Complexity of avian evolution revealed by family-level genomes.

Despite tremendous efforts in the past decades, relationships among main avian lineages remain heavily debated without a clear resolution. Discrepancies have been attributed to diversity of species sampled, phylogenetic method and the choice of genomic regions1-3. Here we address these issues by analysing the genomes of 363 bird species4 (218 taxonomic families, 92% of total). Using intergenic regions and coalescent methods, we present a well-supported tree but also a marked degree of discordance. The tree confirms that Neoaves experienced rapid radiation at or near the Cretaceous-Palaeogene boundary. Sufficient loci rather than extensive taxon sampling were more effective in resolving difficult nodes. Remaining recalcitrant nodes involve species that are a challenge to model due to either extreme DNA composition, variable substitution rates, incomplete lineage sorting or complex evolutionary events such as ancient hybridization. Assessment of the effects of different genomic partitions showed high heterogeneity across the genome. We discovered sharp increases in effective population size, substitution rates and relative brain size following the Cretaceous-Palaeogene extinction event, supporting the hypothesis that emerging ecological opportunities catalysed the diversification of modern birds. The resulting phylogenetic estimate offers fresh insights into the rapid radiation of modern birds and provides a taxon-rich backbone tree for future comparative studies.

ECHOCARDIOGRAPHY IN THIRTY AMERICAN FLAMINGOS (PHOENICOPTERUS RUBER) AND A CASE OF SUSPECTED NEURALLY MEDIATED REFLEX SYNCOPE.

Heart disease in birds contributes to premature death and is usually detected postmortem. Echocardiography is a sensitive and noninvasive diagnostic modality but reported standard values for many species of birds, including American flamingos (Phoenicopterus ruber), are unavailable. Echocardiography was opportunistically performed on 30 unsedated American flamingos during their annual routine health examination. Structural heart disease was not found in any of the examined birds. However, 18 birds showed varying degrees of dynamic intraventricular obstruction. Echocardiographic parameters are reported. Benign neurocardiogenic weakness or syncopal events during handling were suspected in three birds. Stress combined with an intraventricular obstruction is believed to have triggered a cascade of parasympathetic innervation and sympathetic inhibition, similar to neurally mediated reflex syncope in humans.

COMPARISON OF THREE MIDAZOLAM-BASED SEDATION PROTOCOLS IN BUDGERIGARS (MELOPSITTACUS UNDULATUS) AND BLACK-CHEEKED LOVEBIRDS (AGAPORNIS NIGRIGENIS).

This randomized, crossover study evaluated three sedation protocols administered subcutaneously in nine budgerigars (Melopsittacus undulatus) and nine black-cheeked lovebirds (Agapornis nigrigenis). All protocols included midazolam (5 mg/kg), combined with butorphanol (5 mg/kg) (BM), medetomidine (20 lg/kg) (MM), or alfaxalone (13 mg/kg) (AM). Mortalities from suspected cardiorespiratory arrest were observed when AM was used in lovebirds, even after reduction of alfaxalone dosage to 3 mg/kg, and therefore this protocol was excluded from further use in this species. Induction and recovery times were recorded and their quality assessed. Sedation depth and heart and respiratory rates were measured every 5 min and radiographic positioning was attempted at 10 and 20 min. At 30 min, midazolam and medetomidine were reversed with flumazenil (0.05 mg/kg, SC), and atipamezole (0.2 mg/kg, SC), respectively. MM consistently provided deep sedation in both species, with successful radiographic positioning at every attempt. As expected, heart rate was often lower with MM than with other protocols, but no associated complications were noted. In budgerigars, BM had the lowest radiographic positioning success rate (10 min: 5/9, 20 min: 3/9), whereas in lovebirds it provided significantly deeper sedation (P < 0.001), allowing radiographic positioning in all subjects. In both species, BM provided the shortest recovery times. AM resulted in reliable radiographic positioning of all budgerigars at 10 min, but not at 20 min (5/ 9), and provided consistently poor recoveries. This study highlights how differently two psittacine species of similar size may react to the same sedation protocols. AM sedation cannot be fully reversed and produced significant undesirable effects, several of which have been previously reported with alfaxalone administration to avian species. The authors therefore caution against using alfaxalone-midazolam combinations in budgerigars and black-cheeked lovebirds. Both BM and MM provided reliable sedation in these species, and appear to be suitable alternatives to AM.

