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ROBERT R. FITAK (email: email@example.com) is a Postdoctoral Researcher,
ELEANOR M. CAVES is a Postdoctoral Researcher, and SÖNKE JOHNSEN is
a Professor in the Department of Biology, Duke University, Durham,
Pill Bug Magnetoreception Lab: Handout NAME___________________________
Additional materials and procedures can be found through the link below:
Magnetoreception: Potential Mechanisms and Uses of the Magnetic Sense
Numerous behavioral experiments have shown that a variety of organisms, from bacteria to mammals, can sense Earth’s
magnetic field. This ability, called magnetoreception, is similar to how humans use a compass to figure out the direction they
are moving. In addition to identifying a direction, some animals like sea turtles, can actually sense changes in the magnetic field
strength and angle relative to the Earth’s surface to navigate to specific locations. This is like having a natural, built-in GPS sensor!
So, how do these animals sense the magnetic field? Unfortunately, the mechanism is not well known, but scientists have come up
with a few ideas that are supported by their data: (1) a magnetic particle-based mechanism and (2) a chemical mechanism.
The magnetic particle mechanism predicts that animals have tiny crystals of magnetite, a naturally occurring mineral, in
contact with various cells. These magnetite crystals act like little compass needles, so when they attempt to turn or rotate in
response to Earth’s magnetic field, they mechanically stress sensory cells, like hair cells or stretch receptors, or open and close
ion channels in neurons to initiate a signal. The chemical mechanism is a bit more complicated. Certain proteins, like the visual
pigment cryptochrome, have a free pair of electrons, or radical pair, after exposure to light. Each electron in this pair is spinning
in a particular direction, so taken together the two electrons can be spinning the same direction (parallel) or different directions
(antiparallel) – with different chemical reactivity in each state. Because the amount of time spent spinning either parallel or antiparallel depends on the angle of the ambient magnetic field, different chemical reactions can occur as the magnetic field
changes. These reactions are thought to occur in the eyes of many migrating bird species.
How do scientists study magnetoreception in animals? The most common method used is an orientation experiment. The
goal of an orientation experiment is to identify the direction an individual wants to move. Hopefully, by controlling all the possible cues an animal can use to move and manipulating only the magnetic field, scientists can determine the role of the magnetic field. Scientists often compare the directions of control individuals with individuals exposed to some kind of magnetic
field treatment. In today’s laboratory, we are going to expose pill bugs (a terrestrial isopod crustacean) to a magnetic pulse
to see if the pulse affects their movement. To date, it is unknown whether pill bugs can sense a magnetic field, so your experiments will provide some of the first data to answer this question! You can read more about pill bugs, the experimental procedure, and data analysis at the link above. The worksheet below should help guide your thinking along the way and includes
space for recording your data. After completing the lab, please submit your answers to the questions below. Have fun!
1. Briefly describe each of the two proposed mechanisms of magnetoreception:
2. Describe two ways in which animals might use their magnetic sense: