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RESEARCH physiology Motivation MotivationOrganisms in nature must respond to a wide array of environmental conditions in order to survive. Changes in temperature, salinity, light, and food supply--to name just a few--can cause changes in how a plant or animal feeds, reproduces, or can even cause its death. Physiological effects on the individual can potentially translate into changes in populations and entire communities. We are investigating how marine organisms cope at a molecular, cellular, and whole-organism level to environmental stress. Information about how organisms respond physiologically to their environment will help us understand how organisms may respond to environmental change, including global climatic change. Research Questions
ApproachPISCO scientists are using three main approaches to answer these questions. RNA:DNA measurements Heat shock proteins Carbon:Nitrogen Research Findings
RNA:DNA ratiosPISCO Research Fellow Elizabeth Dahlhoff has led our efforts to uncover the first evidence of a functional relationship between a physiological index of organismal condition and large-scale oceanographic patterns. Monthly samples of mussels taken in 1999 and 2000 from Oregon through southern California show that RNA:DNA ratios vary strikingly, both between the major oceanographic regions (north of Cape Blanco, Cape Blanco to Point Conception, and south of Point Conception), and within regions. Variation in RNA:DNA ratios is closely related to mussel growth, which depends on the concentration of food (phytoplankton and detritus) in the waters of the inner shelf. Some evidence suggests that south of Point Conception, mussel growth may also depend on water temperature. These findings indicated that RNA:DNA ratios can be a powerful tool to measure the recent nutritional state in marine organisms. To further hone this tool, we initiated laboratory experiments to isolate the effects of food on RNA:DNA ratios, while controlling other factors such as temperature. Another advance in the use of the RNA:DNA index involves the development of microplate technology, which dramatically improves the efficiency of processing samples. Microplate technology gives ecologists the flexibility to collect and analyze many more samples, which improves our understanding of fine-scale spatial and temporal variation in growth potential.
Heat shock protein (Hsp) responsesScientists expect thermal stress to increase in marine communities as the Earth warms. The synthesis and activities of heat-shock proteins that respond to heat stress may represent a significant energy cost to an organism, directing energy away from growth and towards repair. PISCO scientists are leading the way in studying the response of ecologically important species such as mussels, whelks, limpets, grazing snails and sea stars to thermal stress, at local to geographical scales. Building on earlier studies at OSU, former Postdoctoral Researcher Patricia Halpin, Research Fellow Gretchen Hofmann and others have demonstrated that both mussel and limpet heat shock protein (Hsp 70) levels increase with height on the shore, but that responses differ between sites. While we continue to explore variation in heat shock response to stressful conditions in space and time, results thus far indicate that this response will be a valuable tool in understanding and predicting how marine communities will respond to global warming. Measuring stress using gene chipsPISCO has pioneered the use of a DNA microarray ("gene chip") to evaluate the effects of short-term changes in the environment on diverse physiological systems. Our work is the first exploitation of DNA microarray technology for the study of environmental physiology in an estuarine fish, the longjaw mudsucker (Gillichthys mirabilis). Dramatic changes in gene expression occurred in response to environmental change. Notably, stress led to reductions in expression of genes associated with protein synthesis and cell growth. The promise of this technique for evaluating the influences of environmental stresses, such as ambient oxygen availability and salinity encourages our continuing work using DNA microarrays with "non-model" species, those for which genomic information does not yet exist. By Patricia Halpin, Former Postdoctoral Researcher, and Renee Davis-Born, and Lydia Bergen, Policy Coordinators |
When organisms become hot or otherwise stressed, the proteins in their cells become damaged. Damaged proteins cause harm by sticking to healthy proteins and interfering with their function. Heat shock proteins (HSPs) are a form of "chaperone" protein that binds to damaged proteins and prevents them from improper interactions with other proteins. By measuring the amount of HSP within the cells of organisms, investigators hope to reveal patterns of how much environmental stress organisms experience and how they are using cellular mechanisms to cope with stress. Many questions remain about how production of HSPs varies between individuals, local conditions, and sites. For example, do mussels in the high intertidal express more heat shock protein than those in the low? Can we use HSPs to characterize how stressful a site is in comparison to other sites? How much does the amount of heat shock protein change from one individual to another? Currently, we are conducting a study at two sites in Oregon--Boiler Bay and Strawberry Hill--Oregon on California mussels (Mytilus californianus) to help answer these questions. 
Plants require many nutrients to grow, reproduce, and survive. Often the growth of plants is limited by the amount of certain nutrients such as nitrogen and phosphorous. Past research indicates that intertidal seaweeds can be nutrient limited. Scientists can examine the nutrient status of seaweeds and other plants by quantifying the amount of nitrogen (N) stored within their tissues. Nitrogen is commonly measured in comparison to the amount of carbon (C) in the tissues and expressed as a ratio, C:N. We are using the measurement of C:N to examine how the feather boa kelp (Egregia menziesii) responds to changes in oceanographic conditions along the Oregon and California coastlines. This study will give us information on how ocean conditions affect primary productivity on rocky shores. 
In a specific application of this approach, Postdoctoral Research Lars Tomanek and other PISCO scientists compared snails of the genus Tegula and found that subtidal species are incapable of synthesizing proteins at the highest temperatures encountered by intertidal congeners. Thus, differences in the thermal tolerance of protein synthesis may restrict the vertical distributions of subtidal species. Moreover, unlike their intertidal relatives, subtidal species of Tegula exposed to a thermal stress typical of the mid-intertidal zone are incapable of completing the heat-shock response during the subsequent high tide period, to ready them for the next period of heat stress during low tide. Although intertidal species are more capable than subtidal species of coping with heat stress-as indexed by their higher lethal temperatures and abilities to mount a heat-shock response rapidly-these species face higher energy costs from heat stress due to the need to devote energy to repair and replacement of heat-damaged proteins. These heightened costs of living in the intertidal zone may be important in restricting the upper vertical limits of intertidal species. Reduced times for feeding (shorter periods of immersion) and higher costs for protein synthesis could limit the vertical range of intertidal organisms. On-going field studies of growth rates and heat-shock protein synthesis may provide additional insights into this important issue.