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Dive into the research topics where William N. McFarland is active.

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Featured researches published by William N. McFarland.


Vision Research | 1973

The significance of spectral position in the rhodopsins of tropical marine fishes

F.W. Munz; William N. McFarland

Abstract Visual pigments were extracted from the retinae of a large and diverse sample (179 species, in 40 families) of tropical marinefishes. By the method of partial bleaching, most of these were found to be retinal-1 pigments, with their maxima tightly grouped between 489 and 502 nm; but a few have λmax at shorter wavelengths. The spectral position of these pigments does not correlate with diurnal or nocturnal activity patterns, nor do closely related species necessarily have similar pigments. In general, the deeper-living species have rhodopsins with λmax at shorter wavelengths, a correlation with the bluer quality of light in deeper water. The spectral distribution of light was measured in air and underwater at a coral atoll. During twilight the underwater spectrum narrows and shifts to shorter wavelengths, as a result of increased absorption of yellow-orange light by the atmosphere. This effect at twilight is unique among the general spectral events that constitute each day. The behavioral patterns of reef fishes make clear the relationships between underwater light and the visual pigments. During evening twilight, there is an orderly sequence, in which the diurnal fishes seek cover, and then, after a “Quiet Period”, the nocturnal species emerge. The “Quiet Period” is the most critical and visually difficult time because light intensities are transitional between the thresholds of photopic and scotopic vision. Predation reaches a maximum during the “Quiet Period”. The rhodopsins of all these fishes tend to match the background light available during evening and morning twilight. Photochemically, visual sensitivity is maximized and, as a result, predation is held in check. The relationships between light, behavior and visual physiology are discussed. Although their rhodopsins are spectrally similar to those of the prey, crepuscular predators obtain a visual advantage by having moderate numbers of very large cones, which provide adequate sensitivity and sufficient resolution for motion detection.


Ecology | 1983

Priority Effects in the Recruitment of Juvenile Coral Reef Fishes

Myra J. Shulman; John C. Ogden; John P. Ebersole; William N. McFarland; Steven Miller; Nancy G. Wolf

Competing models of community structure in assemblages of coral reef fishes have suggested that (1) these assemblages are structured by deterministic interactions between species, or between species and resources, or (2) the composition of these assemblages are determined by highly variable settlement from planktonic larvae. We examined interactions among newly recruited juvenile fishes and between juvenile fishes and transplanted resident damslfish on artificial reefs in St. Croix, United States Virgin Island. Two kinds of priority effects occurred: (1) recruitment of three species of settling juveniles significantly decreased in the presence of the territorial damselfish, and (2) prior settlement of a juvenile predator lowered successful recruitment of two juvenile prey species. The first effect increases determinism in the structure of coral reef fish assemblages, while the second decreases their predictability.


Vision Research | 1975

Part III: The evolution of photopic visual pigments in fishes.

William N. McFarland; F.W. Munz

Abstract The feeding strategies of diurnal, tropical marine fishes correlate with the visual pigments extracted from their retinae and with the photic environments in which they hunt prey. Two basic feeding modes prevail: (1) silhouetting prey from below against the surface background light; and (2) contrasting prey against other fields of view, which are more monochromatic. Fishes that silhouette prey from below possess a single visual pigment matched to the spectral distribution of downwelling light. This maximizes the contrast between the brighter background and darker target. To predators that view prey in the horizontal fleld, their targets may appear either darker or brighter than the background. The photocontrast of a nonreflective target is maximized by a class of cones with a matching visual pigment. But the contrast of reflective (“bright”) targets is enhanced by visual pigments offset from the spectral distribution of the monochromatic blue background. Thus, the evolutionary selection of multiple photopic systems, and of color vision itself, is probably related to the maximization of visual contrast against monochromatic backgrounds.


Animal Behaviour | 1982

The ontogeny of twilight migration patterns in grunts (Pisces: Haemulidae)

Gene S. Helfman; Judy L. Meyer; William N. McFarland

Abstract The development of dusk and dawn migratory behaviours was investigated in French and white grunts ( Haemulon flavolineatum and H. plumieri ) at St. Croix, U.S. Virgin Islands. Four juvenile stages were recognized: small, medium, transitional, and large. Each stage differed in age, size, coloration, habitat preference, diel foraging patterns, and twilight migratory behaviour. Comparisons between medium (15 to 30 mm long, 30 to 50 days old) and large juveniles (40 to 120 mm, 80 to 700 days) were emphasized. Medium juveniles occurred in small, diurnally feeding groups near sea urchins in the sand halo around a reef. Group composition varied during the day. They migrated at 15 min after sunset, moving hesitantly from halo to grassbed. Migration routes remained constant over a month, but differed over two years. Large juveniles fed nocturnally, formed daytime resting schools over coral heads, and migrated at 25 min after sunset. Compared with medium fish, resting site constancy was greater during a day, migration activities were significantly less variable, and migration routes remained relatively constant for two years. Ontogenetic differences in constancy of daytime school locales and migration routes may result from learning, facilitated perhaps by greater overlap of age cohorts in large juveniles. Other differences in behavioural variability may result from ontogenetic development of the visual apparatus, plus stabilizing selection due to greater predation on smaller, behaviourally variable fish.


