Ontogenetic shift of spectral phototactic preferences in anuran tadpoles.

Publisher Website
Google Scholar
Abstract
Tadpoles of 3 spp. of anurans [Xenopus laevis, Rana pipiens, R. clamitans] initially had a midspectrum (green) preference in laboratory phototactic tests, which was shown experimentally to involve a form of true color vision in 1 sp. and probably in the other 2 as well. During development, the preference shifted to shorter wavelengths (higher frequencies) until a short-wavelength (blue) preference predominated in the pre- and postmetamorphic stages and in the adults of 6 spp. tested [Bufo americanus, B. woodhousei, Hyla crucifer]; color vision was involved in all of these stages. The green preference of young tadpoles is ecologically adaptive, in that it directs larvae to green plants that provide food or shelter. Tadpoles observed in a pond congregated heavily in vegetated areas rather than in open water. Spectroradiometric field measurements showed that pond illumination in vegetated areas had a highly saturated yellow-green spectral dominance compared with a desaturated white illumination in open water. During all ontogenetic stages and as adults, the animals had a preference for high illuminance of white light, which correlates with the high illumination of their habitat. Microspectrophotometric data from Leibman and Entine suggested that the green rods are active receptors in tadpoles, making unlikely Muntz''s hypothesis that the ontogenetic shift in spectral preferences is due to premetamorphic maturation of these receptors. The visual pigments of all 5 types of photoreceptors shifted from vitamin A2- to vitamin A1-based chromophores during ontogeny and the resulting shift in spectral response of the receptors might be related to the spectral shift in phototactic preferences.