INTRODUCTION: Songbirds, especially corvids, and parrots are remarkably intelligent. Their cognitive skills are on par with primates and their brains contain primate-like numbers of neurons concentrated in high densities in the telencephalon. Much less is known about cognition and neuron counts in more basal bird lineages. Here, we focus on brain cellular composition of galliform birds, which have small brains relative to body size and a proportionally small telencephalon and are often perceived as cognitively inferior to most other birds. METHODS: We use the isotropic fractionator to assess quantitatively the numbers and distributions of neurons and nonneuronal cells in 15 species of galliform birds and compare their cellular scaling rules with those of songbirds, parrots, marsupials, insectivores, rodents, and primates. RESULTS: On average, the brains of galliforms contain about half the number of neurons found in parrot and songbird brains of the same mass. Moreover, in contrast to these birds, galliforms resemble mammals in having small telencephalic and dominant cerebellar neuronal fractions. Consequently, galliforms have much smaller absolute numbers of neurons in their forebrains than equivalently sized songbirds and parrots, which may limit their cognitive abilities. However, galliforms have similar neuronal densities and neuron counts in the brain and forebrain as equally sized non-primate mammals. Therefore, it is not surprising that cognitive abilities of galliforms are on par with non-primate mammals in many domains. CONCLUSION: Comparisons performed in this study demonstrate that birds representing distantly related clades markedly differ in neuronal densities, neuron numbers, and the allocation of brain neurons to major brain divisions. In analogy with the concept of volumetric composition of the brain, known as the cerebrotype, we conclude that distantly related birds have distinct neuronal cerebrotypes.

• Klíčová slova
• Brain size, Cognition, Evolution, Intelligence, Number of neurons,
• Publikační typ
• časopisecké články MeSH

SignificanceThe evolution of brain processing capacity has traditionally been inferred from data on brain size. However, similarly sized brains of distantly related species can differ in the number and distribution of neurons, their basic computational units. Therefore, a finer-grained approach is needed to reveal the evolutionary paths to increased cognitive capacity. Using a new, comprehensive dataset, we analyzed brain cellular composition across amniotes. Compared to reptiles, mammals and birds have dramatically increased neuron numbers in the telencephalon and cerebellum, which are brain parts associated with higher cognition. Astoundingly, a phylogenetic analysis suggests that as few as four major changes in neuron-brain scaling in over 300 million years of evolution pave the way to intelligence in endothermic land vertebrates.

• Klíčová slova
• brain size, cognition, evolution, intelligence, number of neurons,
• MeSH
• biologická evoluce * MeSH
• fylogeneze MeSH
• kvantitativní znak dědičný MeSH
• mozek cytologie   fyziologie   MeSH
• neurony cytologie   MeSH
• obratlovci * klasifikace   MeSH
• počet buněk * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Within-species variation in the number of neurons, other brain cells and their allocation to different brain parts is poorly studied. Here, we assess these numbers in a squamate reptile, the Madagascar ground gecko (Paroedura picta). We examined adults from two captive populations and three age groups within one population. Even though reptiles exhibit extensive adult neurogenesis, intrapopulation variation in the number of neurons is similar to that in mice. However, the two populations differed significantly in most measures, highlighting the fact that using only one population can underestimate within-species variation. There is a substantial increase in the number of neurons and decrease in neuronal density in adult geckos relative to hatchlings and an increase in the number of neurons in the telencephalon in fully grown adults relative to sexually mature young adults. This finding implies that adult neurogenesis does not only replace worn out but also adds new telencephalic neurons in reptiles during adulthood. This markedly contrasts with the situation in mammals, where the number of cortical neurons declines with age.

• Klíčová slova
• brain size, cellular scaling rules, evolution, intraspecific variation, number of glial cells, number of neurons,
• MeSH
• ještěři * MeSH
• mozek MeSH
• myši MeSH
• neurony MeSH
• telencefalon MeSH
• zvířata MeSH
• Check Tag
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Madagaskar MeSH

The stereotyped features of brain structure, such as the distribution, morphology and connectivity of neuronal cell types across brain areas, are those most likely to explain the remarkable capacity of the brain to process information and govern behaviors. Recent advances in anatomical methods, including the simple but versatile isotropic fractionator and several whole-brain labeling, clearing and microscopy methods, have opened the door to an exciting new era in comparative brain anatomy, one that has the potential to transform our understanding of the brain structure-function relationship by representing the evolution of brain complexity in quantitative anatomical features shared across species and species-specific or clade-specific. Here we discuss these methods and their application to mapping brain cell count and cell type distributions-two particularly powerful neural correlates of vertebrate cognitive and behavioral capabilities.

• MeSH
• druhová specificita MeSH
• mapování mozku * MeSH
• mozek * MeSH
• neurony MeSH
• počet buněk MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Research Support, N.I.H., Extramural MeSH