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David Crews - One of the best experts on this subject based on the ideXlab platform.
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Yolk-albumen testosterone in a lizard with Temperature-Dependent Sex Determination: Relation with development
General and Comparative Endocrinology, 2013Co-Authors: V. Huang, Rachel M. Bowden, David CrewsAbstract:The leopard gecko (Eublepharis macularius) exhibits Temperature-Dependent Sex Determination as well as temperature-influenced polymorphisms. Research suggests that in oviparous reptiles with temperaturedependent Sex Determination, steroid hormones in the yolk might influence Sex Determination and Sexual differentiation. From captive leopard geckos that were all from the same incubation temperature regime, we gathered freshly laid eggs, incubated them at one of two female-biased incubation temperatures (26 or 34 C), and measured testosterone content in the yolk-albumen at early or late development. No differences in the concentration of testosterone were detected in eggs from different incubation temperatures. We report testosterone concentrations in the yolk-albumen were higher in eggs of late development than early development at 26 C incubation temperatures, a finding opposite that reported in other TSD reptiles studied to date.
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Molecular mechanisms of Temperature-Dependent Sex Determination in the context of ecological developmental biology.
Molecular and cellular endocrinology, 2011Co-Authors: Yuiko Matsumoto, David CrewsAbstract:Temperature-Dependent Sex Determination (TSD) is a prime example of phenotypic plasticity in that gonadal Sex is determined by the temperature of the incubating egg. In the red-eared slider turtle (Trachemys scripta), the effect of temperature can be overridden by exogenous ligands, i.e., Sex steroid hormones and steroid metabolism enzyme inhibitors, during the temperature-sensitive period (TSP) of development. Precisely how the physical signal of temperature is transduced into a biological signal that ultimately results in Sex Determination remains unknown. In this review, we discuss the Sex determining pathway underlying TSD by focusing on two candidate Sex determining genes, Forkhead box protein L2 (FoxL2) and DoubleSex mab3- related transcription factor 1 (Dmrt1). They appear to be involved in transducing the environmental temperature signal into a biological signal that subsequently determines gonadal Sex. FoxL2 and Dmrt1 exhibit gonad-typical patterns of expression in response to temperature during the TSP in the red-eared slider turtle. Further, the biologically active ligands regulate the expression of FoxL2 and Dmrt1 during development to modify gonad trajectory. The precise regulatory mechanisms of expression of these genes by temperature or exogenous ligands are not clear. However, the environment often influences developmental gene expression by altering the epigenetic status in regulatory regions. Here, we will discuss if the regulation of FoxL2 and Dmrt1 expression by environment is mediated through epigenetic mechanisms during development in species with TSD.
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genetic network underlying temperature dependent Sex Determination is endogenously regulated by temperature in isolated cultured trachemys scripta gonads
Developmental Dynamics, 2010Co-Authors: Christina M Shoemakerdaly, Yuiko Matsumoto, Kyle R Jackson, Ryohei Yatsu, David CrewsAbstract:In reptiles with Temperature-Dependent Sex Determination, gonadogenesis is initially directed by the incubation temperature of the egg during the middle third of embryonic development. The mechanism by which temperature is transduced into a Sex-determining molecular signal remains a mystery, and here we examine the molecular network underlying Sex Determination in gonads in vitro. We use a whole organ culture system to show that expression of putative members of the Sex-determining network (Dmrt1, Sox9, Mis, and FoxL2) are regulated by temperature endogenously within cells in the bipotential gonad and do not require other embryonic tissues to be expressed in a normal pattern in the red-eared slider turtle, Trachemys scripta. Furthermore, following a change in temperature, these factors exhibit temperature-responsive expression patterns that last for the duration of gonadogenesis. Finally, mosaic miSexpression of a fusion Sox9 construct demonstrates the ability to functionally manipulate the gonad at the molecular level. Developmental Dynamics 239:1061–1075, 2010. © 2010 Wiley-Liss, Inc.
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Constraints on Temperature-Dependent Sex Determination in the leopard gecko (Eublepharis macularius): response to Kratochvil et al.
