Abstract

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With the growing market for pet turtles, veterinarians are confronted with new demands. Owners or breeders of turtles generally know that these species are temperature-dependent in terms of sex determination, but lack specific knowledge on how it works. Furthermore, they need advice on how to control incubation conditions taking this phenomenon into account. A guide to answer the most common questions is proposed: (i) In which species sex is determined by temperature, sex chromosomes or both? (ii) How to choose incubation temperature for eggs of turtles to optimize hatchling success, performance of juveniles or sex ratio? (iii) How to decipher sexual phenotype of juveniles?

Introduction

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The pet Turtle market is growing in all the studied countries [1-3] and veterinarians are confronted with recurring demands on information of how to take care of young turtles and turtle eggs. The most common concern is about control or knowledge of sexual phenotype of juveniles. Indeed, pet turtle owners generally know the concept of thermosensibility of sex determination, but specific knowledge necessary to answer some specific questions are lacking. The importance of sexual phenotype of turtles for owners becomes evident when they want to breed the turtles.
The objectives of this review is to bring up-to-date information about the thermosensibility of sex determination in turtles, and to share this information to owners of pet turtles and to answer some specific questions:
(i) In which species is sex determined by temperature, sex chromosomes or both?
(ii) How to choose incubation temperature for turtle eggs to optimize hatchling success, performances of juvenile or sex ratio?
(iii) How to identify the sexual phenotype of juveniles?
Sex determination in turtles
Many species of oviparous reptiles, including crocodilians, a majority of turtles, some lizards and the two closely related species of Sphenodon have displayed temperature-dependent sex determination (TSD). In these species, the differentiation of gonads into ovaries or testes depends on the incubation temperature of the embryo during a critical period of embryonic development designated the thermosensitive period (TSP) [4, 5]. This period begins with the appearance of gonad during embryogenesis and encompasses the middle third of embryo development. It is approximately the same embryonic stages for any TSD species [6-10].
To demonstrate the occurrence of TSD in a species, incubation of eggs at various temperatures were performed and the sex of juveniles were plotted against incubation temperature [11]. For some species, the curve is flat demonstrating that incubation temperature does not affect sexual determination in the range of tested temperatures. This species will be listed has having genotypic sex determination or GSD. Such a species is supposed to have sex chromosomes even if they are not distinguishable on caryotype. When sex chromosomes can be visualized, sex determination is sometimes called CSD for Chromosomal Sex Determination [12] but most GSD will be CSD with a relevant technical analysis [e.g. 13].
When the plot of sex ratio vs. incubation temperatures were plotted, a tendency was revealed. Three patterns were described in Reptiles: (i) MF, (ii) FM and (iii) FMF [14]. In the MF pattern, lower incubation temperatures are masculinizing whereas higher one are feminizing and the reverse is true for FM pattern. In FMF pattern, both the lower and the highest temperatures are feminizing whereas the intermediate ones are masculinizing. Both sexes are produced in variable proportions within a range of intermediate temperatures, called the transitional range of temperature (TRT). At the theoretical “pivotal temperature“ P, 50% of each sex is yielded [5].
TSD is widely distributed among family of turtles (table 1). Eleven families are currently monomorphic for the pattern of sex determination and two (Emydidae and Bataguridae) include species with both TSD and GSD. TSD could be the ancestral state in turtles. During evolution, 5 groups of turtles have acquired, independently, sex chromosomes [15]. Then, it is possible to tentatively infer a pattern of sex determination (GSD or TSD) knowing the family or sub-family that a species belongs to, except for sub-family Emydinae and the familyBataguridae where the analysis should be done at the genus level.
However, the exact reaction norm for the sex ratio vs. incubation temperatures is more difficult to anticipate with the exception of eggs that come from an already studied species and population [review in 16].
Now let’s discuss an unresolved question: is it possible to have both GSD and TSD at the same time in a single species? When first discovered in turtles [17-19], thermosensitivity of sex determination was thought to superimpose a putative chromosomal sex determination [C. Pieau, pers. comm. see also 20]. But rapidly a strong dichotomy between GSD and TSD species has been drawn by some authors, and GSD and TSD were described as two incompatible states [21]. However, the genetic component in sex ratio has been demonstrated for eggs incubated in the range of temperatures where both sexes can be produced in the European Freshwater turtle (Emys orbicularis), the common snapping turtle (Chelydra serpentina), the painted turtle (Chrysemys picta), and the map turtle (Graptemys ouachitensis) [22-25]. However, this genetic component was thought to not been able to express in natural condition [22].
In the 80’th, the serological minor histocompatibility antigen H-Y was supposed to be a marker of the heterogametic sex and has been extensively studied in the European Freshwater turtle, Emys orbicularis. When incubated at male- or female-producing temperatures, high and low expression levels were observed in serum of juveniles, irrespective of their sexual phenotype. On the other hand, when incubated at both sexes-producing temperatures, males hatchlings had low-level of expression and females had high-level of expression. This polymorphism of expression of H-Y antigen had been proposed to reflect the genetic component influencing sex determination at intermediate temperature [26, 27]. Low or high temperatures override this genetic component. Then for incubation at constant temperature, most of the embryos have their sexual phenotype that is determined by incubation temperature except for the narrow zone of temperature where both sexes are produced. When H-Y antigen has been studied among adults from natural population, 80% of individuals have their H-Y antigen status (i.e. sexual genotype) conformed to their sexual phenotype [28]. How a species could have TSD when incubated in artificial condition and a sex determination that looks like GSD in 80% of the individuals in natural conditions? It was proposed that when incubation temperatures fluctuate from male to female temperature, the genetic variability in sex determination could influence sex of the gonad and that only when temperature fluctuates around very high or very low temperature, it overpasses the genetic component. The question was debated until a similar system was deciphered in an Australian lizard with both sex chromosomes and TSD [29]. However, we still lack a molecular marker for this genetic component to validate definitively this model for turtles.
Both in Green turtle, Chelonia mydas [30], and European Freshwater turtle, Emys orbicularis [24, 31] sex specific DNA RFLP bands have been found. However in both cases, validation with eggs incubated in known conditions were lacking. Further researches should be done in this direction.
As a conclusion for this section, a veterinarian should look at table 1 to identify the family or sub-family of the species. The main pet species are reported in table 2 with their pattern of sex determination. For uncommon species, a search in specific literature must be done [32]. If the species is not listed anywhere, the only solution is to refer to the pattern in the most related species based on a composite phylogeny of turtles build from the most recent sources [33-40] and to infer the pattern of sex determination based on parsimony principles for reconstructing evolution [41]. However, a doubt will still exist.

