Transsynaptic Degeneration of Retinal Ganglion Cells Following Lesions to Primary Visual Cortex in Marmosets

Purpose

A lesion to primary visual cortex (V1) in primates can produce retrograde transneuronal degeneration in the dorsal lateral geniculate nucleus (LGN) and retina. We investigated the effect of age at time of lesion on LGN volume and retinal ganglion cell (RGC) density in marmoset monkeys.

Methods

Retinas and LGNs were obtained about 2 years after a unilateral left-sided V1 lesion as infants (n = 7) or young adult (n = 1). Antibodies against RBPMS were used to label all RGCs, and antibodies against CaMKII or GABAA receptors were used to label nonmidget RGCs. Cell densities were compared in the left and right hemiretina of each eye. The LGNs were stained with the nuclear marker NeuN or for Nissl substance.

Results

In three animals lesioned within the first 2 postnatal weeks, the proportion of RGCs lost within 5 mm of the fovea was ∼twofold higher than after lesions at 4 or 6 weeks. There was negligible loss in the animal lesioned at 2 years of age. A positive correlation between RGC loss and LGN volume reduction was evident. No loss of CaMKII-positive or GABAA receptor-positive RGCs was apparent within 2 mm of the fovea in any of the retinas investigated.

Conclusions

Susceptibility of marmoset RGCs to transneuronal degeneration is high at birth and declines over the first 6 postnatal weeks. High survival rates of CaMKII and GABAA receptor-positive RGCs implies that widefield and parasol cells are less affected by neonatal cortical lesions than are midget-pathway cells.

Rare edges and abundant cores: range-wide variation in abundance in North American birds

Understanding how the abundance of species varies across geographical ranges is central to ecology; however, few studies test hypotheses using detailed abundance estimates across the full ranges of species on a continental scale. Here, we use unprecedented, detailed estimates of breeding abundance for North American birds (eBird) to test two hypotheses for how abundance varies across species' ranges. We find widespread support for the rare-edge hypothesis-where the abundance of species declines near the range edge-reflecting both reduced occurrence and lower local abundance near range edges. By contrast, we find mixed support for the abundant-centre hypothesis-where the abundance of species peaks in the centre of the range and declines towards the edges-with limited support in conservative tests within species, but general support in among-species tests that control for unbalanced sampling and consider a broader definition of the range centre. Overall, results are consistent with a gradual decline in suitable conditions and increase in challenge towards the range edge that eventually limit the ability of populations to persist.

The competitive exclusion-tolerance rule explains habitat partitioning among co-occurring species of burying beetles

Habitat partitioning among co-occurring, ecologically similar species is widespread in nature and thought to be an important mechanism for coexistence. The factors that cause habitat partitioning, however, are unknown for most species. We experimentally tested among three alternative hypotheses to explain habitat partitioning among two species of co-occurring burying beetle (Nicrophorus) that occupy forest (Nicrophorus orbicollis) and wetland (Nicrophorus hebes) habitats. Captive experiments revealed that the larger N. orbicollis (forest) was consistently dominant to N. hebes (wetland) in competitive interactions for carcasses that they require for reproduction. Transplant enclosure experiments in nature revealed that N. hebes had poor reproductive success whenever the dominant N. orbicollis was present. In the absence of N. orbicollis, N. hebes performed as well, or better, in forest versus its typical wetland habitat. In contrast, N. orbicollis performed poorly in wetlands regardless of the presence of N. hebes. These results support the competitive exclusion-tolerance rule where the competitively dominant N. orbicollis excludes the subordinate N. hebes from otherwise suitable or preferable forest habitat, while the subordinate N. hebes is uniquely able to tolerate the challenges of breeding in wetlands. Transplant experiments further showed that carcass burial depth-an important trait thought to enhance the competitive ability of the dominant N. orbicollis-is costly in wetland habitats. In the presence of N. hebes, N. orbicollis buried carcasses deeper; deeper burial is thought to provide a competitive advantage in forests but further compromised the reproductive success of N. orbicollis in wetlands. Overall, results provide evidence that the competitive exclusion-tolerance rule underlies habitat partitioning among ecologically similar species and that the traits important for competitive dominance in relatively benign environments are costly in more challenging environments, consistent with a trade-off.

Urban tolerance does not protect against population decline in North American birds

Population declines of organisms are widespread and severe, but some species' populations have remained stable, or even increased. The reasons some species are less vulnerable to population decline than others are not well understood. Species that tolerate urban environments often have a broader environmental tolerance, which, along with their ability to tolerate one of the most human-modified habitats (i.e. cities), might allow them to persist in the face of diverse anthropogenic challenges. Here, we examined the relationship between urban tolerance and annual population trajectories for 397 North American bird species. Surprisingly, we found that urban tolerance was unrelated to species' population trajectories. The lack of a relationship between urban tolerance and population trajectories may reflect other factors driving population declines independent of urban tolerance, challenges that are amplified in cities (e.g. climate warming, disease), and other human impacts (e.g. conservation efforts, broad-scale land-use changes) that have benefitted some urban-avoidant species. Overall, our results illustrate that urban tolerance does not protect species against population decline.

Behavioral dominance interactions between two species of burying beetles (Nicrophorus orbicollis and Nicrophorus pustulatus)

Closely related species with ecological similarity often aggressively compete for a common, limited resource. This competition is usually asymmetric and results in one species being behaviorally dominant over the other. Trade-offs between traits for behavioral dominance and alternative strategies can result in different methods of resource acquisition between the dominant and subordinate species, with important consequences for resource partitioning and community structure. Body size is a key trait thought to commonly determine behavioral dominance. Priority effects (i.e., which species arrives at the resource first), however, can also determine the outcome of interactions, as can species-specific traits besides size that give an advantage in aggressive contests (e.g., weapons). Here, we test among these three alternative hypotheses of body size, priority effects, and species identity for what determines the outcome of competitive interactions among two species of burying beetles, Nicrophorus orbicollis and N. pustulatus. Both overlap in habitat and seasonality and exhibit aggressive competition over a shared breeding resource of small vertebrate carrion. In trials, we simulated what would happen upon the beetles' discovery of a carcass in nature by placing a carcass and one beetle of each species in a container and observing interactions over 13 h trials (n = 17 trials). We recorded and categorized interactions between beetles and the duration each individual spent in contact with the carcass (the key resource) to determine which hypothesis predicted trial outcomes. Body size was our only significant predictor; the largest species won most aggressive interactions and spent more time in contact with the carcass. Our results offer insight into the ecology and patterns of resource partitioning of N. orbicollis and N. pustulatus, the latter of which is unique among local Nicrophorus for being a canopy specialist. N. pustulatus is also unique among all Nicrophorus in using snake eggs, in addition to other carrion, as a breeding resource. Our results highlight the importance of body size and related trade-offs in ecology and suggest parallels with other coexisting species and communities.

