Adaptive loss of shortwave-sensitive opsins during cartilaginous fish evolution

Area of Science:

• Evolutionary biology
• Vision science
• Genomics

Background:

• Cartilaginous fishes, including sharks and skates, exhibit limited color vision, potentially due to the absence of the shortwave-sensitive (sws) opsin gene.
• The evolutionary drivers behind the loss of the sws gene in these species remain largely unknown.

Purpose of the Study:

• To investigate the evolutionary mechanisms of sws gene loss in cartilaginous fishes.
• To understand the functional implications of sws loss on vision and eye health in these species.

Main Methods:

• Whole-genome assembly of Okamejei kenojei (skate) and Prionace glauca (blue shark).
• Analysis of opsin gene distribution and variations within cartilaginous fishes.
• Utilizing a zebrafish model with sws deletion to assess the impact of short-wavelength light on photoreceptors.

Main Results:

• The study identified and analyzed opsin gene characteristics in newly assembled genomes of skate and blue shark.
• A zebrafish model indicated that short-wavelength light (blue and violet) can induce cellular aging and photoreceptor layer thinning.
• The loss of the sws gene appears to protect the eye from damage caused by short-wavelength light.

Conclusions:

• The loss of the sws gene in cartilaginous fishes is likely an adaptive trait to prevent damage from short-wavelength light.
• The presence of the tapetum lucidum, which reflects light in the retinas of many cartilaginous fishes, may be interdependent with sws gene loss.
• This adaptive gene loss may confer a survival advantage, enhancing the fitness of cartilaginous fishes in their natural environments.