How to choose incubation temperature for eggs of turtles?

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When purchasing turtle eggs, the owner will need information on the best incubation procedure. The three main factors that should be taken into account are cleanliness, humidity and temperature [42]. Cleanliness is important to prevent eggs from rotting [43] and pathogen transmission to the eggs [44]. If humidity is lower than required, eggs will dehydrate and die and if higher than required, eggs will break out or rot. The use of moist vermiculite is recommended to maintain viable hygrometry [45]. Similarly, too high and low incubation temperatures could have detrimental effects on the survival of embryos and intermediate ones must be preferred. However, by choosing a specific temperature, the owner can influence the sex of offspring as seen previously but also their performance [for example see 46, 47, 48].
There is no general conclusion on the best-required temperature of incubation for turtle eggs. For example, incubation at feminizing temperatures has been advocated as a conservation measure for threatened species in the case of reintroduction purposes [49] but this recommendation has been criticized from a ecological point of view [50]. Due to the lack of knowledge of the consequences that disrupts the fluctuation of temperature in natural incubation of eggs [51], and any adverse effects on individuals of strongly feminizing conditions [52].
Recently, several authors have published data to compare the effects of fluctuating versus constant incubation temperature. For all the tested parameters (growth rate, temperature choice, locomotor performance, immune response), fluctuating temperatures have a differential impact, often beneficial, when compared to constant temperatures [46, 53-55].
I therefore recommend incubation at diurnal fluctuating temperatures around the pivotal temperature. Average pivotal temperatures for the various turtle families or sub-families are shown in table 1. In case the owner wants a specific sex, species specific pattern of sex determination [16] should serve as a reference to choose incubation temperature. An average incubation temperature of 30 °C for Testudinidae, 31 °C for Podocnemididae and 28.5 °C for Emydidae can be chosen with 2 °C diurnal amplitude.

