National Repository of Grey Literature 24 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Hybridisation of cyprinid fishes in the Czech Republic: genetic and morphometric analysis of the subfamily Leuciscinae
Kaufman, Vít ; Musilová, Zuzana (advisor) ; Choleva, Lukáš (referee)
Hybridization is a process when two interspecific individuals mate and spawn. When backcrossing it often goes hand in hand with admixing unrelated genome into the genome of a species. Nowadays it is well established that hybridization is not as uncommon as it was believed. Especially in vertebrates fish are quite common in such phenomena. In Leuciscids, the family of order Cypriniformes is relatively frequent. It is a rife family in the European freshwater systems. Factors that contribute to such frequent hybridization are extraneous fertilization, sympatric occurrence, competition for spawning grounds, and other ecophysiological traits. It was known since the second half of 20th century that this is an ongoing phenomenon in many species of this family. Previous research was focused mainly on morphological traits. The relative pinnacle of such research was based on allozymic analysis. The goal of our project was to evaluate the level of hybridization in the main water bodies of the Czech Republic with the main focus on the detection of involved hybrid species, the level of such hybridization, and the phenotypic characterization of hybrid individuals. For that reason, it was sampled over 400 specimens giving a dataset of 381 individuals. Tissue samples were sampled for DNA isolation and each of the...
Population connectivity and isolation in cetaceans
Žirovnický, Martin ; Hulva, Pavel (advisor) ; Choleva, Lukáš (referee)
This bachelor thesis focuses on the specifics of research in the field of population connectivity and genetic isolation of marine mammals, with an emphasis on cetaceans. The thesis is divided into three parts. The first part introduces the methods and approaches in landscape genetics and seascape genetics. The second part deals with environmental factors influencing the genetic structure of cetacean populations, such as geographic barriers, water temperature, behaviour, or human-created barriers. The last part addresses the ways of protecting cetaceans and the application of population connectivity research in the areas where cetaceans reside. The aim of the thesis is to present the issue of phylogeography of marine mammals, particularly cetaceans, and to demonstrate the significance of protecting these endangered species in the contemporary world.
How many times and why did (not) hermaphroditism evolve in Deuterostomia?
Tribulová, Lucia ; Vukićová, Jasna (advisor) ; Choleva, Lukáš (referee)
The Deuterostomia are large and highly diversified group that also includes vertebrates. Most species are gonochorists and only a small percentage are hermaphrodites. The predominantly hermaphroditic group is the tunicates, and among the vertebrates, hermaphrodites are known mainly in teleost fishes. In other groups, only a few hermaphroditic species are known. According to general ecological-evolutionary models, hermaphroditism arises in environments where there is a low abundance of individuals ("low density model") or when the reproductive value of one sex is favoured with larger size ("size advantage model"). Deuterostomia are an excellent model group for testing these models; teleost fishes, in particular, abounding in a variety of social and reproductive systems, are well suited for testing the "size advantage" model. The aim of this work is to determine from the available literature how many times and in which groups hermaphroditism has occurred in Deuterostomia, why it has evolved in these groups, and whether the occurrence of hermaphroditism fits general ecological-evolutionary models. Key words: hermaphroditism, deuterostomia, protandry, protogyny, simultaneous hermaphroditism
Mechanisms of reproductive isolation between two hybridizing passerine species, the common nightingale and the thrush nightingale
Poignet, Manon ; Reifová, Radka (advisor) ; Choleva, Lukáš (referee) ; Kratochvíl, Lukáš (referee)
iv - ABSTRACT (in English) - A key step in the origin of new species is the evolution of the reproductive isolation mechanisms separating the gene pools of newly emerging species. Despite a growing number of studies, we still know very little about the molecular, physiological and genetic mechanisms underlying reproductive isolation. Hybrid zones represent useful examples of ongoing species differentiation and can provide information about the nature of reproductive isolation separating the species and mechanisms facilitating or limiting the hybridization. Using two naturally hybridizing passerine species, the common nightingale (Luscinia megarhynchos) and the thrush nightingale (L. luscinia), we evaluated several mechanisms of reproductive isolation at the chromosomal, phenotypic, and genetic levels, with a focus on postmating prezygotic (PMPZ) and postzygotic isolation mechanisms. These nightingale species diverged ~1.8 Mya and currently hybridize in a secondary contact zone running across Central and Eastern Europe. First, we analysed the genetic composition of the secondary contact zone, demonstrating that parental forms are predominant in the hybrid zone, with few F1 hybrids (3.4%), early backcross hybrids (3.1%) and the absence of F2 hybrids. This suggests strong but incomplete reproductive isolation....
