Timothy J. BradleyProfessor, Ecology & Evolutionary Biology |
|
|
Research Interests |
Comparative physiology of ion transport epithelia | |
| URL | Lab webpage | |
|
Academic Distinctions |
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 |
|
|
Research Abstract |
My laboratory is engaged in studies of the physiology, ecology, cell biology and pathology of insects. My interests include the physiological ecology of saline-water insects and the physiology of energy metabolism in Drosophila. Saline-Water Insects The larvae of saline-water mosquitoes survive and indeed flourish in water too saline for any aquatic vertebrate. These capabilities are the result of highly developed osmotic mechanisms. Our studies of saline tolerant mosquitoes have revealed two general mechanisms for increased saline tolerance: osmoregulation and osmoconformation. Species employing the former strategy can be found in the genera Aedes, Anopheles and Opifex. These larvae have highly developed physiological capacities for ion transport and hyperosmotic fluid secretion. We are currently investigating the Malpighian tubules and recta of the larvae, tissues which offer unusual opportunities for comparative study of secreting epithelia. In the genera Culiseta and Culex, the larvae are osmoconformers by virtue of their capacity to accumulate large quantities of organic osmolytes in the hemolymph. Using thin layer and high pressure chromatography, we have demonstrated that the principal osmolytes are proline and trehalose. This mechanism of osmoregulation is distinct from that of any other aquatic insect. We are currently taking advantage of the substantial amount of information available on the taxonomy, and to a lesser extent, the phylogeny of mosquitoes, to reconstruct the evolution of these physiological mechanisms. We have found that saline-tolerant osmoregulation has evolved independently at least three times in the mosquitoes, while osmoconformation has evolved at least twice. Our continuing studies are designed to clarify the physiological, ecological and evolutionary mechanisms of increased saline tolerance in the mosquitoes. Brine flies, in the family Ephydridae, are the most saline tolerant insects known. We are studying the species Ephydra hians, which occurs in Mono Lake, a large saline lake in northern California. Mono Lake is increasing rapidly in salinity due to diversions of inflowing freshwater streams by the Los Angeles Department of Water and Power. The imminent ecological demise of the lake due to increasing salinity has caused an international furor to protect the arthropods in the lake and the thousands of migratory shorebirds which feed on them. We have been investigating the ecology and physiology of the brine flies in an attempt to define the salinity tolerance of the flies, determine other ecological factors which affect their survival and fecundity and to formulate management procedures for the lake which protect the ecosystem and meet the water needs of the city. Our expertise in the physiological ecology of saline tolerant insects has placed us in a particularly suitable position for undertaking these very diverse studies. Recently, we have pursued a study of sulfate transport into the larval flies via the midgut and out of the larvae via the colon. These studies include radioisotope, electrophysiological, and inhibitor studies, as well as analyses of the ion sensitivities of the transport mechanisms. Selection in Drosophila We are examining energy metabolism, storage and allocation in various stocks of Drosophila melanogaster. Dr. Michael Rose's laboratory has developed replicate stocks of Drosophila which differ in life span, reproductive timing, or desiccation and starvation resistance. We are testing the hypothesis that stocks differing in those traits also differ in energy allocation and usage. A long term goal is an understanding at a mechanistic level of pleiotropies involving life history traits, physiological stress responses and energy metabolism. In our initial studies we have quantified the energy outputs of flies which have been subjected to selection for postponed senescence, and their controls. We find that short-lived flies put substantial metabolic resources (joules) into their eggs, and store less metabolic energy as lipid and carbohydrate in the adult body. The long-lived flies show a reverse trend, namely reduced early fecundity and increased storage of lipid and carbohydrate. Energy equivalency analysis demonstrates that the energy saved by reduced fecundity does not show up as stored nutrients, and thus the total energy output and storage is lower in the long-lived flies. In further studies, we are measuring the respiratory quotient (RQ) of flies subjected to desiccation and starvation. RQ analysis is a non-invasive technique for elucidating the metabolic compounds metabolized to support specific activities, in this case resistance to environmental stresses. We intend to use these techniques to investigate differences in metabolic response in flies which are genetically differentiated as a result of laboratory selection for postponed aging, or resistance to desiccation or starvation. |
|
| Publications | Hetz, S. & T.J. Bradley (2005) Insects breathe discontinuously to avoid oxygen toxicity, Nature. 433:516-519. | |
| 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. | ||
| 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. | ||
| Albers, M. & T.J. Bradley (2004) Osmotic regulation in adult Drosophila melanogaster during dehydration and rehydration. J. exp. Biol. 207: 2313-2321. | ||
| Williams, A.E., M.R. Rose & T.J. Bradley. (2004) The respiratory pattern in Drosophila melanogaster selected for desiccation resistance is not associated with the observed evolution of decreased locomotory activity. Physiol. Biochem. Zool. 77(1):10-17. | ||
| Gray, E. & T.J. Bradley. (2003) Metabolic rate in female Culex tarsalis (Diptera: Culicidae) : Age, size, activity and feeding effects. J. Med. Entomol. 40(6) 903-911. | ||
| Patrick, M.L.: R. J. Gonzalez; C. M. Wood; R. W. Wilson; T. J. Bradley & A. L. Val (2002) The characterization of ion regulation in Amazonian mosquito larvae: evidence of phenotypic plasticity, population-based disparity and novel mechanisms of ion uptake. Physiol. Biochem. Zool. 75:223-236. | ||
| Graduate Programs |
Comparative Physiology |
|
| Link to this profile | http://www.faculty.uci.edu/profile.cfm?faculty_id=2131 | |
| Last updated | 01/30/2006 | |