Naturwissenschaften, 2008Co-Authors: Victoria Huang, Turk Rhen, Jon T. Sakata, Patricia Coomber, Sarah Simmonds, David CrewsAbstract:Kratochvil et al. (Naturwissenschaften 95:209–215, 2008 ) reported recently that in the leopard gecko ( Eublepharis macularius ) of the family Eublepharidae with Temperature-Dependent Sex Determination (TSD), clutches in which eggs were incubated at the same temperature produce only same-Sex siblings. Interpreting this result in light of studies of Sex steroid hormone involvement in Sex Determination, they suggested that maternally derived yolk steroid hormones could constrain Sex-determining mechanisms in TSD reptiles. We have worked extensively with this species and have routinely incubated clutches at constant temperatures. To test the consistency of high frequency same-Sex clutches across different incubation temperatures, we examined our records of clutches at the University of Texas at Austin from 1992 to 2001. We observed that clutches in which eggs were incubated at the same incubation temperature produced mixed-Sex clutches as well as same-Sex clutches. Furthermore, cases in which eggs within a clutch were separated and incubated at different temperatures produced the expected number of mixed-Sex clutches. These results suggest that maternal influences on Sex Determination are secondary relative to incubation temperature effects.
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Steroid signaling and Temperature-Dependent Sex Determination-Reviewing the evidence for early action of estrogen during ovarian Determination in turtles.
Seminars in cell & developmental biology, 2008Co-Authors: Mary E. Ramsey, David CrewsAbstract:The developmental processes underlying gonadal differentiation are conserved across vertebrates, but the triggers initiating these trajectories are extremely variable. The red-eared slider turtle (Trachemys scripta elegans) exhibits Temperature-Dependent Sex Determination (TSD), a system where incubation temperature during a temperature-sensitive period of development determines offspring Sex. However, gonadal Sex is sensitive to both temperature and hormones during this period—particularly estrogen. We present a model for temperature-based differences in aromatase expression as a critical step in ovarian Determination. Localized estrogen production facilitates ovarian development while inhibiting male-specific gene expression. At male-producing temperatures aromatase is not upregulated, thereby allowing testis development.
Fredric J. Janzen - One of the best experts on this subject based on the ideXlab platform.
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Temperature-Dependent Sex Determination under Rapid Anthropogenic Environmental Change: Evolution at a Turtle’s Pace?
The Journal of heredity, 2015Co-Authors: Jeanine M. Refsnider, Fredric J. JanzenAbstract:Organisms become adapted to their environment by evolving through natural selection, a process that generally transpires over many generations. Currently, anthropogenically driven environmental changes are occurring orders of magnitude faster than they did prior to human influence, which could potentially outpace the ability of some organisms to adapt. Here, we focus on traits associated with Temperature-Dependent Sex Determination (TSD), a classic polyphenism, in a model turtle species to address the evolutionary potential of species with TSD to respond to rapid climate change. We show, first, that Sex-ratio outcomes in species with TSD are sensitive to climatic variation. We then identify the evolutionary potential, in terms of heritability, of TSD and quantify the evolutionary potential of 3 key traits involved in TSD: pivotal temperature, maternal nest-site choice, and nesting phenology. We find that these traits display different patterns of adaptive potential: pivotal temperature exhibits moderate heritable variation, whereas nest-site choice and nesting phenology, with considerable phenotypic plasticity, have only modest evolutionary potential to alter Sex ratios. Therefore, the most likely response of species with TSD to anthropogenically induced climate change may be a combination of microevolution in thermal sensitivity of the Sex-determining pathway and of plasticity in maternal nesting behavior.
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does Sex ratio selection influence nest site choice in a reptile with temperature dependent Sex Determination
Proceedings of The Royal Society B: Biological Sciences, 2013Co-Authors: Timothy S Mitchell, Jessica A Maciel, Fredric J. JanzenAbstract:Evolutionary theory predicts that dioecious species should produce a balanced primary Sex ratio maintained by frequency-dependent selection. Organisms with environmental Sex Determination, however, are vulnerable to maladaptive Sex ratios, because environmental conditions vary spatio-temporally. For reptiles with Temperature-Dependent Sex Determination, nest-site choice is a behavioural maternal effect that could respond to Sex-ratio selection, as mothers could adjust offspring Sex ratios by choosing nest sites that will have particular thermal properties. This theoretical prediction has generated decades of empirical research, yet convincing evidence that Sex-ratio selection is influencing nesting behaviours remains absent. Here, we provide the first experimental evidence from nature that Sex-ratio selection, rather than only viability selection, is probably an important component of nest-site choice in a reptile with Temperature-Dependent Sex Determination. We compare painted turtle (Chrysemys picta) neonates from maternally selected nest sites with those from randomly selected nest sites, observing no substantive difference in hatching success or survival, but finding a profound difference in offspring Sex ratio in the direction expected based on historical records. Additionally, we leverage long-term data to reconstruct our Sex ratio results had the experiment been repeated in multiple years. As predicted by theory, our results suggest that Sex-ratio selection has shaped nesting behaviour in ways likely to enhance maternal fitness.
