Our research is currently directed at four areas related to the physiology of anoxia tolerance in painted turtles.

Neurophysiology of Anoxia Tolerance. The vertebrate brain is centrally important for an animal’s survival, serving as the integrating center for all physiological functions. The brain receives sensory information from all over the body, integrates that information, and then modifies organ system function or the animal’s behavior to insure its survival. Because of its high activity levels, the brain has a very high tissue-specific metabolic rate. And because oxygen is used by the mitochondria of cells to make energy, the brain of most animals quickly runs out of energy when oxygen is withheld, leading to tissue damage. This is why people who suffer strokes often have neurological impairment. Painted turtles, however, have evolved the natural ability to live without oxygen for many months while overwintering in ice-covered ponds in the most northern portions of their geographic range. Much of our current work aims to determine how the turtle brain continues to function without oxygen and avoid injury from anoxia. This includes studies of the cellular physiology of cultured turtle neurons, of special sensory function, including the visual and auditory systems, and the gene expression patterns that occur throughout the brain.

Molecular and Physiological Adaptations of the Painted Turtle Cardiovascular System. Like the nervous system, the cardiovascular system works very hard to insure an animal’s survival. It does this by continuously circulating blood throughout the body, even when there is no oxygen. The hearts of most animals are very sensitive to periods of oxygen deprivation, which is why so much damage can occur to a person’s heart either during a heart attack (myocardial ischemia) or cardiac arrest. Some of our ongoing work is directed at understanding the cardiovascular responses to anoxia. We currently use approaches at the tissue, cellular and molecular levels to identify mechanisms that are important for maintenance of cardiovascular function.

The Development of the Anoxia-tolerant Phenotype. Adult painted turtles are among the champions of anoxia tolerance, capable of surviving for more than 170 days of complete oxygen deprivation at 3oC. This ability allows them to overwinter in ice-covered lakes. However, painted turtles are not born with this ability. Instead, it develops as they age. Hatchling painted turtles, which overwinter underground in the nest cavities where they hatched, survive anoxia for about 40 days. One of our ongoing research projects is to understand how and when the anoxia-tolerant phenotype emerges, and which factors are responsible for constraining the ability in younger animals.

The Physicochemical Mechanisms Underlying the Use of Bone as a Buffer. It has been established that painted turtles utilize buffers within its shell and skeleton to buffer large metabolic acid loads produced during anoxia. We have learned that this process has little effect on the material properties of the shell until the limits of survival are reached. We have also shown that painted turtles have the highest weight percent carbonate of any vertebrate species known to science. The objective of some of our work is to understand the origins of the high carbonate contents of turtle bone and the cellular and acellular mechanisms that enable it to function as a buffer.