John B. Phillips
Abstracts of Selected Publications

ABSTRACT
Male lek display in birds may reduce nest-related predation by decoying predators away from nests and alerting incubating females when a predator is approaching. The sentinel/decoy model predicts a region of decreased predator density just inside the maximum range at which predators are attracted by displaying males. The expected ring of successful nests is evident in data from three species of North American prairie grouse. Well-documented features of female mate choice in lekking species, including repeated visits to male display sites prior to mating, mate fidelity and mate copying, are consistent with females maximizing the proposed antipredator benefit. The sentinel/decoy model makes a number of unique predictions that will facilitate critical tests of the model.
© 1990 The Association for the Study of Animal Behaviour

SUMMARY
Migrating birds derive compass information from the sun, stars, geomagnetic field and polarized light, but relatively little is known about how these multiple sources of directional information are integrated into a functional orientation system. We found that migratory warblers exposed to a rotated polarized light pattern at sunset oriented at a constant angle to the axis of polarizaiton. When polarized light cues were eliminated, this shifted orientation was maintained relative to the setting sun. Polarized light patterns, thus, appear to provide a calibration reference for the sun compass in nocturnal migrants, and may also play a role in calibrating other compass systems.
© 1992 Springer-Verlag

ABSTRACT
The earth's magnetic field provides an important source of directional information for terrestrial organisms, but the sensory receptor or receptors responsible for magnetic field detection have yet to be identified. Theoretical models of the mechanism of magnetoreception have implicated specialized photoreceptors. The proposed mechanisms would amplify the weak interaction of the geomagnetic field with a single electron spin to the level of photon detection, resulting in a modulation of the photoreceptor response to light. Although behavioural and neurophysiologicval studies have established a link between magnetic field sensitivity and the visual system, definitive evidence for the use of a light-dependent magnetoreception mechanism has been lacking. Here we show that magnetic compass orientation in a semiaquatic salamander is affected by the wavelength of light, and that this wavelength-dependence is due to a direct effect of light on the underlying magnetoreception mechanism.

ABSTRACT
1. Wildtype Oregon-R Drosophila melanogaster were trained in the ambient magnetic field to a horizontal gradient of 365 nm light emanating from one of the 4 cardinal compass directions and were subsequently tested in a visually-symmetrical, radial 8-arm maze in which the magnetic field alignment could be varied. When tested under 365 nm light, flies exhibited consistent magnetic compass orientation in the direction from which light had emanated in training. 2. When the data were analyzed by sex, males exhibited a strong and consistent magnetic compass response while females were randomly oriented with respect to the magnetic field. 3. When tested under 500 nm light of the same quantal flux, females were again randomly oriented with respect to the magnetic field, while males exhibited a 90° clockwise shift in magnetic compass orientation relative to the trained direction. 4. This wavelength-dependent shift in the direction of magnetic compass orientation suggests that Drosophilia may utilize a light-dependent magnetic compass similar to that demonstrated previously in an amphibian. however, the data do not exclude the alternative hypothesis that a change in the wavelength of light has a nonspecific effect on the flies' behavior, i.e., causing the flies to exhibit a different form of magnetic orientation behavior.
© 1993 Springer-Verlag

ABSTRACT
Spectral sensitivity measurements from the retina of the Mexican salamander Ambystoma mexicanum (the 'axolotl') were used to provide evidence for and to characterize an amphibian ultraviolet-sensitive photoreception mechanism. Electroretinograms (transretinal voltage responses) were recorded from open eye cup preparations to analyze the spectral sensitivity of the retina. Both dark-adapted and white light-adapted preparations exhibited a peak in sensitivity between 360-370 mm. Under selective chromatic adaptation with long-wavelength light the eye cups continued to exhibit a peak sensitivity around 360 nm. These data confirm the presence of ultraviolet-sensitive cones in the retina of Ambystoma salamanders. The possible relevance of these results to the development and behavior of this group of salamanders is briefly discussed.
© 1995 Elsevier Science Ireland Ltd. All rights reserved.

