Extracellular hemoglobin and environmental stress tolerance in Chironomus larvae

Abstract

Hemoglobin (Hb) is one of the most common conserved molecules found in organisms belonging to all major kingdoms of life. Chironomid midge larvae are unique among the invertebrates being the only free-living group of organisms possessing extracellular hemoglobins (Hbs) in monomeric and dimeric forms floating in their hemolymph. Remarkable ability of individual species of chironomid midges to tolerate wide range of environmental stressors prevailing in their respective ecosystems has enabled chironomids to sustain as one of the most widely distributed insects in the world. Ability of different Chironomus spp to thrive under extreme hypoxic conditions as well as in the presence of chemical pollution made chironomid midges an efficient model system to assess the effect of environmental stress in different freshwater ecosystems. The modulation of Hb concentration has been found to be a function of different type of abiotic stressors and thus Hb of chironomid midges (Ch-Hb) has attracted the attention as a potential biomarker for environmental biomonitoring. Large body of literature on Ch-Hb accumulated mainly during sixties to eighties of twentieth century has enriched our understanding of its physiological, developmental and biochemical features. Empirical as well as in-silico studies carried out in recent years provided insights into many structure-function relationships of Ch-Hb. However, for the last few decades, majority of the studies were carried out to project and validate Ch-Hb as potential bioindicator for evaluating toxicants, chemical pollutants and environmental gradients of dissolved oxygen concentration. In this review, historical development of the subject has been compiled with notes on future implications of contemporary studies on Ch-Hb.

Habitat expansion of a tropical chironomid by seasonal alternation in use of littoral and profundal zones

“…In Lake Alchichica, the winter diatom bloom consists mainly of the large (>50 um) and fast sinking diatom Cyclotella alchichicana Oliva, Lugo, Alcocer & Cantoral-Uriza 2006 (Ardiles et al, 2012;Alcocer et al, 2014), which provides food for the deep benthos (Hernández et al, 2014). Some Chironomus species thrive in the profundal zone despite anoxia using extracellular haemoglobin (Nath, 2018). High amounts of sulfide during anoxia can cause the disappearance of chironomid species from the profundal area of the lakes even when the species can tolerate oxygen depletion (Prat et al, 1992).…”

Waste water discharge from a large Ni-Zn open cast mine degrades benthic integrity of Lake Nuasjärvi (Finland)

“…This could suggest that a hypolimnetic oxygen threshold has been crossed at sites N7 and N8. In addition to S. coracina-type, C. plumosus-type possesses extracellular hemoglobin, and hence, tolerates very low oxygen concentrations and periods of anoxia (Quinlan et al, 1998;Nath, 2018). In Lake Nuasjärvi, C. plumosus-type, which is also an indicator of toxic metal impact having a very high tolerance (Ilyashuk et al, 2003;Brooks et al, 2005), shows a significant increase at site N7, but disappears from the adjacent site N8 further suggesting that the environmental conditions have become close to a threshold.…”

The Multifaceted Effects of Short-Term Acute Hypoxia Stress: Insights into the tolerance mechanism ofPropsilocerus akamusi(Diptera: Chironomidae)

“…Thus, as bioindicators, they are a suitable taxon to explore the adaptation mechanisms required to endure environmental stress (Lencioni et al, 2008;Rosenberg, 1992). Chironomid midge larvae possess a wide range of tolerance to hypoxia, due to extracellular hemoglobins (Hbs) in monomeric and dimeric forms floating in their hemolymph (Hamburger et al, 1994;Nath, 2018). Especially, P. akamusi of Chironomidae frequently predominates macroinvertebrates in many eutrophic lakes and demonstrated incredibly low fuel consumption at a stage of estivation when the larvae lived in deep sediment and engaged in anaerobic respiration, with ethanol as a major metabolite, to withstand prolonged hypoxia (Gong et al, 2008;Hirabayashi et al, 2004;Zou et al, 2019).…”