麻豆传媒

Work in my research laboratory focuses on examining physiological, biochemical and molecular mechanisms by which animals respond to environmental change. The fundamental questions we ask are: Why do organisms live where they live, and how do they do so? What causes populations to remain stable, grow, fluctuate in size, or go extinct? How does the physical environment, the presence predators, the genetic properties of a population and the abilities of individuals to adapt to the environment all influence their distribution and abundance? As ecosystems experience rapid climate change, it is imperative to understand and address these questions in vulnerable natural populations.

The primary study system in which we explore these questions are populations of the native willow beetle Chrysomela aeneicollis, which experiences extreme climatic conditions in the Sierra Nevada Mountains of California. We are characterizing Sierra beetle populations using molecular markers of genetic variation and environmental adaptation. We are also assessing changes in population size and distribution using these genetic markers, and linking changes to local topography and to climate, which we assess using locally deployed loggers and weather stations. Because we have been studying these populations for over 20 years, we are able to include historical samples from populations that are now extinct in our analysis, which offers us the rare opportunity to analyze changes in populations for which the past environment is characterized. We are also conducting experiments to quantify fecundity, larval survival, and adult over-wintering survival to assess potential mechanisms contributing to population persistence for beetles of differing genetic and environmental backgrounds. 

We also study the adaptive significance of color polymorphisms in coastal populations of leaf beetles. In California, temperatures in the coastal region vary greatly over relatively short spatial scales, with cool, moderate conditions prevailing along the coast and inland valleys, and warm conditions with greatly fluctuating temperatures prevailing inland and along the tops of ridges in coastal mountain ranges. California populations of the leaf beetle Chrysomela schaefferi occurs along the California coast and in the coastal mountains. Melanic (darkly-pigmented) and light-colored forms are found in this beetle species. Melanic individuals are deep brown, non-melanics copper colored. Melanics are found in higher frequency in cooler habitats than further inland, where maximum temperatures are much greater. Some authors propose that melanism represents an adaptation to temperature in other insect systems, but few have investigated physiological mechanisms supporting the thermal melanism hypothesis. We are studying temperature adaptation in this beetle, focusing on how changes in temperature interact with color pattern and genetic variation to affect factors altering performance and reproductive success: heat shock protein expression, running speed, fecundity and mating frequency. 

The heart of this research program are the efforts of undergraduates, who work intensively in the laboratory and field as a collaborative, interdisciplinary team. Team Beetle. This research is currently funded by the National Science Foundation, a Clare Booth Luce Fellowship, an SCU undergraduate research grant, and a Fulbright Scholarship.

Education

B. A. Chemistry and Biology, University of California Santa Cruz

Ph. D. Marine Biology, Scripps Institution of Oceanography, UC San Diego


Andrew Mellon Postdoctoral Fellow, Marine Ecology, Oregon State University

Degree: Ph.D., Colorado State University, 1989

My research interests are in the area of animal physiological ecology and evolutionary physiology.  More specifically, I am interested in how anatomical and physiological capacities meet environmental demands.  For instance: when an animal is confronted by a greater energetic or physiological demand (cold temperatures, hypoxic conditions) can it compensate for that demand by increasing (or decreasing) physiological processing capacity?

Animals often meet changes in demand with changes in the size of organs and organ capacity.   I am most interested in learning how these load/capacity relationships are reflected in an animal's life history.  This approach demands an appreciation of both mechanistic physiology and ecology, and requires both field and laboratory research.  In addition, I study animals at all stages of development, concentrating on the effects of environmental demands in utero and during adulthood.  At present I work primarily in desert and montane systems, using rodents as study species.

Recent and current projects of my students, my colleagues, and myself:

The interplay between physiological acclimation and genetic adaptation to hypoxia in deer mice. 
Limits to metabolic energy output elicited by lactation, cold exposure, and exercise in laboratory mice, house mice and deer mice. 
Effects of sub-lethal parasites on host physiology during lactation, cold exposure and food restriction in mice. 
The correlation between organ size and aerobic performance in junglefowl
Changes in organ size and function in deer mice (Peromyscus maniculatus) along an altitudinal gradient. 

Department of Cell & Developmental Biology

Research Interests:
Define the Molecular Mechanisms Responsible for Tissue Protection and Reversible Metabolic Depression in Hibernation by using High-Throughput-omics Analyses

What we do: We answer both applied and basic questions about how the nervous system helps animals survive in their environments. On the applied side, we study animals that evolved ways to avoid damage to the nervous system. We focus most of our efforts on challenges to the nervous system that tend to be big problems in many human diseases. These include inactivity of neuromuscular systems (think, 鈥渋f you don鈥檛 use it you lose it鈥�) and impaired oxygen transport (think, brain damage in stroke and cardiac arrest). By learning from animals that already 鈥渒now鈥� how to get around these problems, we up our chances of finding new solutions. On the basic side, we use this approach to make new discoveries about how nervous systems use plasticity to help animals adapt to their environments. To do this, we take fundamental concepts about plasticity that were developed outside of real-life contexts (e.g., cell culture, lab settings, modeling, etc.) and test how they work in situations where animals may need them to survive. This allows us to put together new ideas about how these processes are important for behavior and why they may have evolved.

