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Genome of a 28-eyed jellyfish could provide insight on evolution of vision

One of the biggest mysteries of evolution is how species first developed complex vision. Jellyfish are helping scientists solve this puzzle, as the group has independently evolved eyes at least nine separate times. Different species of jellyfish have strikingly different types of vision, from simple eyespots that detect light intensity to sophisticated lens eyes similar to those in humans.

Biologists have studied jellyfish eye structure, light sensitivity, and visual behavior for decades, but the exact genes involved in jellyfish eye formation remain unknown.

Aide Macias-Muñoz, a professor of ecology and evolutionary biology, is exploring how eyes and light detection evolved using genetic tools. Her lab has just completed a , a small jellyfish-like animal in the Hydrozoa group that has an astonishing 28 eyes.

The findings are published in the journal G3: Genes, Genomes, Genetics.

Although the team originally set out to study a more common species—Tripedalia cystophora, or box jellyfish—that they had obtained in its polyp stage, the Bougainvillia unexpectedly appeared in their seawater tank as the jellyfish began to mature, and they turned out to be a scientific treasure trove.

Bougainvillia is notoriously difficult to keep alive in labs and has been largely understudied. The team was able to extract DNA from just 15 tiny individuals and build a detailed genetic map with over 46,000 predicted genes. This is believed to be the first genome available for a jellyfish species with this many eyes.

"This new genome is a great resource for comparative studies to understand how animals evolved and what genetic toolkit was present in their last common ancestor," Macias-Muñoz said.

Bougainvillia's eyes, called ocelli, are simple structures that detect light but lack the complexity of lens eyes. When analyzing its genome, the team found 20 "opsins"—light-sensitive proteins used in vision across the animal kingdom.

By comparison, humans have just four. Interestingly, the opsins in Bougainvillia differ from those in better-known jellyfish, suggesting that this species evolved vision through a different genetic pathway. The researchers also found other genes involved in eye development and light response.

Altogether, this genome offers an important new clue in understanding how vision evolves—particularly how simple eyes emerge in different evolutionary lineages. It's a powerful foundation for future biological research.

Future research on jellyfish vision

The Macias-Muñoz lab remains focused on studying the genetics of eye evolution. Future projects include investigating the roles of the vision-related genes identified in the Bougainvillia genome and determining which ones are truly involved in light detection.

Another research direction is exploring the genetics of eye regeneration. Eyed cnidarians like Bougainvillia can regrow sensory structures containing eyes—similar to how lizards regenerate tails—a rare ability that could unlock new insights into how visual systems form and heal.

In response to criticism of his theory of natural selection, Charles Darwin once admitted, "The eye to this day gives me a cold shudder, but when I think of the fine known gradations, my reason tells me I ought to conquer the cold shudder."

The "fine gradations" found in jellyfish may hold the key to solving this evolutionary mystery—and with more genomes from uniquely eyed species like Macias-Muñoz's 28-eyed Bougainvillia, we're getting closer to an answer.