Identification of sexual phenotype of juveniles

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Many turtle species are highly dimorphic as adults [56] but external morphology of turtle is generally not sexually dimorphic until subadult stage [57]. Hatchling turtles typically exhibit little or no obvious dimorphism that allows for straightforward identi?cation of sex by external observation [58]. Significant sexual dimorphism Chrysemys picta and Podocnemis expansa hatchlings were measured using landmark-based geometric morphometric methods. This method had high accuracy in assigning sex when compared with true sex (98% and 90%, respectively), and cross-validation with hatchlings not used in model definition revealed a correct classi?cation rate of 85% [59]. Multivariate model allows for the differentiation of males and females in 4-years juvenilesGopherus polyphemus but not in hatchling Gopherus agassizii [60]. Difference in possibility to differentiate both sexes in Gopherus genus could reveal that shape morphology dimorphism is acquired during early growth. Size difference between one-year old males and females Trachemys scripta elegans were observed when reared in same conditions [61]. However, size assignation cannot be used when rearing conditions are not standardized and alternative techniques must be used.
External gonadal or sexual ducts morphology is generally studied by dissection of dead animals [62] which cannot be recommended in the context of this review. But external gonadal morphology has been also observed by laparoscopy on live animals in Green turtles, Chelonia mydas [63] and Desert Tortoise, Gopherus agassizii [64]. Laparoscopy has been successfully used in Desert Tortoises as small as 28 g total body mass. Recalling that hatchlings of most turtles weigh less than 10 g [e.g. 6 g in Emys orbicularis, 10], this method cannot be used for very young turtles. Furthermore, this method is very invasive and could be lethal for small turtles (pers. obs.).
The serum testosterone radioimmunoassay procedure has been used conclusively for Lepidochelys olivacea,Chelonia mydas and Gopherus agassizii [64-66]. However, species specific sexing criteria must be developed using both plasma testosterone concentrations and laparoscopic examination of the gonads [67]. The origin of serum testosterone could be extragonadal, perhaps from the brain [68], and then a secondary consequence of sexual phenotype as demonstrated in Alligator [69]. The serum testosterone radioimmunoassay procedure cannot be used for hatchling and estradiol:testosterone ratio has been used conclusively in Caretta caretta egg chorioallantoic/amniotic fluid [70] but should be validated for other species as well before it can be recommended.

Conclusion

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The phenomenon of temperature-dependent sex determination in reptiles is generally known. However the limit of the current knowledge of this sex determination is often not well understood. Specifically, the exact nature of the relationship between TSD and GSD in a single species is still controversial. The most recent review points out that sex determination should be viewed along a continuum TSD-GSD rather than from a dichotomy [71].
When confronted with the demand for incubation conditions, the best solution will be to mimic natural conditions of incubation and then to incubate eggs with daily fluctuating temperatures within the range of viable incubation temperatures. Only when the owner indicates that he specifically wants one sex; for example for breeding purpose, then incubation at low or high nearly constant temperatures could be recommended.
To know the sexual phenotype of hatchlings or juveniles, there is at present for most species no other way than to be patient and to wait until the individual acquires sexually secondary dimorphic characters which can be differentiated in tail length, eye colours, claw lengths, or plastron shape depending on the species [58]

Abbreviation(s)

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TSD: Temperature-dependent sex determination
GSD: Genotypic sex determination

Acknowledgement(s)

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The author thanks Anna Han for careful reading and English correction.

