Brain Behavior and Evolution最新文献

Endocranial casts are capable of capturing the general brain form in extinct mammals due to the high fidelity of the endocranial cavity and the brain in this clade. Camelids, the clade including extant camels, llamas, and alpacas, today display high levels of gyrification and brain complexity. The evolutionary history of the camelid brain has been described as involving unique neocortical growth dynamics which may have led to its current state. However, these inferences are based on their fossil endocast record from approximately ∼40 Mya (Eocene) to ∼11 Mya (Miocene), with a gap in this record for the last ∼10 million years. Here, we present the first descriptions of two camelid endocrania that document the recent history of the camelid brain: a new specimen of Palaeolama sp. from ∼1.2 Mya, and the plaster endocast of Camelops hesternus, a giant camelid from ∼44 to 11 Kya which possessed the largest brain (∼990 g) of all known camelids. We find that neocortical complexity evolved significantly between the Miocene and Pleistocene Epochs. Already ∼1.2 Mya the camelid brain presented morphologies previously known only in extant taxa, especially in the frontal and parietal regions, which may also be phylogenetic informative. The new fossil data indicate that during the Pleistocene, camelid brain dynamics experienced neocortical invagination into the sagittal sinus rather than evagination out of it, as observed in Eocene to Miocene taxa.

The amygdala is a central node in functional networks regulating emotions, social behavior, and social cognition. It develops in the telencephalon and includes pallial and subpallial parts, but these are extremely complex with multiple subdivisions, cell types, and connections. The homology of the amygdala in nonmammals is highly controversial, especially for the pallial part, and we are still far from understanding general principles on its organization that are common to different groups. Here, we review data on the adult functional architecture and developmental genoarchitecture of the amygdala in different amniotes (mammals and sauropsids), which are helping to disentangle and to better understand this complex structure. The use of an evolutionary developmental biology (evo-devo) approach has helped distinguish three major divisions in the amygdala, derived from the pallium, the subpallium, and from a newly identified division called telencephalon-opto-hypothalamic domain (TOH). This approach has also helped identify homologous cell populations with identical embryonic origins and molecular profiles in the amygdala of different amniotes. While subpallial cells produce different subtypes of GABAergic neurons, the pallium and TOH are major sources of glutamatergic cells. Available data point to a development-based molecular code that contributes to shape distinct functional subsystems in the amygdala, and comparative genoarchitecture is helping to delineate the cells involved in same subsystems in non-mammals. Thus, the evodevo approach can provide crucial information to understand common organizing principles of the amygdala cells and networks that control behavior, emotions, and cognition in amniotes.

Here, we present the first evidence for brain adaptation in pigs tolerant to the human presence, as a behavioral trait favoring domestication. The study was carried out on minipiglets from population bred at the Institute of Cytology and Genetics (Novosibirsk, Russia). We compared the behavior, metabolism of monoaminergic neurotransmitter systems, and functional activity of the hypothalamic-pituitary-adrenal system, as well as neurotrophic markers in the brain of minipigs differing by tolerance to human presence (HT and LT - high and low tolerance). The piglets did not differ in the levels of activity in the open field test. However, the concentration of cortisol plasma was significantly higher in minipigs with a low tolerance to the presence of humans. Moreover, LT minipigs demonstrated a decreased level of serotonin in the hypothalamus and augmented levels of serotonin and its metabolite 5-HIAA in the substantia nigra as compared to HT animals. In addition, LT minipigs showed increased content of dopamine and its metabolite DOPAC in the substantia nigra and decreased dopamine level in the striatum as well as reduced content of noradrenaline in the hippocampus. Increased mRNA levels of two markers of the serotonin system - TPH2 and HTR7 genes - in the raphe nuclei and in the prefrontal cortex, respectively, were associated in minipigs with a low tolerance to human presence. However, the expression of genes regulating a dopaminergic system (COMT, DRD1, and DRD2) in HT and LT animal groups varied depending on brain structure. In addition, a decrease in the expression of genes encoding BDNF (brain-derived neurotrophic factor) and GDNF (glial cell line-derived neurotrophic factor) was revealed in LT minipigs. The results may contribute to our understanding of the initial stage of domestication in pigs.

