Growth, metabolism, and chorioallantoic vascular density of developing snapping turtles (Chelydra serpentina): Influence of temperature

In developing vertebrates the effects of temperature on physiological rates are not necessarily predictable. Chelydra serpentina eggs were incubated at either 24° or 30°C on vermiculite with a water potential of approximately — 150 kPa. Measurements of oxygen consumption rate (V̇o2), yolk-free mass, and chorioallantoic membrane (CAM) vascular density index (VDI) were made. Measurements began when the CAM completely covered the inside of the shell and were continued until just before hatching. Eggs incubated at 24°C had a significantly longer incubation time than eggs incubated at 30°C (70 d vs. 51 d, respectively). Embryonic mass and V̇o2 of 24°C-incubated eggs increased and peaked later than in 30°C-incubated eggs. Temperature did not affectpeak egg V̇o2, embryonic mass, or CAM VDI. Graphical overlay and regression analysis of embryonic mass and V̇o2 data against time revealed the presence of similar patterns at both temperatures. These data indicate that 24°C-incubated eggs experienced a slowing of development at the beginning of incubation but that growth and V̇o2 following CAM development (late in incubation) wuere essentially the same as in eggs incubated at 30°C. These results indicate that temperature has its effects primarily during the early portion of development and that later acclimation mitigates temperature effects. It is suggested that investigators should not treat reptilian development as a single homogenous period, but rather as two separate periods.