Ferromagnetic material in the eastern red-spotted newt Notophthalmus viridescens

Behavioral results obtained from the eastern red-spotted newt (Notophthalmu s viridescens) led to the suggestion of a hybrid homing system involving in puts from both a light-dependent and a non-light-dependent mechanism. To ev aluate the possible role of a receptor based on biogenic magnetite in this animal, we performed magnetometry experiments on a set of newts previously used in behavioral assays, The natural remanent magnetization (NRM) carried by these newts was strong enough to be measured easily using a direct-curr ent-biased superconducting quantum interference device functioning as a mom ent magnetometer. Isothermal remanent magnetizations were two orders of mag nitude higher than the NRM, suggesting that ferromagnetic material consiste nt with magnetite is present in the body of the newt. The NRM has no prefer ential orientation among the animals when analyzed relative to their body a xis, and the demagnetization data show that, overall, the magnetic material grains are not aligned parallel to each other within each newt. Although t he precise localization of the particles was not possible, the data indicat e that magnetite is not clustered in a limited area. A quantity of single-d omain magnetic material is present which would be adequate for use in eithe r a magnetic intensity or direction receptor. Our data, when combined with the functional properties of homing, suggest a link between this behavioral response and the presence of ferromagnetic material, raising the possibili ty that magnetite is involved at least in the map component of homing of th e eastern red-spotted newt.