Sex reversal by aromatase inhibitor treatment in the newt Pleurodeles waltl.

Pleurodeles waltl is a newt with a ZZ male-ZW female sex determination mechanism, and a temperature-sensitive gonadal sex differentiation. Raising larvae at 32 degrees C from stage 42 to stage 54 (thermosensitive period) drives genetic females to differentiate into functional males. Estrogens are intimately linked with temperature action in this species, as well as in other vertebrates with temperature-dependent sex determination. We report here the masculinization of female ZW larvae and one WW larva by aromatase inhibitor treatment. Larvae were treated from stage 52 (before the onset of histological differentiation of the gonads) to stage 56 (metamorphosis), with the non-steroidal inhibitors fadrozole or miconazole. Miconazole proved to be very toxic, but not fadrozole. Fadrozole at a concentration of 300 micrograms/l in the rearing water resulted in complete sex reversal of 9 out of 30 ZW larvae and 1 out 9 WW larvae. Only one individual (ZW) was intersex, all the remainder being typical females. Gonadal aromatase activity was measured in several individuals at different developmental stages during treatment. The activity was low in all individuals at the beginning of the treatment, but varied strongly and was well correlated with gonadal structure at the end of the treatment. Despite these differences in individual responses to treatment inhibiting aromatase, results confirm the important role of estrogens in ovary differentiation in Pleurodeles waltl.