Color as an Interspecific Badge of Status: A Comparative Test

AbstractAnimals as diverse as cephalopods, insects, fish, and mammals signal social dominance to conspecifics to avoid costly fights. Even though between-species fights may be equally costly, the extent to which dominance signals are used between species is unknown. Here, we test the hypothesis that differences in color are associated with dominance between closely related species that aggressively interact over resources, examining between-species variation in colors that are used in within-species badges of status (black, white, and carotenoid coloration) in a comparative analysis of diverse species of birds. We found that dominant species have more black, on average, than subordinate species, particularly in regions important for aggressive signaling (face, throat, and bill). Furthermore, dominant species were more likely to have more black in comparisons in which the dominant species was similar in size or smaller than the subordinate, suggesting that black may be a more important signal when other signals of dominance (size) are missing. Carotenoid colors (i.e., red, pink, orange, and yellow) were not generally associated with dominance but may signal dominance in some taxonomic groups. White may have opposing functions: white was associated with dominance in species in which black was also associated with dominance but was associated with subordinance in species in which carotenoid-based dominance signals may be used. Overall, these results provide new evidence that colors may function broadly as signals of dominance among competing species. Such signals could help to mediate aggressive interactions among species, thereby reducing some costs of co-occurrence and facilitating coexistence in nature.

A Case for the "Competitive Exclusion-Tolerance Rule" as a General Cause of Species Turnover along Environmental Gradients

AbstractClosely related, ecologically similar species often segregate their distributions along environmental gradients of time, space, and resources, but previous research suggests diverse underlying causes. Here, we review reciprocal removal studies in nature that experimentally test the role of interactions among species in determining their turnover along environmental gradients. We find consistent evidence for asymmetric exclusion coupled with differences in environmental tolerance causing the segregation of species pairs, where a dominant species excludes a subordinate from benign regions of the gradient but is unable to tolerate challenging regions to which the subordinate species is adapted. Subordinate species were consistently smaller and performed better in regions of the gradient typically occupied by the dominant species compared with their native distribution. These results extend previous ideas contrasting competitive ability with adaptation to abiotic stress to include a broader diversity of species interactions (intraguild predation, reproductive interference) and environmental gradients, including gradients of biotic challenge. Collectively, these findings suggest that adaptation to environmental challenge compromises performance in antagonistic interactions with ecologically similar species. The consistency of this pattern across diverse organisms, environments, and biomes suggests generalizable processes structuring the segregation of ecologically similar species along disparate environmental gradients, a phenomenon that we propose should be named the competitive exclusion-tolerance rule.

Rapid adaptation of primate LGN neurons to drifting grating stimulation

The visual system needs to dynamically adapt to changing environments. Much is known about the adaptive effects of constant stimulation over prolonged periods of time. However, there are open questions regarding adaptation to stimuli that are changing over time, interrupted, or repeated. Feature-specific adaptation to repeating stimuli has been shown to occur as early as primary visual cortex (V1), but there is also evidence for more generalized, fatigue-like adaptation that might occur at an earlier stage of processing. Here, we show adaptation in the lateral geniculate nucleus (LGN) of awake, fixating monkeys following brief (1 s) exposure to repeated cycles of a 4 Hz drifting grating. We examined the relative change of each neuron's response across successive (repeated) grating cycles. We found that neurons from all cell classes (parvocellular, magnocellular, and koniocellular) showed significant adaptation. However, only magnocellular neurons showed adaptation when responses were averaged to a population response. In contrast to firing rates, response variability was largely unaffected. Lastly, adaptation was comparable between monocular and binocular stimulation, suggesting that rapid LGN adaptation is monocular in nature.

Comparative connectomics reveals noncanonical wiring for color vision in human foveal retina

The Old World macaque monkey and New World common marmoset provide fundamental models for human visual processing, yet the human ancestral lineage diverged from these monkey lineages over 25 Mya. We therefore asked whether fine-scale synaptic wiring in the nervous system is preserved across these three primate families, despite long periods of independent evolution. We applied connectomic electron microscopy to the specialized foveal retina where circuits for highest acuity and color vision reside. Synaptic motifs arising from the cone photoreceptor type sensitive to short (S) wavelengths and associated with "blue-yellow" (S-ON and S-OFF) color-coding circuitry were reconstructed. We found that distinctive circuitry arises from S cones for each of the three species. The S cones contacted neighboring L and M (long- and middle-wavelength sensitive) cones in humans, but such contacts were rare or absent in macaques and marmosets. We discovered a major S-OFF pathway in the human retina and established its absence in marmosets. Further, the S-ON and S-OFF chromatic pathways make excitatory-type synaptic contacts with L and M cone types in humans, but not in macaques or marmosets. Our results predict that early-stage chromatic signals are distinct in the human retina and imply that solving the human connectome at the nanoscale level of synaptic wiring will be critical for fully understanding the neural basis of human color vision.

The Verriest Lecture: Pathways to color in the eye and brain

In common with the majority of New World monkeys, marmosets show polymorphic color vision by allelic variation of X-chromosome genes encoding opsin pigments in the medium/long wavelength range. Male marmosets are thus obligate dichromats ("red-green color blind"), whereas females carrying distinct alleles on X chromosomes show one of three trichromatic phenotypes. Marmosets thus represent a "natural knock-out" system enabling comparison of red-green color vision in dichromatic and trichromatic visual systems. Further, study of short-wave (blue) cone pathways in marmosets has provided insights into primitive visual pathways for depth perception and attention. These investigations represent a parallel line to clinical research on color vision defects that was pioneered in studies by Guy Verreist, whom we honor in this eponymous lecture.

