|
|
Detection of positive selection in reproductive genes of songbirds
Cakl, Lukáš ; Reifová, Radka (advisor) ; Těšický, Martin (referee)
Reproductive genes are assumed to play an important role in adaptive evolution and speciation, yet little is known about the patterns of molecular evolution in these genes within avian species. This thesis is focused on identifying reproductive genes under positive selection and analyzing their function in songbirds, the largest and most diverse suborder of modern birds. Using existing bioinformatic approaches and published genomic data of 14 songbird species, we have first constructed 12000 groups of orthologous genes and detected significant traces of recurrent positive selection within 385 of them. Using proteomic data, this genome wide set of genes was then filtered to obtain genes expressed within songbird spermatozoa and fluids from the female reproductive tract. Within spermatozoa 22 out of 940 expressed genes were positively selected, while female fluids were found to be more conserved, as only 6 out of 529 expressed genes have shown traces of positive selection. We have then computed the enrichment of gene ontology terms within the positively selected genes. The enriched terms suggest evolutionary pres- sures acting on spermatozoa cytoskeleton, molecular motors and energetic metabolism, highlighting the importance of sperm morphology and swimming speed. Furthermore, the enrichment results...
|
|
|
Meiotic effect of MutS homolog 6 (Msh6) mutation in two mouse subspecies
Fusek, Karel ; Forejt, Jiří (advisor) ; Reifová, Radka (referee)
To study hybrid sterility our laboratory uses mouse strains PWD/Ph (PWD), derived from Mus musculus musculus wild mice and the common laboratory strain C57BL/6J (B6) mostly of Mus musculus domesticus origin as a model. Crossing between PWD female and B6 male results in sterile male progeny. F1 hybrid males carry defects in the repair mechanisms of asymmetric double-strand DNA breaks (DSBs). Functional interplay of SPO11 and PRDM9 proteins in the meiotic prophase I is necessary for repairs. Its defect leads to incorrect synapse formation between homologous chromosomes, leading to halt in spermatogenesis and thus male sterility. The formation of DSBs and their subsequent repair is essential for first meiotic division. The working hypothesis stems from the findings in yeast model, where supposed antirecombinatorial mechanism of mismatch repair genes Msh6 and Msh2 prevents DSBs repairs during meiosis. Despite the functional mechanism of these two genes is not explicitly known, existence of similar repair system in mice is presumed. Variety of methods was implemented in this thesis. The effects of Msh6 deletion on meiotic prophase I and sperm maturation were performed by designing guide RNAs for CRISPR/Cas9 for creation of three knock-outs in B6 mice. The PCR was used to amplify regions adjacent to the...
|
|
|
Karyotype evolution in estrildid finches of the genus Lonchura
Janáková, Šárka ; Reifová, Radka (advisor) ; Augstenová, Barbora (referee)
The karyotype, the set of all chromosomes in a cell, is an important characteristics of individual species of both animals and plants. The karyotype of birds is typically stable in terms of the number of chromosomes and their size, and rearrangements between different chromosomes are rare. The changes that occur between the karyotypes of avian species are more often intrachromosomal, such as inversions or duplications and deletions. It is still unclear how often such changes occur between closely related species and whether they can contribute to speciation. This work aims to compare the karyotypes of a total of five closely related species of songbirds of the genus Lonchura (munias and mannikins). Comparing chromosomal changes in such recently diverged species allows us to observe changes that might contribute to speciation. The study is based on karyotype analysis by immunofluorescence staining of synapsed pachytene chromosomes and subsequent identification and comparison of chromosome types. This method allows determination of the changes that are manifested by pericentric inversions where the position of the centromere is changed. The results confirm the general idea of avian karyotypes as very conservative in terms of chromosome number and their sizes. However, in some chromosomes we observed...
|
|
|
Speciation mechanisms and the role of reinforcement in mammals
Horký, Jakub ; Hulva, Pavel (advisor) ; Reifová, Radka (referee)
Speciation, the process of the formation of new species, comprises a diverse range of microevolutionary mechanisms acting in unison, which lead to the gradual formation of reproductive barriers between populations. The study of speciation has significantly progressed since its origins around the midpoint of the nineteenth century, owing to progressively improving analytical methods and the data said methods obtained, allowing us to observe previously invisible patterns and form new hypotheses on their basis. From traditional to modern research, this review's goal is to describe the contemporary understanding of speciation's concepts and mechanisms, focusing on those which are most relevant to mammals. Modern understanding of spatial contexts, prezygotic and postzygotic isolating mechanisms, and character displacement, including a type of reproductive character displacement dubbed reinforcement, are discussed. Significant emphasis is placed on the topics of maladaptive and adaptive hybridization, which, together with reinforcement and development of new genomic methods, has this review identified as the current frontier of speciation research. Keywords: reproductive isolating mechanisms, microevolution, character displacement, hybridization, reinforcement, speciation
|
|
|
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....
