CORRELATION AMONG THERMOSENSITIVE PERIOD, ESTRADIOL RESPONSE, AND GONAD DIFFERENTIATION IN THE SEA-TURTLE LEPIDOCHELYS OLIVACEA

Reptile embryos with temperature sex determination have a thermosensit ive period (TSP). The finding that exogenous estradiol (E2) overcomes the effect of male-promoting temperature led to the idea that temperat ure may regulate estrogen concentration in the gonad during TSP. Since interspecific variations in TSP and in the effect of exogenous E2 exi st, we undertook a study in the olive ridley Lepidochelys olivacea. Fo ur parameters were correlated: the TSP (time dimension), the thermosen sitive stages (rate of development), gonad development (histological a spect), and the estradiol response. Two kinds of experiments were perf ormed: (1) Eggs were shifted once, at different stages of development, from a male-promoting temperature to a female-temperature (or vice ve rsa) for the remainder of development. (2) Eggs at male-promoting temp erature were treated once with 6 or 12 mu g of estradiol (E2) at vario us times of incubation. Sex ratio was established around hatching in e ach experimental series. We found that the temporal dimension of the T SP was around 7 days (Days 20-27 of incubation) at a male-promoting or a female-promoting temperature. The rate of development of the whole embryo and gonadal growth was faster at female-promoting temperature t han at male-promoting temperature. Formation of the genital ridge bega n at stage 21-22 and histological differentiation of the gonads occurr ed around stage 26-27. Although these stages coincided with the TSP, a t male-promoting temperature the thermosensitive stages occurred earli er (from stages 20-21 to stages 23-24) than at female-promoting temper ature (from stages 23-24 to stages 26-27). Thus, at male promoting-tem perature, sex was determined in embryos with incipient or undifferenti ated gonads. In contrast, E2 treatment continued to feminize the gonad s of embryos at a male-promoting temperature beyond the TSP up to stag e 25-26, but the E2-induced ovaries were significantly smaller than te mperature-induced ovaries. It is suggested that the doses of E2 used w ere higher than the concentration of endogenous E2 required for normal sex determination. The lack of correlation between sex determination and gonad differentiation suggests that irreversible molecular process es underlying sex determination occur earlier at male-than at female-p romoting temperature. Results suggest that the male sex may be the def ault state and that the female condition must be imposed upon it. (C) 1997 Academic Press.