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Evolution of brain complexity and processing capacity in birds: Cracking the problem using isotropic fractionator technique
Kocourek, Martin ; Němec, Pavel (advisor) ; Sedláček, František (referee) ; Kratochvíl, Lukáš (referee)
The most fundamental principle of comparative sciences has always been and still is the search for similarities and differences. Maybe that is why people are fascinated by the cognitive abilities of birds like corvids and parrots and their similarities to those of humans. For a long time, the prevailing explanation for the unique abilities of these species was their high relative brain size. However, the brain's processing capacity is not based on its size but on its internal architecture and the number of neurons and synapses. Today, we already have data on the numbers of neurons for hundreds of mammalian, avian, and reptilian species, obtained with the isotropic fractionator. In this thesis, I analyse cellular scaling rules for brains of birds and compare them between avian clades. Bird brains are characterized by large numbers of neurons and high neuron densities, which are comparable to those of mammals in gallinaceous birds (Galliformes) and in passerine birds (Passeriformes) and parrots (Psittaciformes) even exceed those observed in primates. The distribution of neurons is also different. In songbirds and parrots, the majority of neurons are typically located in the telencephalon, specifically in the pallium. The latest data suggest that this is a common feature of core land birds...
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Evolution of brain complexity and processing and cognitive capacity in selected vertebrates
Kverková, Kristina ; Němec, Pavel (advisor) ; Stuchlík, Aleš (referee) ; Iwaniuk, Andrew N. (referee)
Brain processing capacity has traditionally been inferred from data on brain size. However, recent studies have shown that similarly sized brains of distantly related species can differ markedly in the number and distribution of neurons, their basic computational units. There- fore, a finer-grained approach is needed to reveal the evolutionary paths to increased cogniti- ve capacity. This quantitative approach to the evolution of brain processing capacity at the cellular level is relatively new, since quick and reliable estimation of the number of neurons in whole brains or large brain regions has only become possible in the past 15 years or so with the introduction of the isotropic fractionator. This method of determining brain cellular com- position is applicable to a wide range of questions. We can assess intraspecific variation, both at the individual and population level, examine the effect of sex and age, and the study se- lection at the intraspecific level. At the other side of the spectrum, we can study large macro- evolutionary trends or try to isolate the effect of specific selective pressures by comparing more closely related and ecologically similar species. In this thesis, I explored variation in brain size and brain cellular composition across vertebrates at both intraspecies and...
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Cellular composition of brains for hornbills, woodpeckers and coraciiform birds
Stehlík, Patrik ; Němec, Pavel (advisor) ; Kratochvíl, Lukáš (referee)
Recent comparative studies have shown that bird brains, although small, have a high processing capacity. The brains of parrots and songbirds have higher neuronal densities than brains of mammals; especially large parrots and corvids compete with or even outnumber primates by the number of telencephalic neurons. However, the processing capacity of the avian brain appears to differ significantly between various phylogenetic lineages. Basal groups such as galliform birds have much lower absolute numbers of neurons and lower neuronal densities than songbirds and parrots. In this Master thesis, I used the isotropic fractionator to determine numbers of neurons and non-neural cells in specific brain regions in 19 species of hornbills (Bucerotiformes), woodpeckers (Piciformes) and coraciiform birds (Coraciiformes). The brains of hornbills and woodpeckers (but not coraciiform birds) have numbers of neurons comparable to that of songbirds and parrots and significantly more neurons than equivalently sized brains of pigeons (Columbiformes) and galliform birds (Galliformes). In the crown groups, we can observe similar trends such as a higher degree of encephalization, a proportionally larger telencephalon and increasing percentage of telencephalic neurons. On the contrary, in pigeons and galliform birds, we can...
