Comparative shell buffering properties correlate with anoxia tolerance in freshwater turtles
Donald C Jackson1, Sarah E Taylor, Vivian S Asare
1Department of Molecular Pharmacology, Physiology, and Biotechnology, Box G, Brown University, Providence, RI 02912, USA. donald_jackson@brown.edu
Summary
Freshwater turtles exhibit varying anoxia tolerance, with shell composition playing a role. More tolerant species, like painted turtles, have shells with higher buffering capacity to manage lactic acid during anoxia.
Area of Science:
- Zoology
- Comparative Physiology
- Biochemistry
Background:
- Freshwater turtles display remarkable anoxia (lack of oxygen) resistance, exceeding other vertebrates.
- Specific species, such as the painted turtle (Chrysemys picta), exhibit exceptionally long anoxic survival periods at low temperatures, a trait not fully understood.
Purpose of the Study:
- To investigate if differences in shell composition and buffering capacity explain the varying anoxia tolerance among five North American freshwater turtle species.
- To test the hypothesis that shell buffering is a key factor in long-term anoxic survival.
Main Methods:
- Compared shell composition of five freshwater turtle species, focusing on anoxia-tolerant (painted, snapping turtles) and less tolerant (musk, map, red-eared slider) species.
- Assessed total shell carbon dioxide concentration.
- Measured the volume of titrated acid needed to maintain pH 7.0 in shell powder, indicating buffer release.
- Determined lactate concentration in shell samples incubated in a standard lactate solution.
Main Results:
- Anoxia-tolerant species had higher total shell CO2 concentrations compared to less tolerant species.
- Shells from more tolerant species released more buffer (higher acid titration volume).
- Lactate concentrations in shell samples were higher for more anoxia-tolerant species.
Conclusions:
- Greater accessible CO2 concentrations (carbonate/bicarbonate) in the shells of tolerant species likely facilitate increased buffer release and lactic acid uptake during acidosis.
- Interspecific variations in shell composition and buffering capacity contribute to, but do not fully account for, the observed differences in anoxia tolerance among freshwater turtles.
