Patterns of Fluctuating Asymmetry and Shape Variation in Chironomus riparius (Diptera, Chironomidae) Exposed to Nonylphenol or Lead
Chironomidae) Exposed to Nonylphenol or Lead. PLoS ONE 7(11): e48844. doi:10.1371/journal.pone.0048844
Patterns of Fluctuating Asymmetry and Shape Variation in Chironomus riparius (Diptera, Chironomidae) Exposed to Nonylphenol or Lead
He le` ne Arambourou 0
Jean-Nicolas Beisel 0
Philippe Branchu 0
Vincent Debat 0
Gabriele Sorci, CNRS, Universite de Bourgogne, France
0 1 CETE Ile de France, Unite qualite des eaux et des sols, IFSTTAR-ERA nu35, Trappes, France, 2 Universite de Lorraine, Laboratoire LIEBE CNRS-UMR 7146, Metz, France , 3 UMR 5202 OSEB , De partement Syste matique et Evolution, Museum National d'Histoire Naturelle , Paris , France
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.
-
Funding: The work has been financially supported by the The Research and Innovation Directorate (DRI) of the French Ministry of Ecology, by the IFSTTAR
organism (French institute of science and technology for transport, development and networks) and by the French Water Agency (AESN). The funders had no role
in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Development of anthropogenic activities in the XIXth century
has lead to generalised river contamination. Aquatic ecosystems
have been exposed to a wide variety of mineral and organic
substances, which induce a stress on living organisms. This stress
acts at the molecular, cellular and physiological levels [1]. It affects
on a long term basis the dynamics of aquatic organisms and could
be involved in fine in many species extinction [2]. If the community
level is an adequate scale to reveal lethal effect, it does not allow to
detect subtle toxic stress that do not lead immediately to a species
disappearance. In this context, investigations at the individual and
population levels are of major interest to highlight sublethal effects
of pollutants [3].
Detecting sublethal effect in natural populations requires the use
of a model that is in some extent tolerant to the pollutant.
Choosing an appropriate bio indicator species thus depends on
a delicate but necessary balance between its sensitivity (the
characteristics used as a biomarker) and its ability to cope with
stress (allowing the species to survive in the polluted area) (see [4]
for a review).
Chironomids have been largely used as a bio indicator of
freshwater quality because they are very abundant [5] even in
highly polluted rivers, where they often present phenotypic and
developmental defects that can be easily detected [6].
Amongst chironomids the genus Chironomus is particularly prone
to such pollution-induced phenotypes [7], [8], and its abundance
in both clean and polluted areas allows powerful statistical
comparisons. Its larvae spend the majority of their life in sediment
making them particularly relevant for sediment bioassay.
Because it can bee reared in the laboratory (short life cycle,
resistance to manipulation) Chironomus riparius has become the most
widely used Chironomus species [9], [10], [11], [12], thereby
providing a good comparative framework. Results of previous
studies on the impact of various pollutants on its morphology are
nevertheless equivocal: while most studies have reported
morphogenetic effects of pollution in the wild [6], [9], [13], [14] some lab
studies failed to detect such effects [15], [16], (...truncated)