Hormones and reproductive cycles in crocodilians

Document Type

Article

Publication Date

1-1-2024

Publication Title

Hormones and Reproduction of Vertebrates Reptiles Volume 3 Second Edition

Abstract

Hormonal influence upon sexual differentiation in crocodilians begins during embryonic development and continues for years until sexual maturation is attained. Shortly after sex determination, estrogen production in the embryonic ovary increases and promotes growth and development of the Müllerian ducts, whereas the testis produces anti-Müllerian hormone, which results in their regression. Following hatching, gonadal production of sex steroids increases gradually with body size, gonads become increasingly responsive to gonadotropins, and secondary sex structures become progressively more modified by steroidal stimulation. As crocodilians approach 1m in total length, males and females begin showing seasonal variations in androgens and estrogens, respectively, but the plasma concentrations of these steroids are considerably lower in large juveniles in comparison to adults at the same time of year. Mature crocodilians exhibit distinct annual cycles that are primarily dictated by temperature and photoperiod in temperate species or are associated with seasonal rainfall patterns in tropical species. The onset of gametogenesis begins approximately 4months prior to the peak of copulation as gonadal and reproductive tract recrudescence is stimulated by increases in sex steroids. Following ovulation, active corpora lutea synthesize progesterone during gravidity, stimulating uterine secretions involved in the production of albumen and egg shelling. Uterine prostaglandin secretions are greatest in postoviposition females, suggesting roles in egg laying and luteolysis. The most recent advances in crocodilian reproduction include the characterization of gene expression involved in sexual differentiation and reproductive cycles; much work remains to clarify interspecific variation and intraspecific variation across latitudinal and environmental gradients.

First Page

271

Last Page

288

DOI

10.1016/B978-0-443-16022-6.00006-8

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