Telestes perspective on the karstic poljes of eastern Herzegovina
Doulíková, Tereza ; Vukićová, Jasna (advisor) ; Choleva, Lukáš (referee)
The Dinaric karst region in the Balkans is one of the hot spots of biodiversity with a high number of endemic freshwater fish. The major cause of the high degree of endemism are numerous paleoclimatic and geological events that have affected the formation of the entire area. Flows of karst poljes represent a specific ecosystem to which some fishes have adapted. The poljes have been periodically flooded and these floods may activate different underground channels, which lead to interconnection of poljes. These fish species spend a part of the year in surface water and a part in groundwater and they may use the underground flows between poljes for migration. The aim of this thesis is to evaluate the genetic variability of two endemic fish species of the genus Telestes living in karst poljes in the region of eastern Herzegovina, and to detect a possible current gene flow between populations of these species due to the connection of underground flows. For this purpose, the DNA from 102 individuals from five different localities was isolated. The mitochondrial marker cytochrom b and 16 microsatellite loci were used for the analyses. The results point to very low variability between species and populations. Based on mitochondrial marker analysis, no link between populations of the species was detected,...
How to become a critically endangered species: a review of the distribution and status of the crucian carp (Carassius carassius)
Janda, Benedikt ; Choleva, Lukáš (advisor) ; Lojkásek, Bohumír (referee)
The Crucian carp (Carassius carassius) is the native species of fish in European standing and slowly flowing waters. Thanks to their high resistance to adverse abiotic conditions, they also inhabited dead arms of river, ponds and floodplains. Despite its resilience, this species has been declining or completely retreating from the most of natural habitats since the middle of the 20th century. The negative direct human interventions into the species populations were, intensive fishing and the elimination of suitable habitats as a result of landscape defragmentation, which was part of flood control measures. Secondly, the human-made introductions of non-native species, the Gibel carp (Carassius gibelio), capable of gynogenetic reproduction, strongly competes with the native species for resources. The extent to which the situation of the native Cruvian carp is critical and ow it has historically occured is revised in the formo f literaly search by this bachelor's Thesis. Keywords The Crucian carp, gynogenesis, molecular genetic methods, cytochrome b gene, taxonomy, hybridization, introduction, microsatellites
Evolution of sex chromosomes and karyotypes in geckos (Squamata: Gekkota)
Koubová, Martina ; Kratochvíl, Lukáš (advisor) ; Choleva, Lukáš (referee)
Gekkota is species-rich and diverse group of squamate reptiles (Reptilia: Squamata) with almost global distribution. There were many hypothesis defined about the phylogeny of this group, traditionally based on morphological data. The essential reversal in phylogenetic relationships occurred with the entry of molecular analysis, whose differ in their conclusions from traditional approach fundamentally, even in positions of mayor lineages. This fact has an essential importance for the karyotype evolution study of this group. The ancestral state is considered as 2n=38 karyotype with all chromosomes acrocentric. In some species is this karyotype kept, in another there is apparent an influence of chromosome changes, mostly Robertsonian fusions and pericentric inversions. Diploid chromosome number is from 16 to 46, but the most common is 2n=38 karyotype of mostly acrocentric chromosomes, gradually decreasing in size. The interesting character of this group is extraordinary variability in sex determining mechanisms. We can find there species with temperature sex determination and also species with genotypic sex determination (both types XX/XY and ZZ/ZW). Sex chromosomes data are documented in only 17 species. Sex chromosomes differ rapidly in their morphology and their homology between sister taxa was not proved...