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behavioural plasticity may compensate for climate change in a long lived reptile with temperature dependent Sex Determination
Biological Conservation, 2012Co-Authors: Jeanine M. Refsnider, Fredric J. JanzenAbstract:How are organisms responding to climate change? The rapidity with which climate is changing suggests that, in species with long generation times, adaptive evolution may be too slow to keep pace with climate change, and that alternative mechanisms, such as behavioural plasticity, may be necessary for population persistence. Species with Temperature-Dependent Sex Determination may be particularly threatened by climate change, because altered temperatures could skew Sex ratios. We experimentally tested nest-site choice in the long-lived turtle Chrysemys picta to determine whether nesting behaviour can compensate for potential skews in Sex ratios caused by rapid climate change. We collected females from five populations across the species′ range and housed them in a semi-natural common garden. Under these identical conditions, populations differed in nesting phenology (likely due to nesting frequency), and in nest depth (possibly due to a latitudinal cline in female body size), but did not differ in choice of shade cover over the nest, nest incubation regime, or in resultant nest Sex ratios. These results suggest that choice of nest sites with particular shade cover may be a behaviourally plastic mechanism by which turtles can compensate for change in climatic temperatures during embryonic development, provided that sufficient environmental variation in potential nest microhabitat is available.
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Field-measured heritability of the threshold for Sex Determination in a turtle with Temperature-Dependent Sex Determination
Evolutionary Ecology Research, 2011Co-Authors: Suzanne E. Mcgaugh, Rachel M. Bowden, Chin Horng Kuo, Fredric J. JanzenAbstract:Problem: For Temperature-Dependent Sex Determination to respond to selection, there should be genetic variance underlying the threshold that switches development from a male-producing program to a female-producing program. Genetic variance for this threshold in reptiles has never been estimated under field conditions. Methods: We estimated variance components of the thermal sensitivity of the Sex Determination threshold under field conditions for the painted turtle, Chrysemys picta, a species that has Temperature-Dependent Sex Determination. Multiple paternity within clutches was identified by genotyping females and their offspring. We endeavoured to statistically account for common nest and maternal effects and estimated the genetic variance underlying the Sex Determination threshold under field conditions by isolating the contribution of sires within a single clutch. Results: With 51 clutches containing 393 offspring, we estimated significant heritability for the Sex Determination threshold (h 2 = 0.351, 95% CI = [0.164, 0.832]). Using a more restrictive dataset, which included only those clutches where each sire was represented by at least two offspring (34 nests, 273 hatchlings), heritability was not significantly different from zero (h 2 = 0.173, 95% CI = [0.000, 0.628]). Paternal siring success did not influence hatchling Sex; thus, we have no evidence to support differential Sex allocation across different sires within the same nest. Conclusion: We used a natural ‘breeding design’ under field conditions to show that the threshold of Temperature-Dependent Sex Determination may have a heritable genetic basis.
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Inheritance of nesting behaviour across natural environmental variation in a turtle with Temperature-Dependent Sex Determination
Proceedings. Biological sciences, 2009Co-Authors: Suzanne E. Mcgaugh, Rachel M. Bowden, Lisa E. Schwanz, Julie E. Gonzalez, Fredric J. JanzenAbstract:Nesting behaviour is critical for reproductive success in oviparous organisms with no parental care. In organisms where Sex is determined by incubation temperature, nesting behaviour may be a prime target of selection in response to unbalanced Sex ratios. To produce an evolutionary change in response to Sex-ratio selection, components of nesting behaviour must be heritable. We estimated the field heritability of two key components of nesting behaviour in a population of painted turtles (Chrysemys picta) with Temperature-Dependent Sex Determination by applying the 'animal model' to a pedigree reconstructed from genotype data. We obtained estimates of low to non-detectable heritability using repeated records across all environments. We then determined environment-specific heritability by grouping records with similar temperatures for the winter preceding the nesting season, a variable known to be highly associated with our two traits of interest, nest vegetation cover and Julian date of nesting. The heritability estimates of nest vegetation cover and Julian date of nesting were qualitatively highest and significant, or nearly so, after hot winters. Additive genetic variance for these traits was not detectable after cold winters. Our analysis suggests that the potential for evolutionary change of nesting behaviour may be dependent on the thermal conditions of the preceding winter, a season that is predicted to be especially subject to climate change.