Authors Contribution(s)

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Marc Girondot writes the paper.

References

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1. Honegger RE. The reptile trade. International Zoo Yearbook. 1974;14(1):47-52.
2. Williams T. The terrible turtle trade. Audubon. 1999;101(44):46-8.
3. Wise JK, Heathcott BL, Gonzalez ML. Results of the AVMA survey on companion animal ownership in US pet-owning households. Journal of the American Veterinary Medical Association. 2002;221(11):1572-3.
4. Yntema CL, Mrosovsky N. Critical periods and pivotal temperatures for sexual differentiation in loggerhead sea turtles. Can J Zool. 1982;60(5):1012-6.
5. Mrosovsky N, Pieau C. Transitional range of temperature, pivotal temperatures and thermosensitive stages for sex determination in reptiles. Amphibia-Reptilia. 1991;12:169-79.
6. Ferguson MWJ, Joanen T. Temperature-dependent sex determination in Alligator mississippiensis. J Zool, Lond. 1983;200:143-77.
7. Webb GJW, Beal AM, Manolis SC, Dempsey KE. The effects of incubation temperature on sex determination and embryonic development rate in Crocodylus johnstoni and C. porosus. In: Webb G, Manolis S, Whitehead P, editors. Wildlife Management: Crocodiles and Alligators. Chipping Norton, New South Wales, Australia: Surrey Beatty and Sons Limited; 1987.
8. Bull JJ. Temperature-sensitive periods of sex determination in a lizard: similarities with turtles and crocodilians. Journal of Experimental Zoology. 1987;241:143-8.
9. Lang JW, Andrews HV. Temperature-dependent sex determination in crocodilians. Journal of Experimental Zoology. 1994;270:28-44.
10.Pieau C, Dorizzi M. Determination of temperature sensitive stages for sexual differentiation of the gonads in embryos of the turtle, Emys orbicularis. J Morph. 1981;170:373-82.
11. Girondot M. Statistical description of temperature-dependent sex determination using maximum likelihood. Evolutionary Ecology Research. 1999;1(3):479-86.
12.Manolakou P, Angelopoulou R, Lavranos G. Sex determinants in the genome: lessons from the animal kingdom. Coll Antropol. 2006;30(3):649-52.
13. Lacroix J-C, Azzouz R, Simon F, Bellini M, Charlemagne J, Dournon C. Lampbrush W and Z heterochromosome characterization with a monoclonal antibody and heat-induced chromosomal markers in the newt Pleurodeles waltl: W chromosome plays a role in female sex determination. Chromosoma. 1990;99:307-14.
14. Ewert MA, Jackson DR, Nelson CE. Patterns of temperature-dependent sex determination in turtles. Journal of Experimental Zoology. 1994;270:3-15.
15. Janzen FJ, Krenz JD. Phylogenetics: Which was first, TSD or GSD? In: Valenzuela N, Lance VA, editors. Temperature-Dependent Sex Determination in Vertebrates. Washington: Smithsonian Books; 2004. p. 121-30.
16. Hulin V, Delmas V, Girondot M, Godfrey MH, Guillon J-M. Temperature-dependent sex determination and global change: are some species at greater risk? Oecologia. 2009;160(3):493-506.
17. Pieau C. Sur la proportion sexuelle chez les embryons de deux Chéloniens (Testudo graeca L. etEmys orbicularis L.) issus d'oeufs incubés artificiellement. C R Acad Sci Paris. 1971;272(D):3071-4.
18. Pieau C. Effets de la température sur le développement des glandes génitales chez les embryons de deux Chéloniens, Emys orbicularis L. et Testudo graeca L. C R Acad Sci Paris. 1972;274(D):719-22.
