Background

I am a research scientist with the USDA National Wildlife Research Center (NWRC). My appointment at Monell is a result of the commitment shared by NWRC and Monell for conducting quality research to enhance our understanding of chemically-mediated animal behaviors. My lab participates in this objective by conducting research at the interface of ecology and chemistry. Our research focuses on animal behavior and the chemical signals that identify friend, foe, and food. We aim to fulfill the mission of NWRC; which is the development of effective tools for resolving problems caused by the interaction of wild animals and society while maintaining the quality of shared environments.

Our research employs both animal subjects and chemical instrumentation. Animal studies are conducted in the laboratory with model species, in pens with captive subjects, and/or with free-ranging wildlife in natural settings. We also rely on chromatographic techniques, mass spectrometry, and ultra-violet and near infrared spectroscopy to characterize the chemicals that influence the behaviors we study.

Current research topics include:

Alteration of the Volatile Metabolome by Disease or Injury. It has long been speculated that certain diseases might be diagnosed using odor changes. Indeed, there is literature on this topic in human medicine and credible reports of dogs detecting human malignancies. Because chemosensory systems of mammals are exquisitely sensitive, it remains likely that mammalian biosensors may be employed for detection of disease in infected animals or in the environment. My research in this unique field demonstrates the powerful link between mammalian physiological systems and the promise for exploiting these effects for disease detection and surveillance.

In the first study, alteration of fecal odors in animals infected with avian influenza viruses (AIV) was demonstrated in mallard ducks (Anas platyrhynchos). Chemical analyses indicated that AIV infection was associated with a marked increase of acetoin (3-hydroxy-2-butanone) in feces. Another study demonstrated that immunization also elicited alteration of volatile metabolites. Biosensor mice were trained to distinguish between urine odors from rabies-vaccinated (RV) and unvaccinated control mice as well as donor mice treated with West Nile Virus vaccine (WNV) or lipopolysaccharide (LPS). Taken together, these experiments demonstrated that: (1) immunization alters urine odor in similar ways for RV and WNV immunizations; and (2) immune activation with LPS also alters urine odor but in ways different from that of RV and WNV.

Based on findings that both immunization and inflammation alter the volatile metabolome, we hypothesized that other assaults accompanied by inflammation might correspondingly modify urinary volatiles. In particular, separate collaborations were initiated to study traumatic brain injury and Alzheimer’s disease (AD). Behavioral assays with trained biosensors and chemical analyses of the urine samples similarly demonstrated that brain injury altered urine volatile profiles. Behavioral and chemical analyses further indicated that alteration of the volatile metabolome induced by brain injury and alteration resulting from lipopolysaccharide-associated inflammation were not synonymous. Similarly, experiments with animal models demonstrated that mutant amyloid precursor protein gene expression entails a uniquely identifiable urinary odor, which if uncovered in clinical AD populations, may serve as an additional biomarker for the disease.

Development of Novel Techniques for Chemical Analyses. I developed a technique that concentrates analytes on a liquid chromatographic guard column and elutes them as a discreet band into the mass spectrometer for tandem mass spectrometric detection. Selectivity and sensitivity are excellent, allowing for low parts-per-trillion detection. This technique also allows for the injection of large sample volumes (limited only by the volume of the injection loop of the instrument). This methodology constitutes a significant improvement over previous techniques that employed solvent extraction of the water samples.

I also developed a novel mathematical transformation of detector response data to allow for precise and accurate determinations of fructose, glucose, and sucrose in plant tissues. Although evaporative light-scattering detection (ELSD) had been previously employed for carbohydrate analyses, its use as a quantitative tool was hindered by its non-linear detector response. The routine solution for this analytical problem is to perform a logarithmic transformation of the responses and concentrations of the calibration curve. However, this practice suffers from severe limitations in quantitation due to the highly significant y-intercept of the calibration function generated from the transformation. The simple exponential transformation that I developed not only produces a calibration function with a y-intercept not different from zero, but also generates quantitative results from a single-point calibration.

Understanding Chemically-Mediated Foraging Behavior in Mammalian Herbivores. Diet selection is a consolidated process inherently similar among herbivorous species. Chemicals present in the diet are the driving forces, while the engine on which they operate is the gastrointestinal tract. Postingestive feedbacks are integrated with associated flavors to form preferences or aversions. This model of diet selection has tremendous predictive power and represents our current understanding of the natural world. Plants have evolved defensive systems that protect them against herbivory, while herbivores employ behavioral and physiological processes to obviate intoxication when sampling unfamiliar forage. These processes represent an evolutionary dynamic that has proven the test of time. Increasing our understanding of these processes is necessary to developing new management tools.

Using model mammalian herbivores (lambs and goats), I designed and conducted experiments to better understand what (and how) herbivores are learning when they consume plants that are chemically defended. The model subjects were shown to be excellent behavioral models for wild ungulates. These experiments demonstrated that any effort to protect a resource may require multiple, or constant, exposure to the aversive agent to produce a persistent avoidance (much as is observed in nature). Limited exposure may not only fail to condition an aversion to the intended target, but could also lead to avoidance of an unintended forage item. Furthermore, the mere presence of alternative forage is central to persistent avoidance as is the nutritive value of the alternative food source.

Elucidating Mechanisms of Herbivore Repellency. I have proposed that, from the herbivore’s point-of-view, repellents are a source of chemical signals which are processed similar to all the chemicals they encounter while foraging. Taste, olfaction, vision, and touch permit herbivores to detect the chemosensory attributes of repellents. Inputs from evolution, mother, conspecifics, and individual experience dictate whether or not these cues are meaningful in the context of foraging. Using this theoretical framework, I conducted a series of experiments to elucidate the mechanisms responsible for reducing intake by foraging herbivores.

My findings demonstrate that persistent aversions to specific foods will result only when the toxin is inexorably paired with the flavor of the food or repellent formulation. These experiments also provided supporting evidence for my theory that responses to certain repellent materials can be predicted by dietary niche. Protein hydrolysates effectively reduced intake in a variety of herbivores, whereas omnivores were indifferent to hydrolysate treatments. Differences among niche-related taxonomic responses to hydrolysates imply that they provide conflicting chemosensory information to herbivores versus omnivores. Taken together, my research has identified two imperative qualities of effective herbivore repellent formulations: 1) persistence of residues applied directly to the plant; and 2) physiological or evolutionary consequences for the herbivore.