Patterns of Fluctuating Asymmetry and Shape Variation in Chironomus riparius (Diptera, Chironomidae) Exposed to Nonylphenol or Lead

Abstract

Deformities and fluctuating asymmetry in chironomid larvae have been proposed as sensitive indicators of biological stress and are commonly used to assess the ecological impact of human activities. In particular, they have been associated in Chironomus riparius, the most commonly used species, with heavy metal and pesticide river pollution. In this study, the effect of lead and 4-nonylphenol on mouthpart morphological variation of Chironomus riparius larvae was investigated by traditional and geometric morphometrics. For this purpose, first to fourth instar larvae were exposed to sediment spiked with lead (from 3.0 to 456.9 mg/kg dry weight) or 4-NP (from 0.1 to 198.8 mg/kg dry weight). Mentum phenotypic response to pollutants was assessed by four parameters: (1) the frequency of deformities, (2) fluctuating asymmetry of mentum length, (3) fluctuating asymmetry of mentum shape and (4) the mentum mean shape changes. Despite the bioaccumulation of pollutants in the chironomid’s body, no significant differences between control and stressed groups were found for mouthpart deformities and fluctuating asymmetry of mentum length. Slight effects on mentum shape fluctuating asymmetry were observed for two stressed groups. Significant mean shape changes, consisting of tooth size increase and tooth closing, were detected for lead and 4-NP exposure respectively. Those variations, however, were negligible in comparison to mentum shape changes due to genetic effects. These results suggest that the use of mentum variation as an indicator of toxic stress in Chironomus riparius should be considered cautiously.

Biochemical and morphological responses in Chironomus riparius (Diptera, Chironomidae) larvae exposed to lead‐spiked sediment

“…This result agrees with those of Bird et al , who did not notice any size variations in Chironomus tentans larvae exposed for 2 wk to Pb sediment concentrations lower than 5000 mg/kg dry weight. Moreover, according to previous studies in Chironomus larvae exposed to Pb‐spiked sediment , no significant increase in the frequency of mouthpart deformities was observed. This result suggests that the energy consumption observed in the present study was insufficient to induce growth retardation and mentum morphological defects.…”

Analyzing Fluctuating Asymmetry with Geometric Morphometrics: Concepts, Methods, and Applications

“…Further non-significant results were reported from mites [128] and wings of Trichogramma egg parasitoids [129]-but both studies reported results only from relatively small subsamples (≤30 specimens per sample) and tiny organisms, raising questions about statistical power and possible artifacts from mounting very small specimens. Further negative results come from two datasets of wings from Chironomus midges [116], whereas other studies found mixed results for wings and larval mouthparts [103,130,131]. Some studies, in a variety of species, have found mixed results, with some structures or subgroups yielding significant results, but others not [132][133][134][135][136][137][138].…”

“…Several studies found greater fluctuating asymmetry in disturbed than in undisturbed habitats for skull shape of voles [250], in areas of worse rather than better climatic suitability for skull shape of Akodon rodents [370], in urban than in rural habitats for head shape of lizards [106], in polluted than unpolluted habitats for crab carapace shape [253] and for mandible shape of shrews [371]. Studies of the larval mentum and adult wings in chironomid midges showed that pollution in the rearing environment had no or only limited effects on fluctuating asymmetry [130,131] or that there was more fluctuating asymmetry in offspring reared in unpolluted sediment in the laboratory than in the parental generation collected from polluted sediment in the field [103]. Temperature stress had no significant effect on fluctuating asymmetry of body shape in bulb mites [372], but fluctuating asymmetry of shape has been shown to be influenced by temperature in aphid [164] and Drosophila wings [62,121].…”

Developmental stability and environmental stress: A geometric morphometrics analysis of asymmetry in the human femur

“…Permutation ANOVA tests were then used to compare FA CS according to age group and sex. Finally, to address the question of size scaling and check whether FA in centroid size increases with size, non‐parametric Spearman correlation tests were performed in each sample between individual FA CS scores and mean size ( R + L )/2 (Arambourou, Beisel, Branchu, & Debat, ; Graham and Ozener, ; Graham, Raz, Hel‐Or, & Nevo, ; Palmer, ).…”