Fluctuating asymmetry and mentum gaps in populations of the midge Chironomus riparius (diptera: Chironomidae) from a metal‐contaminated river

Abstract

AbstractThe developmental stability of both metal‐exposed and nonexposed Chironomus riparius populations from the lowland River Dommel was investigated using fluctuating asymmetry (FA) and the incidence of mentum gaps. It was hypothesized that larval development was affected by the influx of metals, directly by chemical stress, as well as through inbreeding of metal‐adapted and nonadapted specimens. Morphological parameters were therefore assessed in field‐collected larvae and in clean, laboratory‐cultured, first‐generation (F1) larvae. Fluctuating asymmetry values and mentum gap incidence at contaminated field sites were significantly higher than at clean, upstream locations. Furthermore, FA values of clean, laboratory‐cultured F1 larvae generally fell to reference values, indicating the direct effect of metal pollution on developmental aberrations. Mentum gaps were not observed in clean F1 cultures. Slightly elevated FA values were, however, still observed in clean F1 larvae from polluted locations downstream from the metal input. This residual disturbance was thought to reflect genetic stress emerging from interbreeding between metal‐adapted and nonadapted specimens. Fluctuating asymmetry and mentum gaps together serve as a useful ecotoxicological marker for metal stress and, when combined with in situ studies and F1 cultures, allow for analysis of the response of animal populations to spatial and temporal gradients in metal exposure.