19. Pieau C. Sur la différenciation sexuelle chez des embryons d'Emys orbicularis L. (Chélonien) issus d'oeufs incubés dans le sol au cours de l'été 1973. Bulletin de la Société Zoologique de France. 1974;99:363-76.
20. Zaborski P, Dorizzi M, Pieau C. Sur l'utilisation de sérum anti-H-Y de souris pour la détermination du sexe génétique chez Emys orbicularis L. (Testudines, Emydidae). C R Acad Sci Paris. 1979;288(D):351-4.
21. Bull JJ. Evolution of sex determining mechanism. Menlo Park, Ca: The Benjamin/Cummings Publishing Company, Inc.; 1983.
22. Bull JJ, Vogt RC, Bulmer MG. Heritability of sex ratio in turtles with environmental sex determination. Evolution. 1982;36(2):333-41.
23. Janzen FJ. Heritable variation for sex ratio under environmental sex determination in the common snapping turtle (Chelydra serpentina). Genetics. 1992;131:155-61.
24. Girondot M. Analyse des facteurs génétiques et épigénétiques impliqués dans la détermination du sexe chez les reptiles [PhD Thesis]: Université Paris 6- Pierre et Marie Curie; 1993.
25. Rhen T, Lang JW. Among-family variation for environmental sex determination in reptiles. Evolution. 1998;52(5):1514-20.
26. Zaborski P, Dorizzi M, Pieau C. H-Y antigen expression in temperature sex-reversed turtles (Emys orbicularis). Differentiation. 1982;22:73-8.
27. Zaborski P, Dorizzi M, Pieau C. Temperature-dependent gonadal differentiation in the turtle Emys orbicularis: Concordance between sexual phenotype and serological H-Y antigen expression at threshold temperature. Differentiation. 1988;38:17-20.
28.Girondot M, Zaborski P, Servan J, Pieau C. Genetic contribution to sex determination in turtles with environmental sex determination. Genetical Research. 1994;63:117-27.
29.Radder RS, Quinn AE, Georges A, Sarre SD, Shine R. Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard. Biological Letters. 2008;4(2):176-8.
30.Demas S, Duronslet M, Wachtel S, Caillouet C, Nakamura D. Sex-specific DNA in reptiles with temperature sex determination. Journal of Experimental Zoology. 1990;253:319-24.
31.Girondot M, Servan J, Pieau C. Détermination du sexe sensible à la température chez une tortue (Emys orbicularis): importance du composant génétique. Bull Soc Ecophysiol. 1994;XIX:5-17.
32.Ewert MA, Etchberger CR, Nelson CE. Turtle sex-determining modes and TSD patterns, and some TSD patterns correlates. In: Valenzuela N, Bull JJ, editors. Temperature-dependent sex determination. Whashington: Smithsonian Books; 2004. p. 21-32.
33. Bowen BW, Nelson WS, Avise JC. A molecular phylogeny for marine turtles: Trait mapping, rate assessment, and conservation relevance. Proc Natl Acad Sci USA. 1993;90:5574-7.
34. Shaffer HB, Meylan P, McKnight ML. Tests of turtle phylogeny: molecular, morphological, and paleontological approaches. Systematic Biology. 1997;46(2):235-68.
35.Krenz JG, Janzen FJ. Turtle phylogeny: insights from a nuclear gene. American Zoologist. 2000 Dec;40(6):1092-.
36.Noonan BP. Does the phylogeny of pelomedusoid turtles reflect vicariance due to continental drift? Journal of Biogeography. 2000 Sep;27(5):1245-9.
37.Serb JM, Phillips CA, Iverson JB. Molecular phylogeny and biogeography of Kinosternon flavescens based on complete mitochondrial control region sequences. Molecular Phylogenetics and Evolution. 2001 Jan;18(1):149-62.
38.Fujita MK, Engstrom TN, Starkey DE, Shaffer HB. Turtle phylogeny: insights from a novel nuclear intron. Molecular Phylogenetics and Evolution. 2004;31(3).