Neurons share an intense load

Time-of-day-detecting cells in the eye give customized responses to light intensity.

Among-species variation in hormone concentrations is associated with urban tolerance in birds

As cities expand across the globe, understanding factors that underlie variation in urban tolerance is vital for predicting changes in patterns of biodiversity. Endocrine traits, like circulating hormone concentrations and regulation of endocrine responses, might contribute to variation in species' ability to cope with urban challenges. For example, variation in glucocorticoid and androgen concentrations has been linked to life-history and behavioural traits that are associated with urban tolerance. However, we lack an understanding of the degree to which evolved differences in endocrine traits predict variation in urban tolerance across species. We analysed 1391 estimates of circulating baseline corticosterone, stress-induced corticosterone, and testosterone concentrations paired with citizen-science-derived urban occurrence scores in a broad comparative analysis of endocrine phenotypes across 71 bird species that differ in their occurrence in urban habitats. Our results reveal context-dependent links between baseline corticosterone and urban tolerance, as well as testosterone and urban tolerance. Stress-induced corticosterone was not related to urban tolerance. These findings suggest that some endocrine phenotypes contribute to a species' tolerance of urban habitats, but also indicate that other aspects of the endocrine phenotype, such as the ability to appropriately attenuate responses to urban challenges, might be important for success in cities.

An observational study of self-reported migraine triggers and prospective evaluation of the relationships with occurrence of attacks enabled by a smartphone application (App)

OBJECTIVE

To investigate the relationship between self-reported triggers and the occurrence of migraine attacks using a smartphone application.

BACKGROUND

One of several issues around the study of migraine attack triggers is that limited available evidence supports whether self-reported triggers can induce a headache on a particular subject.

METHODS

This is an observational longitudinal cohort study of individuals with migraine registered to track their headaches prospectively using a smartphone application. For 90 days, participants entered daily data about triggers (potential triggers and premonitory symptoms) that may be associated with attack risk, as well as migraine symptoms. The statistical significance of univariate associations between each trigger and migraine recurrent events was determined for each individual. Statistically identified triggers were then compared to self-reported triggers.

RESULTS

In 328 individuals (290/328 [88.4%] female; mean [standard deviation] 4.2 [1.5] migraine attacks/month) the mean (standard deviation) number of triggers moderately or highly endorsed per individual was 28.0 (7.7) in individuals presented with up to 38 possible triggers. Of these, an average (standard deviation) of 2.2 (2.1) triggers per individual were statistically associated with increased risk of attacks. Even the most commonly endorsed triggers (sleep quality, stress, tiredness/fatigue, sleep duration, dehydration, neck pain, missed meals, eyestrain, mean barometric pressure, and anxiety) were statistically associated in fewer than one third of individuals suspecting each, with the exception of neck pain (117/302 [38.7%]).

CONCLUSIONS

Individuals with episodic migraine believe that many triggers contribute to their attacks; however, few of these withstand statistical testing at the individual level. Improved personal knowledge of potential triggers and premonitory symptoms may help individuals adopt behavioral changes to mitigate attack risk.

Lifestyle factors and migraine

Migraine, a common and disabling neurological disorder, is among the top reasons for outpatient visits to general neurologists. In addition to pharmacotherapy, lifestyle interventions are a mainstay of treatment. High-quality daily diary studies and intervention studies indicate intraindividual variations in the associations between lifestyle factors (such as stress, sleep, diet, and physical activity) and migraine attack occurrence. Behaviour change interventions can directly address overlapping lifestyle factors; combination approaches could capitalise on multiple mechanisms. These findings provide useful directions for integration of lifestyle management into routine clinical care and for future research.

Estimates of species-level tolerance of urban habitat in North American birds

Species vary in their responses to urban habitat - most species avoid these environments, while others tolerate or even thrive in them. To better characterize the extent to which species vary in their responses to urban habitat (hereafter urban tolerance), we used several methods to quantify these responses at a continental scale across all birds. Using open access community science-derived data from the eBird Status and Trends Products and two different types of high-resolution geospatial data that quantify urbanization of landscapes, we calculated urban tolerance for 432 species with breeding ranges that overlap large cities in Canada or the United States. We developed six different calculations to characterize species-level urban tolerance, allowing us to assess how each species' relative abundance across their breeding range varied with estimates of urban habitat use and intensity. We assessed correlations among these six indices, then compressed the two best-performing indices into a single principal component (multivariate urban tolerance index) that captured variation in urban tolerance among species. We assessed the accuracy of our single and multivariate urban tolerance indices using 24 test species that are well characterized for their tolerance or avoidance of urban habitat, as well as with previously published, independent urban tolerance estimates. Here, we provide this new dataset of species-level urban tolerance estimates which improves upon previous metrics by incorporating continental-scale, continuous estimates that better differentiate species' tolerance of urban habitat than existing, categorical methods. These refined metrics can be used to test hypotheses that link ecological, life history, and behavioral traits to avian urban tolerance. The dataset is licensed as CC-By Attribution 4.0 International. Users must appropriately cite data paper and dataset if used in publications and scientific presentations.

Experimental test of selection against hybridization as a driver of avian signal divergence

Signal divergence may be pivotal in the generation and maintenance of new biodiversity by allowing closely related species to avoid some costs of co-occurrence. In birds, closely related, sympatric species are more divergent in their colour patterns than those that live apart, but the selective pressures driving this pattern remain unclear. Traditionally, signal divergence among sympatric species is thought to result from selection against hybridization, but broad evidence is lacking. Here, we conducted field experiments on naïve birds using spectrometer-matched, painted 3D-printed models to test whether selection against hybridization drives colour pattern divergence in the genus Poecile. To address selection for male colour pattern divergence without the influence of learning or the evolution of female discrimination in sympatry, we simulated secondary contact between Poecile species, and conducted mate choice experiments on naïve, allopatric females. We found that female black-capped chickadees (Poecile atricapillus) are equally likely to perform copulation solicitation displays to sympatric and allopatric heterospecific congeners when they are paired with conspecifics, but exhibit a strong preference for less divergent males when presented with paired heterospecific congeners. These results suggest that increased colour pattern divergence among sympatric species can reduce the likelihood of mixed mating in some contexts, and therefore should be favoured by selection against hybridization.

Aggressive signaling among competing species of birds

Aggressive interactions help individuals to gain access to and defend resources, but they can be costly, leading to increased predation risk, injury, or death. Signals involving sounds and color can allow birds to avoid the costs of intraspecific aggressive encounters, but we know less about agonistic signaling between species, where fights can be frequent and just as costly. Here, we review photographic and video evidence of aggressive interactions among species of birds (N = 337 interactions documenting the aggressive signals of 164 different bird species from 120 genera, 50 families, and 24 orders) to document how individuals signal in aggressive encounters among species, and explore whether these visual signals are similar to those used in aggressive encounters with conspecifics. Despite the diversity of birds examined, most aggressively signaling birds displayed weapons (bills, talons, wings) used in fighting and placed these weapons closest to their heterospecific opponent when signaling. Most species oriented their bodies and heads forward with their bills pointing towards their heterospecific opponent, often highlighting their face, throat, mouth, and bill. Many birds also opened their wings and/or tails, increasing their apparent size in displays, consistent with the importance of body size in determining behavioral dominance among species. Aggressive postures were often similar across species and taxonomic families. Exceptions included Accipitridae and Falconidae, which often highlighted their talons in the air, Columbidae, which often highlighted their underwings from the side, and Trochilidae, which often hovered upright in the air and pointed their fanned tail downward. Most species highlighted bright carotenoid-based colors in their signals, but highlighted colors varied across species and often involved multiple colors in combination (e.g., black, white, and carotenoid-based colors). Finally, birds tended to use the same visual signals in aggressive encounters with heterospecifics that they use in aggressive encounters with conspecifics, suggesting that selection from aggressive interactions may act on the same signaling traits regardless of competitor identity.

Retinal ganglion cells expressing CaM kinase II in human and nonhuman primates

Immunoreactivity for calcium-/calmodulin-dependent protein kinase II (CaMKII) in the primate dorsal lateral geniculate nucleus (dLGN) has been attributed to geniculocortical relay neurons and has also been suggested to arise from terminals of retinal ganglion cells. Here, we combined immunostaining with single-cell injections to investigate the expression of CaMKII in retinal ganglion cells of three primate species: macaque (Macaca fascicularis, M. nemestrina), human, and marmoset (Callithrix jacchus). We found that in all species, about 2%-10% of the total ganglion cell population expressed CaMKII. In all species, CaMKII was expressed by multiple types of wide-field ganglion cell including large sparse, giant sparse (melanopsin-expressing), broad thorny, and narrow thorny cells. Three other ganglion cells types, namely, inner and outer stratifying maze cells in macaque and tufted cells in marmoset were also found. Double labeling experiments showed that CaMKII-expressing cells included inner and outer stratifying melanopsin cells. Nearly all CaMKII-expressing ganglion cell types identified here are known to project to the koniocellular layers of the dLGN as well as to the superior colliculus. The best characterized koniocellular projecting cell type-the small bistratified (blue ON/yellow OFF) cell-was, however, not CaMKII-positive in any species. Our results indicate that the pattern of CaMKII expression in retinal ganglion cells is largely conserved across different species of primate suggesting a common functional role. But the results also show that CaMKII is not a marker for all koniocellular projecting retinal ganglion cells.

An Integrative Perspective on the Mechanistic Basis of Context Dependent Species Interactions

It has long been known that the outcome of species interactions depends on the environmental context in which they occur. Climate change research has sparked a renewed interest in context dependent species interactions because rapidly changing abiotic environments will cause species interactions to occur in novel contexts and researchers must incorporate this in their predictions of species' responses to climate change. Here we argue that predicting how the environment will alter the outcome of species interactions requires an integrative biology approach that focuses on the traits, mechanisms, and processes that bridge disciplines such as physiology, biomechanics, ecology, and evolutionary biology. Specifically, we advocate for quantifying how species differ in their tolerance and performance to both environmental challenges independent of species interactions, and in interactions with other species as a function of the environment. Such an approach increases our understanding of the mechanisms underlying outcomes of species interactions across different environmental contexts. This understanding will in turn help determine how the outcome of species interactions affects the relative abundance and distribution of the interacting species in nature. A general theme that emerges from this perspective is that species are unable to maintain high levels of performance across different environmental contexts because of trade-offs between physiological tolerance to environmental challenges and performance in species interactions. Thus, an integrative biology paradigm that focuses on the trade-offs across environments, the physiological mechanisms involved, and how the ecological context impacts the outcome of species interactions provides a stronger framework to understand why species interactions are context dependent.

Satb1 expression in retinal ganglion cells of marmosets, macaques, and humans

Recent advances in single-cell RNA sequencing have enabled the molecular distinction of ganglion cell populations in mammalian retinas. Here we used antibodies against the transcription factor special AT-rich binding protein 1 (Satb1, a protein which is expressed by on-off direction-selective ganglion cells in mouse retina) to study Satb1 expression in the retina of marmosets (Callithrix jacchus), macaques (Macaca fascicularis), and humans. In all species, Satb1 was exclusively expressed in retinal ganglion cells. The Satb1 cells made up ∼2% of the ganglion cell population in the central retina of all species, rising to a maximum ∼7% in peripheral marmoset retina. Intracellular injections in marmoset and macaque retinas revealed that most Satb1 expressing ganglion cells are widefield ganglion cells. In marmoset, Satb1 cells have a densely branching dendritic tree and include broad and narrow thorny, recursive bistratified, and parasol cells, all of which show some costratification with the outer or inner cholinergic amacrine cells. The recursive bistratified cells showed the strongest costratification but did not show extensive cofasciculation as reported for on-off direction-selective ganglion cells in rabbit and rodent retinas. In macaque, Satb1 was not expressed in recursive bistratified cells, but in large sparsely branching cells. Our findings further support the idea that the expression of transcription factors in retinal ganglion cells is not conserved across Old World (human and macaque) and New World (marmoset) primates and provides a further step to link a molecular marker with specific cell types.

