Incubation temperature affects sexual differentiation, incubation time, and posthatching survival in desert tortoises (Gopherus agassizi)

1995 ◽  
Vol 73 (11) ◽  
pp. 2091-2097 ◽  
Author(s):  
Vanessa Lewis-Winokur ◽  
Robert M. Winokur

Eggs of captive desert tortoises. Gopherus agassizi, incubated at six temperatures (25, 27, 28, 29, 29.4, and 31 °C) produced 107 specimens. Eggs incubated at 31 °C resulted in a male to female sex ratio of 5:7; all other incubation temperatures resulted in males only. Histological examination of gonads revealed that the testes of newly hatched to 3-month-old individuals showed incomplete and poorly developed seminiferous tubules. Female gonads showed a thickened cortex. Incubation times were longer at lower temperatures. Both hatching success and hatchling survivorship were lower at lower incubation temperatures. We confirm that temperature-dependent sex determination occurs in desert tortoises and that the pivotal temperature is between 31 and 32 °C.

2021 ◽  
Author(s):  
◽  
Kelly Maree Hare

<p>The conditions under which reptilian eggs are incubated affect survival probability and physiological attributes of the progeny. The egg-laying skink, Oligosoma suteri, is the only endemic oviparous lizard in New Zealand. No controlled laboratory incubation had previously been undertaken, and thus no information was available on the requirements for successful captive incubation. I studied the effects of incubation regime on the eggs and hatchlings of O. suteri to four months of age. Oligosoma suteri eggs (n = 174) were randomly distributed among three constant incubation temperatures (18°C, 22°C and 26°C) and two water potentials (-120 kPa and -270 kPa). Hatching success and hatchling survival were greatest at 22°C and 26°C, with hatchlings from 18°C incubation suffering from physical abnormalities. Incubation regime and maternal influence did not affect sex of individuals, with equal sex ratios occurring from each incubation treatment. Hatchlings from the 22°C and -120 kPa incubation treatments were larger, for most measurements, and warmer incubation temperatures resulted in increased growth rates. Juveniles from 22°C and 26°C and individuals with greater mass per unit length (condition index) sprinted faster over 0.25 m. Sprint speed was positively correlated with ambient temperature. At four months of age sprint speed decreased in 18°C individuals and individuals incubated at 26°C and -270 kPa compared to their performance at one month. The results suggest that the most successful captive incubation regime for O. suteri is 22°C and -120 kPa. This study also shows that temperature-dependent sex determination does not occur in O. suteri, but that fitness traits are influenced by incubation temperature.</p>


2021 ◽  
Author(s):  
◽  
Nicola J Nelson

<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>


1991 ◽  
Vol 69 (10) ◽  
pp. 2693-2696 ◽  
Author(s):  
Thane Wibbels ◽  
Flavius C. Killebrew ◽  
David Crews

Sex determination was investigated in Cagle's map turtle, Graptemys caglei, which has a restricted distribution which is the southernmost of all Graptemys species. This species exhibits temperature-dependent sex determination, with high incubation temperatures producing only females and low temperatures producing only males. The estimated pivotal temperature (approximately 30.0 °C) is higher than those reported for other species of Graptemys in North America; however, the interspecific variations in pivotal temperature are small (approximately 0.5–1.0 °C). Temperature appears to affect the ovarian or testicular nature of the gonads in an "all or none" fashion, but exerts a graded effect on the length of ovaries. In addition, temperature appears to exert a graded effect on the regression of the oviducts in males. The occurrence of temperature-dependent sex determination in this species is also of conservational importance, since alterations to a single river system could potentially impact the reproductive success of this species by changing nest temperatures and, thus, population sex ratio(s).


2021 ◽  
Author(s):  
◽  
Nicola J Nelson

<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>


2021 ◽  
Author(s):  
◽  
Kelly Maree Hare

<p>The conditions under which reptilian eggs are incubated affect survival probability and physiological attributes of the progeny. The egg-laying skink, Oligosoma suteri, is the only endemic oviparous lizard in New Zealand. No controlled laboratory incubation had previously been undertaken, and thus no information was available on the requirements for successful captive incubation. I studied the effects of incubation regime on the eggs and hatchlings of O. suteri to four months of age. Oligosoma suteri eggs (n = 174) were randomly distributed among three constant incubation temperatures (18°C, 22°C and 26°C) and two water potentials (-120 kPa and -270 kPa). Hatching success and hatchling survival were greatest at 22°C and 26°C, with hatchlings from 18°C incubation suffering from physical abnormalities. Incubation regime and maternal influence did not affect sex of individuals, with equal sex ratios occurring from each incubation treatment. Hatchlings from the 22°C and -120 kPa incubation treatments were larger, for most measurements, and warmer incubation temperatures resulted in increased growth rates. Juveniles from 22°C and 26°C and individuals with greater mass per unit length (condition index) sprinted faster over 0.25 m. Sprint speed was positively correlated with ambient temperature. At four months of age sprint speed decreased in 18°C individuals and individuals incubated at 26°C and -270 kPa compared to their performance at one month. The results suggest that the most successful captive incubation regime for O. suteri is 22°C and -120 kPa. This study also shows that temperature-dependent sex determination does not occur in O. suteri, but that fitness traits are influenced by incubation temperature.</p>


1977 ◽  
Author(s):  
K. Breddin ◽  
H.J. Krzywanek

ADP-, collagen and epinephrine-induced aggregation change markedly if citrate blood or PRP are kept at different incubation temperatures or/and if the time interval between blood sampling and testing varies. With a growing time interval the response of PRP to ADP, collagen or epinephrine increases. Desaggregation after ADP-aggregation decreases with time. If PRP is incubated at 4°C or 10°C aggregation is increased in comparison with room temperature. At 37°C aggregation is markedly inhibited. This inhibitory effect is almost fully reversible several hours after blood sampling. Corresponding results were obtained with PAT III, measuring spontaneous aggregation tendency. Morphologic platelet changes show some correlation with the time and temperature dependent changes of the aggregation pattern. In clinical studies the time interval between blood sampling and testing and the incubation temperature of PRP should be strictly controlled. If enhanced platelet aggregation is to be studied the time interval between venepuncture and performance of the test should be 30 - 60 min for ADP-or collagen-induced aggregation and between 90 and 360 min for PAT III. PRP should always be kept at 20 - 25°C.


