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.

scholarly journals Molecular and Cellular Mechanisms Underlying Temperature-Dependent Sex Determination in Turtles

2021 ◽  
pp. 1-9
Author(s):  
Horacio Merchant-Larios ◽  
Verónica Díaz-Hernández ◽  
Diego Cortez
Keyword(s):  
Animal Models ◽  
Sex Determination ◽  
Incubation Temperature ◽  
State Of The Art ◽  
Current Understanding ◽  
Temperature Dependent ◽  
Cellular Mechanisms ◽  
Male Phenotype ◽  
History Of ◽  
Reptilian Species

The discovery in mammals that fetal testes are required in order to develop the male phenotype inspired research efforts to elucidate the mechanisms underlying gonadal sex determination and differentiation in vertebrates. A pioneer work in 1966 that demonstrated the influence of incubation temperature on sexual phenotype in some reptilian species triggered great interest in the environment’s role as a modulator of plasticity in sex determination. Several chelonian species have been used as animal models to test hypotheses concerning the mechanisms involved in temperature-dependent sex determination (TSD). This brief review intends to outline the history of scientific efforts that corroborate our current understanding of the state-of-the-art in TSD using chelonian species as a reference.

scholarly journals Temperature-Dependent Sex Determination and Artificial Incubation of Tuatara, Sphenodon Punctatus

2021 ◽  
Author(s):  
◽  
Nicola J Nelson
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Hatching Success ◽  
Conservation Management ◽  
Incubation Temperature ◽  
Management Tool ◽  
Relative Fitness ◽  
Temperature Dependent ◽  
Sphenodon Punctatus ◽  
Artificial Incubation

<p>Juveniles resulting from artificially induced and incubated eggs are often used to found or augment populations of rare reptiles, but both procedures may compromise the health of hatchlings or their fitness in natural environments. I aimed to test whether these procedures affected size or performance of juvenile tuatara, Sphenodon punctatus, New Zealand reptiles with temperature-dependent sex determination (TSD). Size and performance are phenotypic traits likely to influence fitness and eventual lifetime reproductive success, and are thus important measures of the suitability of artificial induction and incubation techniques for conservation management. I incubated 320 tuatara eggs artificially at 18, 21 and 22ºC; 52% of these were obtained by induction, the remainder were collected from natural nests. An additional 25 natural nests were left intact for investigation of TSD and effects of incubation temperature in nature. Juveniles from all incubation regimes were kept for ten months post-hatching in similar rearing conditions and sexed by laparoscopy. Induced eggs were significantly smaller than naturally laid eggs, and resulted in significantly smaller hatchlings, even when variation among clutches was accounted for. Incubation temperature did not greatly influence size at hatching, but was an important determinant of size by ten months of age; initial egg mass was the most important factor affecting size of hatchlings. Data indicate that TSD occurs in nature. The sex of hatchlings from 21 nests was investigated: 10 nests produced 100% male hatchlings, 4 nests produced 100% female hatchlings, and only 7 nests produced mixed sex ratios which ranged from 11% to 88% males. Sex of juveniles was related to temperature with a larger proportion of males produced in warmer nests. The overall percentage of male hatchlings in natural nests was 64%. Hatching success was 65% from natural nests during the 1998/99 season. Incubation temperatures throughout the year ranged from 2.9 to 34.4ºC. Global warming is likely to skew the hatchling sex ratio towards males if female tuatara are unable to select nest sites according to environmental cues. Evidence from size patterns of tuatara incubated in natural nests supports differential fitness models for the adaptive significance of TSD. The evaluation of artificial incubation as a conservation management tool demonstrated that it is a procedure that benefits conservation as it can be used reliably to produce founders; hatching success was 94% during this study. The sex ratio of artificially incubated juveniles can be easily manipulated; the pivotal temperature lies between 21 and 22ºC. Constant artificial incubation conditions resulted in larger juveniles by ten months of age than those from natural incubation. Naturally incubated juvenile tuatara, however, were faster for their size, their reaction norm to predator stimuli was to run, and they were possibly more aggressive, suggesting naturally incubated juveniles could survive better in nature. No firm conclusions can be reached on the quality of artificially incubated juvenile tuatara because further research will be required to establish the relevance of performance test results in nature and consequences of incubation regimes in the longer term with respect to relative fitness of individuals.</p>

scholarly journals Improved genome assembly of American alligator genome reveals conserved architecture of estrogen signaling

2016 ◽  
Author(s):  
Edward S. Rice ◽  
Satomi Kohno ◽  
John St. John ◽  
Son Pham ◽  
Jonathan Howard ◽  
...  
Keyword(s):  
Sex Determination ◽  
Genome Assembly ◽  
Critical Period ◽  
Incubation Temperature ◽  
Current Model ◽  
Alligator Mississippiensis ◽  
Estrogen Signaling ◽  
Sensitive Period ◽  
Temperature Sensitive ◽  
American Alligator

