Bone as a buffer: Consequences for vertebrate design and anaerobic physiological performance

Abstract

Conventional wisdom usually states that mineralized tissues are primarily used by vertebrates as sites for respiratory and locomotory muscle attachment or for physical protection from predators. Often ignored is the role these tissues play in maintaining ionic and acid‐base homeostasis and how this might have shaped vertebrate evolution. We have argued that this latter function may have been important in shaping vertebrate design in early tetrapods, particularly the maintenance of dermal armor in early tetrapods, and is still important for anaerobic physiological performance in many extant vertebrates, especially in reptiles and amphibians. We use physiological, biomechanical, and mineralogical approaches to understand how vertebrate bone, especially that of turtles, interacts with and is affected by extreme deviations in acid‐base homeostasis. Our work, and that of others, has shown that the mineral composition of turtle bone can predict tolerance to extreme acidosis, and that the most derived of these vertebrates, the anoxia‐tolerant painted turtle, is able to utilize calcium and magnesium carbonates within its bone to prevent lethal decreases in body fluid pH in the face of a 180 mM lactic acid load, with minimal effect on whole‐bone material properties.Support or Funding InformationThis work is funded by a CAREER Award from the National Science Foundation.