Adaptation and conservation of turtle visual opsins over a deep phylogenetic divergence

Long-term evolutionary analysis across 59 turtle species shows visual opsin sequences are remarkably conserved, with phylogeny-wide positive selection detected only in LWS.

• Why it matters: Turtle vision is linked to adaptation across light environments, yet opsin evolution in turtles—especially side-neck turtles (Pleurodira)—has been poorly characterized compared with hidden-neck turtles (Cryptodira).
• What they did: Using an eye transcriptome and whole-genome sequences from 59 turtle species plus 42 other reptile species, the study applied codon-based evolutionary models to test positive selection and long-term shifts across five opsins.
• The result: Habitat explained more selective-pressure shifts than taxonomy, and spectral tuning predicts conserved UV sensitivity of SWS1 across cryptodirans while pleurodirans show shared changes linked to violet sensitivity.

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