These Bumpy Little Seahorses Are Amazing Camouflage Artists. Scientists Pinpoint the Gene Loss Behind Their Special Traits

Bargibant’s pygmy seahorses look almost exactly like the gorgonian corals they live in, thanks in part to their unusually stubby snouts

Margherita Bassi | Daily Correspondent

September 4, 2025

Share

Copy linkEmailSMSFacebookXRedditLinkedInBlueskyPrint

Add as preferred source

Pygmy seahorses, among the smallest vertebrates in the world, are exceptional camouflage artists. At an average size of just 0.55 to 1.06 inches, these tiny creatures live symbiotically with gorgonian corals in the western Pacific Ocean, appearing with textures and colors that match the branching reefs. They blend in so well with their surroundings that researchers only discovered the animals within the last 60 years.

To broaden the still limited understanding of pygmy seahorses, researchers from the University of Konstanz in Germany and the South China Sea Institute of Oceanology investigated the genetics of the Bargibant’s pygmy seahorse (Hippocampus bargibanti) to uncover the basis of its special mimicry ability.

The work, published August 25 in the journal PNAS, suggests the tiny seahorse’s camouflage and other traits are driven in part by genetic loss, rather than gain.

“In all of these adaptations, we see examples of massive gene losses and a seemingly paradoxical release of evolutionary creativity,” Axel Meyer, an evolutionary biologist at the University of Konstanz and co-leader of the study, says in a statement, “which ultimately explains the unusual appearance and remarkable biology of these creatures.”

While seahorses typically have a long, horse-like snout, the snouts of Bargibant’s pygmy seahorses are short and stout—exactly like the polyps on the gorgonian corals that host them. This isn’t a coincidence—in fact, the seahorses have polyp-like knobs elsewhere on their bodies, too. If the creature had a regular snout, predators would have an easier time spotting it.

Pygmy seahorses also have a strange biological quirk: It’s the males that carry embryos—and they nourish them inside their bodies. Other male seahorses also carry their young, but they often do so in pouches on their tails.

The pygmy seahorses are “just something very odd and interesting and in need of explanation,” Meyer tells the New York Times’ Carl Zimmer.

Meyer and his colleagues wanted to discover which genes are responsible for the pygmy seahorse’s atypical traits. To examine the camouflage ability, they analyzed the animal’s gene expression pattern during the growth of its snout region.

Like some mammals, seahorses have short heads with squat facial proportions in their early development that align with the “baby schema,” a set of features that trigger caregiving responses. The pygmy seahorse’s head, however, stays in this “childlike” developmental stage into adulthood, Meyer explains in a statement.

“Normally, a combination of different genetic components causes the snout of a seahorse to grow proportionally faster than other parts of the body from a certain age and thus become elongated,” he adds. “In the pygmy seahorse, however, we have now discovered that these different growth rates are suppressed.”

This suppression comes from the loss of a gene called hoxa2b, which the team also demonstrated by using a genome editing tool called CRISPR-Cas9 on zebrafish.

But that wasn’t the only gene lost: The team also studied the genetics behind the seahorse’s skin color, skin knobs and immune system. They revealed that the tiny vertebrates, which branched off from full-sized seahorses around 18 million years ago, evolved to lose an uncommonly large amount of immune genes. What’s more, they discovered that pygmy seahorses have the smallest known set of immune system-related genes of all vertebrates.

According to the statement, this is likely related to the animal’s tolerance to coral toxins. These toxins protect the seahorses from microbes, so their immune systems don’t need the genes that would normally provide this protection.

Additionally, for male pygmy seahorses to carry their young inside their bodies, they likely needed to lose immune genes so that their immune systems don’t attack the eggs, which are foreign tissue.

Unfortunately, however, the paper also “reveals a cruel irony,” Richard Smith, an independent marine biologist who did not participate in the study, tells the New York Times: The pygmy seahorses genetically evolved to live alongside gorgonian corals so perfectly that they are now unable to live any other way. With climate change seriously threatening coral reefs, that means pygmy seahorses are also in danger. “The very traits that made these seahorses successful, such as their perfect mimicry, tiny size and specialized biology, are now their greatest vulnerability,” Smith adds.

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.