scholarly journals A novel cellular structure in the photoreceptors of insectivorous birds

2019 ◽  
Author(s):  
Luke P. Tyrrell ◽  
Leandro B.C. Teixeira ◽  
Richard R. Dubielzig ◽  
Diana Pita ◽  
Patrice Baumhardt ◽  
...  
Keyword(s):  
Cellular Structure ◽  
Bird Species ◽  
Cone Photoreceptor ◽  
Visual Channel ◽  
Low Light ◽  
Oil Droplets ◽  
Unusual Structure ◽  
Rod Photoreceptors ◽  
Light Levels ◽  
Ecological Differences

The keen visual systems of birds have been relatively well-studied. The foundations of avian vision rest on their cone and rod photoreceptors. Most birds use four cone photoreceptor types for color vision, a fifth cone for achromatic tasks, and a rod for low-light levels. The cones, along with their oil droplets, and rods are conserved across birds – with the exception of a few shifts in spectral sensitivity – despite taxonomic, behavioral and ecological differences. Here, however, we describe a novel photoreceptor in a group of New World flycatchers (Empidonax spp.) in which the traditional oil droplet is replaced with a complex of electron-dense megamitochondria surrounded by hundreds of small, orange oil droplets. These photoreceptors were unevenly distributed across the retina, being present in the central region (including in the fovea), but absent from the retinal periphery and the area temporalis. Many bird species have had their oil droplets and photoreceptors characterized, but only the two flycatchers described here (E. virescens and E. minimus) possess this unusual structure. We discuss the potential functional significance of the unique sub-cellular structure in these photoreceptors providing an additional visual channel for these small predatory songbirds.

scholarly journals A novel cellular structure in the retina of insectivorous birds

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Luke P. Tyrrell ◽  
Leandro B. C. Teixeira ◽  
Richard R. Dubielzig ◽  
Diana Pita ◽  
Patrice Baumhardt ◽  
...  
Keyword(s):  
Cellular Structure ◽  
Bird Species ◽  
Insectivorous Birds ◽  
Visual Channel ◽  
Oil Droplets ◽  
Rod Photoreceptors ◽  
Dim Light ◽  
Retinal Structure ◽  
The Many ◽  
Ecological Differences

Abstract The keen visual systems of birds have been relatively well-studied. The foundations of avian vision rest on their cone and rod photoreceptors. Most birds use four cone photoreceptor types for color vision, a fifth cone for achromatic tasks, and a rod for dim-light vision. The cones, along with their oil droplets, and rods are conserved across birds – with the exception of a few shifts in spectral sensitivity – despite taxonomic, behavioral and ecological differences. Here, however, we describe a novel photoreceptor organelle in a group of New World flycatchers (Empidonax spp.) in which the traditional oil droplet is replaced with a complex of electron-dense megamitochondria surrounded by hundreds of small, orange oil droplets. The photoreceptors with this organelle were unevenly distributed across the retina, being present in the central region (including in the fovea), but absent from the retinal periphery and the area temporalis of these insectivorous birds. Of the many bird species with their photoreceptors characterized, only the two flycatchers described here (E. virescens and E. minimus) possess this unusual retinal structure. We discuss the potential functional significance of this unique sub-cellular structure, which might provide an additional visual channel for these small predatory songbirds.

Retinal development of West Australian dhufish, Glaucosoma hebraicum

2001 ◽  
Vol 18 (5) ◽  
pp. 711-724 ◽  
Author(s):  
JULIA SHAND ◽  
MICHAEL A. ARCHER ◽  
NICOLE THOMAS ◽  
JENNIFER CLEARY
Keyword(s):  
Ganglion Cell ◽  
Ganglion Cell Layer ◽  
Light And Electron Microscopy ◽  
Low Light ◽  
Exogenous Feeding ◽  
Rod Photoreceptors ◽  
Outer Segments ◽  
Light Levels ◽  
Single Cone ◽  
Area Centralis

An investigation of retinal specializations was carried out in larval and juvenile dhufish, Glaucosoma hebraicum (Glaucosomidae, Teleostei). The development of photoreceptors and formation of the retinal mosaic was followed by light and electron microscopy. At hatching the eye was undifferentiated. Cone photoreceptors were present by day 3 posthatch (dph), when exogenous feeding began. Single and multiple cones were present in a row arrangement from 3 dph to 20 dph, when the first rod nuclei were observed. Between 20 dph and approximately 3 months posthatch (mph), the row arrangement was replaced by a square mosaic of four double cones surrounding a single cone, and the cones increased in size, with the outer segments reaching up to 30 μm in length. During the period of spatial rearrangement, triple cones were often observed. From their first appearance, rod photoreceptors were added rapidly. Investigation of ganglion cell topography in 3-mph fish that had attained the adult-like square photoreceptor mosaic was carried out using retinal wholemounts. The highest densities of neurones in the ganglion cell layer were in temporal retina but no well-defined area centralis was observed. Microspectrophotometric measurements of the visual pigments within the outer segments of the photoreceptors of 3-mph fish revealed double cones with identical absorption spectra in each member of the outer segment, and the wavelength of maximum absorption (λmax) located at 522 nm. Single cones were found to possess a visual pigment with λmax at 460 nm and rods with a λmax of 498 nm. The results imply that the larvae and juveniles are adapted for survival in coastal waters and may be active in relatively low light levels from early stages of development.