Vision Research | 1975

Part II: The photic environment of clear tropical seas during the day

William N. McFarland; F.W. Munz

Abstract The visible Spectrum of sunlight was measured in quantal units. In air, the irradiance spectrum is broad and flat under both clear and overcast conditions. Measured near the surface, the irradiance spectrum of upwelling light is narrower and more blue than that of downwelling light. The angular distribution of underwater light was determined by restricting the collection angle of the light receptor. The total intensity and the spectrum of these radiance measurements are interrelated. The radiance spectrum of downwelling light is broad, while that of horizontal light is less intense, narrower and shifted to the blue. The radiance spectrum of upwelling light depends on total depth and the proximity of a reflective substrate. Measured far from the bottom, it is narrow and blue, but broadens as the receptor approaches the substrate.


Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology | 1987

Cone photoreceptor mechanisms and the detection of polarized light in fish

Craig W. Hawryshyn; William N. McFarland

SummaryAlthough numerous studies have demonstrated the detection of polarized light in vertebrates, little is known of the photoreceptor mechanisms involved. Recent evidence, however, indicates that cyprinid fishes possess both ultraviolet (UV) and polarization sensitivity suggesting that some vertebrates, like many invertebrates, may employ UV-sensitive cone receptors in polarization sensitivity. In this report, we describe experiments that determine which spectral types of receptors participate in the detection of polarized light. We used a heart-rate conditioning technique to measure increment thresholds of immobilized goldfish for plane-polarized, narrow-band (10 nm half max.) spectral stimuli (380 nm, 460 nm, 540 nm, 660 nm). A typical experiment involved ‘isolating’ the activity of a cone photoreceptor mechanism by chromatic adaptation and measuring increment thresholds for spectral stimuli at e-vector orientations of the polarizer between 0° to 180° in 30° steps. The UV-, green- and red-sensitive cone receptor mechanisms showed clear evidence of polarization sensitivity while the blue-sensitive cone receptor mechanism was polarizationally insensitive. The average amplitude (base to peak height on Fig. 4) of the polarization sensitivity curves (UV-, green- and red-curves) was 0.67 log unit (standard deviation of 0.12 log unit), with the UV-sensitive cone receptor mechanism most sensitive to the vertical e-vector axis and the green- and red-sensitive cone receptor mechanisms most sensitive to the horizontal e-vector axis. The observation that different cone photoreceptor mechanisms have orthogonal polarization sensitivity in fish suggests that the perception of polarized light may enhance the capacity for visual discrimination in lower vertebrates.


Environmental Biology of Fishes | 1979

The influence of light on the twilight migrations of grunts

William N. McFarland; John C. Ogden; J. N. Lythgoe

SynopsisBehaviors that precede the daily migrations of mixed-species schools of juvenile grunts (Pomadasyidae), from patch reefs to grass beds at dusk and vice versa at dawn, are defined and utilized to ascertain the precision of the migrations. Although premigratory behaviors differ at dusk and dawn, the migrations are precise twilight events which occur at the same light intensities during dawn and dusk. Histological sections of the retina reveal that both cones and rods are fully exposed to ambient light during the migrations. Under the difficult photic conditions that prevail during migration, the retina is structured photomechanically to maximize the absorption of ambient light. Body colorations of the grunts, which consist mostly of intense colored stripes during the day, are replaced at night by cryptic melanic patterns. The precision of migration, the photomechanical movements in the retina, and the changes in body coloration are considered adaptive because they reduce predation on grunts when they migrate and are most vulnerable to attack. In support of this conclusion, the migrations take place just before the evening and just after the morning ‘quiet period’ - thus they avoid that period during twilight when predation is highest in tropical fish communities.


Environmental Biology of Fishes | 1983

Wave produced changes in underwater light and their relations to vision

William N. McFarland; Ellis R. Loew

SynopsisMaximal visual sensitivity of most vertebrates and invertebrates coincides with the dominant wave-induced flicker frequencies associated with underwater light. Waves also produce patterns off reflective objects that resemble many of the body markings found on fishes. The close relationship that exists between the physiological properties of spatial and temporal vision thus suggests an ancient adaptation to the wave-induced fluctuations and spatial patterns associated with underwater light.


Science | 1969

Microspikes on the lymphocyte uropod

William N. McFarland

Lymphocytes have anatomic and functional characteristics reiminiscent of the amoeba. The capacity to form microscopikes on the uropod suggests a high degree of specialization essential to the lympphocytes function in immunnologic reactions.


Science | 1967

Internal Behavior in Fish Schools

William N. McFarland; Sanford A. Moss

Structural changes within fish schools correlate with declines in environmental oxygen. The changes may result from the responses of individual fish to the environmental consequences of group metabolism. Individual behaviors are adaptive to the school in that they tend to maintain stability between school members and their environment.

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Steven Miller

University of North Carolina at Wilmington

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John C. Ogden

Florida Institute of Oceanography

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