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Sex steroid concentration in immature hawksbill turtles in the Chagos Archipelago

Dr Jeanne A. Mortimer
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Blood samples from immature foraging hawksbills were collected for radioimmunoassay by the senior author (JAM) during a six week period, between early February and mid-March 1996, as part of the ‘Friends of Chagos’ International Scientific Expedition which visited all of the atolls of the Chagos Archipelago. In the outer islands (at Salomon atoll, Peros Banhos atoll, and Great Chagos Bank) the turtles were captured opportunistically by various members of the expedition while SCUBA diving. On Diego Garcia, we captured turtles while walking at low tide at the south end of the atoll in a shallow tidal creek called “Turtle Cove” (Mortimer & Day, this volume).Total straight-line carapace lengths were measured with calipers from the anterior most margin of the carapace to the posterior most margin of the longest postcentral scute. Blood samples were obtained from the cervical sinuses of the turtles by the method described by Owens and Ruiz (1980). All turtles were sampled within 8 hours of capture. Blood samples were collected in sterile vacuum tubes and placed on ice (for up to 8 hours) until they were centrifuged with a desktop clinical centrifuge. The serum was pipetted off and frozen.Radioimmunoassay procedures for the measurement of testosterone and estradiol-17b were conducted as previously described (Crain et al., 1997; Guillette et al., 1997). The testosterone antibody used has 100% cross-reactivity with testosterone, 44% with dihydrotestosterone, 41% with d-1-testosterone, and 18% with d-1-dihydrotestosterone. Thus, the testosterone radioimmunoassay is more appropriately called an androgen radioimmunoassay, as many androgens are measured in this assay. After radioimmunoassay, concentrations were determined by use of commercially available software (EIA/RIA Immunofit; Beckman Instruments). Linear regression analysis was conducted using Excel to analyze the relationship between hormone concentration and body length.
turtles sex_steroid hawksbill Eretmochelys_imbricata
Crain D , Mortimer Jeanne .