Effects of Incubation Conditions on Sex Determination, Hatching Success, and Growth of Hatchling Desert Tortoises, Gopherus agassizii

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

10.26686/wgtn.16922668.v1 ◽

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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Temperature-sex determination in Podocnemis expansa (Testudines, Podocnemididae)

Iheringia Série Zoologia ◽

10.1590/s0073-47212011000200001 ◽

2011 ◽

Vol 101 (3) ◽

pp. 151-155 ◽

Cited By ~ 2

Author(s):

Kelly Bonach ◽

Adriana Malvasio ◽

Eliana R. Matushima ◽

Luciano M. Verdade

Keyword(s):

Sex Determination ◽

Success Rate ◽

Incubation Period ◽

Clutch Size ◽

Hatching Success ◽

Incubation Temperature ◽

Small Sample ◽

Mato Grosso ◽

Araguaia River ◽

Podocnemis Expansa

This study has been carried out at the central region of the Araguaia river on the border between the states of Goiás and Mato Grosso in the Brazilian Amazon Basin from September to December 2000. We recorded temperature fluctuation, clutch-size, incubation period and hatching success rate and hatchlings' sex ratio of five nests of Podocnemis expansa (Schweigger, 1812). Despite the relatively small sample size we infer that: a) nests of P. expansa in the central Araguaia river have a lower incubation temperature than nests located further south; however, incubation period is shorter, hatching success rate is lower and clutch-size is larger; b) Podocnemis expansa may present a female-male-female (FMF) pattern of temperature sex-determination (TSD); c) thermosensitive period of sex determination apparently occur at the last third of the incubation period; and, d) future studies should prioritize the relationship between temperature variation (i.e., range and cycle) and embryos development, survivorship and sex determination.

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Hydric environment and sex determination in the flatback turtle (Natator depressus Garman) (Chelonia : Cheloniidae)

Australian Journal of Zoology ◽

10.1071/zo00049 ◽

2000 ◽

Vol 48 (6) ◽

pp. 653 ◽

Cited By ~ 14

Author(s):

Suhashini Hewavisenthi ◽

C. John Parmenter

Keyword(s):

Sex Determination ◽

Histological Examination ◽

Constant Temperature ◽

Hatching Success ◽

Temperature Range ◽

Incubation Duration ◽

Natator Depressus ◽

Pivotal Temperature

Eggs of Natator depressus (from eastern Queensland, Australia) were incubated at a constant temperature of 29.5˚C on vermiculite substrate with three different moisture levels: wet (~–180 kPa), intermediate (~–1200 kPa) and dry (~–2000 kPa). The male : female ratios on wet, intermediate and dry substrates were 8 : 7, 5 : 5 and 5 : 8 respectively. Sex determination was not influenced by the hydric environment but was significantly affected by different clutches. A clutch with smaller eggs appeared to produce a higher proportion of females. The pivotal temperature was close to 29.5˚C, with a possibly narrow transitional temperature range of 1˚C. Visual designation of sex was confirmed (100%) by histological examination. Hatching success and the incubation duration were not influenced by the hydric environment.

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

10.26686/wgtn.16922668 ◽

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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Carbon dioxide influences environmental sex determination in two species of turtles

Amphibia-Reptilia ◽

10.1163/156853802760061813 ◽

2002 ◽

Vol 23 (2) ◽

pp. 169-175 ◽

Cited By ~ 1

Author(s):

Michael Ewert ◽

John Phillips ◽

Cory Etchberger ◽

Craig Nelson

Keyword(s):

Carbon Dioxide ◽

Sex Determination ◽

Hatching Success ◽

Sex Ratios ◽

Elevated Carbon Dioxide ◽

Gas Mixtures ◽

Trachemys Scripta ◽

Environmental Sex Determination ◽

Temperature Dependent ◽

Biogenic Carbon

AbstractEggs of wild caught Trachemys scripta and Graptemys pseudogeographica kohnii, two emydine turtles known to have temperature-dependent sex determination, were incubated at 28.5°C in boxes aerated with one of four gas mixtures (two in G. p. kohnii). Across all eggs, elevated levels of carbon dioxide significantly feminized sex ratios in both species and also reduced hatching success. When eggs were grouped into clutches, all comparisons between 0% and elevated carbon dioxide showed feminization in the portions of the clutches at elevated carbon dioxide, a statistically significant result for T. scripta. Accumulation of biogenic carbon dioxide from embryonic respiration and other sources is thus likely to affect sex ratios in natural nests under some conditions, perhaps through an effect on some aspects of embryonic pH.

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Sex determination

AccessScience ◽

10.1036/1097-8542.617400 ◽

2015 ◽

Keyword(s):

Sex Determination

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Sex determination banned in India

Nature ◽

10.1038/379201e0 ◽

1996 ◽

Vol 379 (6562) ◽

pp. 201-201

Keyword(s):

Sex Determination

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Sex determination and Y chromosome constitutive heterochromatin

Current Research in Biochemistry and Molecular Biology ◽

10.33702/crbmb.2019.1.1.1 ◽

2019 ◽

Vol 1 (1) ◽

pp. 1-5

Author(s):

Abyt Ibraimov

Keyword(s):

Sex Determination ◽

Y Chromosome ◽

Constitutive Heterochromatin ◽

Sex Differentiation ◽

Secondary Sexual Characteristics ◽

Biological Meaning ◽

Heterochromatin Block ◽

Sexual Characteristics ◽

Open Question ◽

Efficient Elimination

In many animals, including us, the genetic sex is determined at fertilization by sex chromosomes. Seemingly, the sex determination (SD) in human and animals is determined by the amount of constitutive heterochromatin on Y chromosome via cell thermoregulation. It is assumed the medulla and cortex tissue cells in the undifferentiated embryonic gonads (UEG) differ in vulnerability to the increase of the intracellular temperature. If the amount of the Y chromosome constitutive heterochromatin is enough for efficient elimination of heat difference between the nucleus and cytoplasm in rapidly growing UEG cells the medulla tissue survives. Otherwise it doomed to degeneration and a cortex tissue will remain in the UEG. Regardless of whether our assumption is true or not, it remains an open question why on Y chromosome there is a large constitutive heterochromatin block? What is its biological meaning? Does it relate to sex determination, sex differentiation and development of secondary sexual characteristics? If so, what is its mechanism: chemical or physical? There is no scientifically sound answer to these questions.

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