Adult male loggerhead sea turtles, Caretta caretta, exhibited a "prenuptial" spermatogenic
cycle that was coincident with increased concentrations of serum testosterone (T).
Serum T was high during the months when migration and mating have been recorded for
males. In contrast to females, males appear to be annual breeders. Nine reproductively
active female C. caretta (as verified through laparoscopy) were tagged with sonic
transmitters and were repeatedly bled prior to migration. Four months prior to the
nesting season, the ovaries of reproductively active females had hundreds of vitellogenic
follicles of approximately 1.5 cm in diameter (i.e., half the size of ovulatory follicles).
Approximately 4-6 weeks prior to migration from feeding grounds to mating and nesting
areas, serum estradiol-17 beta (E2) concentrations increased significantly and remained
high for approximately 4 weeks, suggesting a period of increased vitellogenesis. During
a 1- to 2-week period prior to migration, serum E2 decreased significantly, while
serum T concentrations increased (at least) until the time of migration. Serum T,
E2, and progesterone (PRO) were elevated during nesting if a turtle was going to nest
again during that nesting season. During the last nesting of a season, turtles had
low serum concentrations of T, E2, and Pro. The prenuptial pattern of gonadal recrudescence
and gonadal steroid production in both male and female C. caretta contrasts with those
of many temperate freshwater turtles, and this type of reproductive pattern may have
been facilitated by adaptation to a tropical marine environment.