AbstractThe American alligator, Alligator mississippiensis, like all crocodilians, has temperature-dependent sex determination, in which the sex of an embryo is determined by the incubation temperature of the egg during a critical period of development. The lack of genetic differences between male and female alligators leaves open the question of how the genes responsible for sex determination and differentiation are regulated. One insight into this question comes from the fact that exposing an embryo incubated at male-producing temperature to estrogen causes it to develop ovaries. Because estrogen response elements are known to regulate genes over long distances, a contiguous genome assembly is crucial for predicting and understanding its impact.We present an improved assembly of the American alligator genome, scaffolded with in vitro proximity ligation (Chicago) data. We use this assembly to scaffold two other crocodilian genomes based on synteny. We perform RNA sequencing of tissues from American alligator embryos to find genes that are differentially expressed between embryos incubated at male-versus female-producing temperature. Finally, we use the improved contiguity of our assembly along with the current model of CTCF-mediated chromatin looping to predict regions of the genome likely to contain estrogen-responsive genes. We find that these regions are significantly enriched for genes with female-biased expression in developing gonads after the critical period during which sex is determined by incubation temperature. We thus conclude that estrogen signaling is a major driver of female-biased gene expression in the post-temperature sensitive period gonads.

Temperature-Sensitive Period of Sex Determination in the Atlantic Silverside, Menidia menidia

1986 ◽  
Vol 43 (3) ◽  
pp. 514-520 ◽  
Author(s):  
David O. Conover ◽  
Mark H. Fleisher
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Sex Differentiation ◽  
Sensitive Period ◽  
Temperature Sensitive ◽  
Measurable Effect ◽  
Menidia Menidia ◽  
Atlantic Silverside ◽  
Gonad Differentiation ◽  
Hormone Sensitive

We investigated the timing and duration of the temperature-sensitive period of development in the Atlantic silverside, Menidia menidia, by measuring the sex ratio in groups of larvae shifted reciprocally among low and high temperatures as development progressed. The sensitive period of sex determination was dependent on body size, rather than age, and occurred during the middle to later stages of larval development when fish were between 8 and 21 mm in total length. Sex determination was irreversibly fixed earlier in development (i.e. at 15 mm in length) at higher than at lower temperatures. Higher, male-producing temperatures therefore appear to more strongly effect sex determination than do lower, female-producing temperatures. Temperature prior to, or after, the sensitive period had no measurable effect on sex ratio. From histological examination we suggest that gonad differentiation coincided with the end of the temperature-sensitive period. The timing and duration of the temperature-sensitive period in M. menidia is generally similar to the hormone-sensitive period identified in other fishes. Both phenomena reveal a specific developmental period during which the course of primary sex differentiation in fishes is labile.

Intraspecific genome size variation in a turtle (Trachemys scripta) exhibiting temperature-dependent sex determination

1991 ◽  
Vol 69 (9) ◽  
pp. 2306-2310 ◽  
Author(s):  
Samuel F. Lockwood ◽  
Brenden S. Holland ◽  
John W. Bickham ◽  
Brian G. Hanks ◽  
James J. Bull
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Genome Size ◽  
Incubation Temperature ◽  
Size Variation ◽  
Developmental Rate ◽  
Trachemys Scripta ◽  
Temperature Dependent ◽  
Genome Size Variation ◽  
Different Temperatures

Variation in genome size within and among populations of the pond slider, Trachemys scripta, a species with temperature-dependent sex determination, was investigated. Because genome size has been shown to affect developmental rate in various organisms, as does incubation temperature, it was hypothesized that genome size could influence sex determination in species with environmental sex determination. Significant variation in DNA content was found between geographic populations and among clutches. No significant differences in mean genome size were observed among samples incubated at different temperatures or between sexes of turtles hatched at a temperature that yields a mixed sex ratio. Thus, it appears that sex determination in T. scripta is accomplished in the absence of sex-specific and incubation-temperature-specific differences in genome size. Preliminary data from two populations, however, suggest that genome size may be significantly correlated with the threshold incubation temperature at which a mixed sex ratio is produced.