Vision and retina evolution: how to develop a retina

Early in vertebrate evolution, a single homeobox (Hox) cluster in basal chordates was quadrupled to generate the Hox gene clusters present in extant vertebrates. Here we ask how this expanded gene pool may have influenced the evolution of the visual system. We suggest that a single neurosensory cell type split into ciliated sensory cells (photoreceptors, which transduce light) and retinal ganglion cells (RGC, which project to the brain). In vertebrates, development of photoreceptors is regulated by the basic helix-loop-helix (bHLH) transcription factor Neurod1 whereas RGC development depends on Atoh7 and related bHLH genes. Lancelet (a basal chordate) does not express Neurod or Atoh7 and possesses a few neurosensory cells with cilia that reach out of the opening of the neural tube. Sea-squirts (Ascidians) do not express Neurod and express a different bHLH gene, Atoh8, that is likely expressed in the anterior vesicle. Recent data indicate the neurosensory cells in lancelets may correspond to three distinct eye fields in ascidians, which in turn may be the basis of the vertebrate retina, pineal and parapineal. In this review we contrast the genetic control of visual structure development in these chordates with that of basal vertebrates such as lampreys and hagfish, and jawed vertebrates. We propose an evolutionary sequence linking whole-genome duplications, initially to a split between photoreceptor and projection neurons (RGC) and subsequently between pineal and lateral eye structures.

Integrating headache trigger management strategies into cognitive-behavioral therapy: A randomized controlled trial

OBJECTIVE

Traditionally, the standard advice to individuals suffering from migraine and tension-type headache was that the best way to prevent headaches is to avoid the triggers. This advice has been challenged in recent years and the Trigger Avoidance Model of Headache has been proposed, which suggests that one pathway to developing a headache disorder is by avoiding triggers resulting in trigger sensitization. The objective of the study was to evaluate a novel intervention for primary headache comprising a new approach to trigger management that includes exposure to some triggers with the goal of trigger desensitization (learning to cope with triggers [LCT]) integrated into a cognitive-behavioral therapy (CBT) program (LCT/CBT).

METHOD

The study was a randomized controlled trial comparing LCT/CBT to the same treatment program but using the traditional approach to trigger management of encouraging trigger avoidance (avoid/CBT), and to a waiting-list/treatment-as-usual control condition (WL/TAU). Adults suffering from primary headache (88 female/35 male) were allocated to the three conditions.

RESULTS

The three groups significantly differed from baseline to posttreatment on the primary outcome measure of attack frequency, and LCT/CBT significantly differed from WL/TAU but Avoid/CBT did not. Similar results were obtained on the secondary outcome measures, and treatment gains were maintained at 4- and 12-month follow-up.

CONCLUSIONS

The results suggest the value of using LCT as a component of a CBT program but were not conclusive as the direct comparisons between the two treatment conditions failed to reach statistical significance. The findings support a study of LCT/CBT with a larger sample. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Morphology, Molecular Characterization, and Connections of Ganglion Cells in Primate Retina

The eye sends information about the visual world to the brain on over 20 parallel signal pathways, each specialized to signal features such as spectral reflection (color), edges, and motion of objects in the environment. Each pathway is formed by the axons of a separate type of retinal output neuron (retinal ganglion cell). In this review, we summarize what is known about the excitatory retinal inputs, brain targets, and gene expression patterns of ganglion cells in humans and nonhuman primates. We describe how most ganglion cell types receive their input from only one or two of the 11 types of cone bipolar cell and project selectively to only one or two target regions in the brain. We also highlight how genetic methods are providing tools to characterize ganglion cells and establish cross-species homologies.

Short-Wave Sensitive ("Blue") Cone Activation Is an Aggravating Factor for Visual Snow Symptoms

Background and Purpose: Visual Snow (VS) is a disorder characterised by the subjective perception of black-and-white visual static. The aetiology of this condition is not known. In our previous work we suggested that there is a link between short-wave (S or “blue” cone) signals and severity of visual snow symptoms. Therefore we aimed to further characterise this potential link.

Methods: Patients (n = 22) with classic VS based on the diagnostic criteria and healthy controls (n = 12), underwent Intuitive Colorimetry (IC) testing (Cerium Visual Technologies). Twelve hue directions (expressed as angle in CIE 1976 LUV space relative to D65) were rated on a five-point scale from preferred (relieving, positive score) to non-preferred (exacerbating, negative score), and overall preferred and non-preferred angles were chosen.

Results: A non-preferred violet region near the tritanopic confusion line / S-cone axis (267 deg.) was strongly associated with exacerbation of VS symptoms (range 250–310 deg, mean 276 ± 16, n = 20, Rayleigh p < 0.001). Two subjects with non-preferred region > 90 deg from mean were considered as outliers. Median rank at hue angle 270 deg was significantly lower than at angle 90 (−1.5 vs. 0.0, p < 0.001, Wilcoxon non-parametric rank-sum test). Patients showed preference for one of two spectral regions which relieved VS symptoms: orange-yellow (range 50–110 deg., mean 79 ± 24, n = 14) and turquoise-blue (range (210–250 deg., mean 234 ± 27, n = 8).

Conclusion: Our results show that visual snow symptoms are exacerbated by colour modulation that selectively increased levels of S-cone excitation. Because S-cone signals travel on primordial brain pathways that regulate cortical rhythms (koniocellular pathways) we hypothesis that these pathways contribute to the pathogenesis of this disorder.

Composition of the Inner Nuclear Layer in Human Retina

Purpose

The purpose of this study was to measure the composition of the inner nuclear layer (INL) in the central and peripheral human retina as foundation data for interpreting INL function and dysfunction.

Methods

Six postmortem human donor retinas (male and female, aged 31–56 years) were sectioned along the temporal horizontal meridian. Sections were processed with immunofluorescent markers and imaged using high-resolution, multichannel fluorescence microscopy. The density of horizontal, bipolar, amacrine, and Müller cells was quantified between 1 and 12 mm eccentricity with appropriate adjustments for postreceptoral spatial displacements near the fovea.

Results

Cone bipolar cells dominate the INL a with density near 50,000 cells/mm² at 1 mm eccentricity and integrated total ∼10 million cells up to 10 mm eccentricity. Outside central retina the spatial density of all cell populations falls but the neuronal makeup of the INL remains relatively constant: a decrease in the proportion of cone bipolar cells (from 52% at 1 mm to 37% at 10 mm) is balanced by an increasing proportion of rod bipolar cells (from 9% to 15%). The proportion of Müller cells near the fovea (17%) is lower than in the peripheral retina (27%).

