SEASONAL RELIABILITY OF TESTOSTERONE RADIOIMMUNOASSAY (RIA) FOR PREDICTING SEX RATIOS OF JUVENILE LOGGERHEAD (CARETTA CARETTA) TURTLES (original) (raw)
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Estimating sex ratios in Caribbean hawksbill turtles: testosterone levels and climate effects
Aquatic Biology, 2013
Evolutionary theory predicts that male and female offspring should be produced at a 1:1 ratio, but this may rarely be the case for species in which sex is determined during incubation by temperature, such as marine turtles. Estimates of primary sex ratio suggest that marine turtle sex ratios are highly skewed, with up to 9 females per male. We captured juvenile hawksbill turtles Eretmochelys imbricata in waters around Anegada, British Virgin Islands, a regionally important foraging aggregation, and analysed concentrations of plasma testosterone and oestradiol-17β from 62 turtles to estimate sex ratio. There were 2.4 to 7.7 times more females than males. Testosterone concentrations correlated with sampling date and sea surface temperature (SST), with higher con centrations in the late summer when SST was highest, suggesting that assigning sex through threshold values of sex hormones must be carried out cautiously. The sex ratio in the juvenile foraging aggregation around Anegada is more male biased than at other locations, suggesting that turtles at Anegada have resilience against feminising effects of climate change. Future work should (1) integrate the relative contributions of different genetic stocks to foraging aggregations and (2) investigate the annual and seasonal cycles of sex hormones, and differences among individuals and life history stages.
PLOS ONE, 2015
Determining sex ratios of endangered populations is important for wildlife management, particularly species subject to sex-specific threats or that exhibit temperature-dependent sex determination. Sea turtle sex is determined by incubation temperature and individuals lack external sex-based traits until sexual maturity. Previous research utilized serum/ plasma testosterone radioimmunoassays (RIA) to determine sex in immature/juvenile sea turtles. However, there has been a growing application of enzyme-linked immunosorbent assay (ELISA) for wildlife endocrinology studies, but no study on sea turtles has compared the results of ELISA and RIA. This study provides the first sex ratio for a threatened East Pacific green sea turtle (Chelonia mydas) foraging aggregation, a critical step for future management of this species. Here, we validate a testosterone ELISA and compare results between RIA and ELISA of duplicate samples. The ELISA demonstrated excellent correspondence with the RIA for providing testosterone concentrations for sex determination. Neither assay proved reliable for predicting the sex of reproductively active females with increased testosterone production. We then applied ELISA to examine the sex ratio of 69 green turtles foraging in San Diego Bay, California. Of 45 immature turtles sampled, sex could not be determined for three turtles because testosterone concentrations fell between the ranges for either sex (females: 4.1-113.1 pg/mL, males: 198.4-2,613.0 pg/mL) and these turtles were not subsequently recaptured to enable sex determination; using a Bayesian model to predict probabilities of turtle sex we predicted all three 'unknowns' were female (> 0.86). Additionally, the model assigned all turtles with their correct sex (if determined at recapture) with 100% accuracy. Results indicated a female bias (2.83F:1M) among all turtles in the aggregation; when focusing only on putative immature turtles the sex ratio was PLOS ONE |
Predicted Sex Ratio of Juvenile Kemp's Ridley Sea Turtles Captured near Steinhatchee, Florida
Copeia, 2005
The Kemp's Ridley (Lepidochelys kempii) is one of the most endangered sea turtles in the world, and it possesses temperature-dependent sex determination (TSD). Sex ratios produced under TSD can vary widely and can affect the reproductive ecology of a population. Therefore, sex ratios produced from TSD are of ecological and conservation interest. The current study validated and utilized a testosterone radioimmunoassay (RIA) to examine the sex ratio of juvenile Kemp's Ridleys inhabiting the waters near Steinhatchee, Florida. Testosterone levels were measured in blood samples collected from juvenile Kemp's Ridleys captured over a three-year period. Results of this study indicate that a significant female bias (approximately 3.7:1) occurs in the aggregation of juvenile Kemp's Ridleys inhabiting the waters near Steinhatchee.
Biology of Reproduction, 1999
Incubation temperature determines gonadal sex in the redeared slider turtle, Trachemys scripta. However, little is known about the long-term effects of incubation temperature on traits other than gonadal sex in this species. To investigate the hypothesis that incubation temperature (independent of gonadal sex) influences sex steroid levels after hatching, we incubated eggs of the red-eared slider turtle at three temperatures (26, 28.6, and 31؇C). We then measured plasma levels of dihydrotestosterone, estradiol, progesterone, and testosterone in 6-wkold males from 26؇C and 28.6؇C eggs, and in 6-wk-old females from 28.6؇C and 31؇C eggs. We found that dihydrotestosterone levels were not influenced by incubation temperature or gonadal sex. However, progesterone levels were significantly higher in males from 26؇C eggs than in males from 28.6؇C eggs. In contrast, testosterone levels did not differ between males from 26؇C versus males from 28.6؇C eggs, but they were significantly higher in females from 28.6؇C than in females from 31؇C eggs. Progesterone and testosterone levels did not differ between males and females from 28.6؇C eggs. Temperature also influenced estradiol levels in both sexes, but the effects were enigmatic. We conclude that incubation temperature has lasting effects on sex steroid levels even after hatching.