|
|
|
Reproductive isolation barriers in the hybrid zone of the house mouse (Mus musculus)
Albrechtová, Jana ; Piálek, Jaroslav (advisor) ; Sedláček, František (referee) ; Reifová, Radka (referee)
Reproductive isolation occurring at the gamete level is called gametic isolation and almost always prevents gene flow between unrelated species and (to some extent) between closely related species or subspecies. The hybrid zone of the house mouse (HMHZ), which was formed by contact and interbreeding of two subspecies, the Western European house mouse (M. m. domesticus) and the Eastern European house mouse (M. m. musculus) provides a usefull model for the study of speciation processes involving gametic isolation. The probability of sperm competition within the female reproductive tract is high in the house mouse because high levels of sexual promiscuity (in 20˗40 % of all reproductive cycles) have been observed in this species. Thus, the reproductive isolation at gametic level may be determined both by the phenotypic characteristics of sperm (the ability to outcompete heterospecific sperm in the process of sperm- sperm competition) and by the preference of the sperm of conspecific males in the female reproductive tract (cryptic female choice). In my Ph.D. thesis I tested the degree of affinity of male and female gametes reciprocally between the both subspecies of M. musculus and the phylogenetically more distant species M. spretus, which is characterized by a higher degree of promiscuity. Although a...
|
|
|
The role of Prdm9 in the house mouse hybrid sterility model
Mukaj, Amisa ; Parvanov, Emil (advisor) ; Děd, Lukáš (referee) ; Reifová, Radka (referee)
(English) Hybrid sterility is a phenomenon representing reproductive isolation between closely related species and thus assuring the process of speciation. Hybrid sterility is a complex polygenic trait and the most significant advance in its study is achieved in Drosophila melanogaster. Nearly half century ago Forejt and Ivanyi mapped the first hybrid sterility genetic locus in vertebrates (Hybrid sterility 1, Hst1) in crosses of wild mice with laboratory inbred strains where the male offspring is sterile. Further mapping of the locus led to discovery of a gene called PR domain zinc finger protein 9 (Prdm9), a histone methyltransferase, whose deficiency causes meiotic arrest and sterility in mice. Furthermore, it was found that Prdm9 defines the hotspot placement in meiotic recombination by posting trimethylation marks on lysine residues 4 and 36 of histone 3 hence explaining the observed defects in its absence during meiosis. Nonetheless, its exact role in molecular mechanism of hybrid sterility is yet unclear. Prdm9 expression is present during the stage of formation of meiotic DNA double-strand breaks and is a hint about the time of hybrid sterility initiation. Phenotypically in the case of male mouse hybrid sterility is observed incomplete chromosome synapsis, meiotic arrest at mid-to-late...
|
|
|
Parental conflicts and speciation in the house mouse
Kropáčková, Lucie ; Reifová, Radka (advisor) ; Macholán, Miloš (referee)
Hybridization between closely related species of mammals is often accompanied by abnormal growth of placentas and fetuses. From the perspective of evolutionary biology, our knowledge about the contribution of such interspecies incompatibilities in speciation is still insufficient. In my thesis, I was finding out if abnormal placental and fetal growth contributes to reproductive isolation of two subspecies of house mouse, Mus musculus musculus and M. m. domesticus, which are at an early phase of speciation and in nature they still hybridize. Using two inbred strains derived from M. m. musculus (PWD/Ph, STUS) and two inbred strains derived from M. m. domesticus (C57BL6/J, SCHEST) we performed four different intrasubspecies and four different intersubspecies crosses. We found out that the size of the placenta in hybrids is more influenced by father, while the size of the fetus is more influenced by mother. After elimination influence of weight of mother and father we have not recorded a significant difference in the size of placentas and fetuses in intrasubspecies and intersubspecies crosses. Our results show that hybridization between subspecies of house mouse does not produce abnormalities in prenatal development, as was observed in hybrids between distant species of mice. It is thus possible that...
|
|
| |
|
|
Genetic basis of phenotypic variability in domesticated animals
Majerová, Veronika ; Reifová, Radka (advisor) ; Komárek, Stanislav (referee)
Understanding the mechanisms responsible for the origin of morphological variability among different species of animals represents an important goal in evolutionary biology. Origin and changes of the phenotypic variability during the evolution is possible to study in domesticated animals. The domesticated species of animals represent a brilliant model for studying the molecular mechanisms responsible for origin of new phenotypes due to enormous morphological variability of different domesticated breeds, effortless breeding in captivity and frequent knowledge of the genomic sequence. The aim of this bachelor work is to summarize actual findings about concrete mutations which are responsible for the origination of the new morphological characters in the domesticated animals. These findings can help us to clarify how the evolution functions on the molecular level.
|
guest ::
