Abstract
In order to achieve successful captive breeding the Podocnemis expansa, it is necessary to study their reproductive endocrinology. The purpose of this research was to evaluate and characterize plasma concentrations in gonadotrophic, gonadic, corticosterone and prolactin hormones from Giant Amazon Turtles under captive conditions. Blood samples were collected over a 15 month period. The samples were assayed by the use of radioimmunoassay, prolactin, corticosterone, LH, FSH, testosterone, 17β-estradiol and progesterone. We verified significant seasonal pattern increase in 17β-estradiol levels and decrease in progesterone levels in the course of a year, which indicates vitellogenesis. This is related to normal ovarian cycles and possibly to the functional integrity of the hypothalamus-pituitary-gonad axis of captive females. There were negative correlations between testosterone and corticosterone in the male samples, suggestive of stress (management stress) on the reproductive system. The plasma concentrations of gonadotrophic, gonadic, prolactin and corticosterone hormones may be used as a reference for further research and possible therapeutic approaches. The data collected during this research are unprecedented for this species and may serve as a reference for future research regarding the reproductive cycle of this turtle, also allowing reproductive management while in captivity. Information about these hormones must be gathered from wild populations during different periods of the year for better clarification of the reproductive physiology of this species.
Highlights
The Giant Amazon River Turtle (Podocnemis expansa, Schweigger, 1812b) South America’s largest freshwater turtle, has considerable data published concerning clutch size, hatching and nesting behavior and ecology (Vanzolini, 2003; Ferreira Junior and Castro, 2010)
We observed an increase in 17β-estradiol concentrations during the period between July and May, which is the rainy season
We verified a decrease in the plasma levels of the 17β-estradiol of the following year and a subsequent increase in September
Summary
The Giant Amazon River Turtle (Podocnemis expansa, Schweigger, 1812b) South America’s largest freshwater turtle, has considerable data published concerning clutch size, hatching and nesting behavior and ecology (Vanzolini, 2003; Ferreira Junior and Castro, 2010). There has been a great interest in the commercialization of Podocnemis expansa, to alleviate the over collection of wild caught turtles. For this purpose, the research on size at sexual maturity is important once it is considered a potential tool through the study of chronology by carcass morphology; besides, it could answer questions regarding longevity, sexual maturity and population age structure (Chinsamy and Valenzuela, 2008). The pattern observed could be altered in favor of the captive environment (management stress). It is as necessary to clarify aspects of the reproductive life in nature and captivity, generating results that favor the reproductive management of the species in controlled environments as well as in nature
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