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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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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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Sex chromosomes of Nematocera
Ryšan, Tadeáš ; Volf, Petr (advisor) ; Šťáhlavský, František (referee)
The paraphyletic group Nematocera is highly diversified in both body morphology and life strategies. Based on sex chromosome morphology, it can be divided into four groups defined as early as the mid- 20th century. All these systems are based on the presence of the XY/XX sex chromosomes or the loss of the Y chromosome. The different groups are distinguished based on whether the chromosomes are differentiated, whether chiasmata are present and whether the Y chromosome is retained. However, later research has shown much higher sex chromosome diversity, mostly in groups with homomorphic gonosomes. Even though most representatives of this group do not have differentiated sex chromosomes, we find the recurrence of differentiated gonosomes and even the X1X2Y1Y2/ X1X1X2X2 and ZW/ZZ sex systems, which are less typical for Diptera. These findings suggest that the form of sex chromosomes in Diptera may not be as stable as previously thought. The recently discovered non- homology of gonosomes across the Diptera, including several representatives of Nematocera, supports this idea. Multiple independent gonosome formation could also explain the diversity of primary sex- determining factors in those groups where these factors are known. Key words: Nematocera, Phlebotomus, Lutzomyia, sex chromosomes, sex determination
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Can birds manipulate sex ratio of their offspring?
Tomiška, Lubomír ; Kratochvíl, Lukáš (advisor) ; Fuchs, Roman (referee)
The aim of this study is a summary of existing knowledge about skewed sex ratio in birds. This controversial topic represents one of the most important questions of evolutionary ecology. We still miss consistence in finding ultimate causes just as proximate mechanisms although there was an expansion of experimental studies already in the last decade of the 20th century which was caused by an invention of the new technology in sex determination. On the other hand, there are many convincing proofs of skewed primary, secondary, tertiary and even quartenary sex ratio so the facultative manipulation or obligatory sex ratio bias is presumable. My Bachelor's thesis compares studies focused on the similar ultimate causes and tries to point out their deficiencies together with contributions to research of this topic. Observation of sex ratio includes many specifics which are mentioned in theoretical introduction. The second part offers potencial proximate mechanisms which could be responsible for sex ratio manipulation. Within the analysis of studies I found sex ratio manipulation of the first egg in clutch as common trend which could fit to selective ovum resorption as a proximate mechanism.
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Developmental plasticity in reptiles
Peš, Tomáš ; Kratochvíl, Lukáš (advisor) ; Frýdlová, Petra (referee)
The environment during incubation can have significant influence upon phenotype of reptile hatchlings. Temperature is one of the main environmental factors affecting developing embryos. The response to variability in the environment can be diverse: short, long-lasting and potentially also sex-specific. A large number of studies focused on this phenomenon but only a small portion of them studied the persistence of the phenotypic effects. I summarized studies on the influence of environmental factors on the phenotype of reptiles in species with both temperature or genotypic sex determination. These studies were evaluated in terms of duration of these effects and if these are sex specific. I also assessed how much they correspond with the predictions of the adaptive model suggested by Charnov & Bull which explains the origin and maintenance of temperature sex determination. Key words: phenotypic plasticity, environment, development, behaviour, morphology, sex determination, phenotype
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Social interactions and morphometric analysis of populations of Blue-Tongued Skink (Tiliqua gigas)
Jachnická, Kristýna ; Frynta, Daniel (advisor) ; Rehák, Ivan (referee)
A Blue-tongued skink ( Tiliqua gigas) is a rare exotic species which is very popular between breeders. Nevertheless, the social structure of this charismatic skink remains almost unknown. Because of its high aggressive- ness and difficulties connected with study in its natural habitat, experiments based on the odor discrimination looks like a good alternative for its bet- ter understanding. Our results revealed that the reaction on the odor is generally poor and is very individual. We observed the highest response of interest on odors produced throught dorsal parts of skin. The reaction on conspecific's odor did not lead to escape behavior. Behavioral analysis was complemented by morphological analysis of heads in T. gigas and T.scincoides. These species are divided into separate subspecies, which are formed by geographically distinct populations. We wondered whether it is possible to separate these populations by geometric morphometrics and whether this separation is consistent with phylogenetic studies. We found out that if the populations are united in bigger groups based on their congeniality they seem to be distinct according to the head shape. Our results also revealed the monomorphy in head shape. Unfortu- nately, it is very difficult to distinguish between sexes due to the absence of sexual dimorphism....
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Can birds manipulate sex ratio of their offspring?
Tomiška, Lubomír ; Kratochvíl, Lukáš (advisor) ; Fuchs, Roman (referee)
The aim of this study is a summary of existing knowledge about skewed sex ratio in birds. This controversial topic represents one of the most important questions of evolutionary ecology. We still miss consistence in finding ultimate causes just as proximate mechanisms although there was an expansion of experimental studies already in the last decade of the 20th century which was caused by an invention of the new technology in sex determination. On the other hand, there are many convincing proofs of skewed primary, secondary, tertiary and even quartenary sex ratio so the facultative manipulation or obligatory sex ratio bias is presumable. My Bachelor's thesis compares studies focused on the similar ultimate causes and tries to point out their deficiencies together with contributions to research of this topic. Observation of sex ratio includes many specifics which are mentioned in theoretical introduction. The second part offers potencial proximate mechanisms which could be responsible for sex ratio manipulation. Within the analysis of studies I found sex ratio manipulation of the first egg in clutch as common trend which could fit to selective ovum resorption as a proximate mechanism.
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Gene mutations affecting the development of human testes
Macháčová, Simona ; Šebková, Nataša (advisor) ; Ševčíková Jonáková, Jana (referee)
Development of mammalian sex organs is remarkable process. Both ovaries and testes rise from the same precursor but then differentiate into morphologically and functionally different structure. The determining factors that decide the fate of undifferentiated structures are not just the genes themselves but also the timing of transcription regulatory genes and specific amount of their products. Development of male and female gonads manages a large set of regulatory genes that interact with each other. Together it forms the gene regulatory network. Crucial role in male sex differentiation plays an SRY gene which regulates the time and quantity of the other factors expression. Even slight errors (mutations) in genes sequences of regulatory genes could change their expression. This leads to disruption of the development of sex organs or even death of the whole organism. Naturally occurring mutations and their phenotype in humans are suitable for studies of gene sex regulatory factors. Thanks to these studies we are able to detect the cause of many birth defects what is a first step toward their eventual treatment.
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