PhD Project

Below the critical thermal minimum (CT_min), insects enter chill coma: a reversible state of paralysis. Chill coma is accompanied by a disturbance in ion and water balance, but prior cold acclimation can decrease the CT_min and the temperature at which homeostasis is lost. My research focuses on uncovering the mechanisms that underlie the loss of homeostasis during cold exposure and the means by which cold acclimation improves insect cold tolerance.

Using the crickets Gryllus pennsylvanicus and G. veletis, I am investigating the effects of cold exposure and cold acclimation on water and ion transport function across the hindgut and Malpighian tubules (sites of insect ion homeostasis). It is likely that active ion transport fails in the cold such that leak of ions predominates, and that cold acclimation alters transport function in the hindgut or Malpighian tubules such that ion leak is minimized and/or active transport is maintained to lower temperatures.

To generate hypotheses about how transport function is altered with cold acclimation, I first assembled transcriptomes of the hindgut and Malpighian tubules to compare gene expression in warm- and cold-acclimated crickets. I found that cold acclimation causes altered expression of some ion transporters (carbonic anhydrase and Na⁺/K⁺-ATPase among others), and potential restructuring of the hindgut epithelium (e.g. cytoskeletal components tubulin and actin, and tight junctions).

I am now further exploring how cell structure and ion transport enzymes change with cold acclimation. Current projects include:

1) How does cold acclimation affect the activity of enzymes in the hindgut and Malpighian tubules? I am running enzyme activity assays for Na⁺/K⁺-ATPase, V-ATPase (H⁺ pump), and carbonic anhydrase.

2) How do low temperatures and cold acclimation affect transport across the Malpighian tubules? This work involves the Ramsay assay and is being completed by Dr. Soheila Khazraeenia.

3) How do low temperatures and cold acclimation affect transport across the hindgut? I am using an Ussing chamber (electrophysiological methods) to measure rectal active transport function and ‘leakiness’.

4) How does cold acclimation influence hindgut cellular structure? Using light microscopy I have found no effect of cold acclimation on rectal pad cell density or thickness of the endocuticle, muscle, rectal pad length, or rectal pad width. I am now employing fluorescence microscopy to visualize the effect of cold acclimation on the hindgut cytoskeleton (this work is being done in collaboration with Joseph Stinziano, Dr. Way Lab). In future we will expand this project to visualize tight junctional complexes within the rectal pads.

        Publications

 Des Marteaux, L., Habash, M, Schmidt, J., and Hallett, R. 2014. Patterns of diapause frequency and emergence in swede midges of southern Ontario. Agricultural and Forest Entomology. (In press. DOI: 10.1111/afe.12083)

Des Marteaux, L., Habash, M, Schmidt, J., and Hallett, R. 2012. A method for induction and quantification of diapause entry in swede midge (Diptera: Cecidomyiidae). The Canadian Entomologist. 144: 792-800

Xue, Y., Bahlai, C. A., Frewin, A., McCreary, C.M., Des Marteaux, L.E., Schaafsma, A. W., and Hallett, R.H. 2012. Intraguild predation of the aphid parasitoid Aphelinus certus by Coccinella septempunctata and Harmonia axyridis. BioControl. 57: 627-634

Oral presentations

 Des Marteaux, L. and Sinclair, B.J. 2015. How does cold acclimation affect ion transport and ultrastructure of the insect hindgut? (Entomological Society of Ontario Annual General Meeting, Elgin, ON - Honorable mention)

Des Marteaux, L. and Sinclair, B.J. 2015. How does cold acclimation affect ion transport, gene expression, and ultrastructure of the insect hindgut? (Sixth International Symposium on the Environmental Physiology of Ectotherms and Plants, Aarhus, Denmark, and invited lecture at Universität Bielefeld, Chemical Ecology Dept., Bielefeld, Germany)

Des Marteaux, L. and Sinclair, B.J. 2014. What mechanisms underlie low-temperature loss of ion homeostasis in insects? (Canadian Society of Zoologists Annual Meeting, Montreal, QC)

Des Marteaux, L. and Sinclair, B.J. 2013. Does ion transport failure limit insects at low temperatures? (Fifth International Symposium on the Environmental Physiology of Ectotherms and Plants. London, ON)

Des Marteaux, L., Schmidt, J.M., Habash, M.B., and Hallett, R.H. 2012. A method for induction and quantification of diapause entry and investigation of diapause heritability in the swede midge (Entomological Society of Ontario Annual Meeting. Ottawa, ON)

Poster presentations

Des Marteaux, L. and Sinclair, B.J. 2014. Water before ions? Early chill coma ion balance challenges the current mechanistic model of chill coma. (American Physiological Society Intersociety Meeting, San Diego, CA; Entomological Society of Ontario Annual Meeting, Toronto, ON – President’s Prize recipient))

Des Marteaux, L. and Sinclair, B.J. 2013. Does insect chill coma onset correspond with hemolymph ion imbalance? (Entomological Society of Ontario/Entomological Society of Canada Joint Meeting. Guelph, ON)

Des Marteaux, L. and Sinclair, B.J. 2013. Does epithelial transport limit insects at low temperatures? (Canadian Society of Zoologists Annual Meeting. Guelph, ON.)

Des Marteaux, L., Schmidt, J.M., Habash, M.B., and Hallett, R.H. 2011, 2012. A method for induction and quantification of diapause in swede midge, Contarinia nasturtii (Ontario Pest Management Conference, Guelph, ON; Entomological Society of Ontario Annual Meeting

       St. Catharines, ON – President’s Prize recipient)

Des Marteaux, L., Schmidt, J.M., Habash, M.B., and Hallett, R.H. 2012. Longevity and emergence patterns of overwintering swede midge (Ontario Fruit & Vegetable Convention, Niagara Falls, ON – First place poster prize recipient)                                                    

Des Marteaux, L., Habash, M.B., Kullik, S.A., and Schmidt, J.M. 2009, 2010. Presence of Oniscus asellus (Crustacea: Isopoda) in temperate forests alters microbial communities and leaf litter mass loss (U-links Annual Celebration of Research, Haliburton, ON; Entomological Society of Ontario Annual Meeting, Grand Bend, ON)