Our understanding of animal light sensitivity is like an iceberg. Visual photosensitivity is the tip, while nonvisual photosensitivity makes up the often-overlooked ice mass floating below the surface. Nonvisual photosensitivity is responsible for many biologically critical functions, including the calibration of circadian rhythms, regulation of light-seeking behaviors, and initiation of seasonal reproductive changes. These processes are initiated by nonvisual opsins, transmembrane proteins, which, when paired with a light-sensitive chromophore, form the photopigments responsible for nonvisual photosensitivity. Boyette et al. (2024) explored the diversity and molecular evolution of nonvisual opsin genes in 102 frog species, representing 34 of 56 currently recognized frog families. They tested several evolutionary hypotheses. Most notably, the nocturnal ancestry of frogs is hypothesized to reduce the need for the broad spectral sensitivity provided by non-visual opsins. Therefore, they expected to find extensive nonvisual opsin gene losses across frogs, like other ancestrally nocturnal groups including mammals and snakes. Surprisingly, they recovered all 18 ancestral vertebrate nonvisual opsins at the genomic level. Frogs thus demonstrate the lowest documented level of opsin gene loss among ancestrally nocturnal tetrapods. They propose this may be due to the biphasic life history of most frogs. Although many mature frogs are nocturnal, this is not necessarily true of their tadpoles. Such biphasic life histories may subject nonvisual opsins to disparate environmental constraints and selective pressures across metamorphosis, resulting in adaptive decoupling between life stages active in different light conditions. This hypothesis is supported by differences in selective constraint detected between biphasic and direct-developing frog species. These findings indicate that many nonvisual opsins are important in species whose life histories expose them to disparate light environments across development. Such work fills an important gap in our understanding of vertebrate opsin diversity and highlights frogs as an excellent system to explore evolution across diverse environmental, developmental, and morphological adaptations.

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