Abstract
The amount of short wavelength (ultraviolet (UV), violet and blue) light that reaches the retina depends on the transmittance properties of the ocular media, especially the lens, and varies greatly across species in all vertebrate groups studied previously. We measured the lens transmittance in 32 anuran amphibians with different habits, geographical distributions and phylogenetic positions and used them together with eye size and pupil shape to evaluate the relationship with diel activity pattern, elevation and latitude. We found an unusually high lens UV transmittance in the most basal species, and a cut-off range that extends into the visible spectrum for the rest of the sample, with lenses even absorbing violet light in some diurnal species. However, other diurnal frogs had lenses that transmit UV light like the nocturnal species. This unclear pattern in the segregation of ocular media transmittance and diel activity is shared with other vertebrates and is consistent with the absence of significant correlations in our statistical analyses. Although we did not detect a significant phylogenetic effect, closely related species tend to have similar transmittances, irrespective of whether they share the same diel pattern or not, suggesting that anuran ocular media transmittance properties might be related to phylogeny.
Highlights
The lenses of animal eyes need to be transparent to allow the light they focus to reach its final destination, the photoreceptors in the retina
We showed that the lenses of two species of anurans widely used as experimental models in vision research differ by more than 50 nm in the cut-off wavelength at which 50% of incoming light is transmitted [21]
The breadth of the range is similar in Hyloides and Ranoides, the two major lineages of neobatrachians that contain more than 90% of the anuran species diversity [33], the upper boundary for the latter seems to be lower than for the former
Summary
The lenses of animal eyes need to be transparent to allow the light they focus to reach its final destination, the photoreceptors in the retina. It is reasonable to expect that lens transmittance properties would have evolved in such a way that they ‘match’ the light environment in which a given visual system performs It has been hypothesized [14] that nocturnal animals would have highly transmissive lenses to maximize the number of photons that can reach the retina in a context in which they are scarce per se, and that diurnal animals for whom light is an ‘unlimited’ resource could afford to filter out part of the short-wavelength radiation to fine tune resolution while preventing the potential damage caused by the exposure to high amounts of that kind of radiation. We assessed the lens transmit- 2 tance, eye size and pupil morphology of 37 species sampled from across the diversity of anurans and evaluated their relationship with the temporal and geographical environments that they inhabit
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