Seasonal Reproductive Cycle of the Kemp's Ridley Sea Turtle (Lepidochelys kempi) (original) (raw)
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The Veterinary Journal, 2011
Serum levels of gonadal steroid hormones, corticosterone and thyroxin (T 4 ), were monitored monthly in two male and one female captive Loggerhead sea turtles (Caretta caretta) over a period of 12 months in 2004 and 3 months in 2006. Ovary ultrasonography was performed in April and July 2006. The turtles were kept together in an outdoor sea pool in natural temperature and photoperiod conditions from May to November, then in separate indoor pools from December to April. Circulating hormone levels were measured by radioimmunoassay.
General and Comparative Endocrinology, 1997
The seasonal gonadal cycle (including gonadal histology, sex steroids, and gonadotropins) was studied in freshly captured common snapping turtles, Chelydra serpentina, from Wisconsin, and the effects of capture stress were evaluated. The ovarian and testicular cycles are shorter than those reported in other freshwater turtles; the cycles commence in mid-May and terminate in early September, immediately after the completion of gonadal growth and maturation. In the female, testosterone (T), 17beta-estradiol (E2), and progesterone (Pro) were highly correlated with follicular growth and vitellogenesis. Ovulation in captivity and under natural conditions occurred after mid-May. In captivity, ovulation was a rapid process (24-48 hr); as the follicles descended into the uterine horns there was a significant increase in E2 and Pro and eggs were retained in the uterine horns for about 2 weeks before oviposition. In the male, T was significantly correlated with testicular growth and spermiation. Follicle-stimulating hormone (FSH) reached significantly higher levels (P < 0.01) in males (8.99 +/- 0.38 ng/ml) than in females (2.66 +/- 0.22 ng/ml), but luteinizing hormone was undetectable in both sexes. FSH was not correlated with the steroids in either sex. Sex steroids and FSH began to rise before spermiation and vitellogenesis and remained elevated until completion of gonadal growth and maturation. Leydig cells, the main source of plasma androgen in this species, became active shortly after emergence from hibernation and remained steroidogenically active for the rest of the cycle. Sertoli cells became active only after spermatogenesis was under way but also stayed active for the rest of the summer. Courtship and mating behaviors were observed in spring, summer, and fall. The snapping turtle is strictly aquatic with no basking behavior and limited behavioral thermoregulation so there is little daily fluctuation in body temperature. Environmental correlates indicate that the snapping turtle is temperature dependent: recrudesence occurs with a slight increase in water temperature during spring and early summer, while a dramatic drop in gonadal activity accompanies a slight decrease in temperature in fall. Changes in temperature may underlie changes in gonadal activity in the face of relatively stable FSH. Male turtles subjected to captivity and periodic blood sampling show a significant decline in T. The hormonal levels continued to decline whether the turtles are exposed to optimum or extreme temperatures. However, there is more rapid decline in T values in animals with regressed testes (June) than in those with well-developed testes (July). Male and female turtles kept in captivity at different phases of the cycle exhibit different patterns and degrees of response to stress, possibly related to the hormonal levels and the condition of the gonads.
Hormones and Reproductive Cycles in Turtles
Hormones and Reproduction of Vertebrates, 2011
Reproductive cycles of cryptodire turtles and species from the northern hemisphere have been investigated extensively compared to those of pleurodire species from the southern hemisphere. Radiography, laparoscopy, and ultrasonography have been used on a few species of turtle to describe a diversity of ovarian and testicular cycles. Radioimmunoassays (RIAs), on the other hand, have provided evidence of the dynamic cycling of peptides and steroid hormones within a reproductive season. All turtles are cyclic breeders and show a range of annual and multiannual reproductive patternsdregulated by nutritional status and environmental conditionsdwhich are most often described as prenuptial or postnuptial. These cycles may be seasonally coordinated by an active pineal gland in the brain via melatonin secretion affecting the hypothalamus. Moreover, the steroid hormone cycles can be rapid and dynamic, and steroid hormones stimulate a carefully orchestrated mating receptivity period: a series of rapid ovulations in the case of multiclutched turtles, egg production, and oviposition events.
Copeia, 2015
The Pascagoula Map Turtle (Graptemys gibbonsi) is a narrowly endemic species found only in the Pascagoula River drainage in Mississippi. It is among the most poorly known turtle species because of research taxonomic biases and this species' relatively recent recognition as a unique taxon. A recent petition requested protective status for G. gibbonsi under the U.S. Endangered Species Act. We describe population parameters, quantitatively assess sexual dimorphism of G. gibbonsi, and document hormone secretion patterns from the Chickasawhay and Leaf rivers in Mississippi. We demonstrate a significant male-skewed sex ratio and a female-biased size dimorphism in both carapace length and height. Males showed a bimodal peak of plasma testosterone in fall and spring, consistent with the pattern shown by many other southeastern turtles with late summer-fall spermatogenesis and mating during spring and fall. Females did not show seasonal variation in estradiol secretion, an unexpected result that was possibly due to our small sample size of females, none of which were gravid when captured. Although this observation may be due to our limited capacity to sample females, given the reproductive issues reported for Graptemys flavimaculata from the same drainage (e.g., reproductive hormone abnormalities, low nesting frequency and success), this finding warrants concern and necessitates additional research. Finally, in order to put our hormone data in context, we briefly review hormone and reproductive patterns in southeastern U.S. turtles. Our review includes the timing of follicular enlargement, ovulation and nesting, clutch frequency, and estradiol cycles. The review for male turtles includes details on the spermatogenic cycle, spermiation, and the timing and frequency of testosterone peaks.
