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Abstract Light intensity varies 1 million‐fold between night and day, driving the evolution of eye morphology and retinal physiology. Despite extensive research across taxa showing anatomical adaptations to light niches, surprisingly few empirical studies have quantified the relationship between such traits and the physiological sensitivity to light. In this study, we employ a comparative approach in frogs to determine the physiological sensitivity of eyes in two nocturnal (Rana pipiens,Hyla cinerea) and two diurnal species (Oophaga pumilio,Mantella viridis), examining whether differences in retinal thresholds can be explained by ocular and cellular anatomy. Scotopic electroretinogram (ERG) analysis of relative b‐wave amplitude reveals 10‐ to 100‐fold greater light sensitivity in nocturnal compared to diurnal frogs. Ocular and cellular optics (aperture, focal length, and rod outer segment dimensions) were assessed via the Land equation to quantify differences in optical sensitivity. Variance in retinal thresholds was overwhelmingly explained by Land equation solutions, which describe the optical sensitivity of single rods. Thus, at the b‐wave, stimulus‐response thresholds may be unaffected by photoreceptor convergence (which create larger, combined collecting areas). Follow‐up experiments were conducted using photopic ERGs, which reflect cone vision. Under these conditions, the relative difference in thresholds was reversed, such that diurnal species were more sensitive than nocturnal species. Thus, photopic data suggest that rod‐specific adaptations, not ocular anatomy (e.g., aperture and focal distance), drive scotopic thresholds differences. To the best of our knowledge, these data provide the first quantified relationship between optical and physiological sensitivity in vertebrates active in different light regimes.
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This content will become publicly available on November 14, 2025
The relationship between spectral signals and retinal sensitivity in dendrobatid frogs
Research on visually driven behavior in anurans has often focused on Dendrobatoidea, a clade with extensive variation in skin reflectance, which is perceived to range from cryptic to conspicuous coloration. Because these skin patterns are important in intraspecific and interspecific communication, we hypothesized that the visual spectral sensitivity of dendrobatids should vary with conspecific skin spectrum. We predicted that the physiological response of frog retinas would be tuned to portions of the visible light spectrum that match their body reflectance. Using wavelength-specific electroretinograms (ERGs; from 350-650 nm), spectrometer measurements, and color-calibrated photography of the skin, we compared retinal sensitivity and reflectance of two cryptic species (Allobates talamancaeandSilverstoneia flotator), two intermediate species (Colostethus panamansisandPhyllobates lugubris), and two conspicuous aposematic species (Dendrobates tinctoriusandOophaga pumilio). Consistent with the matched filter hypothesis, the retinae of cryptic and intermediate species were sensitive across the spectrum, without evidence of spectral tuning to specific wavelengths, yielding low-threshold broadband sensitivity. In contrast, spectral tuning was found to be different between morphologically distinct populations ofO.pumilio, where frogs exhibited retinal sensitivity better matching their morph’s reflectance. This sensory specialization is particularly interesting given the rapid phenotypic divergence exhibited by this species and their behavioral preference for sympatric skin reflectances. Overall, this study suggests that retinal sensitivity is coevolving with reflective strategy and spectral reflectance in dendrobatids.
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- Award ID(s):
- 2050358
- PAR ID:
- 10573309
- Editor(s):
- Shawkey, Matthew
- Publisher / Repository:
- PLoS
- Date Published:
- Journal Name:
- PLOS ONE
- Volume:
- 19
- Issue:
- 11
- ISSN:
- 1932-6203
- Page Range / eLocation ID:
- e0312578
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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