Thane Wibbels - One of the best experts on this subject based on the ideXlab platform.
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Effect of daily water treatment on hatchling Sex ratios in a turtle with Temperature-Dependent Sex Determination.
Journal of experimental zoology. Part A Ecological genetics and physiology, 2009Co-Authors: Anne Marie Leblanc, Thane WibbelsAbstract:Some previous studies indicate that the local hydric environment may influence Sex Determination in turtles with Temperature-Dependent Sex Determination. In this study, the effect of a daily application of 0.77 mL of ddH20 per egg using an incubation temperature of 29.1°C was examined during the temperature-sensitive period for two consecutive nesting seasons. This regimen yielded Sex ratios of 11.8 and 11.1% male in control groups not receiving water supplementation, whereas daily water treatments resulted in Sex ratios of 86.7 and 45.7% male during the 2006 and 2007 nesting seasons, respectively. The results indicate that daily water treatments significantly influenced Sex ratios (P
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Expression of Dmrt1 in a turtle with Temperature-Dependent Sex Determination
Cytogenetic and genome research, 2003Co-Authors: Chris Murdock, Thane WibbelsAbstract:There is a variety of Sex determining mechanisms among vertebrates. Many reptiles possess Temperature-Dependent Sex Determination (TSD), in which the incubation temperature of the egg determines the Sex of the hatchling. The red-eared slider turtle, Trachemys scripta has often been used as a model system for examining the physiology of TSD. In the current study, the expression of Dmrt1 was examined during TSD in this turtle. Dmrt1 is a putative regulator of Sex Determination/differentiation and has been identified in a variety of vertebrates, including fishes, amphibians, reptiles, birds, and mammals. Specifically, Dmrt1 has been shown to be up-regulated in a male-specific pattern during embryonic development in many vertebrates. In the current study, the expression patterns of Dmrt1 were examined in the developing adrenal-kidney-gonad complexes of T. scripta during embryonic development. Using a quantitative competitive RT-PCR, Dmrt1 was shown to be up-regulated during the thermosensitive period of Sex Determination in males. In contrast, levels of Dmrt1 remained low in females throughout the thermosensitive period. These data suggest that the up-regulation of Dmrt1 may play a role in male Sex Determination/Sex differentiation during TSD in T. scripta.
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Cloning and expression of aromatase in a turtle with Temperature-Dependent Sex Determination.
General and comparative endocrinology, 2003Co-Authors: Chris Murdock, Thane WibbelsAbstract:It has been hypothesized that estrogen production may play a pivotal role in the Sex Determination of reptiles with Temperature-Dependent Sex Determination (TSD). This hypothesis has been furthered by studies that have shown higher aromatase activity in the developing ovaries in some reptiles. However, other studies have not consistently supported this hypothesis. In the current study we addressed this issue by cloning P450 aromatase cDNA in the turtle, Trachemys scripta, and developing a quantitative competitive RT-PCR for aromatase. This assay was then used to quantify aromatase mRNA levels in adrenal-kidney-gonad complexes (AKG) during TSD. Aromatase mRNA was detected in the AKGs at both male- and female-producing temperatures from the earliest stage of development sampled (stage 15), through hatching (stage 26). However, levels remained relatively constant during the thermosensitive period of TSD. Further, no significant difference was detected between male- and female-producing temperatures during the thermosensitive period. After the thermosensitive period, aromatase mRNA levels increased in females (this coincides with the period during which the ovaries are differentiating). These results are consistent with those of several previous studies of certain reptiles with TSD. The current results suggest that the expression of aromatase may not be a pivotal regulatory step in the Sex Determination cascade of this turtle.
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Developmental expression of steroidogenic factor 1 in a turtle with Temperature-Dependent Sex Determination.
