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Timothy J. Bradley

Professor

Comparative and Evolutionary Physiology

 

E-mail: tbradley@uci.edu

Control of Respiration in Insects

A discontinuous gas exchange cycle (DGC) is observed in a variety of insects under a number of environmental circumstances. Insect physiologists have been puzzled and intrigued by this complex respiratory pattern. Two explanations had previously been put forward to explain this behavior; 1) that the pattern serves to reduce respiratory water loss, and 2) that the pattern may have initially evolved in underground insects as a way of dealing with hypoxic/hypercapnic conditions.

We have proposed a third possible explanation based on the notion that oxygen is necessary for oxidative metabolism but also acts as a toxic chemical that, even at relatively low concentrations, can lead to oxidative damage of tissues. At the partial pressures of CO2 at which the insect respiratory system operates, carbon dioxide diffuses out less rapidly than oxygen enters. Therefore, the respiratory system must be opened at intervals to rid the insect of accumulated CO2. This process exposes the tissues to dangerously high levels of oxygen. To protect the tissues, the spiracles are closed. We have argued that the cyclical open and closed pattern demonstrated by insects at rest is a necessary consequence of the need to rid the respiratory system of accumulated carbon dioxide followed by a closed period needed to reduce oxygen toxicity. More recently, we have been investigating the respiratory patterns displayed by insects at higher levels of activity. We have described a respiratory control model for insects that explains the patterns of respiration expressed in insects under all conditions of activity and environmental variability observed in nature.

Osmoregulation in Insects

A major area of study in my laboratory has been the characterization and elucidation of the mechanisms of osmoregulation in saline-water and blood-feeding insects. Saline-water insects are of interest from an ecological and physiological standpoint because of their capacities to osmoregulate in extreme aquatic habitats (environmental salinities up to three times seawater, pH 10, or water rich in magnesium or sulfate). Bloodfeeding insects must deal with extraordinary rates of diuresis (excreting up to five times their previous body volume in two hours). Both groups have an unusual problem for insects, namely excreting large amounts of sodium. All of these ecological peculiarities present very interesting physiological problems and these have been the subject of my studies.

Beginning with my Masterís work and continuing to the recent papers emanating from my laboratory I have elucidated the organs involved in ion transport, the ultrastructure of these tissues, directions and mechanisms of ion transport, hormonal control of ion transport, and the significance of osmotic regulation and ion transport processes in the distribution and ecological success of various saline-water groups. More recently I have also been interested in the evolution of saline tolerance in the larvae of various species of mosquitoes. This has lead to studies of the phylogenetic relationships in mosquito clades in which saline-water forms are common. Our recent physiological studies have concentrated on osmoconforming species and we are actively pursuing the mechanisms involved in the production and regulation of compatible osmolytes.

We are now also investigating water balance, osmoregulation and metabolism in adult mosquitoes. As a result of metamorphosis the organs engaged in these physiological processes are rather different in adults than in the larvae and the environment is, of course, entirely different. We are particularly interested in the role of desiccation resistance and energy metabolism in mosquitoes that are vectors of major human diseases.

Ph.D. Zoology University of British Columbia May 1976
Vancouver, B.C., Canada

M.S. Zoology University of Oklahoma August 1973
Norman, Oklahoma

B.A. Biology Vanderbilt University January 1971
Nashville, Tennessee

National Merit Scholarship Finalist, 1966
Careers '75 Research Scholarship from the Province of British Columbia, 1974
NIH Postdoctoral Fellowship, 1978 1980
Fellow of the American Association for the Advancement of Science, Elected 1992
Excellence in Teaching Award, School of Biological Sciences, 1999
Daniel G. Aldrich, Jr. Distinguished University Service Award, 2009

 

 

Contreras, H.L. & T.J. Bradley (2009)  Transitions in insect respiratory patterns are controlled by changes in metabolic rate.  J. Insect Physiol. (in press).

Timothy J. Bradley, Adriana D. Briscoe, Seán G. Brady, Heidy L. Contreras, Bryan N. Danforth, Robert Dudley, David Grimaldi, Jon F. Harrison, Alexander Kaiser, Christine Merlin, Steven M. Reppert, John M. VandenBrooks, Steve P. Yanoviak (2009)  Episodes in insect evolution.  49(5):590-606.

Contreras, H.L. & T.J. Bradley (2009)  Metabolic rate controls respiratory pattern in insects. J. Exp. Biol. 212: 424-428

Bradley, T.J. (2008)  Active transport in insect recta.  J. Exp. Biol. 211:835-836.

Bradley, T.J. (2008)  Saline-water insects: Ecology, physiology and evolution. In: Aquatic Insects: Challenges to Populations. J. Lancaster & R.A. Briers, eds. CAB International. UK.

Bradley, T.J. (2008) Control of the respiratory pattern in insects. In: Hypoxia and the Circulation. R. Roach. P Wagner & P. Hackett, eds. Adv. in Med. & Biol. 618: 211-220.

Bradley, T.J. (2008) Saline-water insects: Ecology, physiology and evolution. In: Aquatic Insects: Challenges to Populations. J. Lancaster & R.A. Briers, eds. CAB International. UK.

Bradley, T.J. (2008) Active transport in insect recta. J. Exp. Biol. 211:835-836.

Curtis, C; G.N. Landis, D. Folk, N.B. Wahr, N. Hoa, M. Wasker, D. Abdueva, D. Ford, A. Luu, A. Badrinath, R.L. Levine, T.J. Bradley, S. Tavare, & J. Tower (2007) Transcriptional profiling of MnSOD-mediated lifespan extension in Drosophila reveals a species-specific network of aging and metabolic genes. Genome Biology

Albers, M. & T.J. Bradley (2006) Fecundity in Drosophila following desiccation is dependent on nutrition and selection regime. Physiol. Biochem. Zool. 79:857-865.

Bradley, T.J. (2006) Discontinuous ventilation in insects: protecting tissues from O2. Resp Physiol. Neurobiol. 154:30-36.

Gray, E.M. & T.J. Bradley (2006) Evidence from mosquitoes suggests that cyclic gas exchange and discontinuous gas exchange are two manifestations of a single respiratory pattern. J. Exp. Biol. 209:1603-1611.

Folk, D.G. & T.J. Bradley . (2005) Adaptive evolution in the lab: unique phenotypes in fruit flies comprise a fertile field of study. Int. Comp. Biol. 45:492-499.

Gray, E. M. & T. J. Bradley (2005) The physiology of desiccation resistance in Anopheles gambiae and Anopheles arabiensis. Amer. J. Trop. Med & Hyg. 73(3):553-559.

Gray, E.M. & T.J. Bradley (2005) Malarial infection in Aedes aegypti: Effects on feeding, fecundity and metabolic rate. J. Parasitology 132:169-176.

Hetz, S. & T.J. Bradley (2005) Insects breathe discontinuously to avoid oxygen toxicity, Nature. 433:516-519.

Gray, E. M. & T. J. Bradley (2005) The physiology of desiccation resistance in Anopheles gambiae and Anopheles arabiensis. Amer. J. Trop. Med & Hyg. 73(3):553-559.

Bradley, T.J. & D.G. Folk. (2004) Analyses of Physiological Evolutionary Response. Physiol. Biochem. Zool. 77(1):1-9.

Albers, M. & T.J. Bradley (2004) Osmotic regulation in adult Drosophila melanogaster during dehydration and rehydration. J. exp. Biol. 207: 2313-2321.

Folk, D.G. & T.J. Bradley (2004) The evolution of recovery from desiccation stress in laboratory-selected populations of Drosophila melanogaster. J. exp. Biol. 207(15): 2671-2678.