Effects of postovipositional hypoxia and hyperoxia on leatherback turtle reproductive success and hatchling...

Leatherback egg clutches typically experience lower hatching success (~50%) than those of other sea turtle species (>70%). The majority of embryonic death (>50%) occurs at early stages of development, possibly because embryos fail to break preovipositional embryonic arrest after oviposition. The embryonic arrest is maintained by hypoxia in the oviduct and following oviposition increased availability of oxygen is the trigger that breaks arrest in all turtle species studied to date. We conducted an ex situ incubator experiment and an in situ hatchery experiment to examine the influence of oxygen availability on hatching success and hatchling traits in leatherbacks. After oviposition, eggs (n = 1005) were incubated in either normoxia (21% O₂ ), hyperoxia (32%-42% O₂ ) for 5 days, or hypoxia (1% O₂ ) for 3 or 5 days. As with other turtles, hypoxic incubation maintained embryos in arrest, equivalent to the time spent in hypoxia. However, extending arrest for 5 days resulted in greater early-stage death and a significant decrease in hatching success (4% 5-day hypoxia vs. 72% normoxia). Eggs placed in incubators had greater hatching success than those placed into hatchery nests (67% vs. 47%, respectively). We found no impact of hyperoxia on the stage of embryonic death, hatching success, hatchling phenotype, exercise performance, or early dispersal. Our findings indicate that delayed nesting and the subsequent extension of embryonic arrest may negatively impact embryonic development and therefore the reproductive success of leatherbacks. They also indicate that incubation under hyperoxic conditions is unlikely to be a useful method to improve hatching success in this species.