A review of the reproductive system in anuran amphibians

Abstract

Reproductive biology is an important topic that is well explored in many vertebrates, but information about frogs’ reproductive mechanisms could be improved. Therefore, this review aims to provide organized and specific information on frog reproduction. First, we developed schemes that illustrate the general information regarding reproductive biological mechanisms in frogs in a specific way. Then, we described the physiological, histological, and morphological mechanisms of each organ of the reproductive system of male and female frogs. Finally, this manuscript may contribute to a broader understanding of anuran reproductive biology. Since, understanding frogs’ reproductive system permits one to make a comparison with reproduction with other anurans.

A cretaceous frog with eggs from northwestern China provides fossil evidence for sexual maturity preceding skeletal maturity in anurans

“…In living anurans, as in all vertebrates, the female reproductive system is generally divided into two separate parts: the ovary and oviduct [ 63 ]. The ovary is typically located on the posterior side of the body and composed of ovarian follicles, and each ovarian follicle contains a developing egg.…”

Recovery and Characterization of Spermatozoa in a Neotropical, Terrestrial, Direct-Developing Riparian Frog (Craugastor evanesco) through Hormonal Stimulation

“…The occurrence of one or more sperm concentration peaks and the duration-dependence of these after hormonal stimulation could be the result of several factors acting simultaneously: (1) the species; (2) the hormone type and concentration, which will stimulate receptors in a sub-optimal, optimal or supra-optimal manner [52]; (3) time and dose-dependent biphasic response of gonadotropin gene expression to hormonal stimulation [42]; (4) speciesspecific GnRH-A, LH and FSH circulating half-life; (5) the response of the target tissues of these hormones: LH and FSH sub-optimal, optimal or supra-optimal surge (for GnRH) or androgen concentrations (for hCG); ( 6) the species intracystic or intercystic synchrony or asynchrony of spermatogenic stages [53]; (7) the species duration of the different spermatogenic stages, where some of the cysts might contain more mature Sertoli cells than others that are delayed and responding later to the hormonal stimulation [21]; (8) the number of testicular cysts with mature spermatozoa ready for release [53]; (9) the effect of sub-optimal, optimal or supra-optimal gonadotropin concentrations on the required swelling of Sertoli cells to promote adequate expulsion of most mature spermatozoa into the lumen of seminiferous tubules [21]; (10) selection of optimal collection time points [10] and (11) adequate assessment of samples per time point. Given the time points reported in this study, it is possible that additional peaks were missed, or the continuity of a single time point may not have been detected between 6.5, 24, 28 and 48 hpi.…”