Morphology of the eyeball of Neotropical bats with different feeding habits

Vision is an extremely important sense in bats and can influence foraging activities. The present study aimed to evaluate morphometric aspects of the eyeballs of Neotropical bats with different feeding habits. Based on the hypothesis that frugivorous and nectarivorous bats likely possess better visual resolution compared to insectivorous and sanguivorous species due to their foraging modes, we predicted that these bats would have larger eyeballs and internal eye structures comparable to those of insectivorous and blood-eating species. Histological analysis allowed for estimating the thickness of the cornea, choroid, sclera, and retina, as well as counting the number of photoreceptor cells in the external nuclear layer of the retina of two frugivorous species (Artibeus obscurus, A. planirostris), two nectarivorous species (Glossophaga soricina, Anoura geoffroyi), two blood-eating species (Diphylla ecaudata, Desmodus rotundus), and one insectivorous species (Nyctinomops laticaudatus). Macroscopic measurements were obtained in four of these species. There is a statistically significant relationship between the type of diet and the morphological differences of the eyeball, confirming our predictions regarding fruit bats, which presented the highest means of ocular parameters while the insectivorous N. laticaudatus and the nectarivorous G. soricina exhibited the lowest. These latter two species had a thinner cornea, indicating a possible lower refractive power and, consequently, lower visual acuity. The blood-eating species showed divergent results. Additionally, the insectivorous N. laticaudatus also had a smaller number of photoreceptor cell nuclei in the outer nuclear layer of the retina, possibly indicating less transduction of light signals by the retina.