Biomedical subjects

W N McFarland

Publications and source records attributed to W N McFarland.

At least 19 recordsLinked to original sources

PubMed2003

Multidimensional polarization sensitivity in damselfishes.

Using electroretinogram recording and microspectrophotometry we investigated spectral sensitivity and ultraviolet polarization sensitivity in three species of coral reef fishes commonly known as damselfishes. Here we show that three species of damselfishes (three-spot damselfish, Dascyllus trimaculatus; blacktail damselfish, D. melanurus; and blue-green chromis, Chromis viridis) have four classes of cone photoreceptors (lambda(max) ranges: ultraviolet 357-367 nm; short wavelength-sensitive 469-478 nm; medium wavelength-sensitive 482-493 nm; long wavelength-sensitive 512-524 nm; rods 499-500 nm). The three species shared similar combined spectral sensitivity but surprisingly complicated and varied polarization sensitivity. Damselfish examined in this study have three and four channel polarization sensitivity, the most complex polarization sensitivity recorded for any vertebrate. Such capacity could play an important role in mediating a conspecific visual communication network utilizing polarized light signals in the coral reef environment.

Algorithms↗

PubMed2001

Visual pigments in the early life stages of Pacific northwest marine fishes.

Microspectrophotometry was used to measure the visual pigments in the rods and cones of 22 species of marine fish larvae netted from the surface waters off Friday Harbor Laboratories, Washington, USA. 13 species had rods, 12 of which contained visual pigments with a wavelength of maximum absorbance near 500 nm, while one, the sand lance (Ammodytes hexapterus), had its absorbance maximum at 482 nm. The 22 species of fish larvae possessed varied combinations of single, double and twin cones, ranging in peak absorbance from 353 nm to 584 nm. Of these, green-sensitive single cones were present in 20 of the 22 species, and were the dominant cone type. Double and twin cones were present in 13 of the species. Most common were identical green-sensitive (twin) cones (in 11 species). Green/yellow-sensitive double cones occurred in four species. In a single instance (Hemilepidotus hemilepidotus) twin blue-sensitive, twin green-sensitive and double blue/yellow-sensitive cones were recorded. Of particular interest was the finding that 18 of the species had ultraviolet- and/or violet-absorbing single cones. It has been suggested that short-wavelength photosensitivity may be beneficial for planktivory by extending the spectral range over which vision can occur. The high percentage (82%) of ultraviolet and violet visual pigments in Pacific northwest fish larvae supports the prediction that short-wavelength sensitivity may be common in marine fish larvae.

Aging↗

PubMed1994

Ultraviolet visual pigments in marine fishes of the family pomacentridae.

Near-UV visual pigments have been reported in single cones of several freshwater and euryhaline fishes. The presence of UV visual pigments in stenohaline marine fishes have, as yet, not been identified. In the pomacentridae near-UV visual pigments are present in single cones from the three species we examined--the tropical coral fishes Dascyllus trimaculatus and Pomacentrus coelestis, and the temperate Chromis punctipinnis. Maximum absorption of the UV pigments is centered around 360 nm. In juvenile Chromis, however, the UV visual pigment is not present. Instead there is a single cone containing a violet-sensitive pigment absorbing maximally around 420 nm. All three species are obligate diurnal planktivores. The UV sensitivity may function to enhance their ability to forage on zooplankton.

Animals↗

PubMed1992

The eyespot of Euglena gracilis: a microspectrophotometric study.

The eyespots in cells of streptomycin-bleached strains and of dark-grown cultures of Euglena gracilis, were examined by means of fluorescence microscopy and microspectrophotometry. When viewed with light in the region of 380-500 nm, the stigma appeared as a dark spot. Adjacent to this was a second spot, not seen with white light, but which was seen to fluoresce when excited with radiation at 370 +/- 20 nm. This fluorescence proved to be polarized in contrast to other fluorescing bodies in the cell. The absorption curves, obtained by microspectrophotometry of individual eyespots, were found to consist of two spectral maxima, an A-band in the blue and a B-band in the green. Unlike the A-band, the B-band provided evidence of originating from an anisotropic structure. Relating these data to literature findings, we conclude that the B-band is the absorbance of a pigment in the quasi-crystalline paraflagellar body and the A-band perhaps a pigment in the orange-red stigma. The spectrum of the B-band does not appear to be that of a flavoprotein or of a free carotenoid but its resemblance to the spectrum of rhodopsin is significant in relation to published data for the Chlamydomonas eyespot that suggests the presence of a rhodopsin-like pigment as the photosensitive system responsible for phototaxis in this alga.

Animals↗

PubMed1992

The eyespot of Chlamydomonas reinhardtii: a comparative microspectrophotometric study.

The eyespot of Chlamydomonas reinhardtii is believed to utilize a rhodopsin-like pigment in its responses to light. This paper examines its eyespot by means of microspectrophotometry with the finding of an absorption spectrum with two bands, an A-band in the blue, and a B-band in the green. This spectrum is identical to that previously recorded from the eyespot of Euglena gracilis. As with Euglena the B-band was found to have dichroic character and its spectrum was similar to the absorption curve of rhodopsin. This A-B-spectrum was always recorded from a single granule in each cell. It is concluded that both E. gracilis and C. reinhardtii may utilize a rhodopsin-like pigment as the photopigment associated with the eyespot response to light. In both these algae a few particles in each cell were found whose spectra consisted of two other bands, C and D, blue- and red-shifted, respectively, relative to the eyespot A-B-bands. There is some reason to believe that the C-D-granules may also be involved in certain light-controlled activities of the cells.

Animals↗

PubMed1990

Rod and cone pigments of the Atlantic guitarfish, Rhinobatos lentiginosus Garman.

Using both extraction- and micro-spectrophotometric (MSP) methods the visual pigment(s) from the rods and cones of the Atlantic guitarfish, Rhinobatos lentiginosus, were shown to be spectrally similar, if not identical (lambda max = 498-499 nm). Color vision, therefore, is unlikely unless mediated via colored oil droplets in the inner segments. The identical lambda max for the rod and cone pigments suggest that vision in both dim and bright light may correlate with the underwater spectrum over the depths and the times of day that guitarfish are active. The primary advantage of the blue-green sensitive visual pigments, we suggest, is to enhance the contrast of targets silhouetted against the background spacelight.

Animals↗

PubMed1977