The amygdala is a complex brain structure in the vertebrate telencephalon, essential for regulating social behaviors, emotions, and (social) cognition. In contrast to the vast majority of neuron types described in the many nuclei of the mammalian amygdala, little is known about the neuronal diversity in non-mammals, making reconstruction of its evolution particularly difficult. Here, we characterize glutamatergic neuron types in the amygdala of the urodele amphibian Pleurodeles waltl. Our single-cell RNA sequencing data indicate the existence of at least ten distinct types and subtypes of glutamatergic neurons in the salamander amygdala. These neuron types are molecularly distinct from neurons in the ventral pallium (VP), suggesting that the pallial amygdala and the VP are two separate areas in the telencephalon. In situ hybridization for marker genes indicates that amygdalar glutamatergic neuron types are located in three major subdivisions: the lateral amygdala, the medial amygdala, and a newly defined area demarcated by high expression of the transcription factor Sim1. The gene expression profiles of these neuron types suggest similarities with specific neurons in the sauropsid and mammalian amygdala. In particular, we identify Sim1+ and Sim1+ Otp+ expressing neuron types, potentially homologous to the mammalian nucleus of the lateral olfactory tract (NLOT) and to hypothalamic-derived neurons of the medial amygdala, respectively. Taken together, our results reveal a surprising diversity of glutamatergic neuron types in the amygdala of salamanders, despite the anatomical simplicity of their brain. These results offer new insights on the cellular and anatomical complexity of the amygdala in tetrapod ancestors.

The subgenual organ complex in the leg of Polyneoptera (Insecta) consists of several chordotonal organs specialized to detect mechanical stimuli from substrate vibrations and airborne sound. In stick insects (Phasmatodea), the subgenual organ complex contains the subgenual organ and the distal organ located distally to the subgenual organ. The subgenual organ is a highly sensitive detector for substrate vibrations. The distal organ has a characteristic linear organization of sensilla and likely also responds to substrate vibrations. Despite its unique combination of sensory organs, the neuroanatomy of the subgenual organ complex of stick insects has been investigated for only very few species so far. Phylogenomic analysis has established for Phasmatodea the early branching of the sister groups Oriophasmata, the Old World phasmids, and Occidophasmata, the New World phasmids. The species studied for the sensory neuroanatomy, including the Indian stick insect Carausius morosus, belong to the Old World stick insects. Here, the neuroanatomy of the subgenual organ complex is presented for a first species of the New World stick insects, the Peruvian stick insect Oreophoetes peruana. To document the sensory organs in the subgenual organ complex and their innervation pattern, and to compare these between females and males of this species and also to the Old World stick insects, axonal tracing is used. This study documents the same sensory organs for O. peruana, subgenual organ and distal organ, as in other stick insects. Between the sexes of this species, there are no notable differences in the neuroanatomy of their sensory organs. The innervation pattern of tibial nerve branches in O. peruana is identical to other stick insect species, although the innervation pattern of the subgenual organ by a single tibial nerve branch is simpler. The shared organization of the organs in the subgenual organ complex in both groups of Neophasmatodea (Old World and New World stick insects) indicates the sensory importance of the subgenual organ but also of the distal organ. Some variation exists in the innervation of the chordotonal organs in O. peruana though a common innervation pattern can be identified. The findings raise the question for the ancestral neuroanatomical organization and innervation in stick insects.

