Effects of endocrine-active chemicals on the development of sex characteristics of Daphnia magna

Standard reproductive assays with daphnids involve parthenogenetically repr oducing females and exclude the assessment of effects on sexual reproductio n. The goals of this study were to characterize sexual differentiation of m ale and female daphnids (Daphnia magna) and to evaluate whether exposure to putative endocrine-disrupting chemicals may perturb the development of sex characteristics. Anatomical sex differences that developed during maturati on in males included elongated first antennae and morphologic alterations i n the head capsule and carapace edge. Reproductive maturation in females wa s associated with the development of a brood chamber and abdominal process. Alterations in the growth rates of the first antennae of males and the abd ominal process of females were used to evaluate the effects of chemical exp osure on the development of these sex characteristics during maturation. Ex posure of female daphnids to the nonsteroidal vertebrate estrogen diethylst ilbesterol and the insect juvenile hormone analog methoprene at concentrati ons as low as 3.0 and 0.080 mu M, respectively, stimulated development of t he abdominal process. Exposure of males to the steroidal vertebrate androge n androstenedione (greater than or equal to 6.0 mu M) stimulated developmen t of the first antennae. These results demonstrate that the development of secondary sex characteristics in daphnids can be altered by chemical exposu re.