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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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Function of antimicrobial proteins in albumen of precocial birds
Krkavcová, Eva ; Kreisinger, Jakub (advisor) ; Kratochvíl, Lukáš (referee)
Antimicrobial proteins contained in the albumen represent maternal effects, including the non- genetic component allocated into the egg during its oogenesis. Especially for species, whose broods are exposed to environmental influences until completation, these proteins play a crucial role in the viability of embryos due to their potential to influence the risk of microbial infection, which is considered one of the main causes of reduced hatchability. Also, it is assumed that these proteins, beacause of their specific traits, may influence phenotype of chicks, especially its size and immunity in the early postembryonal stage. In my thesis I focused on three antimicrobial proteins of avian egg white - avidin, lysozyme and ovotransferrin, which vary in their antimicrobial activity. For a better understanding of causal relationships between the concentrations of these proteins in the albumen and their effect on hatching success or offspring phenotype, a series of manipulation experiments and correlative measurements were performed. These experiments were held on the eggs of two precocial species - Japanese Quail (Coturnix japonica) and Mallard (Anas platyrhynchos). Our results indicate a crucial role of antimicrobial proteins in reducing the risk of bacterial infection and their natural concentration...
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The factors affecting evolutionary diversification
Černá, Vladimíra ; Storch, David (advisor) ; Kratochvíl, Lukáš (referee)
The number of species on the Earth is estimated to lie between five to ten millions. All these species originated from a common ancestor, which appeared on our planet 3,5 bilion years ago. Speciation and extinction are responsible for the current species richness. Evolutionary diversification is the difference between speciation and extinction. There are several methods used to obtain the values of speciation, extinction and diversification rates. I will briefly explain some of these methods, outline the advantages and disadvantages of them. The aim of this paper is to summarize current knowledge of evolutionary diversification and factors that may affect it. In this search I focused on the studies dealing with factors that may affect several groups of organisms. Although many determinants of diversification were found, most of them affect only one group of organisms. Here I did not find any factor that would be common for the majority of taxa. Evolutionary diversification is probably influenced by different factors in different evolutionary lineages. Key words: diversification, speciation, radiation, diversity gradient
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Relationship between developmental rate and egg size in reptiles
Mrskočová, Jana ; Kratochvíl, Lukáš (advisor) ; Hořák, David (referee)
Existing analyses indicate that there is a positive relationship between egg mass and incubation period at large taxonomical scales. This suggests that animals are able to solve the trade-off between egg mass and developmental rate. However, some studies (not only reptile- focused) prove that this relationship is taxon-specific. Studies performed at the intraspecific level differ in the conclusion whether such relationship actually exists. Moreover, there are many factors which complicate these analyses (for example the ontogenetic shift at the time of oviposition, presence of diapause during the embryonic development, synchronization of the time of hatching, temperature and humidity). I suggest that the main factor is temperature that has been filtered out by various authors by means which I find unsatisfactory. This thesis attempts to prove that the relationship between egg mass and incubation period is not sufficiently and explicitly explained and to discuss the complications regarding its research.
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Genomic imprinting and evolution of sexually dimorphic traits
Farkačová, Klára ; Kratochvíl, Lukáš (advisor) ; Munclinger, Pavel (referee)
Genomic imprinting is a process whereby expression of an allele differs depending upon its parent of origin. It can be found on autosomes and also on sex chromosomes. Basic hypothesis for the evolution of genomic imprinting is the hypothesis based on the existence of sexual conflict. It can be classified into interlocus sexual conflict and intralocus sexual conflict hypotheses. Under interlocus sexual conflict hypothesis we can diffferentiate parental conflict hypothesis and parent-offspring conflict hypothesis. These theories were historically proposed for the first two taxonomical groups, where genomic imprinting was discovered, namely for angiosperms and placental mammals. Theory of parental conflict proposes that genomic imprinting evolved because the paternally inherited alleles are more selfish to mothers than are the maternally inherited alleles. Parent-offspring conflict hypothesis proposes that genomic imprinting evolved because maternal genes try to regulate demands of paternally inherited alleles in embryos. More recently, genomic imprinting has been found also in other taxons and in alleles, which do not bring any advantage during embryonic development. The intralocus sexual conflict hypothesis is applicable for every trait under sexually-specific selection. It provides potential...
