Freeze-tolerance, or the ability to survive internal ice formation, is relatively rare among insects. Larvae of the Antarctic midge Belgica antarctica are freeze-tolerant year-round, but in dry environments, the larvae can remain supercooled (i.e., unfrozen) at subzero temperatures. In previous work with summer-acclimatized larvae, we showed that freezing is considerably more stressful than remaining supercooled. Here, these findings are extended by comparing survival, tissue damage, energetic costs, and stress gene expression in larvae that have undergone an artificial winter acclimation regime and are either frozen or supercooled at −5°C. In contrast to summer larvae, winter larvae survive at −5°C equally well for up to 14 days, whether frozen or supercooled, and there is no tissue damage at these conditions. In subsequent experiments, we measured energy stores and stress gene expression following cold exposure at −5°C for either 24 h or 14 days, with and without a 12 h recovery period. We observed slight energetic costs to freezing, as frozen larvae tended to have lower glycogen stores across all groups. In addition, the abundance of two heat shock protein transcripts, hsp60 and hsp90, tended to be higher in frozen larvae, indicating higher levels of protein damage following freezing. Together, these results indicate a slight cost to being frozen relative to remaining supercooled, which may have implications for the selection of hibernacula and responses to climate change.
|State||Published - Jan 2020|
Bibliographical noteFunding Information:
Funding: This research was funded by the United States Department of Agricultural National Institute of Food and Agriculture Hatch Project grant 1010996 to N.M.T., National Science Foundation grant OPP-1341385 to R.E.L.J., and National Science Foundation grant OPP-1341393 to D.L.D.
© 2019 by the authors. Licensee MDPI, Basel, Switzerland.
- Belgica antarctica
- Energy stores
- Heat shock proteins
ASJC Scopus subject areas
- Insect Science