Bifoveal Vision in Anolis Lizards

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Abstract
The retinas of 14 ecologically diverse species of Anolis lizards have been examined neuroanatomically. Both central and temporal foveas were observed in each eye of all species; however, the two foveas differed with regard to a number of structural and morphological characteristics. All central foveas were deep and convexiclivate, while temporal foveas were shallower and more variable both in shape and retinal location across species. Central foveas had higher cell densities and a broader foveal clivus than did temporal foveas, both within and across species. As eye size increased across species, densities of receptor nuclei per visual degree2 (vis.deg.2) increased more rapidly than did ganglion cell densities/vis.deg.2 in the central fovea. In contrast, both cell types increased at approximately the same rate in the temporal fovea as eye size increased. Several of these relationships have been previously reported for diurnal birds of prey, which are also bifoveate. Analysis of stomach contents revealed that Anolis species which feed upon small prey items have temporal foveas with a relatively deep clivus. Foveal characteristics may influence both species typical foraging behaviors and the type of prey which can be effectively utilized by a given species.