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The sex determination in the gecko genus Phelsuma
Peš, Tomáš ; Kratochvíl, Lukáš (advisor) ; Kverková, Kristina (referee)
Geckos (Gekkota) are a diverse group of squamate reptiles. The species richness of geckos is associated with a wide variety of sex determination systems. We can encounter male and female heterogamety, environmental sex determination, or asexuality in this group of reptiles. The diversity of geckos makes this group very interesting for studying of the evolution of sex determination. Due to the large number of species, we know the type of sex determination in just a fraction of taxa. The genus Phelsuma has been little studied in this respect and, with one exception, published data are not very reliable. In this thesis, sex determination in Phelsuma laticauda and Phelsuma nigristriata was investigated using an incubation experiment. I proved that both species have environmental sex determination. The effect of incubation temperature on morphological characteristics was also investigated in hatchlings. The possible persistence of this effect into adulthood was re-tested in one year old geckos.
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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-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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