Absence of temperature-dependent sex determination in northern populations of two cyprinodontid fishes

1991 ◽  
Vol 69 (2) ◽  
pp. 530-533 ◽  
Author(s):  
D. O. Conover ◽  
S. B. DeMond
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Life Histories ◽  
Laboratory Experiments ◽  
Fundulus Heteroclitus ◽  
Incubation Temperature ◽  
Effect Of Temperature ◽  
Temperature Dependent ◽  
Young Of The Year ◽  
Embryonic And Larval Development

We tested for an effect of temperature during embryonic and larval development on the sex ratio of offspring in two cyprinodontid fishes (Fundulus heteroclitus and Cyprinodon variegatus) having life histories in which temperature-dependent sex determination might be expected to occur. In both species, field collections showed that as young of the year recruited to the population, the sex ratio did not vary over time, nor did it deviate from 1:1. In laboratory experiments, there was no influence of incubation temperature on sex ratio in either species and sex ratios were near unity in all treatments. Although there was no evidence of temperature-dependent sex determination in the populations we studied, this result should be confirmed on other populations before it is generalized to the species level.

Transitional range of temperature, pivotal temperatures and thermosensitive stages for sex determination in reptiles

1991 ◽  
Vol 12 (2) ◽  
pp. 169-179 ◽  
Author(s):  
C. Pieau ◽  
N. Mrosovsky
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Environmental Effects ◽  
Sexual Differentiation ◽  
Incubation Temperature ◽  
Sensitive Stage ◽  
Thermosensitive Period

AbstractThe function relating phenotypic sex ratio to incubation temperature in reptiles can vary in a number of ways in addition to simple differences in the temperatures giving 50% of each sex. This paper offers terminology and definitions for describing these relationships. These definitions accomodate interactions between genetic and environmental effects on sexual differentiation, and variability within populations. The paper also discusses the concept of a sensitive stage/period within incubation during which temperature can affect the direction of sexual differentiation. Thermosensitive period has previously been assessed in a variety of ways. A suggestion for a more general way of defining thermosensitive stage/period is made.

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 Temperature-Dependent Sex Determination and Artificial Incubation of Tuatara, Sphenodon Punctatus

2021 ◽  
Author(s):  
◽  
Nicola J Nelson
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Hatching Success ◽  
Conservation Management ◽  
Incubation Temperature ◽  
Management Tool ◽  
Relative Fitness ◽  
Temperature Dependent ◽  
Sphenodon Punctatus ◽  
Artificial Incubation

<p>Juveniles resulting from artificially induced and incubated eggs are often used to found or augment populations of rare reptiles, but both procedures may compromise the health of hatchlings or their fitness in natural environments. I aimed to test whether these procedures affected size or performance of juvenile tuatara, Sphenodon punctatus, New Zealand reptiles with temperature-dependent sex determination (TSD). Size and performance are phenotypic traits likely to influence fitness and eventual lifetime reproductive success, and are thus important measures of the suitability of artificial induction and incubation techniques for conservation management. I incubated 320 tuatara eggs artificially at 18, 21 and 22ºC; 52% of these were obtained by induction, the remainder were collected from natural nests. An additional 25 natural nests were left intact for investigation of TSD and effects of incubation temperature in nature. Juveniles from all incubation regimes were kept for ten months post-hatching in similar rearing conditions and sexed by laparoscopy. Induced eggs were significantly smaller than naturally laid eggs, and resulted in significantly smaller hatchlings, even when variation among clutches was accounted for. Incubation temperature did not greatly influence size at hatching, but was an important determinant of size by ten months of age; initial egg mass was the most important factor affecting size of hatchlings. Data indicate that TSD occurs in nature. The sex of hatchlings from 21 nests was investigated: 10 nests produced 100% male hatchlings, 4 nests produced 100% female hatchlings, and only 7 nests produced mixed sex ratios which ranged from 11% to 88% males. Sex of juveniles was related to temperature with a larger proportion of males produced in warmer nests. The overall percentage of male hatchlings in natural nests was 64%. Hatching success was 65% from natural nests during the 1998/99 season. Incubation temperatures throughout the year ranged from 2.9 to 34.4ºC. Global warming is likely to skew the hatchling sex ratio towards males if female tuatara are unable to select nest sites according to environmental cues. Evidence from size patterns of tuatara incubated in natural nests supports differential fitness models for the adaptive significance of TSD. The evaluation of artificial incubation as a conservation management tool demonstrated that it is a procedure that benefits conservation as it can be used reliably to produce founders; hatching success was 94% during this study. The sex ratio of artificially incubated juveniles can be easily manipulated; the pivotal temperature lies between 21 and 22ºC. Constant artificial incubation conditions resulted in larger juveniles by ten months of age than those from natural incubation. Naturally incubated juvenile tuatara, however, were faster for their size, their reaction norm to predator stimuli was to run, and they were possibly more aggressive, suggesting naturally incubated juveniles could survive better in nature. No firm conclusions can be reached on the quality of artificially incubated juvenile tuatara because further research will be required to establish the relevance of performance test results in nature and consequences of incubation regimes in the longer term with respect to relative fitness of individuals.</p>

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