Diego-Rasilla, F.J., Luengo, R.M. Magnetic compass orientation in common midwife toad tadpoles, Alytes obstetricans (Anura, Alytidae). J Ethol (2020).


Abstract. We provide the first evidence for y-axis magnetic compass orientation in Alytes obstetricans. Evidence for wavelengthdependent effect of light on magnetic compass orientation is also shown. In the first series of experiments, two groups of tadpoles were tested shortly after being collected from a pond with a natural shoreline and a clearly defined y-axis under two different lighting conditions (full-spectrum and long-wavelength light). Magnetic bearings from tadpoles tested under full-spectrum natural skylight displayed bimodal distribution along an axis that coincided with the magnetic direction of the y-axis in their home pond, while those tested under long-wavelength light failed to exhibit a consistent overall direction of orientation relative to the magnetic field, although a subset of tadpoles exhibited magnetic compass orientation that was rotated about 90° counter-clockwise of the magnetic direction of the y-axis in their home pond. In the second series of experiments, tadpoles were collected from a watering trough without a defined y-axis, trained to learn the direction of the y-axis in tanks with an artificial shore at one end and tested under full-spectrum natural skylight. Tadpoles from the two trained groups showed bimodal magnetic compass orientation along the shore–deep water magnetic axis of their respective training tanks. The present findings widen the number of species with y-axis magnetic compass orientation to include Alytidae, a family of primitive semiterrestrial frogs. 

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