Development and validation of a versatile non-invasive urinary steroidomics method for wildlife biomonitoring.

Wildlife conservation is often challenged by a lack of knowledge about the reproduction biology and adaptability of endangered species. Although monitoring steroids and related molecules can increase this knowledge, the applicability of current techniques (e.g. immunoassays) is hampered by species-specific steroid metabolism and the requisite to avoid invasive sampling. This study presents a validated steroidomics method for the (un)targeted screening of a wide range of sex and stress steroids and related molecules in urine using ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS). In total, 50 steroids (conjugated and non-conjugated androgens, estrogens, progestogens and glucocorticoids) and 6 prostaglandins could be uniquely detected. A total of 45 out of 56 compounds demonstrated a detection limit below 0.01 ng µL-1. Excellent linearity (R2 > 0.99), precision (CV < 20 %), and recovery (80-120 %) were observed for 46, 41, and 39 compounds, respectively. Untargeted screening of pooled giant panda and human samples yielded 9691 and 8366 features with CV < 30 %, from which 84.1 % and 83.0 %, respectively, also demonstrated excellent linearity (R2 > 0.90). The biological validity of the method was investigated on male and female giant panda urine (n = 20), as well as pooled human samples (n = 10). A total of 24 different steroids were detected with clear qualitative and quantitative differences between human and giant panda samples. Furthermore, expected differences were revealed between female giant panda samples from different reproductive phases. In contrast to traditional biomonitoring techniques, the developed steroidomics method was able to screen a wide range of compounds and provide information on the putative identities of metabolites potentially important for reproductive monitoring in giant pandas. These results illustrate the advancements steroidomics brings to the field of wildlife biomonitoring in the pursuit to better understand the biology of endangered species.

Examination of head versus body heading may help clarify the extent to which animal movement pathways are structured by environmental cues?

Understanding the processes that determine how animals allocate time to space is a major challenge, although it is acknowledged that summed animal movement pathways over time must define space-time use. The critical question is then, what processes structure these pathways? Following the idea that turns within pathways might be based on environmentally determined decisions, we equipped Arabian oryx with head- and body-mounted tags to determine how they orientated their heads - which we posit is indicative of them assessing the environment - in relation to their movement paths, to investigate the role of environment scanning in path tortuosity. After simulating predators to verify that oryx look directly at objects of interest, we recorded that, during routine movement, > 60% of all turns in the animals' paths, before being executed, were preceded by a change in head heading that was not immediately mirrored by the body heading: The path turn angle (as indicated by the body heading) correlated with a prior change in head heading (with head heading being mirrored by subsequent turns in the path) twenty-one times more than when path turns occurred due to the animals adopting a body heading that went in the opposite direction to the change in head heading. Although we could not determine what the objects of interest were, and therefore the proposed reasons for turning, we suggest that this reflects the use of cephalic senses to detect advantageous environmental features (e.g. food) or to detect detrimental features (e.g. predators). The results of our pilot study suggest how turns might emerge in animal pathways and we propose that examination of points of inflection in highly resolved animal paths could represent decisions in landscapes and their examination could enhance our understanding of how animal pathways are structured.

A map of white matter tracts in a lesser ape, the lar gibbon.

The recent development of methods for constructing directly comparable white matter atlases in primate brains from diffusion MRI allows us to probe specializations unique to humans, great apes, and other primate taxa. Here, we constructed the first white matter atlas of a lesser ape using an ex vivo diffusion-weighted scan of a brain from a young adult (5.5 years) male lar gibbon. We find that white matter architecture of the gibbon temporal lobe suggests specializations that are reminiscent of those previously reported for great apes, specifically, the expansion of the arcuate fasciculus and the inferior longitudinal fasciculus in the temporal lobe. Our findings suggest these white matter expansions into the temporal lobe were present in the last common ancestor to hominoids approximately 16 million years ago and were further modified in the great ape and human lineages. White matter atlases provide a useful resource for identifying neuroanatomical differences and similarities between humans and other primate species and provide insight into the evolutionary variation and stasis of brain organization.

