropin (ACTH) or acute stress is reduced in individuals chronically exposed to persistent organocholorines compared to reference mudpuppies.

Andree D. Gendron, C.A. Bishop, J.I. DesGranges, G.Van Der Kraak, R. Fortin, A Hontela

Contact Andree D. Gendron, Dept des Sciences Biologiques, Universite du Quebec a Montreal, Montreal, Quebec