47 research outputs found
Complementary shifts in photoreceptor spectral tuning unlock the full adaptive potential of ultraviolet vision in birds
Mate choice for a male carotenoid-based ornament is linked to female dietary carotenoid intake and accumulation
The effects of sun exposure on carotenoid accumulation and oxidative stress in the retina of the House Finch (Haemorhous mexicanus)
Additional file 1: Tables S1–8. Detailed data tables from each of the experimental comparisons
Thyroid hormone regulates distinct paths to maturation in pigment cell lineages
Thyroid hormone (TH) regulates diverse developmental events and can drive disparate cellular outcomes. In zebrafish, TH has opposite effects on neural crest derived pigment cells of the adult stripe pattern, limiting melanophore population expansion, yet increasing yellow/orange xanthophore numbers. To learn how TH elicits seemingly opposite responses in cells having a common embryological origin, we analyzed individual transcriptomes from thousands of neural crest-derived cells, reconstructed developmental trajectories, identified pigment cell-lineage specific responses to TH, and assessed roles for TH receptors. We show that TH promotes maturation of both cell types but in distinct ways. In melanophores, TH drives terminal differentiation, limiting final cell numbers. In xanthophores, TH promotes accumulation of orange carotenoids, making the cells visible. TH receptors act primarily to repress these programs when TH is limiting. Our findings show how a single endocrine factor integrates very different cellular activities during the generation of adult form
Optics of cone photoreceptors in the chicken (Gallus gallus domesticus)
Vision is the primary sensory modality of birds, and its importance is evident in the sophistication of their visual systems. Coloured oil droplets in the cone photoreceptors represent an adaptation in the avian retina, acting as long-pass colour filters. However, we currently lack understanding of how the optical properties and morphology of component structures (e.g. oil droplet, mitochondrial ellipsoid and outer segment) of the cone photoreceptor influence the transmission of light into the outer segment and the ultimate effect they have on receptor sensitivity. In this study, we use data from microspectrophotometry, digital holographic microscopy and electron microscopy to inform electromagnetic models of avian cone photoreceptors to quantitatively investigate the integrated optical function of the cell. We find that pigmented oil droplets primarily function as spectral filters, not light collection devices, although the mitochondrial ellipsoid improves optical coupling between the inner segment and oil droplet. In contrast, unpigmented droplets found in violet-sensitive cones double sensitivity at its peak relative to other cone types. Oil droplets and ellipsoids both narrow the angular sensitivity of single cone photoreceptors, but not as strongly as those in human cones
The Effects of Dietary Carotenoid Supplementation and Retinal Carotenoid Accumulation on Vision-Mediated Foraging in the House Finch
BACKGROUND: For many bird species, vision is the primary sensory modality used to locate and assess food items. The health and spectral sensitivities of the avian visual system are influenced by diet-derived carotenoid pigments that accumulate in the retina. Among wild House Finches (Carpodacus mexicanus), we have found that retinal carotenoid accumulation varies significantly among individuals and is related to dietary carotenoid intake. If diet-induced changes in retinal carotenoid accumulation alter spectral sensitivity, then they have the potential to affect visually mediated foraging performance. METHODOLOGY/PRINCIPAL FINDINGS: In two experiments, we measured foraging performance of house finches with dietarily manipulated retinal carotenoid levels. We tested each bird's ability to extract visually contrasting food items from a matrix of inedible distracters under high-contrast (full) and dimmer low-contrast (red-filtered) lighting conditions. In experiment one, zeaxanthin-supplemented birds had significantly increased retinal carotenoid levels, but declined in foraging performance in the high-contrast condition relative to astaxanthin-supplemented birds that showed no change in retinal carotenoid accumulation. In experiments one and two combined, we found that retinal carotenoid concentrations predicted relative foraging performance in the low- vs. high-contrast light conditions in a curvilinear pattern. Performance was positively correlated with retinal carotenoid accumulation among birds with low to medium levels of accumulation (∼0.5-1.5 µg/retina), but declined among birds with very high levels (>2.0 µg/retina). CONCLUSION/SIGNIFICANCE: Our results suggest that carotenoid-mediated spectral filtering enhances color discrimination, but that this improvement is traded off against a reduction in sensitivity that can compromise visual discrimination. Thus, retinal carotenoid levels may be optimized to meet the visual demands of specific behavioral tasks and light environments
