Transcriptional and biochemical biomarker responses in a freshwater mussel (Anodonta anatina) under environmentally relevant Cu exposure

Abstract

Molecular biomarkers, like gene transcripts or enzyme activities, are potentially powerful tools for early warning assessment of pollution. However, a thorough understanding of response and baseline variation is required to distinguish actual effects from pollution. Here, we assess the freshwater mussel Anodonta anatina as a biomarker model species for freshwater ecosystems, by testing responses of six transcriptional ( cat , gst , hsp70 , hsp90 , mt , and sod ) and two biochemical (AChE and GST) biomarkers to environmentally relevant Cu water concentrations. Mussels ( n = 20), collected from a stream free from point source pollution, were exposed in the laboratory, for 96 h, to Cu treatments (< 0.2 μg/L, 0.77 ± 0.87 μg/L, and 6.3 ± 5.4 μg/L). Gills and digestive glands were extracted and analyzed for transcriptional and biochemical responses. Biological and statistical effect sizes from Cu treatments were in general small (mean log 2 fold-change ≤ 0.80 and Cohen’s f ≤ 0.69, respectively), and no significant treatment effects were observed. In contrast, four out of eight biomarkers ( cat , gst , hsp70 , and GST) showed a significant sex:tissue interaction, and additionally one ( sod ) showed significant overall effects from sex. Specifically, three markers in gills ( cat , mt , GST) and one in digestive gland (AChE) displayed significant sex differences, independent of treatment. Results suggest that sex or tissue effects might obscure low-magnitude biomarker responses and potential early warnings. Thus, variation in biomarker baselines and response patterns needs to be further addressed for the future use of A. anatina as a biomarker model species.

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