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John B. Phillips
B.A., Swarthmore College,
1976
Ph.D., Cornell University 1984
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Neural Basis of Behavior
Areas of interest:
Orientation/Migration (navigation, magnetoreception, cue integration, polarized light detection)
Sexual Selection (coevolution of color signals and chromatic processing mechanisms, origins and evolutionary consequences of sensory 'biases')
Sensory Ecology (ultraviolet and extraocular photoreception in vertebrates)
Behavioral studies carried out by our laboratory
have shown that amphibians have a light-dependent magnetic compass
located in or near the pineal organ. These findings are consistent
with theoretical models that point to the involvement of a specialized
photoreceptor in magnetoreception. Neurophysiological experiments
are now underway to characterize the response of photoreceptors
in the pineal complex of frogs to changes in magnetic field
alignment. Related experiments have provided evidence for a
light-dependent magnetic compass in Drosophila melanogaster
and, in collaboration with colleagues at other universities,
in two species of migratory birds.
To characterize the process underlying the magnetic
compass, we are investigating the effects of 1-20 MHz radio
frequencies on magnetic compass orientation. Radio frequencies
(RF) in this range are predicted to alter magnetic field dependent
energy states in a photoreceptor-based magnetoreceptor and,
thus, disrupt the response of the light-dependent magnetic compass.
In collaborative experiments with colleagues at the University
of Frankfurt in Germany and the University of California at
Irvine, we have demonstrated RF effects on the magnetic compass
orientation of a migratory bird. Members of our laboratory have
also obtained preliminary evidence for RF effects on the magnetic
compass orientation of amphibians and rodents.
A behavioral assay developed by our laboratory
using the C57 BL/6 strain of laboratory mouse is making it possible
for the first time to use gene knockouts to investigate the
molecular basis of the magnetic compass. We are focusing on
a newly discovered class of photopigment molecules ("cryptochromes")
that have been proposed to play a role in a photoreceptor-based
magnetic compass. Behavioral genetic experiments are also planned
using a assay of magnetic compass orientation in the fruit fly
Drosophila melanogaster.
Our laboratory has also been investigating the
involvement of the geomagnetic field in the 'map' or geographic-position
sense of vertebrates. Studies of map-based homing ("true navigation")
by the Eastern red-spotted newt Notophthalmus viridescens
indicate that natural spatial variation in the inclination or
'dip angle' of the magnetic field is used to derive one coordinate
of a bicoordinate map. Ongoing collaborative experiments with
former postdoc Ursula Munro at the Technical University of Sydney,
Australia have also provided evidence for a magnetic map in
a migratory bird, the Tasmanian silvereye Zosterops lateralis.
Experiments are now underway in collaboration with colleagues
at the University of Oslo and the Austevoll Institute of Marine
Fisheries in Norway to investigate the role of magnetic map
cues in the migratory orientation of the European eel Anguilla
anguilla, and with colleagues at the University of Salamanca
in Spain to investigate similar questions in the Alpine newt
Triturus alpestris. Related experiments have provided
evidence that amphibians and birds, in addition to the magnetic
compass, have a second magnetoreception mechanism involving
particles of biogenic magnetite. The magnetite-based receptor
is non-light-dependent and appears to be involved in deriving
spatial (map) rather than directional (compass) information.
Collaborations involving a number of other laboratories have investigated integration of the multiple compass systems used by vertebrates (e.g., sun, star, magnetic, and polarized light compasses). Much of this work has focused on the possibility that birds use polarized patterns present at sunset and/or sunrise as the primary calibration reference for the other compass systems.
Our laboratory has carried out research in several
other areas of sensory biology. Two recent series of experiments
have examined color signals used in courtship and mating. In
one study, psychophysical measurements of spectral sensitivity
and microspectrophotometric measurements of photopigment absorption
were obtained from four species of stickleback fish. Modeling
of the response of the stickleback visual system was then used
to generate novel hypotheses about the functional and evolutionary
relationships between the color vision system and nuptial coloration
of the threespine stickleback Gasterosteus aculeatus.
A second study examined background color matching by the polymorphic
treefrog Hyla regilla. This study documented the presence
of both 'fixed' (green or brown) and "plastic" (able to change
from green to brown, and vice versa) color morphs in this species.
We are also interested in the possibility that the preference
of these frogs for matching background colors may under some
conditions lead to a preference for individuals of the same
body color and, thus, contribute to reproductive isolation of
the two fixed color morphs.
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