Conclusions

Despite large changes in the absolute density of INL cell populations across the retina, their proportions remain relatively constant. These data may have relevance for interpreting diagnostic signals such as the electroretinogram and optical coherence tomogram.

Experimental tests of selection against heterospecific aggression as a driver of avian colour pattern divergence

Signal divergence is thought to reduce the costs of co-occurrence for closely related species and may thereby be important in the generation and maintenance of new biodiversity. In birds, closely related, sympatric species are more divergent in their colour patterns than those that live apart, but the selective pressures driving sympatric divergence in colour pattern are not well-understood. Here, we conducted field experiments on naïve birds using spectrometer-matched, painted, 3D-printed models to test whether selection against heterospecific aggression might drive colour pattern divergence in the genus Poecile. We found that territorial male black-capped chickadees (P. atricapillus) are equally likely to attack sympatric and allopatric congeners, and wintering flocks are equally likely to visit feeders occupied by sympatric and allopatric congeners, despite sympatric congeners being more divergent in colour pattern. These results suggest that either the concerted evolution of additional traits (e.g. discrimination), or interactions in sympatry that promote learning, is required if colour pattern divergence among sympatric species is to reduce heterospecific aggression. Alternatively, colour pattern divergence among sympatric species may be caused by other selective pressures, such as selection against hybridization or habitat partitioning and secondary signal adaptation.

Lévy walk dynamics explain gamma burst patterns in primate cerebral cortex

Lévy walks describe patterns of intermittent motion with variable step sizes. In complex biological systems, Lévy walks (non-Brownian, superdiffusive random walks) are associated with behaviors such as search patterns of animals foraging for food. Here we show that Lévy walks also describe patterns of oscillatory activity in primate cerebral cortex. We used a combination of empirical observation and modeling to investigate high-frequency (gamma band) local field potential activity in visual motion-processing cortical area MT of marmoset monkeys. We found that gamma activity is organized as localized burst patterns that propagate across the cortical surface with Lévy walk dynamics. Lévy walks are fundamentally different from either global synchronization, or regular propagating waves, because they include large steps that enable activity patterns to move rapidly over cortical modules. The presence of Lévy walk dynamics therefore represents a previously undiscovered mode of brain activity, and implies a novel way for the cortex to compute. We apply a biophysically realistic circuit model to explain that the Lévy walk dynamics arise from critical-state transitions between asynchronous and localized propagating wave states, and that these dynamics yield optimal spatial sampling of the cortical sheet. We hypothesise that Lévy walk dynamics could help the cortex to efficiently process variable inputs, and to find links in patterns of activity among sparsely spiking populations of neurons.

Retinal ganglion cells projecting to superior colliculus and pulvinar in marmoset

We determined the retinal ganglion cell types projecting to the medial subdivision of inferior pulvinar (PIm) and the superior colliculus (SC) in the common marmoset monkey, Callithrix jacchus. Adult marmosets received a bidirectional tracer cocktail into the PIm (conjugated to Alexa fluor 488), and the SC (conjugated to Alexa fluor 594) using an MRI-guided approach. One SC injection included the pretectum. The large majority of retrogradely labelled cells were obtained from SC injections, with only a small proportion obtained after PIm injections. Retrogradely labelled cells were injected intracellularly in vitro using lipophilic dyes (DiI, DiO). The SC and PIm both received input from a variety of ganglion cell types. Input to the PIm was dominated by broad thorny (41%), narrow thorny (24%) and large bistratified (25%) ganglion cells. Input to the SC was dominated by parasol (37%), broad thorny (24%) and narrow thorny (17%) cells. Midget ganglion cells (which make up the large majority of primate retinal ganglion cells) and small bistratified (blue-ON/yellow OFF) cells were never observed to project to SC or PIm. Small numbers of other wide-field ganglion cell types were also encountered. Giant sparse (presumed melanopsin-expressing) cells were only seen following the tracer injection which included the pretectum. We note that despite the location of pulvinar complex in dorsal thalamus, and its increased size and functional importance in primate evolution, the retinal projections to pulvinar have more in common with SC projections than they do with projections to the dorsal lateral geniculate nucleus.

Behavioral dominance interactions between Nicrophorus orbicollis and N. tomentosus burying beetles (Coleoptera: Silphidae)

Asymmetric interference competition, where one species is behaviorally dominant over another, appears widespread in nature with the potential to structure ecological communities through trade-offs between competitive dominance and environmental tolerance. The details of how species interact and the factors that contribute to behavioral dominance, however, are poorly known for most species, yet such details are important for understanding when and why trade-offs occur. Here, we examine behavioral interactions between two species of burying beetles (Coleoptera: Silphidae) that compete for limited breeding resources (i.e., small vertebrate carcasses) in nature, to identify behaviors involved in interference competition and to test if large body size, species identity, or time of arrival best predict behavioral dominance among species. To test these ideas, we placed same-sex individuals of Nicrophorus orbicollis (early to mid-summer breeder) and N. tomentosus (late summer to fall breeder) into an enclosure together with a 25–30 g mouse carcass (Mus musculus). We then video-recorded all behaviors, including neutral and aggressive interactions, for 13 h per trial (N = 14 trials). For each interaction, we assigned a winner based on which beetle retained its position instead of fleeing or retained possession of the carcass; the overall behavioral dominant was determined as the individual that won the most interactions over the length of the trial. We found that large body size was the best predictor of behavioral dominance. In most interactions, N. orbicollis was larger and dominant over N. tomentosus; however, when N. tomentosus was larger they outcompeted smaller N. orbicollis, illustrating the importance of body size in aggressive contests. The order of arrival to the carcass (priority effects) did not predict behavioral dominance. The larger size and abundance of N. orbicollis in nature suggest a competitive asymmetry between the species, supporting the idea that N. orbicollis constrains the ability of N. tomentosus to breed earlier in the summer.

