Gonadal sex differentiation in Alligator mississippiensis, a species with temperature-dependent sex determination

1993 ◽  
Vol 273 (1) ◽  
pp. 149-162 ◽  
Author(s):  
Craig A. Smith ◽  
Jean M. P. Joss
Keyword(s):  
Sex Determination ◽  
Sex Differentiation ◽  
Alligator Mississippiensis ◽  
Temperature Dependent

Environmental regulation of sex determination in reptiles

1988 ◽  
Vol 322 (1208) ◽  
pp. 19-39 ◽  
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Growth And Development ◽  
Incubation Temperature ◽  
Sex Differentiation ◽  
Developmental Time ◽  
Alligator Mississippiensis ◽  
Phylogenetic Implications ◽  
History Of ◽  
Determining Factor

The various patterns of environmental sex determination in squamates, chelonians and crocodilians are described. High temperatures produce males in lizards and crocodiles but females in chelonians. Original experiments on the effects of incubation at 30 °C (100% females) or 33 °C (100% males) on development in Alligator mississippiensis are described. These include an investigation of the effect of exposing embryos briefly to a different incubation temperature on the sex ratio at hatching, and a study of the effects of 30 °C and 33 °C on growth and development of alligator embryos and gonads. A 7-day pulse of one temperature on the background of another was insufficient to alter the sex ratio dramatically. Incubation at 33 °C increased the rate of growth and development of alligator embryos. In particular, differentiation of the gonad at 33 °C was enhanced compared with 30 °C. A hypothesis is developed to explain the mechanism of temperature-dependent sex determination (TSD) in crocodilians. The processes of primary sex differentiation are considered to involve exposure to a dose of some male-determining factor during a specific quantum of developmental time during early incubation. The gene that encodes for the male- determining factor is considered to have an optimum temperature (33 °C). Any change in the temperature affects the expression o f this gene and affects the dose or quantum embryos are exposed to. In these cases there is production of females by default. The phylogenetic implications of TSD for crocodilians, and reptiles in particular, are related to the life history of the animal from conception to sexual maturity. Those animals that develop under optimal conditions grow fastest and largest and become male. A general association between the size of an animal and its sex is proposed for several types of vertebrate.

The temperature-sensitive period (TSP) during incubation of broad-snouted caiman (Caiman latirostris) eggs

2007 ◽  
Vol 28 (1) ◽  
pp. 123-128 ◽  
Author(s):  
Carlos Piña ◽  
Alejandro Larriera ◽  
Pablo Siroski ◽  
Luciano Verdade ◽  
Valentine Lance
Keyword(s):  
Sex Determination ◽  
Egg Laying ◽  
Alligator Mississippiensis ◽  
Sensitive Period ◽  
Temperature Sensitive ◽  
American Alligator ◽  
Temperature Dependent ◽  
The Many

AbstractAll crocodiles studied to date exhibit temperature-dependent sex determination. During the many weeks from egg laying to hatch there is a period of 10 to 15 d in the middle third of incubation (in the American alligator) during which the sex of the embryo is irreversibly fixed, referred to as the temperature-sensitive period or TSP. In this work we investigated the TSP in Caiman latirostris eggs incubated at female-inducing and male-inducing temperatures (29° C and 33° C respectively) by switching eggs from 29° C to 33° C and vice versa at timed interval throughout incubation. Compared to Alligator mississippiensis the duration of TSP was longer, and the onset of TSP was at an earlier stage of incubation.

scholarly journals RNA-seq analysis of the gonadal transcriptome during Alligator mississippiensis temperature-dependent sex determination and differentiation

BMC Genomics ◽  
2016 ◽  
Vol 17 (1) ◽  
Author(s):  
Ryohei Yatsu ◽  
Shinichi Miyagawa ◽  
Satomi Kohno ◽  
Benjamin B. Parrott ◽  
Katsushi Yamaguchi ◽  
...  
Keyword(s):  
Sex Determination ◽  
Alligator Mississippiensis ◽  
Rna Seq ◽  
Temperature Dependent

scholarly journals Thyroid hormone modulates offspring sex ratio in a turtle with temperature-dependent sex determination

2016 ◽  
Vol 283 (1841) ◽  
pp. 20161206 ◽  
Author(s):  
Bao-Jun Sun ◽  
Teng Li ◽  
Yi Mu ◽  
Jessica K. McGlashan ◽  
Arthur Georges ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Sex Ratio ◽  
Sex Determination ◽  
Sex Differentiation ◽  
Developmental Rate ◽  
Temperature Dependent ◽  
Gene Encoding ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Underlying Mechanisms

The adaptive significance of temperature-dependent sex determination (TSD) has attracted a great deal of research, but the underlying mechanisms by which temperature determines the sex of a developing embryo remain poorly understood. Here, we manipulated the level of a thyroid hormone (TH), triiodothyronine (T 3 ), during embryonic development (by adding excess T 3 to the eggs of the red-eared slider turtle Trachemys scripta , a reptile with TSD), to test two competing hypotheses on the proximate basis for TSD: the developmental rate hypothesis versus the hormone hypothesis . Exogenous TH accelerated embryonic heart rate (and hence metabolic rate), developmental rate, and rates of early post-hatching growth. More importantly, hyperthyroid conditions depressed expression of Cyp19a1 (the gene encoding for aromatase) and levels of oestradiol, and induced more male offspring. This result is contrary to the direction of sex-ratio shift predicted by the developmental rate hypothesis , but consistent with that predicted by the hormone hypothesis . Our results suggest an important role for THs in regulating sex steroid hormones, and therefore, in affecting gonadal sex differentiation in TSD reptiles. Our study has implications for the conservation of TSD reptiles in the context of global change because environmental contaminants may disrupt the activity of THs, and thereby affect offspring sex in TSD reptiles.

scholarly journals Molecular evolution of Dmrt1 accompanies change of sex-determining mechanisms in reptilia

2014 ◽  
Vol 10 (12) ◽  
pp. 20140809 ◽  
Author(s):  
Daniel E. Janes ◽  
Christopher L. Organ ◽  
Rami Stiglec ◽  
Denis O'Meally ◽  
Stephen D. Sarre ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Molecular Evolution ◽  
Sex Determination ◽  
Sex Differentiation ◽  
Evolution Of Sex ◽  
Temperature Dependent ◽  
Exon 2 ◽  
Ancestral Condition ◽  
Genotypic Sex Determination

In reptiles, sex-determining mechanisms have evolved repeatedly and reversibly between genotypic and temperature-dependent sex determination. The gene Dmrt1 directs male determination in chicken (and presumably other birds), and regulates sex differentiation in animals as distantly related as fruit flies, nematodes and humans. Here, we show a consistent molecular difference in Dmrt1 between reptiles with genotypic and temperature-dependent sex determination. Among 34 non-avian reptiles, a convergently evolved pair of amino acids encoded by sequence within exon 2 near the DM-binding domain of Dmrt1 distinguishes species with either type of sex determination. We suggest that this amino acid shift accompanied the evolution of genotypic sex determination from an ancestral condition of temperature-dependent sex determination at least three times among reptiles, as evident in turtles, birds and squamates. This novel hypothesis describes the evolution of sex-determining mechanisms as turnover events accompanied by one or two small mutations.

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