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Brains of African mole-rats in numbers: Data for testing the social brain hypothesis
Kverková, Kristina ; Němec, Pavel (advisor) ; Pavelková, Věra (referee)
The social brain hypothesis (SBH) posits that complex social environments exert a major selection pressure driving the evolution of large brains and intelligence. The hypothesis was first proposed to explain the remarkable cognitive abilities of primates and has since been extended to other vertebrate groups and gained a substantial popularity. Nevertheless, the empirical support is equivocal in virtually every group where the hypothesis has been tested. In this thesis, the SBH is tested in the African mole-rats (Bathyergidae). Mole-rats share a subterranean mode of life and similar ecologies while covering the whole social spectrum, from solitary to "eusocial". The number of brain neurons is considered a better proxy for intelligence than relative or absolute brain size. Therefore, a novel approach, the isotropic fractionator, was used to estimate the total number of neurons and other cells in five brain parts (olfactory bulbs, cerebral cortex, cerebellum, diencephalon and basal ganglia, brain stem) of eleven bathyergid species. This simultaneously allows for examining if and how mole-rats differ from other rodents with respect to brain cellular scaling rules. We found that, contrary to expectations, mole-rats generally conform to these rules, with a few exceptions. They tend to have higher...
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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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Brains of African mole-rats in numbers: Data for testing the social brain hypothesis
Kverková, Kristina ; Němec, Pavel (advisor) ; Pavelková, Věra (referee)
The social brain hypothesis (SBH) posits that complex social environments exert a major selection pressure driving the evolution of large brains and intelligence. The hypothesis was first proposed to explain the remarkable cognitive abilities of primates and has since been extended to other vertebrate groups and gained a substantial popularity. Nevertheless, the empirical support is equivocal in virtually every group where the hypothesis has been tested. In this thesis, the SBH is tested in the African mole-rats (Bathyergidae). Mole-rats share a subterranean mode of life and similar ecologies while covering the whole social spectrum, from solitary to "eusocial". The number of brain neurons is considered a better proxy for intelligence than relative or absolute brain size. Therefore, a novel approach, the isotropic fractionator, was used to estimate the total number of neurons and other cells in five brain parts (olfactory bulbs, cerebral cortex, cerebellum, diencephalon and basal ganglia, brain stem) of eleven bathyergid species. This simultaneously allows for examining if and how mole-rats differ from other rodents with respect to brain cellular scaling rules. We found that, contrary to expectations, mole-rats generally conform to these rules, with a few exceptions. They tend to have higher...
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