Fluctuating asymmetry in crayfish populations inhabiting lead and cadmium polluted aquatic systems.

Abstract

Due to past mining practices, high concentrations of lead and cadmium have been found in the streams and rivers of southeastern Cherokee County, Kansas. These heavy metals are known to cause gross developmental anomalies in a diverse group of organisms. To assess more subtle effects on the crayfish of Cherokee County, specimens were examined for asymmetrical development of bilateral characteristics (fluctuating asymmetry). Sediments and crayfish from seven locations were analyzed for lead and cadmium concentrations. Metal concentrations from the sediments and crayfish tissues of locations in close proximity to heavily mined areas were significantly higher than those from upstream control locations. Three axial and three appendicular measurements from both sides of the plane of symmetry were taken from 155 Orconectes neglectus and 125 O. virilis from seven populations. Variances of right side minus left side character differences were compared between the two species and among the different locations. No significant differences were found to exist between fluctuating asymmetry values of the two species. Linear regression analysis revealed that no relationship exists between the level of fluctuating asymmetry and the concentration of heavy metals in body tissues. These results suggest that chronic exposure to lead and cadmium at the levels in the streams of Cherokee County does not affect the homeostatic mechanisms operating during the ontogenetic development of O. neglectus and O. virilis.