2008 ◽  
Vol 275 (1652) ◽  
pp. 2703-2706 ◽  
Author(s):  
Yvonne A Eiby ◽  
Jessica Worthington Wilmer ◽  
David T Booth

Sex ratios have important evolutionary consequences and are often biased by environmental factors. The effect of developmental temperature on offspring sex ratios has been widely documented across a diverse range of taxa but has rarely been investigated in birds and mammals. However, recent field observations and artificial incubation experiments have demonstrated that the hatching sex ratio of a megapode, the Australian brush-turkey ( Alectura lathami ), varied with incubation temperature; more females hatched at high incubation temperatures and more males hatched at low temperatures. Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.


2021 ◽  
Vol 4 (4) ◽  
pp. 321-330
Author(s):  
Randy Calderón Peña ◽  
Julia Azanza Ricardo

Elevated incubation temperatures of sea turtle nests decrease hatching success and alter the resulting hatchlings' morphology. There is an absence of studies assessing the relationships between temperature and hatching success in Cuba, even when they could improve understanding the limits of thermal tolerance in these species. This study evaluated the influence of incubation temperature on hatching success and phenotypic malformations in green turtle hatchlings (Chelonia mydas); and analyzed the temporal variation in hatching success on the studied beaches. In 48 green turtles nests distributed along two beaches, incubation temperature and hatching success were recorded between 2014 and 2019. Increasing incubation temperature caused a decrease in the hatching success and an increase in the frequency of supernumerary scutes. Despite the elevated temperatures (average > 30°C), hatching was higher than 80%. Significant differences in hatching success were only observed among seasons for nests in Antonio Beach (lower values in 2016 and 2019 compared to 2014).


1994 ◽  
Vol 143 (2) ◽  
pp. 279-289 ◽  
Author(s):  
D Crews ◽  
J M Bergeron

Abstract In many turtles the temperature during the middle of incubation determines the gonadal sex of the hatchling. In the red-eared slider turtle (Trachemys scripta), an incubation temperature of 26 °C results in all male offspring, whereas an incubation temperature of 31 °C results in all female offspring; at temperatures intermediate to these (e.g. 29, 29·2, 29·4 °C) a mixed sex ratio is obtained. Administration of exogenous oestrogens will overcome the effects of an all-male producing incubation temperature to cause female sex determination, whereas administration of exogenous dihydrotestosterone (DHT) or testosterone to eggs incubating at an all-female temperature will have no discernible effect. Administration of DHT will cause male sex determination only if administered at intermediate incubation temperatures whereas administration of testosterone to eggs incubating at all male-producing and male-biased intermediate temperatures results in a significant number of female offspring, an effect presumably due to aromatization of testosterone to oestradiol (OE2), Since testosterone serves as the precursor to both DHT and OE2, being metabolized by reductase and aromatase respectively, three experiments were conducted to determine whether various putative reductase and aromatase inhibitors would overcome the effect of incubation temperature. First, while administration of testosterone to eggs incubating at all male-producing and male-biased intermediate temperatures produced females in a dose- and temperature-dependent manner, significant numbers of intersex individuals resulted from high dosage testosterone treatment to eggs incubating at a female-biased intermediate temperature. The reductase inhibitors 4MA and MK906 were capable of producing female offspring if administered at intermediate temperatures, but not in a dose-dependent fashion. Administration of the aromatase inhibitors CGS16949A and CGS20267 resulted in male offspring at both female-biased intermediate and at all female-producing temperatures in a dose-dependent fashion. Second, similar findings were obtained with combined doses of testosterone and reductase or aromatase inhibitors. Combined treatment of eggs at male-biased intermediate incubation temperatures with testosterone and reductase inhibitor resulted in female hatchlings, whereas combined treatment of testosterone and aromatase inhibitor at both female-biased intermediate and at all female-producing temperatures resulted in male hatchlings. Finally, treatment with reductase inhibitor and aromatase inhibitor combined resulted in only male offspring at all incubation temperatures with the exception of the all-female incubation temperature; in the latter instance almost all offspring were female. These studies indicate that in the red-eared slider turtle (i) male and female sex determination are independent cascades residing equally in each individual and regulated by incubation temperature, (ii) steroid hormones are involved in temperature-dependent sex determination, and (iii) testosterone plays a pivotal role in this process. The data also suggest that aromatase and oestrogen receptors may be involved in the initiation of an ovary determining cascade and that reductase and androgen receptors may be involved in the initiation of a testis determining cascade. Journal of Endocrinology (1994) 143, 279–289


1991 ◽  
Vol 69 (9) ◽  
pp. 2306-2310 ◽  
Author(s):  
Samuel F. Lockwood ◽  
Brenden S. Holland ◽  
John W. Bickham ◽  
Brian G. Hanks ◽  
James J. Bull

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.


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