Historical development of the survivorship of zoo rhinoceroses-A comparative historical analysis.

Zoo animal husbandry is a skill that should be developing constantly. In theory, this should lead to an improvement of zoo animal survivorship over time. Additionally, it has been suggested that species that are at a comparatively higher risk of extinction in their natural habitats (in situ) might also be more difficult to keep under zoo conditions (ex situ). Here, we assessed these questions for three zoo-managed rhinoceros species with different extinction risk status allocated by the IUCN: the "critically endangered" black rhino (Diceros bicornis), the "vulnerable" greater one-horned (GOH) rhino (Rhinoceros unicornis), and the "near threatened" white rhino (Ceratotherium simum). Comparing zoo animals ≥1 year of age, the black rhino had the lowest and the white rhino the highest survivorship, in congruence with their extinction risk status. Historically, the survivorship of both black and white rhino in zoos improved significantly over time, whereas that of GOH rhino stagnated. Juvenile mortality was generally low and decreased even further in black and white rhinos over time. Together with the development of population pyramids, this shows increasing competence of the global zoo community to sustain all three species. Compared to the continuously expanding zoo population of GOH and white rhinos, the zoo-managed black rhino population has stagnated in numbers in recent years. Zoos do not only contribute to conservation by propagating ex situ populations, but also by increasing species-specific husbandry skills. We recommend detailed research to understand specific factors responsible for the stagnation but also the general improvement of survivorship of zoo-managed rhinos.

Effect of atropine and propofol on the minimum anaesthetic concentration of isoflurane in the freshwater turtle Trachemys scripta (yellow-bellied slider).

OBJECTIVE: To determine if the administration of atropine would reduce the measured minimum anaesthetic concentration of isoflurane (MACisoflurane) in freshwater turtles - the yellow-bellied slider (Trachemys scripta scripta). STUDY DESIGN: Paired, blinded, randomized, prospective studies of 1) the effect of atropine in isoflurane anaesthetized freshwater turtles (T. scripta scripta) and 2) the effect of atropine in yellow-bellied sliders in which anaesthesia was induced with propofol and maintained with isoflurane. ANIMALS: T. scripta scripta (n = 8), female, adult. METHODS: Atropine (2 mg kg-1) or an isovolumetric control injection of saline was administered intraperitoneally 15 minutes prior to induction of anaesthesia with isoflurane. Individual MACisoflurane was then determined by end-tidal gas analysis in a bracketing design by an experimenter blinded to the administered drug, with a 2 week washout period. The experiment was repeated, with atropine (2 mg kg-1) or saline administered intravascularly in combination with propofol for anaesthetic induction. Linear mixed modelling was used to determine the effects of atropine and propofol on the individual MACisoflurane. Data are presented as mean ± standard deviation. RESULTS: Premedication with atropine significantly reduced MACisoflurane (p = 0.0039). In isoflurane-induced T. scripta scripta, MACisoflurane decreased from 4.2 ± 0.4% to 3.3 ± 0.8% when atropine had been administered. Propofol as an induction agent had a MAC-sparing effect (p < 0.001) such that MACisoflurane following propofol and a control injection of saline was 2.3 ± 1.0%, which decreased further to 1.5 ± 0.8% when propofol was combined with atropine. CONCLUSIONS AND CLINICAL RELEVANCE: Atropine, presumably by inhibiting parasympathetically mediated pulmonary artery constriction, decreases right-to-left cardiac shunting and the MACisoflurane in yellow-bellied sliders, and thereby may facilitate control of inhalant anaesthesia. Propofol can be used for induction of anaesthesia and reduces the required concentration of inhaled anaesthesia assessed 1.5 hours following induction.

Orexinergic neurons in the hypothalami of an Asiatic lion, an African lion, and a Southeast African cheetah.

