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Sex ratios in reptiles according to the type of sex determination
Palata, Tomáš ; Kratochvíl, Lukáš (advisor) ; Rehák, Ivan (referee)
There are many factors influencing sex ratios in reptile populations and these factors can differ among sex ratios in different developmental stages. The observed ratio is the result of many complex processes. One of the key factors is the mechanism of sex determination. In reptiles we distinguish two mechanisms of sex determination. The first is genotypic sex determination (GSD), where sex is determined during the fusion of gametes. Species with GSD show just little variation in sex ratios after birth or hatching and during adulthood there is a higher mortality rate of the heterogametic sex. Secondarily, there are reptiles possesing environmental sex determination (ESD). The sex of the developing individual of this species is influenced by incubation temperature during the thermosensitive phase of development. Reptiles with ESD show much greater variability in sex ratios after hatching and this variability may persist to adulthood. This thesis focuses mainly on the differences in sex ratios between GSD and ESD species. One of its interests is also the question of vulnerability of reptiles with ESD in terms of skewed sex ratios during contemporary climate change. Key words: sex ratio, reptiles, sex determination, GSD, ESD, climate change
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Evolution of sex chromosomes and karyotypes in iguanids (Squamata: Iguanidae sensu lato)
Altmanová, Marie ; Kratochvíl, Lukáš (advisor) ; Symonová, Radka (referee)
Iguanids are greatly diversed group of squamate reptiles (Reptilia, Squamata). Although there were many phylogenetical studies made, the relationships among main lineages are still unclear. In cytogenetical point of view is this group relatively conservative. In three species-rich genus only, the diversity of karyotypes is relatively considerable: Anolis, Liolaemus a Sceloporus. Diploid chromosome number varies between 19 and 48. Ancestral karyotype is defined as 2n=36, with 12 macrochromosomes and 24 microchromosomes. Morphologically the macrochromosomes are mostly metacentric, rarely acrocentric or telocentric. In karyotype evolution Robertsonian rearrangements dominate apparently, where number of chromosome arms is preserved. Interspecific variability or variability between populations were observed. Sex seems to be determined by genotype for whole group (GSD). Across the group probably attended conditionally to multiple differentiation of sex chromosomes. In 75 of 219 caryotyped were detected XX/XY type of sex chromosomes or derived multiple sex system X 1X 1X 2X 2/X 1X 2Y. The transition from multiple sex chromosomes back to XX/XY type was observed in one species. Chromosome Y shows morphological variability in size and shape, from microchromosom to huge metacentric macrochromosom. Homology of sex...
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Mechanisms of gonad determination and differentiation in reptiles
Ehl, Jan ; Kratochvíl, Lukáš (advisor) ; Krylov, Vladimír (referee)
Reptiles, as a group, have a~lot of various types of sex-determining mechanisms. Evolution of sex- deter- mining mechanisms took place in different groups of reptiles by different way and got to different types of sex determination. Gene network underlying gonadal diferenciation has been investigated in many studies, for revealing of principles causing this diversity. Thanks to that, it is very difficult to determine ultimate trigger of switching between male of female fate.Interesting fenomenon is sexreversal, which is enabled by mechanism activated only by unusual circumstances. I have summerized basic facts about sex determination in reptiles in this work. Also, expresion patterns of some genes important for gonadal diferenciation in vertebrates, are recapitulated there. The last things, what this work posses, is summary of knowledge about sex-reversal in reptiles and short treatise about its evotution.
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Role of steroid hormones in control of sexually dimorphic traits in eyelid geckos (Eublepharidae)
Tóthová, Lucia ; Kratochvíl, Lukáš (advisor) ; Landová, Eva (referee)
The importance of sex hormones in formation, development and regulation of sexually dimorphic behavior does not need to be stressed. However, their actual organizational and activational effects and interactions in sexual differentiation and determination are not fully understood yet. The aim of our study was to explore the effects of hormonal manipulation in eyelid-geckos (family Eublepharidae) and enlighten the role of steroid hormones in formation of sexual differences. In the first part of our work we tried to reverse sex of Yucatán banded gecko (Coleonyx elegans) by hormonal manipulation in the early embryogenesis. This species has genotypic sex determination with chromosome set X1X2Y. In reverted individuals we aimed to examine the effects of steroid hormones on sexually dimorphic traits and in case of full sexual reversion and fertility of progeny, we would search for the sex-determining gene. In the second part, we studied masculinization effects of testosterone in females of leopard gecko (Eublepharis macularius). In contrast with the Coleonyx elegans mentioned above, this species has temperature dependent sex determination, even though these two species are closely related. Experimental females were implanted with testosterone implants and therefore their testosterone levels were increased in...
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Evolution of sex chromosomes and karyotypes in iguanids (Squamata: Iguanidae sensu lato)
Altmanová, Marie ; Kratochvíl, Lukáš (advisor) ; Symonová, Radka (referee)
Iguanids are greatly diversed group of squamate reptiles (Reptilia, Squamata). Although there were many phylogenetical studies made, the relationships among main lineages are still unclear. In cytogenetical point of view is this group relatively conservative. In three species-rich genus only, the diversity of karyotypes is relatively considerable: Anolis, Liolaemus a Sceloporus. Diploid chromosome number varies between 19 and 48. Ancestral karyotype is defined as 2n=36, with 12 macrochromosomes and 24 microchromosomes. Morphologically the macrochromosomes are mostly metacentric, rarely acrocentric or telocentric. In karyotype evolution Robertsonian rearrangements dominate apparently, where number of chromosome arms is preserved. Interspecific variability or variability between populations were observed. Sex seems to be determined by genotype for whole group (GSD). Across the group probably attended conditionally to multiple differentiation of sex chromosomes. In 75 of 219 caryotyped were detected XX/XY type of sex chromosomes or derived multiple sex system X 1X 1X 2X 2/X 1X 2Y. The transition from multiple sex chromosomes back to XX/XY type was observed in one species. Chromosome Y shows morphological variability in size and shape, from microchromosom to huge metacentric macrochromosom. Homology of sex...
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Evolution of sex-determining mechanisms and genomes in squamate reptiles (Reptilia: Squamata)
Pokorná, Martina ; Kratochvíl, Lukáš (advisor) ; Marec, František (referee) ; Vyskot, Boris (referee)
Evolution of sex determining mechanisms in squamate reptiles (Reptilia: Squamata) Martina Pokorná Ph.D. thesis Abstract This Ph.D. thesis is focused on the evolution of sex determining mechanisms and genomes in squamate reptiles. It is based on three published articles and two manuscripts. The evolution of sex determining mechanisms, sex chromosomes and genomes, and their organisation, was studied on a wide phylogenetic scale of the whole group of squamate reptiles and some lineages of other Sauropsids, as well as on the small phylogenetic range as a detailed comparative study inside individual lineages of squamates. This thesis is based upon the use of classical cytogenetic methods, methods of molecular cytogenetic (especially fluorescent in situ hybridisation) and the results were analysed using phylogenetic approaches. The results and outputs of this study represent an important contribution to the general knowledge of the principals of sex determination and the evolution of these phenomena not only in squamate reptiles but also in the whole group of amniotes. Using the results obtained during the work on this thesis we can conclude that sex chromosomes evolved in particular lineages of amniotes independently. This origin was in some cases followed by accumulation of microsatellite sequences on sex...
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