Estrogen, when present in early embryonic development, regulates sexual differentiation in the avian nestling and adult. In this study, I developed a procedure to extract and quantify levels (by radioimmunoassay) of the estrogen, 17[beta]-estradiol, in house wren (Troglodytes aedon) egg yolk. Levels of 17[beta]-estradiol found in one clutch of eggs increased with the order of laying, indicating female house wrens may be capable of regulating the levels of 17[beta]-estradiol received by the offspring. Since the attraction of mates is often aided by the display of sex differences, maternal control of 17[beta]-estradiol levels in the embryo may influence the future reproductive success of her offspring.



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