Employing orexin-A immunohistochemistry, we describe the distribution, morphology, and nuclear parcellation of orexinergic neurons within the hypothalami of an Asiatic lion (Panthera leo subsp. persica), an African lion (Panthera leo subsp. melanochaita), and a Southeast African cheetah (Acinonyx jubatus subsp. jubatus). In all three felids, the clustering of large, bipolar, and multipolar hypothalamic orexinergic neurons primarily follows the pattern observed in other mammals. The orexinergic neurons were found, primarily, to form three distinct clusters-the main, zona incerta, and optic tract clusters. In addition, large orexinergic neurons were observed in the ventromedial supraoptic region of the hypothalamus, where they are not typically observed in other species. As has been observed in cetartiodactyls and the African elephant, a cluster of small, multipolar orexinergic neurons, the parvocellular cluster, was observed in the medial zone of the hypothalamus in all three felids, although this parvocellular cluster has not been reported in other carnivores. In both subspecies of lions, but not the cheetah, potential orexin-immunopositive neurons were observed in the paraventricular hypothalamic nucleus, supraoptic nucleus, the lateral part of the retrochiasmatic area, and the inner layer of the median eminence. The distribution and parcellation of orexinergic neurons in the hypothalami of the three felids studied appear to be more complex than observed in many other mammals and for the two subspecies of lion may be even more complex. These findings are discussed in terms of potential technical concerns, phylogenetic variations of this system, and potentially associated functional aspects of the orexinergic system.

Cholinergic, catecholaminergic, serotonergic, and orexinergic neuronal populations in the brain of the lesser hedgehog tenrec (Echinops telfairi).

The current study provides an analysis of the cholinergic, catecholaminergic, serotonergic, and orexinergic neuronal populations, or nuclei, in the brain of the lesser hedgehog tenrec, as revealed with immunohistochemical techniques. For all four of these neuromodulatory systems, the nuclear organization was very similar to that observed in other Afrotherian species and is broadly similar to that observed in other mammals. The cholinergic system shows the most variation, with the lesser hedgehog tenrec exhibiting palely immunopositive cholinergic neurons in the ventral portion of the lateral septal nucleus, and the possible absence of cholinergic neurons in the parabigeminal nucleus and the medullary tegmental field. The nuclear complement of the catecholaminergic, serotonergic and orexinergic systems showed no specific variances in the lesser hedgehog tenrec when compared to other Afrotherians, or broadly with other mammals. A striking feature of the lesser hedgehog tenrec brain is a significant mesencephalic flexure that is observed in most members of the Tenrecoidea, as well as the closely related Chrysochlorinae (golden moles), but is not present in the greater otter shrew, a species of the Potomogalidae lineage currently incorporated into the Tenrecoidea. In addition, the cholinergic neurons of the ventral portion of the lateral septal nucleus are observed in the golden moles, but not in the greater otter shrew. This indicates that either complex parallel evolution of these features occurred in the Tenrecoidea and Chrysochlorinae lineages, or that the placement of the Potomogalidae within the Tenrecoidea needs to be re-examined.

Forebrain nuclei linked to woodpecker territorial drum displays mirror those that enable vocal learning in songbirds.

Vocal learning is thought to have evolved in 3 orders of birds (songbirds, parrots, and hummingbirds), with each showing similar brain regions that have comparable gene expression specializations relative to the surrounding forebrain motor circuitry. Here, we searched for signatures of these same gene expression specializations in previously uncharacterized brains of 7 assumed vocal non-learning bird lineages across the early branches of the avian family tree. Our findings using a conserved marker for the song system found little evidence of specializations in these taxa, except for woodpeckers. Instead, woodpeckers possessed forebrain regions that were anatomically similar to the pallial song nuclei of vocal learning birds. Field studies of free-living downy woodpeckers revealed that these brain nuclei showed increased expression of immediate early genes (IEGs) when males produce their iconic drum displays, the elaborate bill-hammering behavior that individuals use to compete for territories, much like birdsong. However, these specialized areas did not show increased IEG expression with vocalization or flight. We further confirmed that other woodpecker species contain these brain nuclei, suggesting that these brain regions are a common feature of the woodpecker brain. We therefore hypothesize that ancient forebrain nuclei for refined motor control may have given rise to not only the song control systems of vocal learning birds, but also the drumming system of woodpeckers.

A high-quality, long-read genome assembly of the endangered ring-tailed lemur (Lemur catta).

BACKGROUND: The ring-tailed lemur (Lemur catta) is a charismatic strepsirrhine primate endemic to Madagascar. These lemurs are of particular interest, given their status as a flagship species and widespread publicity in the popular media. Unfortunately, a recent population decline has resulted in the census population decreasing to <2,500 individuals in the wild, and the species's classification as an endangered species by the IUCN. As is the case for most strepsirrhine primates, only a limited amount of genomic research has been conducted on L. catta, in part owing to the lack of genomic resources. RESULTS: We generated a new high-quality reference genome assembly for L. catta (mLemCat1) that conforms to the standards of the Vertebrate Genomes Project. This new long-read assembly is composed of Pacific Biosciences continuous long reads (CLR data), Optical Mapping Bionano reads, Arima HiC data, and 10X linked reads. The contiguity and completeness of the assembly are extremely high, with scaffold and contig N50 values of 90.982 and 10.570 Mb, respectively. Additionally, when compared to other high-quality primate assemblies, L. catta has the lowest reported number of Alu elements, which results predominantly from a lack of AluS and AluY elements. CONCLUSIONS: mLemCat1 is an excellent genomic resource not only for the ring-tailed lemur community, but also for other members of the Lemuridae family, and is the first very long read assembly for a strepsirrhine.

DEVELOPMENT OF A QUANTITATIVE IMMUNOASSAY FOR SERUM HAPTOGLOBIN AS A PUTATIVE DISEASE MARKER IN THE SOUTHERN WHITE RHINOCEROS (CERATOTHERIUM SIMUM SIMUM).

Objective disease markers in the southern white rhinoceros (Ceratotherium simum simum) are in high demand. In the field, such markers are typically needed to decide whether a captured white rhinoceros is fit to cope with quarantine, transport, or both. Captive white rhinoceros have a need for unbiased biomarkers for early detection of disease. Acute phase proteins, including haptoglobin, are proteins that significantly change their plasma concentration in response to tissue perturbation or inflammation, such as that occurring during infection or neoplastic disease. Acute phase proteins are well known diagnostic tools in both human and veterinary medicine. In this study, an ELISA with commercially available anti-human haptoglobin antibodies for quantification of haptoglobin in white rhinoceros serum was developed. The validity of the haptoglobin assay and haptoglobin as a biomarker of disease was investigated with the use of serum samples from both captive and free-ranging animals with a well-described health status. The assay was precise (intra-assay and interassay reproducibility were 5.0% and 13.1%, respectively) and reliably quantified white rhinoceros haptoglobin serum concentrations consuming low volumes of sample. The assay was sensitive to the presence of free hemoglobin in the sample at levels corresponding to a visibly hemolyzed sample. Haptoglobin was readily measurable, baseline levels (in white rhinoceros with no clinical signs of disease) did not differ between genders, and a significant increase was seen in captive as well as in free-ranging white rhinoceros with inflammatory disease. Thus, haptoglobin is a positive acute phase protein in southern white rhinoceros with potential for use as an objective marker of disease.

The Digital Brain Bank, an open access platform for post-mortem imaging datasets.

Post-mortem magnetic resonance imaging (MRI) provides the opportunity to acquire high-resolution datasets to investigate neuroanatomy and validate the origins of image contrast through microscopy comparisons. We introduce the Digital Brain Bank (open.win.ox.ac.uk/DigitalBrainBank), a data release platform providing open access to curated, multimodal post-mortem neuroimaging datasets. Datasets span three themes-Digital Neuroanatomist: datasets for detailed neuroanatomical investigations; Digital Brain Zoo: datasets for comparative neuroanatomy; and Digital Pathologist: datasets for neuropathology investigations. The first Digital Brain Bank data release includes 21 distinctive whole-brain diffusion MRI datasets for structural connectivity investigations, alongside microscopy and complementary MRI modalities. This includes one of the highest-resolution whole-brain human diffusion MRI datasets ever acquired, whole-brain diffusion MRI in fourteen nonhuman primate species, and one of the largest post-mortem whole-brain cohort imaging studies in neurodegeneration. The Digital Brain Bank is the culmination of our lab's investment into post-mortem MRI methodology and MRI-microscopy analysis techniques. This manuscript provides a detailed overview of our work with post-mortem imaging to date, including the development of diffusion MRI methods to image large post-mortem samples, including whole, human brains. Taken together, the Digital Brain Bank provides cross-scale, cross-species datasets facilitating the incorporation of post-mortem data into neuroimaging studies.

