The general belief that amphibans are particularly vulnerable to environmental pollutants is not yet sufficiently supported by scientific evidence. Data available concerning the nature and seriousness of the impact of toxic stress on the integrity of individuals and populations are insufficient to evaluate the importance of this anthropic influence as a cause of decline. In this study, the impact of persistant organochlorines on a long-lived aquatic salamander, the mudpuppy (Necturus maculosus), was assessed through the comparison of nine populations along mixed pollution gradients in the St. Lawrence and Ottawa River systems (Quebec and Ontario), sampled on two consecutive winters (1992-1993). The mudpuppies, were found to accumulate PCBs and organochlorine pesticides in their eggs, at concentrations apt to cause reproductive and developmental dysfunction (max levels: total PCBs=58.2 mg/kg wwt, DDE= 1.66 mg/kg wwt). Among sites differences in the circulating levels of sexual steroids, fecundity, egg diameters and GSI of vitellogenic females caught during the winter were not detected, suggesting that the endocrine control of gonad maturation was unimpaired at this time of the year. However, high prevalences of skeletal deformities revealed by X-ray analyses, were observed in the contaminated populations of both systems (max level: 58.3%), where adult mudpuppies were found significantly more at risk to develop limb defects relative to reference sites (8.7-8.9%). The frequencies of terata, including oligodactyly and polydactyly, were positively correlated with the concentrations of embryotoxic and teratogenic chemicals in gonads such as certain pesticides and tetra-substituted isomers of PCB. These defects could have occured by the interference of pollutants with the regeneration of accidentally injured limbs at any stages of life or could originate from a toxic impact during critical embryonic or larval development. Occurence of minor morphologic defects at high frequency in the adults, might signal that severe types of malformations compromising survival are prevalent at earlier life stages. In support of this argument, we found a significant ageing of the population at the most polluted site, suggesting a decrease in recruitement. Prevalence of malformations could be utilized with other indicators to monitor the health of mudpuppy populations for long term surveillance of environments before and after remedial actions.
Key Words: Amphibian, Reproduction, Sex steroids, Skelettal defects, Organochlorines
Andrée Gendron
Département des Sciences Biologiques
Université du Québec à Montréal
C.P. 8888, succ. Centre-ville
Montréal, Québec, Canada
H3C 3P8
Phone: (514)-762-9836
d345510@er.uqam.ca
Presented at DAPCAN meeting in Burlington (October 1995)