Use of a Magnetic Compass for Y-Axis Orientation in Larval Bullfrogs, Rana catesbeiana
The use of a magnetic compass plays a significant role in the daily and seasonal movements of numerous organisms; however among amphibians, magnetic compass orientation has been convincingly demonstrated only in eastern red-spotted newts, Notophthalmus viridescens, with some indirect evidence coming from several species of bufonid toads. In this study, larval bullfrogs, Rana catesbeiana, were trained in outdoor tanks with two different Y-axis (shore/deep water) directions and then tested in an indoor arena in one of four symmetrical alignments of an earth-strength magnetic field. The tadpoles oriented bimodally along the correct magnetic direction of the Y-axis experienced during training, demonstrating that this anuran species is able to learn and orient along the Y-axis by sensing the geomagnetic field.Abstract
Schematic of test arena. An hydraulically operated release device (A) is centered on a transparent plexiglass disk (B) in a water-filled (C) arena (D). The arena is placed on a wooden table (E), both of which are enclosed within a cube-surface coil (F). A light housing (G) is centered over the release device, and the entire apparatus is covered with a lightweight black cotton curtain (H).
Bimodal magnetic orientation of bullfrog tadpoles along a trained Y-axis. (A) Bearings of tadpoles trained in a tank with the Y-axis aligned north-south (deep end toward the south) and (B) with the Y-axis aligned east-west (deep end toward the west). Each dot represents the bearings of one tadpole, tested once. Double-headed arrows at the center of each plot indicate the mean vector of each distribution. The length of each arrow is proportional to the mean vector length (r), with the diameter of the circle corresponding to r = 1. Large black triangles outside the plots indicate the magnetic direction of the deep end of the Y-axis. Dashed lines represent the 95% confidence intervals for the mean vector.