Critical Windows of Cardiovascular Susceptibility to Developmental Hypoxia in Common Snapping Turtle (Chelydra serpentina) Embryos.

Environmental conditions fluctuate dramatically in some reptilian nests. However, critical windows of environmental sensitivity for cardiovascular development have not been identified. Continuous developmental hypoxia has been shown to alter cardiovascular form and function in embryonic snapping turtles (Chelydra serpentina), and we used this species to identify critical periods during which hypoxia modifies the cardiovascular phenotype. We hypothesized that incubation in 10% O2 during specific developmental periods would have differential effects on the cardiovascular system versus overall somatic growth. Two critical windows were identified with 10% O2 from 50% to 70% of incubation, resulting in relative heart enlargement, either via preservation of or preferential growth of this tissue, while exposure to 10% O2 from 20% to 70% of incubation resulted in a reduction in arterial pressure. The deleterious or advantageous aspects of these embryonic phenotypes in posthatching snapping turtles have yet to be explored. However, identification of these critical windows has provided insight into how the developmental environment alters the phenotype of reptiles and will also be pivotal in understanding its impact on the fitness of egg-laying reptiles.