Hypersensitivity to light of the iris (Sphincter pupillae) of the albino axolotl (Ambystoma mexicanum)

Albino Xenopus laevis tadpoles prefer dark environments compared to wild type

Tadpoles display preferences for different environments but the sensory modalities that govern these choices are not well understood. Here, we examined light preferences and associated sensory mechanisms of albino and wild-type Xenopus laevis tadpoles. We found that albino tadpoles spent more time in darker environments compared to the wild type, although they showed no differences in overall activity. This preference persisted when the tadpoles had their optic nerve severed or pineal glands removed, suggesting these sensory systems alone are not necessary for phototaxis. These experiments were conducted by an undergraduate laboratory course, highlighting how X. laevis tadpole behavior assays in a classroom setting can reveal new insights into animal behavior.

The pupillary light responses of animals; a review of their distribution, dynamics, mechanisms and functions

The timecourse and extent of changes in pupil area in response to light are reviewed in all classes of vertebrate and cephalopods. Although the speed and extent of these responses vary, most species, except the majority of teleost fish, show extensive changes in pupil area related to light exposure. The neuromuscular pathways underlying light-evoked pupil constriction are described and found to be relatively conserved, although the precise autonomic mechanisms differ somewhat between species. In mammals, illumination of only one eye is known to cause constriction in the unilluminated pupil. Such consensual responses occur widely in other animals too, and their function and relation to decussation of the visual pathway is considered. Intrinsic photosensitivity of the iris muscles has long been known in amphibia, but is in fact widespread in other animals. The functions of changes in pupil area are considered. In the majority of species, changes in pupil area serve to balance the conflicting demands of high spatial acuity and increased sensitivity in different light levels. In the few teleosts in which pupil movements occur they do not serve a visual function but play a role in camouflaging the eye of bottom-dwelling species. The occurrence and functions of the light-independent changes in pupil size displayed by many animals are also considered. Finally, the significance of the variations in pupil shape, ranging from circular to various orientations of slits, ovals, and other shapes, is discussed.