Data from: Rapid cold hardening protects against sublethal freezing injury in an Antarctic insect

Rapid cold hardening (RCH) is a type of beneficial phenotypic plasticity
that occurs on extremely short time scales (minutes to hours) to enhance
insects' ability to cope with cold snaps and diurnal temperature
fluctuations. RCH has a well-established role in extending lower lethal
limits, but its ability to prevent sublethal cold injury has received less
attention. The Antarctic midge, Belgica antarctica is Antarctica's
only endemic insect and has a well-studied RCH response that extends
freeze tolerance in laboratory conditions. However, the discriminating
temperatures used in previous studies of RCH are far below those ever
experienced in the field. Here, we tested the hypothesis that RCH protects
against nonlethal freezing injury. Larvae of B. antarctica were exposed to
either control (2&[deg]C), direct freezing (-9&[deg]C for
24 h), or RCH (-5&[deg]C for 2 h followed by -9&[deg]C for
24 h). All larvae survived both freezing treatments, but RCH larvae
recovered more quickly from freezing stress and had significantly higher
metabolic rates during recovery. RCH larvae also sustained less damage to
fat body and midgut tissue and had lower expression of two heat shock
protein transcripts (hsp60 and hsp90), which is consistent with RCH
protecting against protein denaturation. The protection afforded by RCH
resulted in energy savings; directly frozen larvae experienced a
significant depletion in glycogen energy stores that was not observed in
RCH larvae. Together, these results provide strong evidence that RCH
protects against a variety of sublethal freezing injuries and allows
insects to rapidly fine-tune their performance in thermally variable
environments.