Orientation behavior is a good biomarker of trace metal contamination in Parallelomorphus laevigatus (Coleoptera, Carabidae)

Behavioral ecotoxicology has become very important in the short time since a change in behavior is very often the first response to environmental altered conditions. We investigated the influence of trace metal intake on the spatial orientation performances of the carabid beetle Parallelomorphus laevigatus, fundamental ability for its survival. The aim of this study was to consider the solar orientation as behavioral biomarker for exposure to trace metal contamination. Therefore, we tested the ability of solar orientation of specimens of this species, fed with shrimps contaminated with three different concentrations of Cu, Zn, or Hg. We carried out the orientation tests after 1, 3, 7, and 10 days of contaminated feeding. Subsequently, we fed these beetles with not contaminated shrimps and again tested them after 1, 3, 7, and 10 days. For all three metals considered and, regardless of the degree of contamination of the food, we have found a progressive and significant counterclockwise displacement of the angle of orientation and a corresponding progressive reduction in the precision in the directional choices by the animals. We also noticed a clear growing recovery in the normal orientation by these insects after returning to their feeding with uncontaminated food. In conclusion, we can consider the orientation in space of P. laevigatus as a behavioral biomarker for exposure to trace metal contamination. We believe that the intake of trace metals may induce the insects to make mistakes in their spatial orientation, due to an acceleration of their biological clock. Such a clock malfunction is not definitive, since the return to a normal diet restores P. laevigatus the ability to re-make the correct directional choices. Ultimately, our results confirm the usefulness of behavioral ecotoxicology investigations; moreover, they stimulate the opportunity to deepen the understanding of functioning of the biological clock in the animals.