Rapid cold-hardening increases the freezing tolerance of the Antarctic midgeBelgica antarctica

Abstract

Rapid cold-hardening (RCH) is well known to increase the tolerance of chilling or cold shock in a diverse array of invertebrate systems at both organismal and cellular levels. Here, we report a novel role for RCH by showing that RCH also increases freezing tolerance in an Antarctic midge, Belgica antarctica (Diptera, Chironomidae). The RCH response of B. antarctica was investigated under two distinct physiological states: summer acclimatized and cold acclimated. Summer-acclimatized larvae were less cold tolerant, as indicated by low survival following exposure to -10°C for 24·h; by contrast, nearly all coldacclimated larvae survived -10°C, and a significant number could survive -15°C. Cold-acclimated larvae had higher supercooling points than summer larvae. To evaluate the RCH response in summer-acclimatized midges, larvae and adults, maintained at 4°C, were transferred to -5°C for 1·h prior to exposures to -10, -15 or -20°C. RCH significantly increased survival of summer-acclimatized larvae frozen at -10°C for 1·h compared with larvae receiving no cold-hardening treatment, but adults, which live for only a week or so in the austral summer, lacked the capacity for RCH. In coldacclimated larvae, RCH significantly increased freeze tolerance to both -15 and -20°C. Similarly, RCH significantly increased cellular survival of fat body, Malpighian tubules and gut tissue from cold-acclimated larvae frozen at -20°C for 24·h. These results indicate that RCH not only protects against non-freezing injury but also increases freeze tolerance.

Upregulation of two actin genes and redistribution of actin during diapause and cold stress in the northern house mosquito, Culex pipiens

“…In our study, we did not observe changes of actin within the Malpighian tubules, ovaries, or thoracic muscles; only the midgut displayed obvious actin changes in response to low temperature. Specific tissues in different species and different developmental stages have their own distinct responses related to survival at high or low temperature (Krebs and Feder, 1997;Yi and Lee, 2003;Lee et al, 2006), and it appears that the midgut is one of the tissues most responsive to low temperature in Cx. pipiens..…”

The protective effect of rapid cold-hardening develops more quickly in frozen versus supercooled larvae of the Antarctic midge, Belgica antarctica

“…Larvae were cooled in the presence of water (~200μl), and a small piece of ice was added to ensure the water froze at or slightly below 0°C. Because larvae are highly susceptible to inoculative freezing (Lee et al, 2006b;Elnitsky et al, 2008), contact with surrounding ice would induce internal ice formation at the melting point of larval body fluids (~-0.7°C). Direct exposure to -18°C for 24h caused >60% mortality in larvae and increased survival at this temperature was used as evidence for RCH induction.…”

“…By contrast, late in the austral summer, larvae experience diurnal fluctuations and unpredictable weather conditions that result in sudden, acute exposure to subzero temperatures. In addition to remaining freeze tolerant year-round (Baust and Lee, 1987), these larvae are capable of quickly enhancing their cold tolerance by the process of rapid cold-hardening (RCH) (Lee et al, 2006b).…”

“…Documented in over 30 species from six different orders, it is now clear that the RCH response is widespread among freeze-intolerant insects ). However, only recently was the RCH response extended to freeze-tolerant insects when it was first reported in frozen larvae of B. antarctica (Lee et al, 2006b).…”

Contrasting strategies of resistance vs. tolerance to desiccation in two polar dipterans

“…It is possible that E. murphyi possesses similar physiological adaptations that underlie its high level of desiccation tolerance. Indeed, the capacity to which they respond to temperature is very similar (Lee et al 2006;Everatt et al 2012). …”