Lead effects on the predictability of reproductive behavior in fathead minnows (Pimephales promelas): A mathematical...

Lead (Pb) has been shown to affect the behavior of a wide variety of vertebrates, including fish, amphibians, and mammals. This article re-examines previous data on the effect of short-term, sublethal levels of waterborne Pb on the reproductive behavior of fathead minnows (Pimephales promelas). Previous research has found that Pb decreased the time spent in displaying specific reproductive behaviors in male minnows. Because each activity performed within a sequence depends upon previous parts of the sequence, the reproductive behavior of fish is not randomly distributed but is presented as a long-range self-similar correlation. By treating these data as a fractal dimension, it is now possible to determine changes in the long-term correlation of different behavioral sequences involved in nest maintenance owing to Pb exposure (0.5 ppm Pb as Pb acetate), both before and after adult males attain reproductive maturity. We hypothesized that the scaling exponent of this fluctuation varies in relation with environmental contaminants. Known Pb-induced changes in hormonal activity may account for changes in observed reproductive and nest maintenance behaviors. Pb-exposed fish exhibited higher levels of predictability (less complexity) in their behavioral sequences, i.e., they demonstrated an increase in the scaling parameter of the fluctuation a. However, if Pb was introduced after sexual maturity was observed, there was no significant difference in the scaling component a. Thus, the use of fractal dimension may provide a useful tool to analyze the effects of environmental contaminants and other stresses.