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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).
© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution. Visual systems adapt to different light environments through several avenues including optical changes to the eye and neurological changes in how light signals are processed and interpreted. Spectral sensitivity can evolve via changes to visual pigments housed in the retinal photoreceptors through gene duplication and loss, differential and coexpression, and sequence evolution. Frogs provide an excellent, yet understudied, system for visual evolution research due to their diversity of ecologies (including biphasic aquatic-terrestrial life cycles) that we hypothesize imposed different selective pressures leading to adaptive evolution of the visual system, notably the opsins that encode the protein component of the visual pigments responsible for the first step in visual perception. Here, we analyze the diversity and evolution of visual opsin genes from 93 new eye transcriptomes plus published data for a combined dataset spanning 122 frog species and 34 families. We find that most species express the four visual opsins previously identified in frogs but show evidence for gene loss in two lineages. Further, we present evidence of positive selection in three opsins and shifts in selective pressures associated with differences in habitat and life history, but not activity pattern. We identify substantial novel variation in the visual opsins and, using microspectrophotometry, find highly variable spectral sensitivities, expanding known ranges for all frog visual pigments. Mutations at spectral-tuning sites only partially account for this variation, suggesting that frogs have used tuning pathways that are unique among vertebrates. These results support the hypothesis of adaptive evolution in photoreceptor physiology across the frog tree of life in response to varying environmental and ecological factors and further our growing understanding of vertebrate visual evolution.
Author(s): Schott RK, Fujita MK, Streicher JW, Gower DJ, Thomas KN, Loew ER, Bamba Kaya AG, Bittencourt-Silva GB, Guillherme Becker C, Cisneros-Heredia D, Clulow S, Davila M, Firneno TJ, Haddad CFB, Janssenswillen S, Labisko J, Maddock ST, Mahony M, Martins RA, Michaels CJ, Mitchell NJ, Portik DM, Prates I, Roelants K, Roelke C, Tobi E, Woolfolk M, Bell RC
Publication type: Article
Publication status: Published
Journal: Molecular Biology and Evolution
Year: 2024
Volume: 41
Issue: 4
Online publication date: 04/04/2024
Acceptance date: 26/02/2024
Date deposited: 22/04/2024
ISSN (electronic): 1537-1719
Publisher: Oxford University Press
URL: https://doi.org/10.1093/molbev/msae049
DOI: 10.1093/molbev/msae049
PubMed id: 38573520
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