Identification of retinal ganglion cell types expressing the transcription factor Satb2 in three primate species

In primates, the retinal ganglion cells contributing to high acuity spatial vision (midget cells and parasol cells), and blue-yellow color vision (small bistratified cells) are well understood. Many other ganglion cell types with large dendritic fields (named wide-field ganglion cells) have been identified, but their spatial density and distribution are largely unknown. Here we took advantage of the recently established molecular diversity of ganglion cells to study wide-field ganglion cell populations in three primate species. We used antibodies against the transcription factor Special AT-rich binding protein 2 (Satb2) to explore its expression in macaque (Macaca fascicularis, M. nemestrina), human and marmoset (Callithrix jacchus) retinas. In all three species, Satb2 cells make up a low proportion (1.5-4%) of the ganglion cell population, with a slight increase from central to peripheral retina. Intracellular dye injections revealed that in macaque and human retinas, the large majority (over 80%) of Satb2 cells are inner and outer stratifying large sparse cells. By contrast, in marmoset retina the majority (over 60%) of Satb2 expressing cells were broad thorny cells, with smaller proportions of recursive bistratified (putative direction-selective), large bistratified, and outer stratifying narrow thorny cells. Our findings imply that Satb2 expression has undergone rapid species specific adaptations during primate evolution, because expression is not conserved across Old World (macaque, human) and New World (marmoset) suborders.

Body size variation in a guild of carrion beetles

Body size is a key biological trait, influencing the biomechanics, physiology, behaviour, and ecology of species. Describing variation in body size within and among co-occurring species within an ecological guild can provide important context for understanding the ecology of species and the structure of ecological communities. Here, we focus on a guild of carrion beetles (Coleoptera: Silphidae) co-occurring in southeastern Ontario, Canada. We examine how body size varies (i) among species, (ii) within species, including among sexes, and (iii) across the active season, contrasting estimates of size based on mass with those based on morphological structure (elytron length). We find that body size varies significantly both within and among species. Five focal species show evidence for sexual dimorphism in size. All focal species show significant seasonal variation in size, but these patterns differ across species, and depend on our estimates of size. Overall, the observed variation in body size is most consistent with widespread environmental constraints on size and (or) diverse selective pressures favouring different sizes within and among species. We discuss possible selective pressures acting on size within and among species; however, the causes and consequences of the variation in body size that we describe remain to be discovered.

Plasticity versus Evolutionary Divergence: What Causes Habitat Partitioning in Urban-Adapted Birds?

AbstractHabitat partitioning can facilitate the coexistence of closely related species and often results from competitive interference inducing plastic shifts of subordinate species in response to aggressive, dominant species (plasticity) or the evolution of ecological differences in subordinate species that reduce their ability to occupy habitats where the dominant species occurs (evolutionary divergence). Evidence consistent with both plasticity and evolutionary divergence exist, but the relative contributions of each to habitat partitioning have been difficult to discern. Here we use a global data set on the breeding occurrence of birds in cities to test predictions of these alternative hypotheses to explain previously described habitat partitioning associated with competitive interference. Consistent with plasticity, the presence of behaviorally dominant congeners in a city was associated with a 65% reduction in the occurrence of subordinate species, but only when the dominant was a widespread breeder in urban habitats. Consistent with evolutionary divergence, increased range-wide overlap with dominant congeners was associated with a 56% reduction in the occurrence of subordinates in cities, even when the dominant was absent from the city. Overall, our results suggest that both plasticity and evolutionary divergence play important, concurrent roles in habitat partitioning among closely related species in urban environments.

Analysis of Parvocellular and Magnocellular Visual Pathways in Human Retina

Two main subcortical pathways serving conscious visual perception are the midget-parvocellular (P), and the parasol-magnocellular (M) pathways. It is generally accepted that the P pathway serves red-green color vision, but the relative contribution of P and M pathways to spatial vision is a long-standing and unresolved issue. Here, we mapped the spatial sampling properties of P and M pathways across the human retina. Data were obtained from immunolabeled vertical sections of six postmortem male and female human donor retinas and imaged using high-resolution microscopy. Cone photoreceptors, OFF-midget bipolar cells (P pathway), OFF-diffuse bipolar (DB) types DB3a and DB3b (M pathway), and ganglion cells were counted along the temporal horizontal meridian, taking foveal spatial distortions (postreceptoral displacements) into account. We found that the density of OFF-midget bipolar and OFF-midget ganglion cells can support one-to-one connections to 1.05-mm (3.6°) eccentricity. One-to-one connections of cones to OFF-midget bipolar cells are present to at least 10-mm (35°) eccentricity. The OFF-midget ganglion cell array acuity is well-matched to photopic spatial acuity measures throughout the central 35°, but the OFF-parasol array acuity is well below photopic spatial acuity, supporting the view that the P pathway underlies high-acuity spatial vision. Outside the fovea, array acuity of both OFF-midget and OFF-DB cells exceeds psychophysical measures of photopic spatial acuity. We conclude that parasol and midget pathway bipolar cells deliver high-acuity spatial signals to the inner plexiform layer, but outside the fovea, this spatial resolution is lost at the level of ganglion cells.SIGNIFICANCE STATEMENT We make accurate maps of the spatial density and distribution of neurons in the human retina to aid in understanding human spatial vision, interpretation of diagnostic tests, and the implementation of therapies for retinal diseases. Here, we map neurons involved with the midget-parvocellular (P pathway) and parasol-magnocellular (M pathway) through human retina. We find that P-type bipolar cells outnumber M-type bipolar cells at all eccentricities. We show that cone photoreceptors and P-type pathway bipolar cells are tightly connected throughout the retina, but that spatial resolution is lost at the level of the ganglion cells. Overall, the results support the view that the P pathway is specialized to serve both high acuity vision and red-green color vision.

