Uncovering the Mystery: Why Do Some Fish Have Oversized Lips?

The large, striking lips of some cichlid fish have intrigued both scientists and fish enthusiasts for a long time. Why do these fish have such noticeable lips? Recent research by Dr. Nagatoshi Machii and his team at the Tokyo Institute of Technology is shedding light on this unique feature.

Cichlids aren’t the only species with oversized lips; they have developed this trait in parallel with other fish in different environments. This phenomenon, called parallel evolution, occurs when distinct species evolve similar traits due to similar environmental pressures. The isolated lakes of Victoria, Malawi, and Tanganyika serve as natural laboratories, where various species of cichlids have independently developed these thick lips to adapt to their habitats.

According to evolutionary biologist Jonathan Losos from Harvard, “Parallel evolution shows how natural selection leads to similar adaptations in response to environmental challenges.” For cichlids, their lips likely evolved to help them forage and navigate through rocky environments.

Dr. Machii’s study revealed that cichlid lips are rich in proteoglycans, which are molecules made of proteins and sugar chains. These compounds help maintain tissue structure, making the lips plump by attracting and retaining water. Specifically, cichlids with larger lips have high concentrations of chondroitin sulfate proteoglycans, promoting lip expansion and volume.

This growth isn’t random. The genes responsible for building the connective tissue in these lips are active even in young fish. Species with the potential for larger lips show early gene expression that sets the stage for their eventual development. The Wnt signaling pathway—a network of proteins essential for cell growth and function—plays a central role in this process, affecting both embryonic development and the maintenance of adult tissues.

This genetic connection might extend beyond cichlids. The proteoglycans that help shape their lips also relate to human health issues like keloids—raised scars formed from excess connective tissue. Understanding these similarities could offer new insights into human connective tissue disorders.

In conclusion, the research on cichlid lips not only deepens our understanding of evolutionary biology but may also lead to advances in medical science. As we study these fascinating creatures, we uncover potential applications that cross the boundaries of species.

For more information on the genetic basis of these adaptations, you can read the original research published in eLife.

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