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Temperature of egg incubation determines sex in Alligator mississippiensis hatchlings. To define the timing and morphology of sexual differentiation, alligator gonads were examined histologically and ultrastructurally throughout embryogenesis. At the male-producing temperature (33° C), the onset of testis differentiation occurred in most embryos during developmental stages 21–22, when a number of somatic cells in the medulla of the gonad became enlarged, forming presumptive Sertoli cells. Some enlarged somatic cells were also observed at the female-producing temperature (30° C) during gonadogenesis, but they were less widespread than at 33° C. Ovarian differentiation at 30° C began slighlty later, during stage 22–23, and was characterised by proliferation of germs cells in the cortex of the gonad. Testis formation in alligators may depend upon presumptive Sertoli cells differentiating prior to a critical event in embryogenesis, such as germ cell proliferation and meiosis. If follows that ovary formation occurs if this requirement is not met, as at lower incubation temperatures. 相似文献
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正Dear Editor,Sex determination is highly plastic across vertebrates. The mechanisms of sex determination can be broadly divided into genetic sex determination (GSD) and environmental sex determination (ESD). GSD is the most popular sex-determining type in vertebrates, while ESD mainly occurred in 相似文献
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Environmental sex determination is reported in various fish species, including some fishes subject to stock enhancement.
We studied the influence of stock enhancement on the sex-determining system of fish with both genotypic and environmental
sex determination. We constructed and analyzed recurrence formula models for the dynamics of gene frequency in the male heterogametic
(XX female and XY male) sex-determining system of the Japanese flounder (Paralichthys olivaceus). In this species, an XX individual can develop as a phenotypic male (sex-reversed male) depending on the conditions experienced
by a juvenile. We show that the release of sex-reversed males may result in the extinction of the Y gene that determines sex.
We also studied how the risk depends on the kind of hatchery broodstock used (e.g., fish collected from the wild or fish from
a lineage established in a hatchery), sex-reversal rates in the hatchery and in the wild, and the relative contribution of
released fish to reproduction in the wild. We propose some ways to reduce the risk.
Received: October 10, 2001 / Accepted: December 17, 2001 相似文献
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Although the adaptive significance of temperature-dependent sex determination (TSD) remains a puzzle, recent models implicate a seasonal bias in offspring sex production that translates into sex-specific fitness benefits later in life. Sex-specific emergence has been linked to fitness gains in some fish, birds and reptiles, but field data supporting the occurrence of a seasonal pattern of sex ratios in oviparous lizards are lacking. We tested the hypothesis that patterns of nest site selection and seasonal temperature changes combine to inhibit the materialization of sex-biased hatching times in a population of water dragons (Intellagama lesueurii). As predicted, a seasonal increase in air and nest temperatures resulted in a sex bias by nesting date; male-producing clutches were laid 17.8 days sooner than female-producing clutches, on average. However, the seasonal ramping of nest temperatures also caused shorter relative incubation periods in the later, all-female clutches. As a consequence of this developmental ‘catch-up’, the mean hatching date for male-producing nests preceded the mean hatching date for female-producing nests by only 7.2 days. We suggest that a contracted distribution of hatching dates compared to the distribution of oviposition dates represents a general pattern for oviparous reptiles in seasonal climates, which in TSD species may largely offset the temporal disparity in nesting dates between the sexes. Although data are needed for other TSD species, such minor age differences between male and female hatchlings may not translate into fitness differences later in life, an assumption of some models for the evolution and maintenance of TSD. 相似文献
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Temperature-dependent sex determination (TSD) was first reported in 1966 in an African lizard. It has since been shown that TSD occurs in some fish, several lizards, tuataras, numerous turtles and all crocodilians. Extreme temperatures can also cause sex reversal in several amphibians and lizards with genotypic sex determination. Research in TSD species indicates that estrogen signaling is important for ovary development and that orthologs of mammalian genes have a function in gonad differentiation. Nevertheless, the mechanism that actually transduces temperature into a biological signal for ovary versus testis development is not known in any species. Classical genetics could be used to identify the loci underlying TSD, but only if there is segregating variation for TSD. Here, we use the ‘animal model'' to analyze inheritance of sexual phenotype in a 13-generation pedigree of captive leopard geckos, Eublepharis macularius, a TSD reptile. We directly show genetic variance and genotype-by-temperature interactions for sex determination. Additive genetic variation was significant at a temperature that produces a female-biased sex ratio (30 °C), but not at a temperature that produces a male-biased sex ratio (32.5 °C). Conversely, dominance variance was significant at the male-biased temperature (32.5 °C), but not at the female-biased temperature (30 °C). Non-genetic maternal effects on sex determination were negligible in comparison with additive genetic variance, dominance variance and the primary effect of temperature. These data show for the first time that there is segregating variation for TSD in a reptile and consequently that a quantitative trait locus analysis would be practicable for identifying the genes underlying TSD. 相似文献