Triggers of Primary Headaches: Issues and Pathways Forward

The triggers of primary headaches have considerable significance for our understanding and management of headache and migraine. Triggers explain the variance in headaches - why they occur when they do. Trigger management is generally viewed as an important component of a comprehensive treatment approach for headaches. Historically, however, triggers have not had a prominent place in the headache literature. This situation began to change 20 to 30 years ago, and the pace of change has increased exponentially in recent times. Nevertheless, the field is beset with issues that have held it back from achieving more. This review will focus on elaborating those issues with the goal of suggesting ways forward. The first issue considered will be the definition of a trigger, and how specific triggers are labeled. Consideration will then be given to a classification system for triggers. The review will discuss next the evidence relating to whether self-reported triggers can, indeed, precipitate headaches, and how the capacity to elicit headaches may be acquired or extinguished. Attention will be given to the very important clinical issue of trigger management. Finally, the pathways forward will be proposed. Perhaps the most useful thing to accomplish at this point in time would be agreement on a definition of headache triggers, a list of triggers, and a classification system for triggers. This would greatly assist in comparing research on triggers from different research groups as well as eliminating some of the issues identified in this review. An authoritative body such as the American Headache Society or the International Headache Society, could establish a multidisciplinary committee that would complete these tasks. Consideration should also be given to incorporating triggers into the International Classification of Headache Disorders as an axis or via the use of codes, as this would raise the profile of triggers in assessment and management.

Cell types and cell circuits in human and non-human primate retina

This review summarizes our current knowledge of primate including human retina focusing on bipolar, amacrine and ganglion cells and their connectivity. We have two main motivations in writing. Firstly, recent progress in non-invasive imaging methods to study retinal diseases mean that better understanding of the primate retina is becoming an important goal both for basic and for clinical sciences. Secondly, genetically modified mice are increasingly used as animal models for human retinal diseases. Thus, it is important to understand to which extent the retinas of primates and rodents are comparable. We first compare cell populations in primate and rodent retinas, with emphasis on how the fovea (despite its small size) dominates the neural landscape of primate retina. We next summarise what is known, and what is not known, about the postreceptoral neurone populations in primate retina. The inventories of bipolar and ganglion cells in primates are now nearing completion, comprising ~12 types of bipolar cell and at least 17 types of ganglion cell. Primate ganglion cells show clear differences in dendritic field size across the retina, and their morphology differs clearly from that of mouse retinal ganglion cells. Compared to bipolar and ganglion cells, amacrine cells show even higher morphological diversity: they could comprise over 40 types. Many amacrine types appear conserved between primates and mice, but functions of only a few types are understood in any primate or non-primate retina. Amacrine cells appear as the final frontier for retinal research in monkeys and mice alike.

Size-dependent costs of migration: Migrant bird species are subordinate to residents, but only at small body sizes

Migrant species are commonly thought to be poor competitors in aggressive interactions with resident species. However, no studies have tested whether this relationship is widespread. Here, we compare the behavioural dominance of closely related species of migratory and nonmigratory birds, testing whether migrants are consistently subordinate to resident species in aggressive contests. We compiled published behavioural dominance data involving migrant and resident congeners, gathering additional data on the body mass and migratory distance of each species. Focal species included a diverse array of birds (28 taxonomic families, 12 orders) from around the world. We found that migrant species are usually subordinate to resident species, but that this relationship disappears at larger body sizes. For smaller birds (<500 g), resident species were behaviourally dominant in 83%-88% of comparisons; for larger birds (>500 g), resident species were dominant in only 25%-30% of comparisons. The relative difference in body mass best predicted dominance relationships among species, with larger species dominant in 80%-84% of comparisons. When migrant and resident masses were equal, however, resident species were still more likely to be dominant in smaller birds, suggesting that other factors may also contribute to the subordinate status of migrants. Overall, our results suggest that in smaller species, the evolution of migration is associated with lighter weights and other traits that compromise the competitive abilities of migrants relative to residents. In contrast, larger species appear able to evolve migration without compromising their size or competitive abilities in aggressive contests, suggesting size-dependent constraints on the evolution of migration.

Topography of Neurons in the Rod Pathway of Human Retina

Purpose

The objective of this study was to map the distribution and density of the three major components of the classical scotopic "night vision" pathway (rods, rod bipolar, and AII amacrine cells) in postmortem human retinas.

Methods

Four postmortem donor eyes (male and female, aged 44-56 years) were used to cut vertical sections through the temporal horizontal meridian. The sections were processed for immunohistochemistry and imaged using high-resolution multichannel confocal microscopy. Rods, rod bipolar, and AII amacrine cells were counted along the temporal horizontal meridian. Two additional retinas were used for intracellular injections.

Results

Rod peak density is close to 150,000 cells/mm2 at 4 to 5 mm (15° to 20°) eccentricity, declining to below 70,000 cells/mm2 in peripheral retina. Rod bipolar density is lower but follows a similar distribution with peak density near 10,000 cells/mm2 between 2 and 4 mm (7° to 15°) eccentricity declining to below 4000 cells/mm2 in peripheral retina. The peak density of AII amacrine cells (near 4000 cells/mm2) is located close to the fovea, at 0.5- to 2 mm-eccentricity (2° to 7°) and declines to below 1000 cells/mm2 in the periphery. Thus, convergence between rods and AII cells increases from central to peripheral retina.

Conclusions

Comparison with human psychophysics and ganglion cell density indicates that the spatial resolution of scotopic vision is limited by the AII mosaic at eccentricities below 15° and by the midget ganglion cell mosaic at eccentricities above 15°.

Relation of koniocellular layers of dorsal lateral geniculate to inferior pulvinar nuclei in common marmosets

Traditionally, the dorsal lateral geniculate nucleus (LGN) and the inferior pulvinar (IPul) nucleus are considered as anatomically and functionally distinct thalamic nuclei. However, in several primate species it has also been established that the koniocellular (K) layers of LGN and parts of the IPul have a shared pattern of immunoreactivity for the calcium-binding protein calbindin. These calbindin-rich cells constitute a thalamic matrix system which is implicated in thalamocortical synchronisation. Further, the K layers and IPul are both involved in visual processing and have similar connections with retina and superior colliculus. Here, we confirmed the continuity between calbindin-rich cells in LGN K layers and the central lateral division of IPul (IPulCL) in marmoset monkeys. By employing a high-throughput neuronal tracing method, we found that both the K layers and IPulCL form comparable patterns of connections with striate and extrastriate cortices; these connections are largely different to those of the parvocellular and magnocellular laminae of LGN. Retrograde tracer-labelled cells and anterograde tracer-labelled axon terminals merged seamlessly from IPulCL into LGN K layers. These results support continuity between LGN K layers and IPulCL, providing an anatomical basis for functional congruity of this region of the dorsal thalamic matrix and calling into question the traditional segregation between LGN and the inferior pulvinar nucleus.