scholarly journals The Optimal Synapse for Sparse, Binary Signals in the Rod Pathway

2006 ◽  
Vol 18 (1) ◽  
pp. 26-44 ◽  
Author(s):  
Paul T. Clark ◽  
Mark C. W. van Rossum
Keyword(s):  
Transfer Function ◽  
Signal To Noise Ratio ◽  
Bipolar Cells ◽  
Signal To Noise ◽  
Low Light ◽  
Rod Photoreceptors ◽  
Light Levels ◽  
Noise Ratio ◽  
Simulated Images ◽  
Rod Bipolar Cells

The sparsity of photons at very low light levels necessitates a nonlinear synaptic transfer function between the rod photoreceptors and the rod-bipolar cells. We examine different ways to characterize the performance of the pathway: the error rate, two variants of the mutual information, and the signal-to-noise ratio. Simulation of the pathway shows that these approaches yield substantially different performance at very low light levels and that maximizing the signal-to-noise ratio yields the best performance when judged from simulated images. The results are compared to recent data.

Growth ofPseudotsuga menziesiiandTsuga heterophyllaseedlings along a light gradient: resource allocation and morphological acclimation

1997 ◽  
Vol 75 (9) ◽  
pp. 1424-1435 ◽  
Author(s):  
D. Mailly ◽  
J. P. Kimmins
Keyword(s):  
Leaf Morphology ◽  
Biomass Accumulation ◽  
Tsuga Heterophylla ◽  
Douglas Fir ◽  
Western Hemlock ◽  
Low Light ◽  
Growing Seasons ◽  
Light Levels ◽  
Light Gradient ◽  
Relative Light Intensity

Silvicultural alternatives that differ in the degree of overstory removal may create shady environments that will be problematic for the regeneration of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Gradients of light in the field were used to compare mortality, growth, and leaf morphological acclimation of two conifer species of contrasting shade tolerances: Douglas-fir and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Results after two growing seasons indicated that Douglas-fir mortality occurred mainly at relative light intensity (RLI) below 20%, while western hemlock mortality was evenly distributed along the light gradient. Height, diameter, and biomass of the planted seedlings increased with increasing light for both species but at different rates, and maximum biomass accumulation always occurred in the open. Douglas-fir allocated more resources to stem biomass than western hemlock, which accumulated more foliage biomass. Increases in specific leaf area for Douglas-fir seedlings occurred at RLI ≤ 0.4 and red/far red (R/FR) ratio ≤ 0.6, which appear to be the minimal optimum light levels for growth. Conversely, western hemlock seedlings adjusted their leaf morphology in a more regular pattern, and changes were less pronounced at low light levels. These results, along with early mortality results for Douglas-fir, suggest that the most successful way to artificially regenerate this species may be by allowing at least 20% of RLI for ensuring survival and at least 40% RLI for optimum growth. Key words: light, light quality, leaf morphology, acclimation.

Photoinhibition of DCMU-Enhanced Fluorescence in Lake Ontario Phytoplankton

1987 ◽  
Vol 44 (12) ◽  
pp. 2144-2154 ◽  
Author(s):  
M. Putt ◽  
G. P. Harris ◽  
R. L. Cuhel
Keyword(s):  
Vertical Mixing ◽  
Natural Populations ◽  
Bright Light ◽  
Euphotic Zone ◽  
Lake Ontario ◽  
Enhanced Fluorescence ◽  
Low Light ◽  
Light Levels ◽  
Phosphorus Status

Measurement of 1-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) enhanced fluorescence (FDCMU) suggested that photoinhibition of photosynthesis was frequently an artifact of in situ bottle incubations in Lake Ontario phytoplankton. In a seasonal study, FDCMU of all populations was depressed by bright light in an incubator. However, when the euphotic zone did not exceed the depth of the mixed layer, vertical transport of phytoplankton into either low-light or dark regions apparently allowed reversal of photoinhibition of FDCMU. Advantages of FDCMU as a bioassay of vertical mixing include rapidity of response time, ease of measurement in the field, and insensitivity of this parameter to changes in phosphorus status of the population. Because of seasonal changes in the photoadaptive response of natural populations, the rate constants and threshold light levels required to cause the response must be determined at each use if the method is to be quantitative.

Image classification at low light levels

1986 ◽  
Vol 3 (12) ◽  
pp. 2179 ◽  
Author(s):  
Miles N. Wernick ◽  
G. Michael Morris
Keyword(s):  
Image Classification ◽  
Low Light ◽  
Light Levels
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