The same set of genes that gives mammals hair and birds feathers helps the pufferfish grow spines.
While the spines that cover pufferfish are readily apparent, how they got to be there isn't. New research, however, has identified the genes responsible for the evolution and development of these striking skin ornaments, finding that the process is similar to how other vertebrates get their hair or feathers.
"Pufferfish are some of the strangest fish in the ocean, particularly because they have a reduced skeleton, beak-like dentition and they form spines instead of scales -- not everywhere, but just in certain patches around the body," says corresponding author Gareth Fraser, an Assistant Professor at the University of Florida.
"It just blows me away that regardless of how evolutionarily-different skin structures in animals are, they still use the same collection of genes during development."
Fraser and his team analyzed the development of the spines in pufferfish embryos. Initially, they expected to see them form from scales, in essence, that some of the scales themselves would morph into the spines. However, what they found was that the spines' development is independent of that of the scales. In addition to this, they identified the genetic network that underpins the development of the scales, and it's the same one that governs hair and feather formation in other vertebrates.
After identifying these genes, the team decided to block some (CRISPR-Cas9 and other genetic techniques) that are classic markers of skin appendage development to see what would happen. This approach allowed the researchers to reduce the number of spines that grew on pufferfish, and make them 'sprout' in more varied places around their body. Normally, the spines are localized to specific areas on the pufferfish where they can offer the most protection, Fraser explains.
"When pufferfish inflate by ingesting water or in some cases air, their skin becomes stretched, especially around the abdomen and is more susceptible to damage, such as being torn," he says. "Spines reinforce the puffed-up abdomen. In extreme cases, some pufferfish have lost all other spines on their body and retain only the abdominal spines."
The diversity seen in spine location among pufferfish is likely the result of different ecological pressures, he adds. Different morphological set-ups of spines may allow pufferfish to access new ecological niches. "As the climate changes and environments become different, pufferfish may use these evolving traits to tolerate and adapt to change," Fraser says. Ultimately, him and his team hope to identify the genetic differences that create the wealth of diversity in spine layout and morphology.
"We can manipulate different things associated with pufferfish diversity, which gives us clues about the function of genes that are necessary for normal development and helps us understand the evolution and patterns of pufferfish spines."
"Pufferfish are wildly-derived fish that are incredibly different from other groups, and ultimately, we want to see if there's something specific to the genome of the pufferfish that can provide clues to suggest mechanisms that allow them to create these weird structures."
The paper "Evolution and developmental diversity of skin spines in pufferfishes" has been published in the journal iScience.