Exogenous estradiol alters gonadal growth and timing of temperature sex determination in gonads of sea turtle

AbstractGlobal warming could drive species with temperature-dependent sex determination to extinction by persistently skewing offspring sex ratios. Evolved mechanisms that buffer these biases are therefore paramount for their persistence. Here, we tested whether maternally-derived sex steroid hormones affect the sex-determination cascade and provide a physiological mechanism to buffer sex ratio bias in the endangered loggerhead sea turtle (Caretta caretta). We quantified estradiol and testosterone in nesting females and their egg yolks at oviposition, before incubating nests in situ at standardised temperatures. Upon hatchling emergence, we developed a new, non-lethal method to establish the sex of individuals. Despite standardised incubation temperatures, sex ratios varied widely among nests, correlating non-linearly with the estradiol:testosterone ratio in egg yolks. Males were produced at an equal ratio, with females produced either side of this optimum. This result provides evidence that maternal hormone transfer forms a physiological mechanism that impacts sex determination in this endangered species.

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Influence of short-term temperature drops on sex-determination in sea turtles

10.1101/2021.03.29.437634 ◽

2021 ◽

Author(s):

Ellen Porter ◽

David T Booth ◽

Col J Limpus

Keyword(s):

Sex Determination ◽

Heavy Rainfall ◽

Incubation Temperature ◽

Sea Turtles ◽

Sex Ratios ◽

Temperature Drop ◽

Sea Turtle ◽

Short Term ◽

Sand Temperature

All sea turtles exhibit temperature-dependent sex-determination, where warmer temperatures produce mostly females and cooler temperatures produce mostly males. As global temperatures continue to rise, sea turtle sex-ratios have become increasingly female-biased, threatening the long-term viability of many populations. Nest temperatures are dependent on sand temperature, and heavy rainfall events reduce sand temperatures for a brief period. However, it is unknown whether these short-term temperature drops are large and long enough to produce male hatchlings. To discover if short-term temperature drops within the sex-determining period can lead to male hatchling production, we exposed green and loggerhead turtle eggs to short-term temperature drops conducted in constant temperature rooms. We dropped incubation temperature at four different times during the sex-determining period for a duration of either 3 or 7 days to mimic short-term drops in temperature caused by heavy rainfall in nature. Some male hatchlings were produced when exposed to temperature drops for as little as 3 days, but the majority of male production occurred when eggs were exposed to 7 days of lowered temperature. More male hatchlings were produced when the temperature drop occurred during the middle of the sex-determining period in green turtles, and the beginning and end of the sex-determining period in loggerhead turtles. Inter-clutch variation was evident in the proportion of male hatchlings produced, indicating that maternal and or genetic factors influence male hatchling production. Our findings have management implications for the long-term preservation of sea turtles on beaches that exhibit strongly female-biased hatchling sex-ratios.

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Hox gene expression in the embryonic genital system of the sea turtle Lepidochelys olivacea (Eschscholt, 1829), a species with temperature-dependent sex determination

Gene Expression Patterns ◽

10.1016/j.gep.2010.06.004 ◽

2010 ◽

Vol 10 (6) ◽

pp. 290-298 ◽

Cited By ~ 8

Author(s):

Itzel Sifuentes-Romero ◽

Horacio Merchant-Larios ◽

Alejandra García-Gasca

Keyword(s):

Gene Expression ◽

Sex Determination ◽

Sea Turtle ◽

Genital System ◽

Temperature Dependent ◽

Hox Gene ◽

Lepidochelys Olivacea

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Spatiotemporal Expression of Foxl2 and Dmrt1 before, during, and after Sex Determination in the Sea Turtle Lepidochelys olivacea

Sexual Development ◽

10.1159/000507838 ◽

2019 ◽

Vol 13 (5-6) ◽

pp. 286-296

Author(s):

Verónica Díaz-Hernández ◽

Paloma Dominguez-Mora ◽

Luis Chino-Palomo ◽

Alejandro Marmolejo-Valencia ◽

Martha Harfush ◽

...

Keyword(s):

Sex Determination ◽

Sea Turtle ◽

Sexually Dimorphic ◽

Cell Nuclei ◽

Temperature Dependent ◽

Olive Ridley ◽

Lepidochelys Olivacea ◽

Spatiotemporal Expression ◽

Dimorphic Expression ◽

Medullary Cords

The sex of sea turtles is determined by temperature during egg incubation. Thus, climate change affects the sex ratio, exacerbating their vulnerability to extinction. Understanding spatiotemporal effects of temperature on sex determination at the gonadal level may facilitate the design of strategies to mitigate the effects of global warming. Here, we used qRT-PCR and immunofluorescence to analyze the spatiotemporal expression of Dmrt1 and Foxl2 in developing gonads of Lepidochelys olivacea incubated at male-producing temperature (MPT, 26°C) or female-producing temperature (FPT, 33°C). Although both transcription factors are expressed in bipotential gonads up to stage 25, the timing of their sexually dimorphic regulation differs. Whereas the dimorphic expression of Dmrt1 protein initiates at stage 24, Foxl2 protein was expressed specifically in females at stage 25. Interestingly, whereas Dmrt1 colocalizes with Sox9 in cell nuclei of primary medullary cords to form the testis cords, Foxl2 protein is first detected in Sox9-negative cells of primary medullary cords, prior to its substantial expression in the ovarian cortex. Thus, results suggest that the temperature-dependent regulation of sexual pathways is stochastic among the cells of primary medullary cords in undifferentiated bipotential gonads of the olive ridley.

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