General and comparative endocrinology, 1999Co-Authors: Alice Fleming, Thane Wibbels, James K. Skipper, David CrewsAbstract:Abstract A variety of reptiles possess Temperature-Dependent Sex Determination (TSD) in which the incubation temperature of a developing egg determines the gonadal Sex. Current evidence suggests that temperature signals may be transduced into steroid hormone signals with estrogens directing ovarian differentiation. Steroidogenic factor 1 (SF-1) is one component of interest because it regulates the expression of steroidogenic enzymes in mammals and is differentially expressed during development of testis and ovary. Northern blot analysis of SF-1 in developing tissues of the red-eared slider turtle ( Trachemys scripta ), a TSD species, detected a single primary SF-1 transcript of approximately 5.8 kb across all stages of development examined. Analysis by in situ hybridization indicated nearly equivalent SF-1 expression in early, bipotential gonads at male (26°C)- and female (31°C)-producing incubation temperatures. In subsequent stages, as gonadal Sex first becomes histologically distinguishable during the temperature-sensitive period, SF-1 expression increased in gonads at a male-producing temperature and decreased at a female-producing temperature, suggesting a role for SF-1 in the Sex differentiation pathway. SF-1 message was also found in adrenal and in the periventricular region of the preoptic area and diencephalon, but there was no apparent Sex bias in these tissues at any stage examined. The overall developmental pattern of SF-1 mRNA expression in T. scripta appears to parallel that found in mammals, indicating possible homologous functions.
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temperature dependent Sex Determination in the red eared slider turtle trachemys scripta
Journal of Experimental Zoology, 1998Co-Authors: Thane Wibbels, Jon W Cowan, Robert D LeboeufAbstract:Temperature-Dependent Sex Determination (TSD) in the red-eared slider turtle, Trachemys scripta, has been the subject of a variety of past studies. Incubation temperature ap- pears to affect Sex Determination in a dose-dependent fashion. This suggests that temperature could be affecting a dosage-sensitive element in the Sex-Determination cascade. Sex Determination in T. scripta is sensitive to estrogen, and data from many studies support the hypothesis that endogenous estrogen production may be involved in female Sex Determination. However, this hy- pothesis has not yet been evaluated through aromatase expression studies in this species. Several recent studies have cloned cDNAs for genes that could be involved in Sex Determination and/or Sex differentiation. The cDNAs for SF-1 and MIS have been cloned in T. scripta, indicating that these may represent conserved elements in the Sex-Determination/Sex-differentiation cascade of reptiles. The SOX9 cDNA also has been cloned in T. scripta (Spotila et al., '98), and it shows a Sex-specific expression pattern. Future studies targeted at aromatase expression as well as the expression of factors such as SOX9, SF-1, and MIS will begin to provide a more comprehensive picture of the events involved in TSD in T. scripta. Further, such studies could help pinpoint the temperature- sensitive element(s). J. Exp. Zool. 281:409n416, 1998. © 1998 Wiley-Liss, Inc.
Richard Shine - One of the best experts on this subject based on the ideXlab platform.
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thyroid hormone modulates offspring Sex ratio in a turtle with temperature dependent Sex Determination
Proceedings of The Royal Society B: Biological Sciences, 2016Co-Authors: Baojun Sun, Arthur Georges, Jessica K Mcglashan, Richard ShineAbstract: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 (T3), during embryonic development (by adding excess T3 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.
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Interactions among thermal parameters determine offspring Sex under Temperature-Dependent Sex Determination
Proceedings. Biological sciences, 2010Co-Authors: Daniel A. Warner, Richard ShineAbstract:In many animals, temperatures experienced by developing embryos determine offspring Sex (e.g. Temperature-Dependent Sex Determination, TSD), but most studies focus strictly on the effects of mean temperature, with little emphasis on the importance of thermal fluctuations. In the jacky dragon (Amphibolurus muricatus), an Australian lizard with TSD, data from nests in the field demonstrate that offspring Sex ratios are predictable from thermal fluctuations but not from mean nest temperatures. To clarify this paradox, we incubated eggs in a factorial experiment with two levels of mean temperature and three levels of diel fluctuation. We show that offspring Sex is determined by an interaction between these critical thermal parameters. Intriguingly, because these two thermal descriptors shift in opposing directions throughout the incubation season, this interactive effect inhibits seasonal shifts in Sex ratio. Hence, our results suggest that TSD can yield offspring Sex ratios that resemble those produced under genotypic Sex-determining systems. These findings raise important considerations for understanding the diversity of TSD reaction norms, for designing experiments that evaluate the evolutionary significance of TSD, and for predicting Sex ratios under past and future climate change scenarios.
