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Enamel cover of the mammalian teeth: structural, functional, developmental and phylogenetic aspects.
Hanousková, Pavla ; Horáček, Ivan (advisor) ; Němec, Pavel (referee)
Specificities of the mammalian teeth and their enamel coat with particular re- spect to the autapomorphies establishing the mammalian organization. Basic structural and organizational levels of the enamel histology (nanocrystals, elementary crystallites, prismatic enamel, IPM, schmelzmuster, ultimate characteristics of particular dentitions). Basic survey of comparative data: characterization of enamel of mammals in particular clades and a brief summary of their specificities. Concluding remarks on current state of knowledge and per- spectives of further study. 1
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Effect of weak magnetic fields on animal physiology and behavior
Štefanská, Lucie ; Němec, Pavel (advisor) ; Vácha, Martin (referee)
Weak magnetic fields from different sources constitute a part of the environment, in which animals live. Therefore one can suppose their effect on animal behavior and physiology, including ontogenetic development. The geomagnetic field is ubiquitous and life on Earth has been accompanied by it from the very beginning. Therefore it seems not to be surprising, that diverse animals are able to detect the geomagnetic field and use it as a cue for orientation and navigation, the ability referred to as magnetoreception. Despite being phylogenetically widespread, the transduction mechanisms and the neural basis of magnetoreception and magnetic orientation remain largely unclear. Three major hypotheses are gaining experimental support: mechanisms based on electromagnetic induction, biogenic magnetite and radical pair reactions. In addition to magnetoreception, various other effects of week magnetic fields on organisms have been reported. Most notably, irregular changes of the geomagnetic field (especially geomagnetic storms) and alternating artificial magnetic fields, which have appeared in the environment due to electrification, are considered to have an effect on locomotor activity, learning and memory, nociception, melatonin synthesis and circadian rhythms, cardiovascular system, gene expression and...
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Neuromorphology of the visual system in microphthalmic mammals: Identification of the primary visual cortex in strictly subterranean African mole-rats and visual acuity in echolocating bats
Miklušová, Zuzana ; Němec, Pavel (advisor) ; Druga, Rastislav (referee)
Microphthalmia has evolved in evolution many times independently within unrelated groups of mammals (e.g., subterranean rodents, insectivores, afrosoricids and marsupials; echolocating bats, and shrews). Due to such extensive convergent evolution, investigation of mammals with reduced eyes provides a unique approach for understanding the adaptive significance of sensory regression and the impact of peripheral reduction on organization of central sensory structures. This thesis focuses on two issues. In the first part of this thesis, a search for the primary visual cortex (V1) has been conducted in two bathyergid species, the Ansell's mole-rat, Fukomys anselli and the giant mole-rat Fukomys mechowii. Utilizing retrograde tracing and the technique of flattening and sectioning the cortex to visualize area boundaries, I have evidenced the presence of the V1 in the both species. It was small and, in comparison to other rodents, displaced laterally. Multiple injections of different tracers in different regions of the V1 resulted in retrograde labeling of distinct region of the dorsal lateral geniculate nucleus (DLG), implying conservation of the retinotopic organization within the geniculo-striate pathway. However, any injection into V1 resulted also in a robust retrograde labeling of the multimodal...
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Magnetic orientation in mammals
Tejmlová, Kristýna ; Němec, Pavel (advisor) ; Vácha, Martin (referee)
Earth's magnetic field can provide animal with both directional and positional information. The ability to perceive and utilize information extracted from the geomagnetic field is called magnetoreception. Magnetoreception mechanisms remain largely unknown. Three main hypotheses are currently supported by experimental evidence. The light-independent mechanisms are based either on electromagnetic induction or on biogenic magnetite. The light-dependent mechanism is based on specific chemical reaction between radical pairs. Perception of the geomagnetic field facilitates both long- and short-distance orientation of animals. Some animals exhibit the magnetic alignment, i.e., spontaneuos preference for a certain geomagnetic direction. Another manifestation of magnetoreception is magnetic compass (polarity- or inclination-based, depending on species), which enable an animal to determine the azimuth, i.e., the angle between the direction of motion and geomagnetic field vector. Magnetic map sense enable an animal to determine its position and direction to the goal destination, most likely utilizing the inclination and the intensity of the geomagnetic field as navigational cues. Magnetic orientation of mammals seems to be a widespread phenomenon. Light- independend, polarity compass has been reported in...