General and Comparative Endocrinology, 1990
Adult male loggerhead sea turtles, Caretta caretta, exhibited a "prenuptial" spermatogenie cycle that was coincident with increased concentrations of serum testosterone (T). Serum T was high during the months when migration and mating have been recorded for males. In contrast to females, males appear to be annual breeders. Nine reproductively active female C. caretta (as verified through laparoscopy) were tagged with sonic transmitters and were repeatedly bled prior to migration. Four months prior to the nesting season, the ovaries of reproductively active females had hundreds of vitellogenic follicles of approximately 1.5 cm in diameter (i.e., half the size of ovulatory follicles). Approximately 4-6 weeks prior to migration from feeding grounds to mating and nesting areas, serum estradiol-17f3 (E,) concentrations increased significantly and remained high for approximately 4 weeks, suggesting a period of increased vitellogenesis. During a 1-to 2-week period prior to migration, serum E, decreased significantly, while serum T concentrations increased (at least) until the time of migration. Serum T, E,, and progesterone (PRO) were elevated during nesting if a turtle was going to nest again during that nesting season. During the last nesting of a season, turtles had low serum concentrations of T, E,, and Pro. The prenuptial pattern of gonadal recrudescence and gonadal steroid production in both male and female C. caretta contrasts with those of many temperate freshwater turtles, and this type of reproductive pattern may have been facilitated by adaptation to a tropical marine environment.
Comparative Biochemistry and Physiology Part A: Physiology, 1991
l. Survey of androgens and estrogens in serum, liver and testes of male yellow-bellied slider turtles, Trachemys (= Pseudemys) scripta, a species exhibiting dissociated gametogenesis age-dependent melanism, revealed the presence of numerous androgen precursors, androgens, androgen metabolites. and estrogens in quantities varying with season, tissue, and male coloration.
General and Comparative Endocrinology, 1979
Circulating levels of gonadotropins (FSH and LH) and several sex steroids were studied in a captive colony of green sea turtles, Chelonia mydas, in association with the annual reproductive cycles in 3 years. Limited data for prebreeding and copulating males indicated that gonadotropins remained low and that androgen levels were lower during copulation than in the prebreeding season. Females showed consistent hormonal profiles from year to year. All steroids were relatively low and increased gradually between the prebreeding and mating season. Estrogen dropped while testosterone peaked in the season of maximal sexual receptivity and both steroids then remained relatively low througout the remainder of the nesting season. In contrast, progesterone (PRO) continued to rise progressively during the prebreeding and mating season and up to the time of nesting. Both gonadotropins were low during the prebreeding season, but only LH rose during the mating season. FSH showed a pronounced but relatively brief "surge" at the time of nesting (oviposition), while LH and PRO were only slightly elevated and variable at this time. FSH levels fell rapidly (with a half-life of 12-21 min) immediately after the completion of laying and remained at baseline levels until the next nesting (in about 11 days). In contrast, simultaneous surges in LH and PRO began between 6 and 12 hr after nesting and lasted for about 24 hr; these hormones then returned to low baseline levels until the next nesting-ovulatory cycle. These intemesting peaks in LH and PRO, which were also occasionally observed in mating animals shortly before the start of nesting, were highly correlated with the timing of ovulation. These data are compared with information on the hormonal profiles of the avian ovulatory cycle and seasonal breeding cycles of other turtles. The implications of the relationships among endogenous hormones in the green turtle are discussed in relation to the hypothalamic control ofthe pituitary and the physiological actions of the gonadotropins and steroids. In particular, data suggest that the secretion of FSH and LH may be regulated independently; and, contrary to existing physiological data, these two gonadotropins may have distinctive roles in ovarian regulation that differ from those suggested by hormone therapy studies.
Reproductive hormonal profile in Eastern Pacific green turtles captured in-water
The Eastern Pacific green turtle (EPGT) has been differentiating from the green turtle and is currently considered a separate population. This study determined the values of reproductive hormones and total thyroxine of 56 resident foraging green turtles captured between 2012 and 2014 at Golfo Dulce, Costa Rica. All of them underwent a physical examination and were deemed as healthy individuals. The progesterone values were 0.31-2.723 ng/ml, estradiol 25.54-104.129 pg/ml, testosterone 1.94-228.97 ng/dl, and thyroxine 0.5-0.9 µg/dl. Since our population did not show sexual dimorphism, and the curved carapace length sizes did not match previous reports, turtles' sex was determined based on high testosterone concentrations. Our results showed that 48 males (> 3 ng/dl), three females (< 2 ng/dl), and five yet undetermined individuals (2-3 ng/dl) were sampled. The green turtle populations at the Golfo Dulce seem to be formed by subpopulations at different stages of their reproductive cycle; among them could be males and females close to mating season, foraging females between seasons and sub-adults in their final developing habitat. The sampled population included 3 juveniles (one male and two not defined), 45 sub-adults (40 males, three females and one not determined), 7 adults (all males), and one undetermined individual (not sex determined either). The progesterone results indicated that none of the females were nesting; this might indicate that they nest far from the area. The information provided by this study is extremely valuable in the attempts to determine the health status for conservation programs of EPGT in the area.