David Julian, Ph.D
University of Florida
Associate Professor
Department of Zoology
Ph.D., University of California - San Francisco

I am a comparative, ecological physiologist with an interest in the cellular responses and adaptations of animals to environmental stressors. To an ecological physiologist, a stressor is any environmental condition that threatens an organism’s survival by pushing it outside its normal homeostatic boundaries; that is, any condition that limits an organism’s ability to regulate its physiological processes. The core focus of my lab is on the adaptations that allow some marine and aquatic animals to thrive in seemingly inhospitable “extreme” environments. Animals in the most extreme environments, such as those at deep-sea hydrothermal vents and under Antarctic ice sheets, are referred to as extremophiles. However, animals in many environments that are more familiar to us also face comparatively extreme conditions. Such environments include the mud of tidal marshes and mangroves (which have very low oxygen and high hydrogen sulfide concentrations), exposed
pools in rocky intertidal zones (which have widely variable oxygen, salinity and temperature), and the waters of many tropical and subtropical swamps (which have low oxygen and high hydrogen sulfide concentrations, and can be highly acidic). It is well known from studies on cells of nonextremophiles (especially mammalian cells) that exposure to such stressors has the potential to cause catastrophic molecular damage, resulting in widespread cell death. Therefore, to survive and reproduce, animals faced with extreme stressors must have a variety of adaptations to minimize and/or repair the cellular damage. Very few of these adaptations have been discovered and even fewer are well understood. The overall goal of my research is to help elucidate the cellular, biochemical and molecular adaptations that allow animals to avoid cellular damage when faced with extremes of hydrogen sulfide, oxygen, salinity, pH and temperature.

My lab uses a variety of animal and cell models, focusing primarily on the sulfide-tolerant worm Glycera dibranchiata (from coastal mudflats) and two clams tolerant of low oxygen: Mercenaria mercenaria, from mudflats, and Sphaerium sp., from an African swamp system. My interest and expertise in measuring the physiological responses of animals and their cells to stressful conditions has also led to very fruitful collaborations with UF researchers addressing similar questions, although in very different “model systems”. This has included investigating the effects of aging and cancer drugs in mammalian heart muscle and immortalized heart cells in culture, the recycling of damaged sub-cellular components in yeast and mammalian skeletal muscle, and the metabolic costs of electric field generation in Amazonian electric fish.

Representative Publications:

Joyner-Matos JL, Downs CA, Julian D. Increased expression of stress proteins in the surf clam Donax variabilis following hydrogen sulfide exposure. Comparative Biochemistry and Physiology 2006; in press.

Wohlgemuth SE, Arp AJ, Bergquist DC, Julian D. Rapid induction and disappearance of electron-dense organelles following sulfide exposure in the marine annelid Branchioasychis americana. Invertebrate Biology 2006; in press.

Julian D, Statile J, Roepke T, Arp AJ. Sodium nitroprusside potentiates H2S-induced contractions in body wall muscle from a marine worm. Biological Bulletin 2005; 209: 6-10.