Context matters: Epistasis in a whale visual gene

What is it about?

The molecule responsible for dim-light vision is rhodopsin, a light-sensitive protein in the retina's rod cells. We discovered that naturally occurring mutations in killer whale rhodopsin inconsistently affect the protein's light-response properties when applied across species, a phenomenon called epistasis. Our results also indicate that ancestral differences in the background genetic context of rhodopsin influenced the protein's evolution as whales transitioned from their terrestrial ancestors into aquatic environments.

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Why is it important?

Does a genetic mutation in one organism have the same effect in another from a different species? How to predict the effects of genetic change is a central question in evolutionary biology. Our work highlights a case where parallel genetic changes don't necessarily correspond to parallel phenotypic (trait) changes, due to the background genetic contexts that vary among species. This epistasis means that the functional roles of rhodopsin mutations in the visual evolution of whales, and the nature of the selective pressures behind them, need to be reassessed.

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