Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae) following a sublethal chronic exposure to cadmium

A laboratory study on the sublethal effects of cadmium (Cd) on the net-spin ning process of the larvae of Hyqdrosyche slossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposur e to Cd. Two major anomalies with different frequency levels were identifie d after chronic exposure to 0.37, 1.2, 11.6, 21.4 and 43.3 mu g l(-1) of Cd . The first was a distortion of the midline meshes where the diamond-shape structure is disrupted and the meshes are separated by extra strands (calle d 'midline' anomaly). The second aberration consisted of a distortion of th e rectilinear structure of net opening by strands being fused or added over the meshes (called 'crossover' anomaly). The midline distortion may be lin ked to a physiological stress caused by Cd, which can affect the control of the net-spinning process. It was not possible to relate the crossover aber rations to a specific toxic action of Cd, but data indicated that both anom alies are independent from each other and that two modes of action could be implicated. Protein analyses of capture nets have revealed silk polypeptid e modifications at the highest Cd concentration tested, indicating a possib le effect of Cd interaction with silk proteins. However, neither a gradient -concentration nor a time-dependent response could be established with both aberration frequencies. Silk protein modifications would rather play a sec ondary role in the appearance of both net anomalies, and mostly at a high c oncentration level. Finally, the toxicity curves (EC50) show that the sensi tivity threshold for both types of aberration ranged from 1 to 5 mu g l(-1) which is highly sensitive compared with other sublethal effects of Cd on o ther macroinvertebrate species. Hence, the use of capture-net anomalies of hydropsychid larvae would represent a valuable indicator of sublethal toxic ity induced by Cd and possibly by other metals in running waters. (C) 2000 Elsevier Science Ltd. All rig-hts reserved.