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Nest-site selection in two eublepharid gecko species with temperature-dependent sex determination and one with genotypic sex determination 总被引:1,自引:0,他引:1
WENDY K. BRAGG JAMES D. FAWCETT THOMAS B. BRAGG BRIAN E. VIETS 《Biological journal of the Linnean Society. Linnean Society of London》2000,69(3):319-332
At present, most turtles, all crocodilians, and several lizards are known to have temperature-dependent sex determination (TSD). Due to the dependence of sex determination on incubation temperature, the long-term survival of TSD species may be jeopardized by global climate changes. The current study was designed to assess the degree to which this concern is justified by examining nest-site selection in two species of Pattern II TSD geckos (Eublepharis macularius and Hemitheconyx caudicinctus) and comparing these preferences with those of a species with genotypic sex determination (GSD) (Coleonyx mitratus). Temperature preferences for nest sites were found to be both species-specific and female-specific. While H. caudicinctus females selected a mean nest-site temperature (32.4°) very close to the upper pivotal temperature (32°C) for the species, E. macularius females selected a mean nest-site temperature (28.7°C) well below this species' lower pivotal temperature (30.5°C). Thus, the resultant sex ratios are expected to differ between these two TSD species. Additionally, nest-site temperatures for the GSD species were significantly more variable (SE=+0.37) than were temperatures for either of the TSD species (E. macularius SE=±0.10; H. caudicinctus SE =+ 0.17), diereby further demonstrating temperature preferences within the TSD species. 相似文献
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正Most vertebrates present two sexes,and females and males are determined via two diverse strategies including genotypic sex determination(GSD)and environmental sex determination(ESD)(Mei and Gui,2015;Ma et al.,2016).The most common form of ESD is temperature-dependent sex determination(TSD).Although several master sex-determining genes and their molecular pathways have been elucidated in vertebrates with GSD,the molecular mechanism underlying TSD remains unclear(Bachtrog et al.,2014; 相似文献
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Sexual determination and differentiation in teleost fish 总被引:3,自引:0,他引:3
Guerrero-Estévez Sandra Moreno-Mendoza Norma 《Reviews in Fish Biology and Fisheries》2010,20(1):101-121
The present work reviews the latest information on the cellular, molecular and physiological aspects of sexual determination
and differentiation in teleost fish. The group exhibits a large variety of mechanisms of sexual determination. These may be
genetic, or depend on environmental conditions such as temperature, pH, and social factors, all of which can influence the
proportion of the sexes. Additionally, sex steroids play an important role in the regulation of sexual differentiation. The
patterns of gonadal sexual differentiation are diverse, and species may be hermaphroditic or gonochoristic, some of the latter
displaying juvenile hermaphroditism. In recent years, several genes involved in the sexual determination and differentiation
pathways in vertebrates, particularly in mammals, have also been characterized in teleosts. Conserved as well as diversified
functions have been proposed. 相似文献
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D Crews 《The Journal of experimental zoology》1989,252(3):318-320
Eggs from congeneric gonochoristic and parthenogenetic whiptail lizards were incubated at various temperatures. There was no significant deviation from a sex ratio of one-half in the sexual species at any temperature, whereas no males were produced in the parthenogenetic species. Temperature-dependent sex determination appears to be completely absent in these lizards. 相似文献
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Mammalian sex differentiation involves the action of a cascade of genes. Discovery of the sex-determining region of the Y chromosome (SRY) marked the beginning of the delineation of the genes in the cascade. Studies of the genetics of mammalian sex reversal and the embryogenesis of the mice are essential in this endeavor. A number of genes involved in the pathway have been identified and all except one of these genes have a putative role in male sex differentiation. Besides SRY being the master switch in male sex differentiation the hierarchical relationship of the genes identified are far from being understood. Similarly, our knowledge of the genetic regulation of female sex differentiation is minimal. Differential screening and gene expression profiling bring a new dimension to the pursuit with the identification of a number of genes previously unknown to be involved in sex differentiation. Wider application of functional genomic techniques and introduction of proteomic analyses are expected to shed light to our understanding of this complicated developmental process. 相似文献
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Although gonadogenesis has been extensively studied in vertebrates with genetic sex determination, investigations at the molecular level in nontraditional model organisms with temperature-dependent sex determination are relatively new areas of research. Results show that while the key players of the molecular network underlying gonad development appear to be retained, their functions range from conserved to novel roles. In this review, we summarize experiments investigating candidate molecular players underlying temperature-dependent sex determination. We discuss some of the problems encountered unraveling this network, pose potential solutions, and suggest rewarding future directions of research. 相似文献
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