Synchronised nesting aggregations are associated with enhanced capacity for extended embryonic arrest in olive ridley sea turtles

Sea turtle species in the genus Lepidochelys exhibit an unusual behavioural polymorphism, nesting in both aggregations and solitarily. Aggregated nesting events, termed ‘arribadas’, involve hundreds of thousands of females congregating at a single nesting beach over a few days to oviposit their eggs. Aggregate and solitary nesting behaviours are associated with distinct inter-nesting intervals, three and four weeks for non-arribada and arribada nesters respectively. Consequently, embryos are maintained in pre-ovipositional embryonic arrest in the hypoxic oviduct for different lengths of time depending on the mother’s reproductive behaviour. However, sea turtle embryos are limited in their capacity to remain in arrest and will subsequently die if held in hypoxia too long. Here, we tested whether embryos oviposited during arribada or non-arribada nesting differ in their capacity to be maintained in pre-ovipositional arrest. Olive ridley turtle (Lepidochelys olivacea) eggs from eight clutches (four from each nesting tactic) were divided among seven treatments after oviposition; normoxia (control; 21% O(2)), or hypoxia (1% O(2)) for 3, 3.5, 4, 8, 15 or 30 days, before being returned to normoxia. Arribada eggs were capable of extending pre-ovipositional arrest for longer, with some eggs from the 8- and 15-day hypoxia treatment still hatching while no non-arribada eggs hatched after more than four days in hypoxia. This difference in embryonic capacity to survive extended periods of arrest may be an important mechanism facilitating arribada behaviour by allowing longer inter-nesting intervals. Our finding provides an intriguing insight into the physiological mechanisms that are integral to this unique mass-nesting behaviour.