HEART-RATE DURING DEVELOPMENT IN THE TURTLE EMBRYO - EFFECT OF TEMPERATURE

Growth and development can occur over a wide range of physical conditi ons in reptiles. Cardiovascular function must be critical to this abil ity. However, information on cardiovascular function in developing rep tiles is lacking. Previous work indicated that in reptiles the effects of temperature on growth and metabolism are largely restricted to ear ly development. This study examined whether the previously observed ef fects of temperature and different perinatal patterns of metabolism ob served in amniotic vertebrates are correlated with cardiovascular func tion. Embryonic and hatchling carcass mass, heart mass and heart rate (HR) were compared for snapping turtle eggs (Chelydra serpentina) incu bated at 24 degrees and 29 degrees C. Incubation time was shorter at 2 9 degrees C (56.2 days) than at 24 degrees C (71.1 days). Carcass and heart growth showed a sigmoidal pattern at both temperatures. However, cardiac growth showed a relative decrease as incubation proceeded. In cubation temperature significantly affected the HR pattern during deve lopment. The HR of embryos incubated at 24 degrees C was constant for most of incubation (51.8 +/- 4.8 min(-1)). A small decrease was observ ed just prior to and a large decrease immediately following hatching ( posthatch, 22.3 +/- 4.1 min(-1)). At 29 degrees C embryonic HR was gre ater than at 24 degrees C early in development (72.3 +/- 3 min(-1)). T he HR steadily decreased to values equivalent to those at 24 degrees C . The HRs of 24 degrees C and 29 degrees C hatchlings were not differe nt. Cardiac output (estimated as the product of heart mass and HR) inc reased rapidly during early development and then slowed dramatically a t both temperatures. These data are consistent with the suggestion tha t temperature exerts its effects primarily early in development. Furth ermore, the changes in cardiovascular function are correlated with met abolic changes in hatching vertebrates.