Plasma Testosterone and Seasonal Reproductive Changes in the Scorpion Mud Turtle
Pakistan Journal of Zoology, 2014
The scorpion mud turtle (Kinosternon scorpioides) is a freshwater chelonian that is consumed by local populations in states of Pará and Maranhão, Brazil. Current analysis evaluates the reproductive parameters of recently captured turtles. Turtles underwent histological analysis of testes and hormone levels to establish and investigate the species´s natural cycle in different stages, with special focus on aestivation behavior as it relates to such as reproductive strategies. This information will help inform sustainable strategies of conservation and reproduction which would contribute towards studies on other animals with similar behaviors. Twenty adult male animals were dissected and their testes removed for the morphometric analysis of epithelial thickness and tubular and luminal diameters. Testosterone concentrations were measured by radioimmunoassay. Results indicated that the hormonal testosterone profile was linked to the mating season and the highest spermatogenic activity occurred during the rainy season when testosterone concentrations were lower than those during the dry season. Biological observations on the reproductive behavior revealed that seasonal variations in gonad size, morphological characteristics of the testes and hormone concentrations all indicate that the environmental conditions of the scorpion mud turtle´s natural habitat influenced reproductive seasonality.
Canadian Journal of Zoology, 1991
. Female-biased sex ratio of immature loggerhead sea turtles inhabiting the Atlantic coastal waters of Florida. Can. J. Zool. 69: 2973-2977. The sex ratio of immature loggerhead sea turtles, Caretta caretta, inhabiting the Atlantic coastal waters of Florida was investigated. Blood samples were obtained from 223 turtles that were captured in the intake channel of a power plant on Hutchinson Island. A serum androgen sexing technique was utilized to sex individual turtles. The sex ratio of the turtles (2.1 female : 1.0 male) differed significantly from 1: 1 and thus appears to differ from predictions of sex allocation theory. These observations are consistent with those of a previous study, and collectively the results suggest that the sex ratio of immature C. caretta inhabiting the Atlantic coastal waters of the United States is significantly female biased: approximately two females per male.
Maternally derived sex steroid hormones impact sex ratios of loggerhead sea turtles
An optimal sex ratio is arguably one of the most important demographic traits of species. Rising global temperatures threaten temperature-dependent sex determination (TSD) species with extreme sex ratio bias and ultimately extinction. Because sex steroid hormones can impact sex determination in TSD reptiles, variation in their maternal transfer within the egg yolk may form a buffer mechanism against raising temperatures. We tested this hypothesis by quantifying the effect of maternal oestradiol (E2) and testosterone (T) on offspring sex in a threatened TSD population of loggerhead sea turtles (Caretta caretta). Circulating levels of E2 and T in nesting females, in egg yolks at oviposition and in neonates were measured. Immediately after oviposition, nests were relocated into an in situ experimental hatchery where temperatures were controlled by standardising the incubation depth. We used affinity propagation clustering on hormone profiles guided by incubation duration, to sex indivi...
MATURATIONAL CHANGES IN MALE SLIDER TURTLES (TRACHEMYS SCRIPTA) FROM ILLINOIS
Herpetological …, 2008
Accurate identification of sexually mature individuals is essential for life-history studies. In emydid turtles, secondary sexual characters (SSCs) are most often used to identify male maturity while numerous other methods exist. In this study, we examined the association between body size, age, foreclaw length (FCL), preanal tail length (PTL), testis mass, and plasma androgen level in Slider Turtles (Trachemys scripta; n = 40) from multiple populations in Illinois. We determined the accuracy of these methods by dissecting male Slider Turtles and used the presence of sperm as a definitive test of sexual maturity. Male T. scripta matured at 98 mm plastron length, between 3-5 years old, and generally had FCLs > 7 mm, PTLs > 13 mm, and testis weights > 0.06 g. Androgen levels were significantly higher in mature males compared to immature males and immature females. Overlap in the individual raw values for androgens between categories limits their use for identifying maturity in this species. Overall, size and SSCs appear to be the least invasive and most accurate methods available to identify male maturity.
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.
Journal of The Marine Biological Association of The United Kingdom, 2005
The sex ratio of 100 immature Kemp's ridley turtles (Lepidochelys kempi) captured in Gullivan Bay, Ten Thousand Islands, south-west Florida was determined through radioimmunoassay analysis (RIA) of plasma testosterone levels. We determined the sex ratio to be 1.9F:1.0M, corroborating the female dominance reported from other studies. The mean sizes of female (N¼57) and male turtles (N¼30) were 40.9 cm ( AE6.9 SD) and 41.9 cm ( AE6.2 SD), respectively. There were an additional 13 turtles (41.3 cm AE6.5 SD) for which sex could not be determined by this technique. Female-biased sex ratios are not uncommon in reptiles with temperature dependent sex determination. If fecundity is not male-limited, the occurrence of a female-biased sex ratio could enhance the recovery of the endangered Kemp's ridley turtle.