Grant: Discovery Grants Program - Individual

My long-term goal is to develop an integrative understanding of how temperature sets limits to animal performance, and I will begin with a focus on chill tolerance. The majority of insects are chill-susceptible, meaning they suffer non-freezing injury at relatively mild low temperatures. A primary consequence of cold exposure for these insects is a disruption of ion and water homeostasis; a cold-induced rise in extracellular [K+] depolarizes cells, causing injury and death. Through thermal adaptation or plasticity, however, insects can better maintain ion homeostasis in the cold, and thereby avoid injury. Thus, modifications to the physiology of ionoregulatory organs likely underlie variation in insect chill tolerance. Insect ion balance is maintained by the coordinated transport properties of the Malpighian tubules (MT) and gut. These organs are highly relevant to chill tolerance, but the mechanisms by which chilling impairs their function are unknown. In my first grant cycle I propose to use fruit flies, locusts, and crickets to examine: 1) the effects of chilling on the transport physiology of the ionoregulatory organs, 2) the effects of chilling on paracellular epithelial barriers, and 3) endocrine control of chill tolerance.In my first objective, the migratory locust will be used to examine how temperature directly impacts transcellular ion transport in the MT and gut epithelia. To accomplish this, I will use a variety of techniques to examine temperature effects on ion and water transport, and quantify the relative contributions of individual transporters to maintaining ion balance in the cold. These techniques will then be adapted to cricket species that vary in chill tolerance to examine epithelial thermal adaptation.Molecules can cross epithelia through not only transcellular, but also paracellular routes, the tightness of which are mediated by the septate junctions (SJ). In my second objective, I will determine the role of SJs and their component proteins in Drosophila chill tolerance. I will begin by examining how thermal acclimation modulates gut barrier properties and tissue-specific expression patterns of SJ proteins in Drosophila. In parallel, I will use locusts to determine whether cold-induced SJ disruption is a common challenged faced by insects, and to localize barrier disruption to key organs.Within insects a range of neuropeptides regulate transcellular and paracellular transport across epithelia. In my third objective, I will screen neuropeptides for effects on chill tolerance, and determine whether induced variation in chill tolerance is associated with an altered ability of flies to maintain ion homeostasis in the cold. Further, I will determine which neuropeptides and receptors are most likely to be relevant to chill tolerance adaptation and plasticity, using tissue-specific RNA-seq.