Histological description of immature Chironomus columbiensis (Diptera: Chironomidae): A potential contribution to environmental monitoring

Abstract

Chironomids have been widely used in environmental monitoring and toxicity assays. Assessment criteria for chironomids range from the molecular‐biochemical level to the population level. However, the use of markers to evaluate cellular and anatomical changes in organs and systems of individuals under contaminant exposure is still incipient. In this study, we conducted a histological description of the main systems and organs of immature Chironomus columbiensis. We used fourth instar larvae, obtained from a standardized culture, and confirmed this state through morphological and molecular methods. Larvae were fixed in Duboscq solution for insects during 48 hr, dehydrated in increasing dilutions of ethanol, and embedded and mounted in historesin to obtain 3 μm sections. The digestive, nervous, excretory, and integumentary systems and the fat body and testicles were analyzed through longitudinal and transversal sections, stained with hematoxylin–eosin (HE), and further photographed and described through light microscopy. This is the first description of internal morphology performed for C. columbiensis and can help in future histopathological analysis, because through bioaccumulation some of these organs are contaminant targets. It can even be a great taxonomic tool, since the characteristics of the histological pattern of C. columbiensis presented differences compared to other descriptions made in chironomids.

Histopathology of Chironomus riparius (Diptera, Chironomidae) exposed to metal oxide nanoparticles

“…In the present study, histological analyses of non-treated C. riparius larvae did not show any differences in internal morphology in comparison to existing data [28,33,36]. These findings are of great potential for defining the general histopathological biomarkers that could be used in the histopathological assessment of related species.…”

“…At present there are no references regarding the histological description of the main systems and organs in healthy individuals, or the histopathological changes that could be used as biomarkers of pollutant cytotoxicity for this species. Similar species have been described and these studies can be used as guidelines for further studies [28,36]. Since the histological patterns can vary even between close species [33], determination of the normal organ architecture of C. riparius is crucial as it will be used as the foundation for determining potential histopathological biomarkers.…”

“…Given that this larval phase requires a substrate, a coarse quartz sand in a thin layer was provided. The use of the 4 th larval stage is common in histopathological studies [28,32,33,36].…”

“…The significance level was set at P<0.05. Sections of treated larvae were compared to the control and available data from studies on closely related species [28,32,33,36] and tissue alterations were recorded and described.…”

“…Microscopic analyses of tissues show early warning signs for the severity of toxic effects on animals. This approach allows for the results describing the health condition of several studied individuals to be extrapolated to the whole community in the studied ecosystem [28]. Histopathology is frequently used in in vivo toxicity assessments of nanoparticles in animal models, including rats, mice and fish [29].…”