Decision rules for determining terrestrial movement and the consequences for filtering high-resolution global positioning system tracks: a case study using the African lion (Panthera leo).

The combined use of global positioning system (GPS) technology and motion sensors within the discipline of movement ecology has increased over recent years. This is particularly the case for instrumented wildlife, with many studies now opting to record parameters at high (infra-second) sampling frequencies. However, the detail with which GPS loggers can elucidate fine-scale movement depends on the precision and accuracy of fixes, with accuracy being affected by signal reception. We hypothesized that animal behaviour was the main factor affecting fix inaccuracy, with inherent GPS positional noise (jitter) being most apparent during GPS fixes for non-moving locations, thereby producing disproportionate error during rest periods. A movement-verified filtering (MVF) protocol was constructed to compare GPS-derived speed data with dynamic body acceleration, to provide a computationally quick method for identifying genuine travelling movement. This method was tested on 11 free-ranging lions (Panthera leo) fitted with collar-mounted GPS units and tri-axial motion sensors recording at 1 and 40 Hz, respectively. The findings support the hypothesis and show that distance moved estimates were, on average, overestimated by greater than 80% prior to GPS screening. We present the conceptual and mathematical protocols for screening fix inaccuracy within high-resolution GPS datasets and demonstrate the importance that MVF has for avoiding inaccurate and biased estimates of movement.

Nuclear organization of serotonergic neurons in the brainstems of a lar gibbon and a chimpanzee.

In the current study, we detail, through the analysis of immunohistochemically stained sections, the morphology and nuclear parcellation of the serotonergic neurons present in the brainstem of a lar gibbon and a chimpanzee. In general, the neuronal morphology and nuclear organization of the serotonergic system in the brains of these two species of apes follow that observed in a range of Eutherian mammals and are specifically very similar to that observed in other species of primates. In both of the apes studied, the serotonergic nuclei could be readily divided into two distinct groups, a rostral and a caudal cluster, which are found from the level of the decussation of the superior cerebellar peduncle to the spinomedullary junction. The rostral cluster is comprised of the caudal linear, supralemniscal, and median raphe nuclei, as well as the six divisions of the dorsal raphe nuclear complex. The caudal cluster contains several distinct nuclei and nuclear subdivisions, including the raphe magnus nucleus and associated rostral and caudal ventrolateral (CVL) serotonergic groups, the raphe pallidus, and raphe obscurus nuclei. The one deviation in organization observed in comparison to other primate species is an expansion of both the number and distribution of neurons belonging to the lateral division of the dorsal raphe nucleus in the chimpanzee. It is unclear whether this expansion occurs in humans, thus at present, this expansion sets the chimpanzee apart from other primates studied to date.

Nuclear organization of catecholaminergic neurons in the brains of a lar gibbon and a chimpanzee.

Using tyrosine hydroxylase immunohistochemistry, we describe the nuclear parcellation of the catecholaminergic system in the brains of a lar gibbon (Hylobates lar) and a chimpanzee (Pan troglodytes). The parcellation of catecholaminergic nuclei in the brains of both apes is virtually identical to that observed in humans and shows very strong similarities to that observed in mammals more generally, particularly other primates. Specific variations of this system in the apes studied include an unusual high-density cluster of A10dc neurons, an enlarged retrorubral nucleus (A8), and an expanded distribution of the neurons forming the dorsolateral division of the locus coeruleus (A4). The additional A10dc neurons may improve dopaminergic modulation of the extended amygdala, the enlarged A8 nucleus may be related to the increased use of communicative facial expressions in the hominoids compared to other primates, while the expansion of the A4 nucleus appears to be related to accelerated evolution of the cerebellum in the hominoids compared to other primates. In addition, we report the presence of a compact division of the locus coeruleus proper (A6c), as seen in other primates, that is not present in other mammals apart from megachiropteran bats. The presence of this nucleus in primates and megachiropteran bats may reflect homology or homoplasy, depending on the evolutionary scenario adopted. The fact that the complement of homologous catecholaminergic nuclei is mostly consistent across mammals, including primates, is advantageous for the selection of model animals for the study of specific dysfunctions of the catecholaminergic system in humans.