ABSTRACT
Recent evidence suggests that some amphibians, reptiles and birds may be capable of homing using information about geographic position ("map" information) derived from subtle geographic gradients in the earth's magnetic field. The "magnetic map" hypothesis faces numerous theoretical difficulties, however, doe to the extremely high level of sensitivity that would be necessary to detect natural magnetic gradients, and to the presence of spatial irregularities and temporal variation in the geomagnetic field that might make map coordinates derived from magnetic gradients unreliable. To date, the majority of studies carried out to test the magnetic map hypothesis have involved field observations for the effects on homing orientation of naturally occurring spatial or temporal variation in the geomagnetic field. While providing an important first step, these studies are subject to the criticism that the observed changes in homing orientation could result from effects on a magnetic compass, or some other unidentified component of the navigational system, rather than from effects on a magnetic map. The recent development of experimental systems in which navigational ability can be studied under controlled or semi-controlled laboratory conditions has opened up the possibility of using new experimental approaches to more rigorously test the magnetic map hypothesis. After briefly reviewing the available evidence for the geomagnetic field's involvement in the map component of homing, a simple graphical model is presented which describes how the home direction derived from a bicoordinate map varies as a function of the value of one of the map coordinates when the value of thee second map coordinate is held constant. In studies of homing orientation in which the value of a specific magnetic field parameter (e.g., total intensity, inclination, etc.) can be varied independently of other putative map parameters, the graphical model can be used to generate qualitative predictions about the changes in the direction of homing orientation that should be observed if the magnetic field parameter being manipulated serves as one coordinate of a bicoordinate map. The relationship between the direction of homing orientation and the value of a putative magnetic map parameter can also be used to generate quantitative predictions about characteristics of the local gradient of that magnetic field parameter in the vicinity of the home site (i.e., the alignment and "home value" of the local gradient), which can then be compared with actual measured values. Together, the qualitative and quantitative predictions of the graphical model permit rigorous tests of whether one or both coordinates of a bicoordinate navigational map are derived from the geomagnetic field.
© 1996 Academic Press Limited

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ABSTRACT
Geomagnetic orientation is widespread among organisms, but the mechanism(s) of magnetoreception has not been identified convincingly in any animal. In agreement with biophysical models proposing that the geomagnetic field interacts with photo-receptors, changes in the wavelength of light have been shown to influence magnetic compass orientation in an amphibian, an insect and several species of birds (reviewed in ref. 5). We find that light-dependent magnetic orientation in the eastern red-spotted newt, Notophthalmus viridescens, is mediated by extraocular photoreceptors, probably located in the pineal complex or deeper in the brain (perhaps the hypothalamus).
© 1999 Macmillan Publishers Ltd.

ABSTRACT
Laboratory tests were carried out on the magnetic compass response of the Eastern red-spotted newt (Notophthalmus viridescens). Groups of 30 to 40 newts were each housed in an elongate rectangular training tank aligned either on the magnetic north-south or east-west axis and located adjacent to the laboratory building in which tests were conducted. In each test, approximately equal numbers of newts were run in four horizontal magnetic field conditions (where magnetic north = N, E, S, or W). Data were analyzed after rotating and pooling the magnetic bearings from the four field conditions to obtain a distribution reflecting the component of the newts' orientation that was a consistent response to the magnetic fields, thus factoring out any geographically fixed cues. Newts that were tested without prior treatment exhibited bimodal magnetic orientation along the trained magnetic axis in tests carried out during January through March. However, during April and early May (coinciding with the natural spring migratory period of newts in the Ithaca area) the groups exhibited orientation along an axis coinciding with the direction of the pond from which they had been collected the previous year. A short-lived, unimodal response in the trained compass direction was obtained by exposing newts to an abrupt drop in water level in the training tank just prior to testing. A more long-lasting unimodal compass response in the trained direction was elicited by elevating the water temperature in the training tank to 33 to 34.5 degrees centigrade immediately prior to testing, after a period of relatively stable water temperatures. If this elevation of water temperature followed a period of widely fluctuating water temperatures, the newts switched from the trained direction to exhibit unimodal homeward orientation. Newts orienting in the trained compass direction responded to an inversion of the vertical component of the magnetic field by reversing their direction of orientation, while newts orienting in the homeward direction did not show this reversal of orientation in the inverted field. It appears that newts utilize an axially-sensitive magnetic compass similar to that exhibited by migrating birds for simple-compass orientation. However, a magnetic compass mechanism with different functional properties may be associated with homing orientation in newts.

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