How we do it: We tend to ask questions using the neural system that regulates breathing in amphibians for two reasons. First, breathing is a tractable, rhythmic behavior that is easily studied across scales of organization (genes to proteins to cells to networks to behavior) compared to other behaviors like learning and memory. Second, amphibians have interesting life history traits that allow us to ask questions about how different forms of plasticity have adaptive importance in nature. On the technical side, we use an integrative approach that spans whole animal behavior down to the molecular biology of single neurons. We use a range of tools that include patch-clamp electrophysiology to study electrical properties of neurons, single-cell quantitative PCR and RNA sequencing to assess gene expression in individual neurons, in vivo measurements of behavior (measurements of breathing and EMG to record muscle activity), extracellular recording to measure circuit activity, and fluorescence imaging microscopy.

Interests
Cellular neuroscience, comparative neurobiology, electrophysiology

Education
Ph.D., Wright State University


Research:
What we do: We answer both applied and basic questions about how the nervous system helps animals survive in their environments. On the applied side, we study animals that evolved ways to avoid damage to the nervous system. We focus most of our efforts on challenges to the nervous system that tend to be big problems in many human diseases. These include inactivity of neuromuscular systems (think, 鈥渋f you don鈥檛 use it you lose it鈥�) and impaired oxygen transport (think, brain damage in stroke and cardiac arrest). By learning from animals that already 鈥渒now鈥� how to get around these problems, we up our chances of finding new solutions. On the basic side, we use this approach to make new discoveries about how nervous systems use plasticity to help animals adapt to their environments. To do this, we take fundamental concepts about plasticity that were developed outside of real-life contexts (e.g., cell culture, lab settings, modeling, etc.) and test how they work in situations where animals may need them to survive. This allows us to put together new ideas about how these processes are important for behavior and why they may have evolved.

Recent Publications:
Adams, S., Zubov, T., Bueschke, N., & Santin, J. M. Neuromodulation or energy failure? Metabolic limitations silence network output in the hypoxic amphibian brainstem. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. 2020. In press. doi.org/10.1152/ajpregu.00209.2020

Burton, M. T., & Santin, J.M. A direct excitatory action of lactate ions in the central respiratory network. 2020. Journal of Experimental Biology. In press. doi: 10.1242/jeb.235705
Northcutt, N.J., Kick, D.R., Otopalik, A.G., Goetz, B.M., Harris, R.M., Santin, J.M., Hoffman, H.A., Marder, E., Schulz, D.J. Molecular profiling of single neurons of known identity in two ganglia from the crab Cancer borealis. Proceedings of the National Academy of Sciences. 2019. doi: https://doi.org/10.1073/pnas.1911413116

Santin, J.M. Motor inactivity in hibernating frogs: Linking plasticity that stabilizes neuronal function to behavior in the natural environment. Developmental Neurobiology. 2019, in press doi: https://doi.org/10.1002/dneu.22721

Cassondra鈥檚 work focuses on understanding baseline physiology in diving animals and how physiological responses are altered from natural or anthropogenic disturbances. Her past work includes investigating cardiovascular responses to routine and anthropogenic disturbances in loggerhead marine turtles and freshwater turtles. Her current research with northern elephant seals investigates muscle and cardiovascular physiology during routine diving and in response to natural disturbances.

Cassondra Williams received her PhD from Scripps Institution of Oceanography for research on the diving physiology of emperor penguins in Antarctica. 

The Williams lab studies the evolution of metabolic physiology in ectotherms, using insects as models. We are interested in the mechanisms and consequences of metabolic responses to emerging winter environments. This is important because winter climate change is altering energy balance, phenology, and cold stress in overwintering organisms leading to cascading biological impacts that carry over into the growing season and affect survival and fitness. The ability to adapt or acclimate metabolic systems to compensate for changing winter conditions will strongly determine organismal responses to winter climate change. However, we know little about the mechanisms underlying metabolic plasticity in ectotherms, nor the evolutionary potential of metabolic systems on macro or micro scales. As climate change leads to the emergence of novel climates, we can no longer rely on bioclimatic envelope models to predict organismal responses to climate change; we need a mechanistic and predictive understanding that explicitly includes winter processes. 

We use an integrative 鈥済enes to fitness鈥� approach through the lens of intermediary metabolism and metabolic physiology to find the genes that influence overwintering energetics, from the level of naturally segregating variation within populations, through inter-population local adaptation, to interspecific divergence. This provides a novel framework for predicting ecological and evolutionary responses to winter climate change based on a mechanistic understanding of metabolic physiology. Addressing genotype 鈥� phenotype interactions through the lens of intermediary metabolism is advancing our understanding of the genetic control of complex, fitness-relevant traits.