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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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Origin, degeneration and detection of sex chromosomes
Jílková, Klára ; Král, Jiří (advisor) ; Kratochvíl, Lukáš (referee)
Sex chromosomes evolved from a pair of autosomes and they are differentiated as a result of supression of recombination. This process leads to a successive degradation of odd sex chromosome (alosome), which is becoming genetically inert finally or even excluded. Fundamental processes taking part in degeneration of alosome are Muller's ratchet, genetic hitchhiking, background selection, accumulation of transposable elements and constitutive heterochromatin. Indeed, these processes take part in either degeneration of both Y or W chromosomes. Remarkably, these alosomes show different rates of degeneration, most probably due to 1) different structure of male and female gonads as well as 2) different course of gametogenesis in both sexes. Furthermore, rate of alosome degeneration is usually lower in plants because they are haploid during the major part of life cycle. Other mechanisms of sex chromosome evolution involve rearrangements between autosomes and gonosomes, nondisjunctions and fissions of original sex chromosomes, transformation of B chromosomes into sex chromosomes or non-random segregation of autosomes with sex chromosomes. Other phenomenon that appears in sex chromosome evolution is transition between XY/XX and ZW/ZZ systems or transition between chromosomal sex determination and epigamy. Actually,...
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Reproductive Strategies of Geckos: The Role of Macroevolutionary Novelties and Phenotypic Plasticity
Kubička, Lukáš ; Kratochvíl, Lukáš (advisor) ; Rehák, Ivan (referee) ; Boukal, David (referee)
Presented Ph.D. thesis contains an introduction and four chapters concerning reproductive strategies in geckos. The chapters include four peer-reviewed papers and a submitted manuscript. All geckos share rather exceptional reproductive trait known as invariant clutch size, which is characterised by low and invariable clutch size. The first chapter demonstrates that invariant clutch size probably evolved in geckos under selection for enlargement of investment per offspring. On the other hand, in anoles (a group not related to geckos possessing the same mode of reproduction) invariant clutch size allowed considerable decrease of female reproductive burden. Moreover, the interspecific allometries of egg mass and clutch mass in anoles and geckos are informative for understanding of reproductive allometries in a broader context of squamate reptiles. The second chapter is focused on a trade-off in energy investment among reproduction, growth and fat storage in a gecko Paroedura picta. Surprisingly, there seems to exist a clear hierarchical rule for allocation among particular life-history traits. Effect of temperature on reproductive rate in the same species of gecko is the subject of the third chapter. Observed thermal dependence is in contrast to the general relationship suggested under the so-called...
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Evolution of brain size in bats (Chiroptera)
Králová, Zuzana ; Němec, Pavel (advisor) ; Kratochvíl, Lukáš (referee)
According to the prevailing doctrine, brain size has mainly increased throughout the evolution of mammals and reductions in brain size were rare. On the other hand, energetic costs of developing and maintaining big brain are high, so brain size reduction should occur every time when the respective selective pressure is present. Modern phylogenetic methods make it possible to test the presence of evolutionary trend and to infer the ancestral values of the trait in question based on knowledge of phylogeny and trait values for recent species. However, this approach has been rarely applied to study brain evolution so far. In this thesis, I focus on bats (Chiroptera). Bats are a suitable group for demonstrating the importance of brain size reductions. Considering their energetically demanding mode of locomotion, they are likely to have been under selection pressure for brain reduction. Furthermore, there is a large amount of data on body and brain mass of recent species available. Finally, phylogenetic relationships among bats are relatively well resolved. My present study is based on body masses and brain masses of 334 recent bat species (Baron et al., 1996) and on a phylogeny obtained by adjusting existing bat supertree (Jones et al., 2002) according to recent molecular studies. Analysing the data for...
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