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Primary sensory cortices of microphthalmic mammals, adaptations to habitat and lifestyle
Miklušová, Zuzana ; Němec, Pavel (advisor) ; Druga, Rastislav (referee)
Microphthalmia has evolved in evolution many times independently within unrelated groups of mammals (e.g., rodens, echolocating bats, shrews). Due to such extensive convergent evolution, investigation of mammals with reduced eyes provides a unique approach for understanding the adaptive significance of sensory regression, the impact of peripheral reduction on organization of central sensory structures and cross-modal reorganization or compensation. In this thesis I review our current knowledge concerning the organization of the primary sensory cortex in microphthalmic mammals. In subterranean species (the eastern mole, Scalopus aquaticus; the star-nosed mole, Condylura cristata; the blind mole rat, Spalax ehrenbergi; the naked mole rat, Heterocephalus glaber) is obvious expansion of somatosensoty cortex, which processes tactile information.The sense of touch plays a pivotal role in orientation in their dynamically changing three-dimensional burrow systems. Microphthalmic, echolocating bats whose body is adapted to flight have topographicly reorganized somatosensory cortex, reduced the visual cortex and expanded, complexly organized acoustic cortex. Terrestrial shrews (Soricidae, Insectivora) do not posses any specific adaptations at level of the sensory cortex. Interestingly, their primary visual cortex is...
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Neural crest biology with respect to diversity of vertebrates
Štundl, Jan ; Černý, Robert (advisor) ; Němec, Pavel (referee)
Neural crest is an extensively migrating population of cells that arise during early development of vertebrate embryos. It provides a huge variety of different cell types that generate new tissues which occur only in vertebrates. Neural crest cells together with the mesoderm participate on the formation of the head of vertebrates, which is viewed as one of the most important innovations in the evolution of vertebrates. Thanks to their skeletogenic potencial neural crest cells are percieved as a key factor causing massive craniofacial diversity. The aim of this thesis was to get acquainted with the population of neural crest cells and try to understand its importance for the evolution of vertebrates and especially for generating craniofacial diversity.
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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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Cognitive functions of birds based on abstract visual stimuli
Štorchová, Zuzana ; Landová, Eva (advisor) ; Němec, Pavel (referee)
Spatial orientation of pigeons on a small scale was intensivelly studied in experiments using various types of arenas or mazes. In these experiments pigeons usually searched for food hidden in the goal area and they based their orientation on available landmarks. The development of new technologies allowed to test spatial cognition of pigeons also in virtual tasks, based exclusively on a schematic representation of an arena or maze on a touch screen. In experiments of this type pigeon marks the goal by pecking and it is rewarded by food from a feeder, located near the monitor. Study presented in this diploma thesis was based on combination of both types of spatial tasks. The information crucial for locating the goal was presented to pigeons on a computer screen in form of graphic stimuli, whereas the goal itself was formed by one of the 4 holes in corners of a transparent rectangular desk, standing in front of the monitor. Experiment with similar design was not yet published in the study of spatial cognition of pigeons. Two types of abstract graphic stimuli were tested. The first stimuli provided a spatial information about the location of a goal and had a form of small rectangular frame with a white spot in one of its corners. The frame represented the space of the response desk and the white spot...
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Photoreceptors properties in strictly subterranean African mole-rats
Krejčová, Tereza ; Němec, Pavel (advisor) ; Kott, Ondřej (referee)
4 Photoreceptor properties and distribution in strictly subterranean African mole-rats (Rodentia, Bathyergidae) The visual system of subterranean rodents is assumed to be regressed in response to their lightless ecotope. According to the prevailing doctrine, negative or non-selective processes have driven evolutionary regression of the visual system in many unrelated groups of rodents that has adopted strictly subterranean mode of life. Among rodents this has been exemplified by detailed studies of the blind mole-rat Spalax ehrenbergi. However, recent studies involving a larger spectrum of subterranean rodent species demonstrated unexpected diversity of retinal properties and visual system designs among subterranean rodent species and thus challenged the widely held view that the visual system has undergone extensive convergent evolution in subterranean mammals. This paper examines the presence, the distribution, and photoreceptor properties in the African mole-rats (Bathyergidae, Rodentia). It describes rodopsin, S- and L-opsin expression patterns, photoreceptor densities and rod/cones proportions in five species of bathyergid mole-rats, namely Bathyergus suillus, Georychus capensis, Fukomys damarensis, Cryptomys natalensis and Heliophobius argenteocinereus. Spectral cone types and rods were assessed...
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