Complementary shifts in photoreceptor spectral tuning unlock the full adaptive potential of ultraviolet vision in birds
Color vision in birds is mediated by four types of cone photoreceptors whose maximal sensitivities (λmax) are evenly spaced across the light spectrum. In the course of avian evolution, the λmax of the most shortwave-sensitive cone, SWS1, has switched between violet (λmax > 400 nm) and ultraviolet (λmax < 380 nm) multiple times. This shift of the SWS1 opsin is accompanied by a corresponding short-wavelength shift in the spectrally adjacent SWS2 cone. Here, we show that SWS2 cone spectral tuning is mediated by modulating the ratio of two apocarotenoids, galloxanthin and 11',12'-dihydrogalloxanthin, which act as intracellular spectral filters in this cell type. We propose an enzymatic pathway that mediates the differential production of these apocarotenoids in the avian retina, and we use color vision modeling to demonstrate how correlated evolution of spectral tuning is necessary to achieve even sampling of the light spectrum and thereby maintain near-optimal color discrimination
Precision orbital dynamics from interstellar scintillation arcs for PSR J0437-4715
Intensity scintillations of radio pulsars are known to originate from
interference between waves scattered by the electron density irregularities of
interstellar plasma, often leading to parabolic arcs in the two-dimensional
power spectrum of the recorded dynamic spectrum. The degree of arc curvature
depends on the distance to the scattering plasma and its transverse velocity
with respect to the line-of-sight. We report the observation of annual and
orbital variations in the curvature of scintillation arcs over a period of 16
years for the bright millisecond pulsar, PSR J0437-4715. These variations are
the signature of the relative transverse motions of the Earth, pulsar, and
scattering medium, which we model to obtain precise measurements of parameters
of the pulsar's binary orbit and the scattering medium itself. We observe two
clear scintillation arcs in most of our 5000 observations and we show that
they originate from scattering by thin screens located at distances pc and pc from Earth. The best-fit scattering model
we derive for the brightest arc yields the pulsar's orbital inclination angle
, and longitude of ascending node,
. Using scintillation arcs for precise astrometry and
orbital dynamics can be superior to modelling variations in the diffractive
scintillation timescale, because the arc curvature is independent of variations
in the level of turbulence of interstellar plasma. This technique can be used
in combination with pulsar timing to determine the full three-dimensional
orbital geometries of binary pulsars, and provides parameters essential for
testing theories of gravity and constraining neutron star masses.Comment: 19 pages, 10 figures. Accepted for publication in Ap
Cyp27c1 red-shifts the spectral sensitivity of photoreceptors by converting Vitamin A<sub>1</sub> into A<sub>2</sub>
Some vertebrate species have evolved means of extending their visual sensitivity beyond the range of human vision. One mechanism of enhancing sensitivity to long-wavelength light is to replace the 11-cis retinal chromophore in photopigments with 11-cis 3,4-didehydroretinal. Despite over a century of research on this topic, the enzymatic basis of this perceptual switch remains unknown. Here, we show that a cytochrome P450 family member, Cyp27c1, mediates this switch by converting vitamin A(1) (the precursor of 11-cis retinal) into vitamin A(2) (the precursor of 11-cis 3,4-didehydroretinal). Knockout of cyp27c1 in zebrafish abrogates production of vitamin A(2), eliminating the animal's ability to red-shift its photoreceptor spectral sensitivity, and reducing its ability to see and respond to near-infrared light. Thus, the expression of a single enzyme mediates dynamic spectral tuning of the entire visual system by controlling the balance of vitamin A(1) and A(2) in the eye