A COMPARISON OF SPECTRAL RESPONSE FUNCTIONS OF POSITIVE AND NEGATIVE PHOTOTAXIS IN 2 ANURAN AMPHIBIANS, RANA-PIPIENS AND LEPTODACTYLUS-PENTADACTYLUS

Anuran (tailless) amphibians exhibit preferences for light; some species (photopositive) are attracted to light while others (photonegative) are repelled. The photopositive anuran Rana pipiens and the photonegative anuran Leptodactylus pentadactylus were tested in a Y-maze on a light versus dark task where the 'light' stimuli were monochromatic and equated for energy. During each trial the window in one of the choice alleys of the Y-maze was illuminated while the window in the other was dark. Photopositive behavior was defined as greater than 50% choice of the alley with the illuminated stimulus, while photonegative behavior was defined as less than 50% choice. Based on previously reported spectral response functions, it was expected that the photonegative species (L. pentadactylus) would exhibit a maximum photonegativity in the 490-570 nm range while the photopositive species (R. pipiens) would be most strongly attracted by short wavelengths. However, our results indicate that both species are affected most strongly by short wavelength light; only the sign of the response (repulsion versus attraction) is inverted for L. pentadactylus, the photonegative species. This suggests that the retinal circuitry for wavelength discrimination may be equivalent in photopositive and photonegative anurans.