Nuclear organization of orexinergic neurons in the hypothalamus of a lar gibbon and a chimpanzee.

Employing orexin-A immunohistochemical staining we describe the nuclear parcellation of orexinergic neurons in the hypothalami of a lar gibbon and a chimpanzee. The clustering of orexinergic neurons within the hypothalamus and the terminal networks follow the patterns generally observed in other mammals, including laboratory rodents, strepsirrhine primates and humans. The orexinergic neurons were found within three distinct clusters in the ape hypothalamus, which include the main cluster, zona incerta cluster and optic tract cluster. In addition, the orexinergic neurons of the optic tract cluster appear to extend to a more rostral and medial location than observed in other species, being observed in the tuberal region in the anterior ventromedial aspect of the hypothalamus. While orexinergic terminal networks were observed throughout the brain, high density terminal networks were observed within the hypothalamus, medial and intralaminar nuclei of the dorsal thalamus, and within the serotonergic and noradrenergic regions of the midbrain and pons, which is typical for mammals. The expanded distribution of orexinergic neurons into the tuberal region of the ape hypothalamus, is a feature that needs to be investigated in other primate species, but appears to correlate with orexin gene expression in the same region of the human hypothalamus, but these neurons are not revealed with immunohistochemical staining in humans. Thus, it appears that apes have a broader distribution of orexinergic neurons compared to other primate species, but that the neurons within this extension of the optic tract cluster in humans, while expressing the orexin gene, do not produce the neuropeptide.

Distribution of cholinergic neurons in the brains of a lar gibbon and a chimpanzee.

Using choline acetyltransferase immunohistochemistry, we describe the nuclear parcellation of the cholinergic system in the brains of two apes, a lar gibbon (Hylobates lar) and a chimpanzee (Pan troglodytes). The cholinergic nuclei observed in both apes studied are virtually identical to that observed in humans and show very strong similarity to the cholinergic nuclei observed in other primates and mammals more generally. One specific difference between humans and the two apes studied is that, with the specific choline acetyltransferase antibody used, the cholinergic pyramidal neurons observed in human cerebral cortex were not labeled. When comparing the two apes studied and humans to other primates, the presence of a greatly expanded cholinergic medullary tegmental field, and the presence of cholinergic neurons in the intermediate and dorsal horns of the cervical spinal cord are notable variations of the distribution of cholinergic neurons in apes compared to other primates. These neurons may play an important role in the modulation of ascending and descending neural transmissions through the spinal cord and caudal medulla, potentially related to the differing modes of locomotion in apes compared to other primates. Our observations also indicate that the average soma volume of the neurons forming the laterodorsal tegmental nucleus (LDT) is larger than those of the pedunculopontine nucleus (PPT) in both the lar gibbon and chimpanzee. This variability in soma volume appears to be related to the size of the adult derivatives of the alar and basal plate across mammalian species.

Cortical Morphology and White Matter Tractography of Three Phylogenetically Distant Primates: Evidence for a Simian Elaboration.

Comparative neuroimaging has been used to identify changes in white matter architecture across primate species phylogenetically close to humans, but few have compared the phylogenetically distant species. Here, we acquired postmortem diffusion imaging data from ring-tailed lemurs (Lemur catta), black-capped squirrel monkeys (Saimiri boliviensis), and rhesus macaques (Macaca mulatta). We were able to establish templates and surfaces allowing us to investigate sulcal, cortical, and white matter anatomy. The results demonstrate an expansion of the frontal projections of the superior longitudinal fasciculus complex in squirrel monkeys and rhesus macaques compared to ring-tailed lemurs, which correlates with sulcal anatomy and the lemur's smaller prefrontal granular cortex. The connectivity of the ventral pathway in the parietal region is also comparatively reduced in ring-tailed lemurs, with the posterior projections of the inferior longitudinal fasciculus not extending toward parietal cortical areas as in the other species. In the squirrel monkeys we note a very specific occipito-parietal anatomy that is apparent in their surface anatomy and the expansion of the posterior projections of the optical radiation. Our study supports the hypothesis that the connectivity of the prefrontal-parietal regions became relatively elaborated in the simian lineage after divergence from the prosimian lineage.