Abstract

Publisher Summary During embryonic development, hormonal influence upon sexual differentiation in crocodilians begins and continues for years until sexual maturation is attained. Shortly after sex determination, estrogen production in the embryonic ovary increases and promotes proliferation of the Musllerian ducts, whereas the testis produces anti-Mullerian hormone, which results in its regression. Following hatching, gonadal production of sex steroids increases gradually with body size, and secondary sex structures become increasingly responsive to steroidal stimulation. As crocodilians approach one meter in length, males and females begin showing subdued seasonal variations in androgens and estrogens, respectively. Mature crocodilians exhibit distinct annual cycles that are primarily dictated by temperature and photoperiod in temperate species or by seasonal rainfall patterns in tropical species. The onset of gametogenesis begins approximately four months prior to the peak of copulation, as gonadal and reproductive tract recrudescence is stimulated by increases in sex steroids. Following ovulation, active corpora lutea produce progesterone (P4) during gravidity, stimulating uterine secretions involved in the production of albumen and egg shelling. Secretions of prostaglandins from the uterus are greatest in postoviposition females, suggesting a role in egg laying and luteolysis. The most recent advances in crocodilian reproduction include the cloning of genes involved in hormone signaling. Further efforts are needed to place the expression of these genes within the context of ontogenetic development and reproductive cycles of crocodilians.

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