Changes in gonadal and adrenal steroid levels in the leatherback sea turtle (Dermochelys coriacea) during the nesting cycle

The reproductive endocrinology of nesting leatherback turtles (Dermochelys coriacea) was studied during the 1996-1997 and 1997-1998 nesting seasons at Los Baulas National Park, Playa Grande, Costa Pica. Blood samples were col lected from nesting females throughout the season. Females were observed to nest up to 10 times during the nesting season. Plasma steroids were measur ed by radioimmunoassay and total plasma calcium was measured by flame atomi c absorption spectrophotometry. Plasma testosterone and plasma estradiol le vels declined throughout the nesting cycle of the female. Testosterone decl ined from a mean of 10.18 +/- 0.77 ng/ml at the beginning of the nesting cy cle to 1.73 +/- 0.34 ng/ml at the end of the nesting cycle. Estradiol decli ned in a similar manner, ranging from a mean of 190.95 +/- 16.80 pg/ml at t he beginning of the nesting cycle to 76.52 +/- 12.66 pg/ml at the end of th e nesting cycle. Plasma progesterone and total calcium levels were relative ly constant throughout the nesting cycle. Lack of fluctuation of total calc ium levels, ranging from a mean high of 97.46 +/- 11.37 mug/ml to a mean lo w of 64.85 +/- 11.20 mug/ml, further suggests that vitellogenesis is comple te prior to the arrival of the female at the nesting beach. Clutch size (bo th yolked and yolkless eggs) did not vary over the course of the nesting cy cle. (C) 2001 Academic Press.