39.Sasaki T, Takahashi K, Nikaido M, Miura S, Yasukawa Y, Okada N. First application of the SINE (short interspersed repetitive element) method to infer phylogenetic relationships in Reptiles: an example from the turtle superfamily Testudinoidea. Molecular Biology and Evolution. 2004;21(4):705-15.
40. Spinks PQ, Thomson RC, Lovely GA, Shaffer HB. Assessing what is needed to resolve a molecular phylogeny: simulations and empirical data from emydid turtles. BMC Evolutionary Biology. 2009;9(1):56.
41.Maddison WP, Maddison DR. MacClade: Analysis of phylogeny and character evolution. Sunderland, Massachusetts: Sinauer Associates; 1992.
42.Gunther K. Reptile egg incubation. Malabar, Florida: Krieger Publishers; 2005.
43.Girondot M, Fretey J, Prouteau I, Lescure J. Hatchling success for Dermochelys coriacea in a French Guiana hatchery. In: Richardson TH, Richardson JI, Donnelly M, editors. 10th Annual Workshop on Sea Turtle Biology and Conservation; Hilton Head, USA: NOAA Technical Memorandum NMFS-SEFC-278; 1990. p. 229-32.
44.Feeley JC, Treger MD. Penetration of turtle eggs by Salmonella braenderup. Public Health Reports. 1969;84(2):156.
45.Delmas V, Bonnet X, Girondot M, Prévot-Julliard A-C. Varying hydric conditions during incubation influence egg water exchange and hatchling phenotype in the red-eared slider turtle. Physiological and Biochemical Zoology. 2008;81(3):345-55.
46.Delmas V, Baudry E, Girondot M, Prévot-Julliard A-C. The righting response as a fitness index in freshwater turtles. Biological Journal of the Linnean Society. 2007;91(1):99-109.
47.O'Steen S. Embryonic temperature influences juvenile temperature choice and growth rate in snapping turtles Chelydra serpentina. Journal of Experimental Biology. 1998;201:439-49.
48.Bobyn ML, Brooks RJ. Interclutch and interpopulation variation in the effects of incubation conditions on sex, survival and growth of hatchling turtles (Chelydra serpentina). Journal of Zoology, London. 1994;233:233-57.
49.Vogt RC. Temperature controlled sex determination as a tool for turtle conservation. Chelonian Conservation and Biology. 1994;1(2):159-62.
50.Lovich JE. Possible demographic and ecologic consequences of sex ratio manipulation in turtles. Chelon Conserv Biol. 1996;2(1):114-7.
51.Mrosovsky N, Godfrey MH. Manipulating sex ratios: turtle speed ahead! Chelon Conserv Biol. 1995;1(3):238-40.
52.Girondot M, Fouillet H, Pieau C. Feminizing turtle embryos as a conservation tool. Conservation Biology. 1998;12(2):353-62.
53.Paitz RT, Gould AC, Holgersson MCN, Bowden RM. Temperature, phenotype, and the evolution of temperature-dependent sex determination: how do natural incubations compare to laboratory incubations? Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 2010;314B(1):86-93.
54.Booth DT. Influence of incubation temperature on hatchling phenotype in reptiles. Physiological and Biochemical Zoology. 2006;79(2):274-81.
55.Les HL, Paitz RT, Bowden RM. Living at extremes: development at the edges of viable temperature under constant and fluctuating conditions. Physiological and Biochemical Zoology. 2009;82(2):105-12.
56.Gibbons JW, Lovich JE. Sexual dimorphism in turtles with emphasis on the slider turtle (Trachemys scripta). Herpetological Monographs. 1990;4:1-29.
57.Wibbels T, Owens DW, Limpus CJ. Sexing juvenile sea turtles: is there an accurate and practical method? Chelonian Conservation and Biology. 2000;3:756-61.
58.Ernst CH, Barbour RW. Turtles of the World. Washington, DC Smithsonian Institution Press; 1989.
