Browsing by Author "Vielma, Alex"

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    Retinal Photoreceptor Arrangement, SWS1 and LWS Opsin Sequence, and Electroretinography in the South American Marsupial Thylamys elegans (Waterhouse, 1839)
    (2010) Palacios, Adrian G.; Bozinovic, Francisco; Vielma, Alex; Arrese, Catherine A.; Hunt, David M.; Peichl, Leo
    We studied the retinal photoreceptors in the mouse opossum Thylamys elegans, a nocturnal South American marsupial. A variety of photoreceptor properties and color vision capabilities have been documented in Australian marsupials, and we were interested to establish what similarities and differences this American marsupial showed. Thylamys opsin gene sequencing revealed two cone opsins, a longwave-sensitive (LWS) opsin and a shortwave-sensitive (SWS1) opsin with deduced peak sensitivities at 560 nm and 360 nm (ultraviolet), respectively. Immunocytochemistry located these opsins to separate cone populations, a majority of LWS cones (density range 1,600 5,6 5,600/mm(2)) and a minority of SWS1 cones (density range 100-690/mm(2)). With rod densities of 440,000-590,000/mm(2), the cones constituted 0.4-1.2% of the photoreceptors. This is a suitable adaptation to nocturnal vision. Cone densities peaked in a horizontally elongated region ventral to the optic nerve head. In ventral-but not dorsal-retina, roughly 40% of the LWS opsin-expressing cones occurred as close pairs (double cones), and one member of each double cone contained a colorless oil droplet. The corneal electroretinogram (ERG) showed a high scotopic sensitivity with a rod peak sensitivity at 505 nm. At mesopic light levels, the spectral ERG revealed the contributions of a UV-sensitive SWS1 cone mechanism and an LWS cone mechanism with peak sensitivities at 365 nm and 555 nm, respectively, confirming the tuning predictions from the cone opsin sequences. The two spectral cone types provide the basis for dichromatic color vision, or trichromacy if the rods contribute to color processing at mesopic light levels. J. Comp. Neurol. 5 18:1589-1602, 2010. (C) 2009 Wiley-Liss, Inc.
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    Spectral sensitivities of photoreceptors and their role in colour discrimination in the green-backed firecrown hummingbird (Sephanoides sephaniodes)
    (2008) Herrera, Gonzalo; Zagal, Juan Cristobal; Diaz, Marcelo; Fernandez, Maria Jose; Vielma, Alex; Cure, Michel; Martinez, Jaime; Bozinovic, Francisco; Palacios, Adrian G.
    We studied the photopic spectral sensitivity in the green-backed firecrown, Sephanoides sephaniodes, a South American hummingbird, and its possible ecological relationship with preferred flowers and body colouration. Avian colour vision is in general tetrachromatic with at least four types of cones, which vary in sensitivity from the near ultraviolet (UV) to the red wavelength range. Hummingbirds represent an important family of birds, yet little is known about their eye sensitivity, especially about the role of photoreceptors and their oil droplet complements. The photopic electroretinogram shows a main sensitivity peak at 560 nm and a secondary peak in the UV, and may be explained by the presence of four single cones (lambda(max) at similar to 370, 440, 508 and 560 nm), and a double cone (lambda(max) at 560 nm) screened by oil droplets. The flowers preferred by the firecrown are those in which the red-green wavelength region predominates and have higher contrast than other flowers. The crown plumage of males is highly iridescent in the red wavelength range (peak at 650 nm) and UV; when plotted in a high-dimensional tetrachromatic space, it falls in a "red + UV" purple hue line, suggesting a potential significant communication signal for sexual differentiation.