Selection favours low hsp70 levels in chronically metal-stressed soil arthropods

Authors

  • KÖhler,

    1. Cell Biology, Zoological Institute, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany,
    Search for more papers by this author
  • Zanger,

    1. Zoological Institute I (Morphology/Ecology), University of Heidelberg, Im Neuenheimer Feld 230, D-69120 Heidelberg, Germany
    Search for more papers by this author
  • Eckwert,

    1. Cell Biology, Zoological Institute, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany,
    2. Zoological Institute I (Morphology/Ecology), University of Heidelberg, Im Neuenheimer Feld 230, D-69120 Heidelberg, Germany
    Search for more papers by this author
  • Einfeldt

    1. Cell Biology, Zoological Institute, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany,
    Search for more papers by this author

Heinz-R. Köhler Cell Biology, Zoological Institute, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany. Tel.: +49 7071 2978864; fax: +49 7071 294634; e-mail: heinz-r.koehler@uni-tuebingen.de

Abstract

Thirty-eight populations of woodlice (Oniscus asellus, Porcellio scaber) and millipedes (Julus scandinavius) from 28 differently metal-polluted field sites were analysed for their 70-kDa stress protein (hsp70) level. Although ANOVA revealed significant dependence of the hsp70 level on the concentrations of water-soluble lead, cadmium and zinc and the soil pH, each of these parameters accounted for at most 18% of the intersite variability of the stress protein level only. A multivariate model based on multiple regression analysis explained more than 96% of hsp70 variance and revealed both the pollution history of a site (strong metal contamination for more than 70 years) and invertebrate species identity to act as the most important parameters. The model accounted for the observation that most of the populations from long-term polluted sites exhibited comparatively low stress protein levels in response to their own (contaminated) habitats. In contrast, isopods (O. asellus) from a control site were not able to maintain a low hsp70 level when they were exposed to either an artificial metal cocktail or soil taken from one of the contaminated field sites. They did not acclimatize to the exposure conditions within 3 months. We propose that selection of insensitive phenotypes in long-term polluted soils has taken place so as to minimize the stress protein level which, in turn, is indicative of high intracellular protein integrity. Long-term selection for a high hsp70 level to compensate for adverse metal impact was not observed, which suggests that such a strategy may trade off against other fitness consequences. In this context, insensitivity to metal stress involved increased selectivity in food choice and reduced variability in stress response. Multiple regression models showed species-specificity in those abiotic factors which determined (1) high hsp70 levels in sensitive populations as well as (2) low hsp70 levels in insensitive ones. Therefore, abiotic factors can be assigned to act as the main components of selection: lead and cadmium for J. scandinavius and O. asellus, zinc for P. scaber.

Ancillary