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The effect of incubation temperature on cognition and brain cellular composition in geckos Paroedura picta
Polonyiová, Alexandra ; Němec, Pavel (advisor) ; Sedláček, František (referee)
The effect of incubation temperature on different morphological, physiological, cognitive and behavioral characteristics in reptiles is a well-studied topic, although the underlying mechanism leading to the differences between individuals incubated at different temperatures remains largely unknown. In this thesis I studied the effect of incubation temperature on cognitive abilities and the number of neurons and non-neuronal cells in the gecko Paroedura picta incubated at two different temperatures, 24řC and 30řC. The geckos were tested in two cognitive tasks with simulated predatory attack. 14-day-old hatchlings were tested in a Y-maze, while 6-months-old geckos were tested in an arena with shelters of different colors. After testing, the number of neurons and non- neuronal cells in several parts of the brain were estimated using the isotropic fractionator in selected individuals. Although incubation temperature did not affect the success in the cognitive task in hatchlings, it did affect the total time needed to find the shelter. This difference remained significant also in adult geckos. The number of neurons, which was used as a proxy for the information processing capacity of the brain, did not affect success in the cognitive tasks. However, absolute brain size correlated with success in the...
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Cellular scaling rules for dog brains: Effect of domestication and miniaturization of dog breeds
Salajková, Veronika ; Němec, Pavel (advisor) ; Chaloupková, Helena (referee)
The process of domestication of the grey wolf (Canis lupus) resulted in more than 350 dog breeds attesting for an immense phenotypic plasticity of this species, reflected in the enormous variation of sizes, shapes and behavioural profiles of today's dogs. The differences in body size can be 50-fold, which exceeds the body size variation of all recent canids. The differences in brain size are significantly smaller, only about 2.5-fold. It is also well known that, compared to their wolf ancestor, dogs, and especially small breeds, have reduced brain size. However, up till now, no comparative data about neuron numbers in different dog breeds are available. In this thesis, I use the isotropic fractionator to assess number of neurons and glial cells in eight dog breeds and three species of wild canids. When compared across dog breeds analysed, the differences in neuron numbers are lower than the differences in brain size - it seems that small breeds compensate for smaller brains with higher neuronal density. Interestingly, miniaturization of dog breeds is associated with brain size reduction that is smaller than expected from brain-body scaling reported for wild canids and seems to be accompanied by compensatory increase of neuronal density. Thus, brains of small dogs are bigger and harbour more neurons...
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Cellular scaling rules for brains of gallinaceous birds
Zhang, Yicheng ; Němec, Pavel (advisor) ; Kratochvíl, Lukáš (referee)
Galliform birds (Galliformes) make up together with anseriform birds (Anseriformes) the clade Galloanserae, the sister group of Neoaves and the most basal clade of Neognathae. However, to date no quantitative data on cellular composition of their brains have been available. Here, I used the isotropic fractionator to determine numbers of neurons and non-neuronal cells in specific brain regions of 15 species of galliform birds. I find that cellular scaling rules for galliforms differ starkly from those for songbirds and parrots. When compared to these crown avian lineages, galliform birds feature lower degree of encephalization, a proportionally smaller telencephalon, small telencephalic and dominant cerebellar neuronal fractions, generally lower neuronal densities and larger glia/neuron ratios. Consequently, their brains and especially their forebrains harbor much smaller absolute numbers of neurons than those of equivalently sized songbird and parrots, the fact that undoubtedly constrains cognitive abilities of galliforms. However, this not to say that galliform birds are "bird brains" with low numbers of neurons and a limited ability to learn. Because they have high neuronal densities, their relatively small brains contain about equal numbers of neurons as brains of equivalently sized rodents and...
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Cellular scaling roles for passerine brains
Kocourek, Martin ; Němec, Pavel (advisor) ; Kratochvíl, Lukáš (referee)
Many passerine birds, particularly corvids, are known to express complex cognitive skills comparable to those observed in primates. In order to examine how these similarities are reflected at the cellular level, I counted neurons and nonneuronal cells in passerine brains using the isotropic fractionator method. I show that, in these birds, neuronal numbers scale almost isometrically with telencephalic size, i.e., the average neuron size shows little increase and neuronal density decreases minimally as brains get larger. Neuronal densities in the passerine telencephalon exceed those observed in the primate cerebral cortex by a factor of 3-6. As a result, the number of telencephalic neurons in the Common Raven (Corvus corax) equals those observed in the cerebral cortex of small monkeys. The cerebellum features similar scaling rules. However, because the relative size of the cerebellum is smaller than in mammalian brains, cerebellar neurons make a much smaller proportion of total brain neurons than in mammals. In contrast to the little variation in neuronal densities in telencephalon and cerebellum, the density of neurons rapidly decreases with increasing structure size in the diencephalon, optic tectum and brain stem. For all examined brain structures, the densities of nonneuronal cells remain constant...
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