Multiple-trait analysis of fluctuating asymmetry levels in anthropogenically and naturally stressed sites: a case study using Chironomus riparius Meigen, 1804 larvae.

Fluctuating asymmetry levels were measured in fourth-instar Chironomus riparius larvae collected from various sampling sites in Galicia (northwest Spain) subjected to different types and degrees of stress. Specifically, we selected sites with contamination of anthropogenic origin, ranging from urban and industrial sewages to organic wastes, as well as two sites without chemical contamination, but with marked diurnal variations in their physicochemical conditions. Fluctuating asymmetry levels were determined for various structures of the head capsule (antennal segment I length, antennal segment II length, mentum width, and number of pecten epipharyngis teeth). The results obtained group the sampling sites in a similar way to other measures of stress. In particular, grouping resulted to be similar to that obtained after analysis of head capsule deformities. Moreover, results of our work are consistent with the hypothesis that some characters may possibly be useful indicators of specific types of stress.