The human brain is composed of a complex web of pathways. Diffusion magnetic resonance (MR) tractography is a neuroimaging technique that relies on the principle of diffusion to reconstruct brain pathways. Its tractography is broadly applicable to a range of problems as it is amenable for study in individuals of any age and from any species. However, it is well known that this technique can generate biologically implausible pathways, especially in regions of the brain where multiple fibers cross. This review highlights potential misconnections in two cortico-cortical association pathways with a focus on the aslant tract and inferior frontal occipital fasciculus. The lack of alternative methods to validate observations from diffusion MR tractography means there is a need to develop new integrative approaches to trace human brain pathways. This review discusses integrative approaches in neuroimaging, anatomical, and transcriptional variation as having much potential to trace the evolution of human brain pathways.

In Atlantic salmon (Salmo salar), seasonal photoperiod is shown to regulate the onset of sexual maturation, yet which brain region(s) is involved, and how light information impacts the neuroendocrine system are still not fully understood in teleosts. Detailed knowledge about the photoperiodic regulation of maturation in fish is still missing. In birds, it is shown that gonadotropin-releasing hormone (Gnrh) is located in the same neurons as vertebrate ancient (VA) opsin, suggesting a direct photoreceptive regulation for the onset of sexual maturity. This study presents a comprehensive topographic mapping of gnrh2, gnrh3, kisspeptin 2 (kiss2), gonadotropin-inhibiting hormone (gnih), and VA opsin using in situ hybridization on mature Atlantic salmon brains. Neurons positive for gnrh3 are expressed in the olfactory bulb and ventral telencephalon, while gnrh2-positive neurons are located dorsally in the midbrain tegmentum. Gonadotropin-inhibiting hormone (Gnih)-expressing cell bodies are present in the ventral thalamus and extend caudally to the hypothalamus with kiss2-expressing cells appearing in a lateral position. VA opsin-positive cells are present in the telencephalon, the rostro-dorsal ring of the left habenula, the ventral thalamus, and the midbrain tegmentum. The results show no similar co-location as found in birds, hypothesizing that the photoreceptive modulation of Gnrh in salmon may interact through neuronal networks. The topography analyses of the essential neuroendocrine cells related to sexual maturation in the Atlantic salmon brain show that diencephalic (thalamus, hypothalamus) and midbrain (tegmentum) regions seem central for controlling sexual maturation.

Brain size evolution in hominins constitutes a crucial evolutionary trend, yet the underlying mechanisms behind those changes are not well understood. Here, climate change is considered as an environmental factor using multiple paleoclimate records testing temperature, humidity, and precipitation against changes to brain size in 298 Homo specimens over the past fifty thousand years. Across regional and global paleoclimate records, brain size in Homo averaged significantly lower during periods of climate warming as compared to cooler periods. Geological epochs displayed similar patterns, with Holocene warming periods comprising significantly smaller brained individuals as compared to those living during glacial periods at the end of the Late Pleistocene. Testing spatiotemporal patterns, the adaptive response appears to have started roughly fifteen thousand years ago and may persist into modern times. To a smaller degree, humidity and precipitation levels were also predictive of brain size, with arid periods associated with greater brain size in Homo. The findings suggest an adaptive response to climate change in human brain size that is driven by natural selection in response to environmental stress.

Introduction: Shared selection pressures often explain convergent trait loss, yet anurans (frogs and toads) have lost their middle ears at least 38 times with no obvious shared selection pressures unifying "earless" taxa. Anuran tympanic middle ear loss is especially perplexing because acoustic communication is dominant within Anura and tympanic middle ears enhance airborne hearing in most tetrapods.

Methods: Here, we use phylogenetic comparative methods to examine whether particular geographic ranges, microhabitats, activity patterns, or aspects of acoustic communication are associated with anuran tympanic middle ear loss.

Results: Although we find some differences between the geographic ranges of eared and earless species on average, there is plenty of overlap between the geographic distributions of eared and earless species. Additionally, we find a higher prevalence of diurnality in earless species, but not all earless species are diurnal. We find no universal adaptive explanation for the many instances of anuran tympanic middle ear loss.

Conclusion: The puzzling lack of universally shared selection pressures among earless species motivates discussion of alternative hypotheses, including genetic or developmental constraints, and the possibility that tympanic middle ear loss is maladaptive.