THERMAL STRESS INDUCES HSP70 PROTEINS SYNTHESIS IN LARVAE OF THE COLD STREAM NON‐BITING MIDGE Diamesa cinerellaMeigen

Abstract

Laboratory experiments on the cold stenothermal midge Diamesa cinerella (Diptera, Chironomidae) were performed to study the relationship between increasing temperature and heat shock proteins (HSP70) expression at translational level (Western blotting). Thermotolerance of IV instar larvae collected in nature at 1.5-4.3°C during seasons was analyzed through short-term (1 h at ten different temperatures from 26°C to 35°C) and long-term (1-14 h at 26°C and 1-4 h at 32°C) heat shocks. A high thermotolerance was detected (LT50=30.9-32.8°C and LT100=34.0-37.8°C). However, survival decreased consistently with increasing exposure time, especially at higher temperature (LTime50=7.64 h at 26°C and LTime50=1.73 h at 32°C). The relationship between such heat resistance and HSP70 expression appeared evident because a relationship between HSP70 level and larval survival rate was generally found. A heat shock response (HSR) was consistent only in the summer larvae. The absence of HSR in the other populations coupled with even higher amounts of HSP70 than in summer, led us to hypothesize that other macromolecules and other adaptive mechanisms, apart from biochemical ones, are involved in the response of D. cinerella larvae to high temperature. Altogether these results stressed how in this midge the HSP70 protein family confers resistance against cold, being detected under natural conditions in control larvae collected in all seasons, but also against warm under experimental heat shocks. These results give new insights into possible responses to climate changes in freshwater insects within the context of global warming.

ADrosophilaheat shock response represents an exception rather than a rule amongst Diptera species

“…Although we analysed only one cold-water species of Chironomidae here, Di. permacra, there are many publications that describe HSR peculiarities in different species of this family that belong to different evolutionary lineages, although this information is still fragmentary (Karouna-Renier & Zehr, 2003;Rinehart et al, 2006;Lencioni et al, 2013). Thus, species within Chironomidae differ dramatically in terms of Hsp70 and the correspondent mRNA induction kinetics and range after HS (Table 2).…”

“…Furthermore, we investigated the cold-water species Diamesa permacra, which belongs to the family Chironomidae (nonbiting midges) and resides in fast-flowing springs and spring brooks near St Petersburg, Russia. The accumulated results were compared with the available data for other Chironomidae species obtained by other researchers Rinehart et al, 2006;Yoshimi et al, 2009;Bernab o et al, 2011;Lencioni et al, 2013). In addition, we studied three congeneric species from the family Ceratopogonidae (biting midges).…”

Thermal survival limits of young and mature larvae of a cold stenothermal chironomid from the Alps (Diamesinae: Pseudodiamesa branickii [Nowicki, 1873])

“…Thermotolerance has been largely investigated in eurythermal chironomid species such as Chironomus riparius Meigen, 1804 (Carretero et al, 1991), Chironomus plumosus (Linnaeus, 1758) and Polypedilum vanderplanki Hinton, 1951, but less in cold stenothermal species (Bernabò et al, 2011). To our knowledge, B. antarctica from the Antarctic region, Pseudodiamesa branickii (Nowicki, 1873) and Diamesa cinerella Meigen, 1835 from alpine streams are the sole cold stenothermal chironomid species investigated for heat tolerance using molecular approaches (Rinehart et al, 2006;Bernabò et al, 2011;Lencioni et al, 2013). Mature larvae of these species are able to survive short-term heat shocks at substantially higher temperatures than those they normally encountered in nature and gene expression analyses highlighted that their heat shock response is correlated to the up-regulation of inducible hsp70 (= 70 kDa heat shock protein) gene.…”

Cold adaptive potential of chironomids overwintering in a glacial stream

“…Previous studies in this laboratory have recorded a similar differential response in larvae of these two species but, under acute heat stress, P. branickii shows a heat shock response (= hsp70 gene expression) (Bernabò et al ., ), whereas D. cinerella does not have this capacity (Lencioni et al ., ). Notwithstanding, they both have comparable lethal temperatures ( P. branickii : LT 50 = 32.2 °C, LT 100 = 36 °C; D. cinerella : LT 50 = 31.7 °C, LT 100 = 35 °C).…”

“…Among the aquatic insects, the focus of the present study is on nonbiting midges (Diptera Chironomidae), which are the most widely distributed insect family in cold freshwaters, and are usually dominant in glacier-fed streams (Lencioni & Rossaro, 2005). Chironomids therefore constitute an appropriate taxon for studying the adaptive strategies that evolve to survive stresses such as low temperatures and temperature variations, as also associated with glacier retreating (Lencioni et al, 2013). Previous studies on the cold hardiness of polar and temperate chironomids report both freeze avoidance (Kohshima, 1984;Bouchard et al, 2006b) and freeze tolerance (Scholander et al, 1953;Hinton, 1960;Danks, 1971;Baust & Edwards, 1979;Block, 1982;Bouchard et al, 2006a), as well as evidence of the adoption of different strategies throughout their life cycle (Baust & Edwards, 1979;Bouchard et al, 2006a).…”