Freeze tolerance in an arctic Alaska stonefly

Abstract

SUMMARYMost aquatic insects do not survive subzero temperatures and, for those that do, the physiology has not been well characterized. Nemoura arctica is a species of stonefly widely distributed throughout arctic and subarctic Alaska. We collected nymphs from the headwaters of the Chandalar River, where we recorded streambed temperatures as low as -12.7°C in midwinter. When in contact with ice, autumn-collected N. arctica cool to -1.5±0.4°C before freezing, but individuals survived temperatures as low as -15°C, making this the first described species of freeze-tolerant stonefly. N. arctica clearly survive freezing in nature, as winter-collected nymphs encased in ice demonstrated high survivorship when thawed. In the laboratory, 87% of N. arctica nymphs frozen to -15°C for 2.5 weeks survived and, within one month of thawing, 95% of the last-instar nymphs emerged. N. arctica produce both glycerol and ice-binding factors (e.g. antifreeze protein) in response to low temperature. Hemolymph glycerol concentrations increased from 3 mmol l -1 to 930±114 mmol l -1 when temperatures were decreased from 4°C to -8°C, and N. arctica continued to produce glycerol even while frozen. Although the hemolymph of individual cold-acclimated nymphs occasionally exhibited more than a degree of thermal hysteresis, typically the hemolymph exhibited only hexagonal crystal growth, indicating a low concentration of ice-binding factor. Hemolymph of nymphs acclimated to subzero temperatures had recrystallization inhibition. These results demonstrate that, in the face of freezing conditions, N. arctica exhibit overwintering adaptations similar to those of terrestrial insects.

A nonprotein thermal hysteresis-producing xylomannan antifreeze in the freeze-tolerant Alaskan beetle Upis ceramboides

“…We typically observed TH values Ͻ0.1°C and often detected only hexagonal ice crystal morphology in the hemolymph of cold-adapted insects, indicating the presence of a low concentration of THF and/or a low specific activity THF (6). The sporadic presence of Ͼ0.5°C of TH in the hemolymph of U. ceramboides is consistent with observations on other freezetolerant arthropods (16,20).…”

“…Thermal Hysteresis Measurements. TH was measured using a Clifton Nanoliter Osmometer (Clifton Technical Physics) (16). NMR Spectroscopy.…”

“…Although the physiological role of THFs in freeze-tolerance is not well understood, THFs do appear to promote cold tolerance. Recrystallization inhibition and/or TH activity are known to increase in response to low temperature in freeze-tolerant insects (16,17), other arthropods (20) and plants (6). For the centipede, Lithobius forficatus, experiments showed that THFs (i.e., AFPs) significantly increased cell survivorship under freez- ing conditions (29), although the mechanism remains unclear.…”

“…In insects, for instance, TH has been identified in more than 50 species (9), but antifreeze protein (AFP) sequences have been published for only four of these (4). Furthermore, TH has been observed in multiple species of freeze-tolerant insects (9,16,17), namely, those able to survive extracellular freezing; however, none of the responsible THFs have been structurally characterized.…”

Caddisflies (Trichoptera) as good indicators of environmental stress in mountain lotic ecosystems

“…Comparing two streams in near natural condition -site 9 with constantly low temperature and site 8 with a highly variable temperature regime, we did not observe higher functional or species diversity at the latter. This may be explained by freezing of the stream-bed (Bulánková et al 2001), which can have a negative impact on macroinvertebrates (Irons et al 1993;Walters et al 2009). But we recorded a remarkably high proportion of crenal species, especially grazers at site 9; this is a naturally open stream with a boulder stream-bed, a favourable substrate for periphyton growth (Uehlinger 1991) providing food for scrapers (Boyero 2003).…”