Plasma steroid interactions during high-density green turtle nesting and associated disturbance

Area of Science:

• Marine Biology
• Reproductive Endocrinology
• Conservation Science

Background:

• Raine Island hosts a high-density green turtle (Chelonia mydas) rookery, leading to intense competition for nesting space and frequent disturbances.
• High-density nesting can delay oviposition, but little is known about how female reptile hormones respond to such competitive reproductive events.

Purpose of the Study:

• To investigate the relationship between nesting density, nesting success, and plasma steroid profiles in green turtles.
• To examine how delays in oviposition due to disturbance affect hormone levels.
• To compare steroid hormone levels between high-density and low-density nesting sites.

Main Methods:

• Compared plasma corticosterone (B) and testosterone + 5alpha-dihydrotestosterone (T + DHT) levels across five oviposition stages in high-density (1 turtle/m2) and low-density (0.1 turtle/m2) sectors.
• Assessed the relationship between oviposition delays (0-6 days) and plasma B and T + DHT levels.
• Compared steroid hormone levels in females from high-density (Raine Island) and low-density (Number Seven Sandbank) rookeries.

Main Results:

• Plasma corticosterone (B) showed a small, albeit significant, increase in high-density nesting turtles, potentially due to increased metabolic demand.
• Plasma testosterone + 5alpha-dihydrotestosterone (T + DHT) levels remained stable irrespective of nesting density.
• Prolonged oviposition delays due to disturbance did not alter plasma B or T + DHT levels.

Conclusions:

• Green turtles may exhibit adrenal desensitization, down-regulating the acute adrenocortical response to prevent disturbances from interfering with reproduction.
• This adaptive trade-off may optimize current reproductive success at a potential cost to long-term survivorship.