Effects of temperature and water on critical oxygen tension of turtle embryos

The influences of temperature and water on the ability of turtle embryos to tolerate hypoxia were investigated by measuring critical oxygen tension, P_c, at different levels of temperature (22, 27, and 32°C) and hydric conditions (3 and 13% gravimetric water content). Eggs were half‐buried in sand with 3 or 13% gravimetric water content and incubated at a constant 30°C. Using a closed metabolic chamber, oxygen consumption, \documentclass{article}\pagestyle{empty}$ \mathop {\rm V}\limits^{\rm .} $ , was measured at decreasing oxygen tensions. Embryonic \documentclass{article}\pagestyle{empty}$ \mathop {\rm V}\limits^{\rm .} $ varied as a function of incubation day and temperature, whereas the P_c differed among temperatures but not among incubation days. At a given incubation day, the P_c increased in direct proportion to temperature. Eggs incubated in sand with 13% gravimetric water content achieved greater mass at days 30 and 39 than did those in sand with 3% gravimetric water content. However, \documentclass{article}\pagestyle{empty}$ \mathop {\rm V}\limits^{\rm .} $ , P_c, and masses of yolk‐free hatchlings were similar in the two hydric conditions, indicating that hypoxic tolerance of turtle eggs is not curtailed by excessive water absorption. The similarity in P_c is likely attributable to the small \documentclass{article}\pagestyle{empty}$ \mathop {\rm V}\limits^{\rm .} $ /surface area ratio of turtle eggs. Within the range of parameters studied, temperature, but not water, can modify the P_c of turtle embryos.