Earlier evolutionary dead-ends, now the creators of a reproductive strategy: the origin and reproduction of the all-male water frog lineage Pelophylax esculentus
Doležálková, Marie ; Choleva, Lukáš (advisor) ; Mikulíček, Peter (referee) ; Kratochvíl, Lukáš (referee)
Asexual modes of reproduction are usually based on the principle of copying (cloning) DNA from the female and passing it on to the offspring. For most asexually reproducing vertebrates the progeny develop from an unreduced and often unfertilised egg. This is driven by the mechanisms of parthenogenetic and gynogenetic reproduction. While in the former the clonal germ cell develops spontaneously and separately, in the latter a sexual partner is needed to activate the cleavage of the ovum, although without the fusion of the sperm and egg. Therefore in both cases there is no fertilization and the clonal progeny consist solely of daughters, hence the majority of previous studies have only focused on asexual female lineages. However, on rare occasions asexual clonal males can arise when the right fertilization occurs. Whilst these offspring are usually infertile, fertile diploid asexual males have been discovered in just three genera of hybrid origin in vertebrates. One of these unique cases is the European water frog complex of the genus Pelophylax, whose distribution includes the Czech Republic. In areas around the upper Odra River populations of hybrid males were recently discovered who form stable all-male lineages, similar to those formed by asexual females. The results of this study show that males produce...
Whole-genome analysis of the house mouse hybrid zone
Janoušek, Václav ; Munclinger, Pavel (advisor) ; Choleva, Lukáš (referee) ; Chan, Yingguang Frank (referee)
Hybrid zones provide a valuable opportunity to study the process of speciation in real time. Untested combinations of genes from diverging populations come to the contact here causing a breakdown of genetic interactions and giving rise to reproductive isolation. Two house mouse subspecies (Mus musculus musculus/Mus musculus domesticus) form a narrow zone of secondary contact across Central Europe which is thought to be maintained by a balance between selection against unfit hybrids and dispersion of individuals. During my PhD study my collaborators and I used an array of ~ 1400 SNP markers to study patterns of introgression on a genome-wide scale across two/three house mouse hybrid zone transects. Our aim was to identify the genomic regions putatively harboring genes which are involved in the reproductive isolation between the two subspecies, characterize their distribution in mouse genome and assess genomic features associated with them. We were able to confirm on a genome-wide scale the importance of the X chromosome in the evolution of reproductive isolation. This chromosome exhibited introgression corresponding to strong negative epistasis and the patterns were consistent between transects pointing out to a common basis of reproductive isolation playing a role in two transects. Contrary to the...
Out of Asia Minor into Danube Drainage: Phylogeography and colonisation pathways in the loach fish Cobitis strumicae
Majtánová, Zuzana ; Choleva, Lukáš (advisor) ; Reichard, Martin (referee)
The spiny loach Cobitis strumicae is a small bottom-dwelling freshwater fish whose progenitor colonised the Balkan Peninsula from the Near East through the Asia Minor. The current geographic distribution of C. strumicae forms a ring around the Stara Planina (Balkan mountains), inhabitting Danube Basin and coastal rivers of Black Sea and Aegean Sea. Using one marker of mitochondrial DNA (gene for cytochrom b) and one marker of nuclear DNA (S7 gene, first intron), we reconstructed the species distribution and phylogenetic relationship of 44 populations throughout C. strumicae distribution. We also analysed its sister species, C. punctilineata, which lives inside the distribution area of C. strumicae. Aplication of four phylogenetic approaches confirm the monophyly and species statut and endemicity of C. punctilineata, and, moreover, the evidence of secondary hybridization with C. strumicae was found. The network analysis using median-joining method showed deep divergence between the both species. Phylogenetic analyses for cyt b gene confirmed the monophyly of C. strumicae, with internal substructure into at least two well divided lineages, which suggests the process of local speciation. Phylogenetic analyses of S7 gene did not support the monophyly of C. strumicae. Instead, the two separated...

National Repository of Grey Literature : 24 records found   1 - 10nextend  jump to record:
Interested in being notified about new results for this query?
Subscribe to the RSS feed.