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Relationship between egg size and incubation time in geckos (Squamata: Gekkota)
Mrskočová, Jana ; Kratochvíl, Lukáš (advisor) ; Frynta, Daniel (referee)
Previous studies of the relationship between egg size and the embryonic development time showed a positive correlation between the two variables at interspecies level, thus offering the idea that the evolution of the latter could be a limiting factor for enlarging the size of eggs during evolution. Some research into interspecies and intraspecific level of reptiles doesn't confirm this correlation. At the same time, the relationship between the development time and egg size is influenced by many factors, such as shifts in ontogenetic stages of the embryo at the time of ablation of eggs, due to temperature and humidity, the presence of embryonic diapause during embryogenesis or synchronization of hatching time, of which the authors of previous studies took no account or filtered out inaccurately. I think that most of these factors can be well controlled in intraspecific studies, but, variation in egg size within species also tends to be small, which prevents a reliable test for correlation. The solution can be to compare closely related species with high variability in the size of the eggs, in our case the geckos of the genus Paroedura and family Eublepharidae. I eliminated temperature effects by comparing the time of incubation in two equal constant temperatures. The results show that, in this...
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Turtles (Testudines) - their Occurence and Breeding in the Czech Republic
Chotěborová, Tereza ; Andreska, Jan (advisor) ; Hanel, Lubomír (referee)
Bachelor thesis titled "Turtles" (Testudines) - their occurrence and breeding in the Czech Republic was primarily conceived as a research. The objective of this study is to create an information unit about turtles and is divided into several specific areas such as history, origin, anatomy and physiology, occurrence, breeding and diseases. The thesis compares the knowledge of turtles from available resources. KEY WORDS: reptiles, turtle, breeding, red-eared slider (Trachemys scripta elegans)
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Endocrine disruptors in reptiles
Semerád, Jaroslav ; Kratochvíl, Lukáš (advisor) ; Cajthaml, Tomáš (referee)
The ability of environmental contaminants to influence reproduction and development in vertebrates via disruption of the endocrine system is widespread. The mechanisms through which xenobiotics act can be complex and vary greatly among species. Reptiles are particularly good models for studying endocrine affecting compounds due to the fact that different species differ in modes of sex determination (genotypic sex determination or temperature-dependent sex determination) and parity (oviparity or viviparity). The sex of individual is often determined by egg incubation temperature, and exogenous application of steroid hormones and their analogs or steroidogenic enzyme inhibitors can reproduce effects of temperature. The lability of sex determination in some reptile species offers opportunity to use gonadal sex as a marker for effects of endocrine disrupting compounds (EDC), even for the effects of extremely low dosages of EDCs or EDC mixtures. The neonatal offsprings exposed to EDCs during embryogenesis provide yet another way to assess endocrine disruption, i.e., measurement of steroid hormone levels in their blood. In addition, many reptile species are highly aquatic, they use habitats near agricultural areas, where usage of pesticides is the most intense, and they are carnivores or scavengers. Therefore,...
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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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Spatial orientation in reptiles focused on methods of testing of allothetic navigation
Voňavková, Monika ; Landová, Eva (advisor) ; Telenský, Petr (referee)
Recently are known several different navigational systems in reptiles, mainly large scale navigational abilities based on sun and magnetic compass. The turtles are frequently used species in studies of spatial cognition, however, informations about spatial cognitive abilities in snakes and lizards (order Squamata) are only a few. Current knowledge concerning mechanism of small scale navigation based on allothetic orientation in snakes and lizards is only poorly understood. Aim of this thesis is review the literature about the mechanisms of reptile spatial orientation focused on allothetic navigation (using of external landmarks). As extension of this thesis is review of the principles of testing allothetic orientation in other groups (e. g. mammals) that were frequently used as a subject for testing allothetic orientation). The design of tests of allothetic orientation in model species of lizards (Eublepharis macularius) is one of the results of this thesis. Keywords: reptiles, spatial orientation, allothetic navigation
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Parthenogenetic lizards of the genus Darevskia as an evolutionary model
Abramjan, Andran ; Frynta, Daniel (advisor) ; Janko, Karel (referee)
Several parthenogenetic lineages occur within the lizards of the genus Darevskia (Sauria: Lacertidae) which are endemic to southern Transcaucasus. High level of heterozygosity, cause by thein hybrid origin, is one of the crucial aspects of thein evolutionary potential, as well as the asexual reproduction. Heterosis on one side is in the opposition to the outbreeding depression and genetic uniformity of the clones on the other side. Aim of this work is to evaluace if these aspects influence viability of parthenogenetic species and differ them from the sexual ones. We chose the amount of asymmetries as a measure of developmental instability, which we studied on three meristic characters. We also evaluated the pattern of asymmetries in lateral blue spots, which are of signaling importace in lacertid lizards. Our results suggest that there isn't significant difference between parthenogenetic and sexual species in developmental stability, but the sexual ones are more sensitive to population changes. Absence of males may have perhaps the greatest influence on coloration, resulting in loss of symmetry in the blue spots.
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Noninvasive measurement of steroid homones and effect of hormonal manipulation on behaviour in the gecko Paroedura picta
Matušková, Lucie ; Kratochvíl, Lukáš (advisor) ; Fraňková, Marcela (referee)
Hormones influence life of all animals. Not only they affect physiological changes in organisms, but also impact their behaviour. This work focuses at two main groups of steroid hormones: glucocorticoids and androgens. Glucocortiods are activated in response to stress. Their levels can be measured using non-invasive methods, which have a range of advantages. The main advantage is the feedback-free sample collection for enzyme immunoassay. As the measurement involves metabolites of the hormones rather than the hormones themselves, prior validation of the method is, however, necessary. This work reports on a study aiming to validate non-invasive measurement on the Madagascar Ground Gecko (Paroedura Picta). The validation was based on ACTH challenge test: Synacthen Depot was injected, which should lead to increased blood level of glucocorticoids. The validation, however, was not successful. The measurement did not discover significant increase in the levels of the metabolites of glucocorticoids. In addition, the work focuses on behavioural effects of testosterone, the primary androgen. Hormonal manipulations have been carried out on several male and female specimens. The results have discovered differences in sexual behaviour between control groups. On the other hand, the hormonal manipulations had no...
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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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Evolutionary contraints in the origin of viviparity in Amniotes Why there are no viviparous birds?
Chmelová, Kristýna ; Kratochvíl, Lukáš (advisor) ; Gvoždík, Václav (referee)
Evolution of life-bearing have fascinated biologists for over a long time. Viviparity has evolved many times within separate vertebrate lineages and it is a geographically widespread phenomenon. The majority of these independent origins have occured within lizards and snakes. Several hypotheses have been suggested to explain the selective pressures leading to viviparity in reptiles. One of the most frequently supported hypotheses views viviparity as an adaptation to a cold climate, i.e. viviparous mothers ensure favorable thermoregulation to developing embryos. It is generally supposed that egg retention is an intermediate stage in the evolution of live-bearing. Inclination to egg retention seems to be one of the most important preadaptations of viviparity in vertebrates. Additional limiting factors are probably for instance type of eggshell, mode of sex determinantion or egg guarding as an alternative mode of parental care.
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