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maternal nest site choice in a lizard with temperature dependent Sex Determination
Animal Behaviour, 2008Co-Authors: Daniel A. Warner, Richard ShineAbstract:In oviparous species, mothers can optimize the incubation environments of their offspring by selecting nest sites with conditions conducive to embryonic development. Hence, maternal nest-site selection can enhance egg survival and offspring fitness. However, the challenge to a nesting female is complex because of trade-offs among relevant parameters (e.g. hotter nests may be drier) and seasonal shifts in ambient conditions. Moreover, the influence of nest conditions on offspring Sex ratios adds another level of complexity for species with environmental Sex Determination. To elucidate these issues, we need field data on nesting behaviour that incorporate the multiple influences that operate under natural conditions. We radiotracked gravid jacky dragons, Amphibolurus muricatus, in open forest habitats of southeastern Australia to document the lizards' criteria for nest-site choice. Females selected sites with lower than average canopy cover, resulting in relatively warm nests throughout the prolonged nesting season. Although soil moisture levels decreased over this period and were strongly correlated with mean temperatures, female lizards were able to locate nesting sites that provided consistently moist (and increasingly warm) incubation conditions as the season progressed. Such sites apparently became more difficult to find later in the season, resulting in a higher incidence of test holes prior to nest excavation. Seasonal shifts in diel maximum temperatures also pushed the daily time of digging activity into the evening. Because jacky dragons have Temperature-Dependent Sex Determination, the seasonal shift in mean incubation temperatures of natural nests would generate seasonal shifts in offspring Sex ratios in a direction likely to enhance maternal fitness.
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The adaptive significance of Temperature-Dependent Sex Determination in a reptile
Nature, 2008Co-Authors: Daniel A. Warner, Richard ShineAbstract:In mammals and birds, Sex is determined by genotype, at fertilization. But many reptiles, hedge their bets, determining the Sex of an individual by interaction with the environment, typically temperature. Thirty years ago, Eric Charnov and James Bull (Nature 266, 828–830; 1977) speculated that environmental Sex Determination will be favoured by selection if it could be shown that different temperature regimes maximized reproductive fitness for each Sex. Until now it has not been confirmed, partly because of the difficulty of setting up a 'control' experiment in which the 'wrong' Sex is produced at a given temperature. Hormone treatments have been used to overcome this difficulty, and Daniel Warner and Rick Shine now confirm, in a species of Australian lizard, that the Charnov/Bull model is correct. In mammals and birds, Sex is determined by genotype at fertilization, but reptiles determine the Sex of an individual by interaction with the environment, typically temperature. The Charnov–Bull model speculates that environmental Sex Determination will be favoured by selection if it could be shown that different temperature regimes maximized reproductive fitness for each Sex. This has not been confirmed, partly because of the difficulty of setting up the 'control' experiment. However, hormone treatments have been used to overcome this difficulty, and a short-lived species of lizard shows that the Charnov–Bull model is correct. Understanding the mechanisms that determine an individual’s Sex remains a primary challenge for evolutionary biology. Chromosome-based systems (genotypic Sex Determination) that generate roughly equal numbers of sons and daughters accord with theory1, but the adaptive significance of environmental Sex Determination (that is, when embryonic environmental conditions determine offspring Sex, ESD) is a major unsolved problem2,3. Theoretical models predict that selection should favour ESD over genotypic Sex Determination when the developmental environment differentially influences male versus female fitness (that is, the Charnov–Bull model)4, but empirical evidence for this hypothesis remains elusive in amniote vertebrates—the clade in which ESD is most prevalent5. Here we provide the first substantial empirical support for this model by showing that incubation temperatures influence reproductive success of males differently than that of females in a short-lived lizard (Amphibolurus muricatus, Agamidae) with Temperature-Dependent Sex Determination. We incubated eggs at a variety of temperatures, and de-confounded Sex and incubation temperature by using hormonal manipulations to embryos. We then raised lizards in field enclosures and quantified their lifetime reproductive success. Incubation temperature affected reproductive success differently in males versus females in exactly the way predicted by theory: the fitness of each Sex was maximized by the incubation temperature that produces that Sex. Our results provide unequivocal empirical support for the Charnov–Bull model for the adaptive significance of Temperature-Dependent Sex Determination in amniote vertebrates.
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Do operational Sex ratios influence Sex allocation in viviparous lizards with Temperature-Dependent Sex Determination?
