Most insects can’t handle the cold. I don’t even mean freezing cold: most insects get injured or die at temperatures far above their freezing points.
For my PhD research in the MacMillan Lab, I will be taking a closer look at what happens inside an insect when it cools down, and what the renal systems of more cold tolerant insects do to help them avoid injury and death.
We think the renal system is important because when insects get cold, they lose ion and water homeostasis. The Malpighian tubules (actively secreting ions into the gut; water follows) and rectal pads (actively absorbing ions from the gut; water follows) are important for both. Most of the time, the renal organs can correct any ion or water imbalance, and they do it fast. When an insect cools down, however, active ion transport slows more than passive ion leak, and when you combine this with barrier failure (ions leaking between cells, not just through them), the renal organs just can’t keep up. The end result is a lot of sodium leaking out into the gut, water following it, and an increased potassium concentration in the remaining haemolymph (toxic; indirectly causes tissue damage) that gets worse over time.
Insects can improve their cold tolerance: better cold tolerance (as measured by e.g. speed of recovery from a chill coma) seems to correlate with a better ability to maintain ion homeostasis in the cold. If you take an insect that evolved in a cold climate and plunge it into the cold, it will generally do better than a related species from the tropics. Makes sense, right? Interestingly, a lot of insects can also cold acclimate (e.g. when you rear them in a cooler incubator, they become more cold tolerant) — and this is what I’m most interested in (and will be exploring in depth).
I’m going to be using fruit flies (Drosophila melanogaster) for the most part, but my background is in termite biology. For my MSc, I explored the collective behaviours that termites use to defend their colonies from disease. For now, the termite work is on the back burner, but I am very interested in seeing how chilling injury affects their behaviour, and whether it can be mitigated by acclimation.
Davis HE, Meconcelli S, Radek R, & McMahon DP. (2018) Termites shape their collective behavioural response based on stage of infection. Scientific Reports, 8(1): 14433. doi: 10.1038/s41598-018-32721-7. (Also available as a Preprint)
Fernandez-Triana J, Buffam J, Beaudin M, Davis H, Fernandez-Galliano A, Griffin E, Lin S-Y, McAulay MK, Richter R, Rodriguez F, & Várkonyi G. (2017) An annotated and illustrated checklist of Microgastrinae wasps (Hymenoptera, Braconidae) from the Canadian Arctic Archipelago and Greenland. ZooKeys, 691: 49-101. doi: 10.3897/zookeys.691.14491.
Davis HE, Meconcelli S, Radek R, McMahon DP. (2018) When to care and when to kill: termites shape their collective response based on stage of infection. bioRxiv 287441.