|Degrees:||B.Sc., Ph.D. (Western)|
|Website:||Visit my Lab Website|
The MacMillan lab studies how temperature impacts animal physiology. We are integrative and comparative physiologists working to build mechanistic models of how stress directly alters tissue function, and how this perturbation cascades through multiple organ systems to ultimately cause injury and death. We aim to directly link mechanisms of injury to their biochemical and molecular roots, and to do so we use a variety of techniques and a network of talented interdisciplinary collaborators.
The majority of insects are chill susceptible, meaning that like us, they suffer a loss of homeostasis and die at low temperatures above those that cause their body fluids to freeze. When exposed to low temperatures, chill susceptible insects lose ion and water balance, leading to a rise in extracellular [K+] that depolarizes cells and triggers apoptosis. However, insects are both remarkably diverse and remarkably plastic, and limits to stress tolerance can vary enormously among species through evolutionary adaptation and within individuals in response to their immediate environment. Our primary focus is on how temperature impacts transcellular and paracellular solute transport in insects in an effort to understand: 1) the mechanisms that set the limits to thermal tolerance, 2) the biochemical means by which phenotypic plasticity modifies those limits, and 3) how variation in thermal tolerance evolves within and among insect species. To accomplish this, we use a variety of techniques, including ion-selective microelectrodes, atomic absorption spectrometry, biochemical assays, immunohistochemistry, and bioinformatics. Beyond the cold, the MacMillan lab also dabbles in other forms of abiotic stress, including heat, desiccation, and food deprivation.
Heath welcomes inquiries from talented and motivated scientists looking to start an graduate or undergraduate thesis on insect physiology, biochemistry, and/or molecular biology. See the lab website for details on available positions.
Overgaard, J.O., MacMillan H.A. (2017) The integrative physiology of insect chill tolerance. Annual Review of Physiology 79, 187-208.
Yerushalmi, G.Y., Misyura, L., Donini, A., MacMillan, H.A. (2016) Chronic dietary salt stress mitigates hyperkalemia and facilitates chill coma recovery in Drosophila melanogaster. Journal of Insect Physiology. 95: 89-97.
Jørgensen, L.B., Overgaard, J., MacMillan, H.A. (in press) Paralysis and heart failure precede ion balance disruption in heat-stressed European green crabs. Journal of Thermal Biology.
MacMillan, H.A., Knee, J.M., Dennis, A.B., Udaka, H., Marshall, K.E., Merritt, T.J.S., Sinclair, B.J. (2016) Cold acclimation wholly reorganizes the Drosophila melanogaster transcriptome and metabolome. Scientific Reports. 6: 28999.
MacMillan, H.A. Baatrup, E., Overgaard, J. (2015) Concurrent effects of cold and hyperkalemia cause insect chilling injury. Proceedings of the Royal Society B. 282, 20151483.
MacMillan, H.A. Andersen, J.L., Davies, S.A., Overgaard, J. (2015) The capacity to maintain ion and water homeostasis underlies interspecific variation in Drosophila cold tolerance. Scientific Reports. 5, 18607.