Responses to Hypoxia and Hyperoxia in Embryonic Tiger Keelbacks (<i>Rhabdophis tigrinus lateralis</i>; Colubridae)

Studies examining the oxygen dependency of embryonic survival, growth, and differentiation have been conducted for decades in a diverse array of animal taxa but including only one oviparous snake, the viperine water snake Natrix maura. Here, we describe a study incubating eggs of the tiger keelback Rhabdophis tigrinus lateralis (Colubridae) under four oxygen conditions, hypoxia (7% and 11% O₂), normoxia (21% O₂), and hyperoxia (31% O₂), for different lengths or at different stages of incubation. The length of hypoxic exposure is important in affecting embryonic development in R. t. lateralis, with prolonged hypoxic exposure retarding embryonic growth and differentiation, increasing embryonic mortality and deformity, reducing hatchling size and mass, and altering hatchling body shape relative to normoxic controls. Embryonic tiger keelbacks are most susceptible to hypoxia late in development, as revealed by the fact that a 5-day exposure of eggs to hypoxia of 7% O₂ reduced embryo mass and hatchling mass if it occurred at late stages of incubation. Hyperoxia of 31% O₂ did not enhance development of R. t. lateralis embryos, only affecting hatchling head width, which slightly differed between hyperoxic hatchlings and their normoxic siblings. This study demonstrates the importance of avoiding hypoxic exposure at late stages of embryonic development in snakes.