Tree frogs and day-active frogs block UV light from their eyes with filters in their lenses

Kate N. Thomas, David J. Gower, Jeffrey W. Streicher, Rayna C. Bell, Matthew K. Fujita, Ryan K. Schott, H. Christoph Liedtke, Célio F. B. Haddad, C. Guilherme Becker, Christian L. Cox, Renato A. Martins, Ron H. Douglas

This is a plain language summary of a Functional Ecology research article which is published here.

This summary is available in Portuguese here

Pictured is the tree frog Dendropsophus leucophyllatus sitting on a branch in French Guiana. This species has shortwave-filtering pigments in the lenses of its eyes, which may help it to see fine detail while navigating its complex arboreal environment. Photo by Christian Cox.

Animal eyes are exceptionally diverse, and the world an animal sees depends on the structure
and biology of its eyes. For example, species can differ in the colours they can detect, the level of
detail they can resolve, and how sensitive their vision is in low light. In vertebrates, one of the
many aspects of vision that can differ across species is the filtering effects of the ocular lens as
light passes through it on its way to the retina. While many vertebrates have highly transparent
lenses to let through as much light as possible, some (including humans) have pigmented lenses
that absorb short wavelengths (e.g. UV light) but let longer wavelengths (the visible spectrum)
through. This can make the image that reaches the retina higher in resolution and can protect
the retina from UV damage, but it also prevents the viewer from seeing UV patterns and
reduces the total amount of light available for vision. Here, we measured light transmission
through the lenses of 85 species of frogs and salamanders and tested whether ecology was
associated with shortwave filtering in the lenses. We found that species that are primarily
active in the day more commonly evolve lenses that filter out UV light, while night-active
species typically had more transparent lenses. We also found that species that typically climb
up into plants (e.g. tree frogs) show selection for stronger shortwave filtering in their lenses
than species that tend to be found on the ground or in water. Shortwave-absorbing lens
pigments likely help day-active frogs and climbing frogs (who are mostly night active) to see in
fine detail, while species lacking these pigments should have some level of visual sensitivity to
short wavelengths.

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