59.Valenzuela N, Adams DC, Bowden RM, Gauger AC. Geometric morphometric sex estimation for hatchling turtles: A powerful alternative for detecting subtle sexual shape dimorphism. Copeia. 2004;2004(4):735–42.
60.Burke RL, Jacobson ER, Griffith MJ, Guillette LJJ. Non-invasive sex identification of juvenile gopher and desert tortoises (genus Gopherus). Amphibia-Reptilia. 1994;15:183-9.
61.Delmas V. La tortue à tempes rouges, une espèce exotique et introduite en France : Premiers résultats sur les potentialités de colonisation de l'espèce [Thèse de Doctorat]. Orsay, France: Université Paris-Sud; 2006.
62.Ceriani SA, Wyneken J. Comparative morphology and sex identification of the reproductive system in formalin-preserved sea turtle specimens. Zoology. 2008;111:179-87.
63.Wood JR, Wood FE, Critchley KH, Wildt DE, Bush M. Laparoscopy on the Green sea turtle,Chelonia mydas. Brit J Herpetol. 1983;6:323–7.
64.Rostal DC, Grumbles JS, Lance VA, Spotila JR. Non-lethal sexing techniques for hatchling and immature Desert Tortoises (Gopherus agassizii). Herpetological Monographs. 1994;8:72-82.
65.Valverde RA. Corticosteroid dynamics in a free-ranging population of Olive Ridley sea turtles (Lepidochelys olivacea eschscholtz, 1829) at Playa Nancite, Costa Rica, as a function of their reproductive behavior [PhD Doctoral dissertation]. College Station, Texas: Texas A&M University; 1996.
66.Owens DW, Hendrickson JR, Lance V, Callard IP. A technic for determining sex of immatureChelonia mydas using a radio immunoassay. Herpetologica. 1978;34(3):270-3.
67.Coyne MS, Landry AM. Plasma testosterone sexing criteria and sex ratio of the Kemp’s ridley sea turtle (Lepidochelys kempii). In: Abreu-Grobois FA, Briseño-Duen R, Márquez R, Sarti L, editors. Proceedings of the Eighteenth Annual Symposium on Sea Turtle Biology and Conservation; Mazatlán, Sinaloa, México: U.S. Department of Commerce. NOAA Technical Memorandum NMFS-SEFSC-436; 2000. p. 286.
68.Willingham E, Baldwin R, Skipper JK, Crews D. Aromatase activity during embryogenesis in the brain and adrenal-kidney-gonad of the red-eared slider turtle, a species with temperature-dependent sex determination. General and Comparative Endocrinology. 2000 Aug;119(2):202-7.
69.Lance VA, Conley AJ, Mapes S, Steven C, Place AR. Does alligator testis produce estradiol? A comparison of ovarian and testicular aromatase. Biology of Reproduction. 2003;69:1201-7.
70.Gross TS, Crain DA, Bjorndal KA, Bolten AB, Carthy RR. Identification of sex in hatchling loggerhead turtles (Caretta caretta) by analysis of steroid concentrations in chorioallantoic/amniotic fluid. General and Comparative Endocrinology. 1995 Aug;99(2):204-10.
71.Sarre S, Georges A, Quinn A. The ends of a continuum: genetic and temperature-dependent sex determination in reptiles. Bioessays. 2004;26(6):639-45.
72.Senneke D. Declared turtle trade from the United States.  Vacaville, CA: World Chelonian Trust; 2010 [cited 2010 March, 10th 2010]; Available from:http://www.chelonia.org/articles/us/USmarketintropage.htm.
73.Paukstis GL, Janzen FJ, editors. Sex determination in reptiles: summary of effects of constant temperatures of incubation on sex ratios of offspring 1990.

Source(s) of Funding

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CNRS and University Paris Sud

 

Competing Interests

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None

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