Journal of evolutionary biology, 2006Co-Authors: David J. Allsop, Daniel A. Warner, Tracy Langkilde, Richard ShineAbstract:Under certain environmental situations, selection may favour the ability of females to adjust the Sex ratio of their offspring. Two recent studies have suggested that viviparous scincid lizards can modify the Sex ratio of the offspring they produce in response to the operational Sex ratio (OSR). Both of the species in question belong to genera that have also recently been shown to exhibit Temperature-Dependent Sex Determination (TSD). Here we test whether pregnant montane water skinks (Eulamprus tympanum) utilise TSD to select offspring Sex in response to population wide imbalances in the OSR, by means of active thermoregulation. We use a combination of laboratory and field-based experiments, and conduct the first field-based test of this hypothesis by maintaining females in outdoor enclosures of varying OSR treatments throughout pregnancy. Although maternal body temperature during pregnancy was influenced by OSR, the variation in temperature was not great enough to affect litter Sex ratios or any other phenotypic traits of the offspring.
Mary E. Ramsey - One of the best experts on this subject based on the ideXlab platform.
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Steroid signaling and Temperature-Dependent Sex Determination-Reviewing the evidence for early action of estrogen during ovarian Determination in turtles.
Seminars in cell & developmental biology, 2008Co-Authors: Mary E. Ramsey, David CrewsAbstract:The developmental processes underlying gonadal differentiation are conserved across vertebrates, but the triggers initiating these trajectories are extremely variable. The red-eared slider turtle (Trachemys scripta elegans) exhibits Temperature-Dependent Sex Determination (TSD), a system where incubation temperature during a temperature-sensitive period of development determines offspring Sex. However, gonadal Sex is sensitive to both temperature and hormones during this period—particularly estrogen. We present a model for temperature-based differences in aromatase expression as a critical step in ovarian Determination. Localized estrogen production facilitates ovarian development while inhibiting male-specific gene expression. At male-producing temperatures aromatase is not upregulated, thereby allowing testis development.
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Steroid signaling system responds differently to temperature and hormone manipulation in the red-eared slider turtle (Trachemys scripta elegans), a reptile with Temperature-Dependent Sex Determination.
Sexual development : genetics molecular biology evolution endocrinology embryology and pathology of sex determination and differentiation, 2007Co-Authors: Mary E. Ramsey, David CrewsAbstract:Many reptiles, including the red-eared slider turtle ( Trachemys scripta elegans ), exhibit Temperature-Dependent Sex Determination (TSD). Temperature determines gonadal Sex during th
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expression of sox9 mis and dmrt1 in the gonad of a species with temperature dependent Sex Determination
Developmental Dynamics, 2007Co-Authors: Christina M Shoemake, Mary E. Ramsey, Joanna Quee, David CrewsAbstract:Sex Determination in vertebrates, the process of forming an ovary or testis from a bipotential gonad, can be initiated by genetic or environmental factors. Elements of the downstream molecular pathways underlying these different Sex-determining mechanisms have been evolutionarily conserved. We find the first evidence that Sox9 expression is preferentially organized in the testis early in the temperature-sensitive period in a species with Temperature-Dependent Sex Determination (Trachemys scripta). This pattern occurs before Sexually dimorphic Mis expression and in a temporal hierarchy that is similar to mammals. Furthermore, we extend previous findings that Dmrt1 expression at early stages of Sex Determination has a dimorphic pattern consistent with a possible upstream role in determining the fate of the bipotential gonad.
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Expression of Sox9, Mis, and Dmrt1 in the gonad of a species with temperature‐dependent Sex Determination
Developmental dynamics : an official publication of the American Association of Anatomists, 2007Co-Authors: Christina M. Shoemaker, Mary E. Ramsey, Joanna H. Queen, David CrewsAbstract:Sex Determination in vertebrates, the process of forming an ovary or testis from a bipotential gonad, can be initiated by genetic or environmental factors. Elements of the downstream molecular pathways underlying these different Sex-determining mechanisms have been evolutionarily conserved. We find the first evidence that Sox9 expression is preferentially organized in the testis early in the temperature-sensitive period in a species with Temperature-Dependent Sex Determination (Trachemys scripta). This pattern occurs before Sexually dimorphic Mis expression and in a temporal hierarchy that is similar to mammals. Furthermore, we extend previous findings that Dmrt1 expression at early stages of Sex Determination has a dimorphic pattern consistent with a possible upstream role in determining the fate of the bipotential gonad.
