At first glance, our skin may look boring to you. But if you take a closer look, every cell carries within them a hidden world of microbes that orchestrate intricate networks on their surface. These tiny organisms might not be visible to the naked eye, but they play a pivotal role in maintaining the health and balance of all of us – including the biggest fish in the sea.
Despite their massive size, whale sharks (Rhincodon typus) are generally considered gentle and harmless to humans. Famous for their massive bodies being covered in a unique pattern of white spots and lines on a dark background, these filter feeders are found in tropical and warm-temperate waters around the world. While generally solitary animals, they can occasionally be seen in groups when they form aggregations where food is especially concentrated, such as plankton blooms or spawning events. Whale sharks are considered vulnerable by the International Union for Conservation of Nature (IUCN). Scientists are actively studying whale sharks to better understand their behavior, biology, migration patterns, and genetics. Advances in technology, such as satellite tagging and genetic analysis, have provided valuable insights into their lives. Recent research has shed light on how these microbes come together to form a complex community that is surprisingly similar across the globe, regardless of the sharks’ distinct environments.
Microbes, short for microorganisms, are tiny living organisms that are too small to be seen with our eyes without a little bit of help. Despite their small size, microbes play a crucial role in various biological processes, are essential for life on Earth, and come in a wide range of forms, from bacteria and archaea to fungi, viruses, and protozoa! These microscopic inhabitants can significantly influence the well-being of their host, too. However, their diversity is ever-changing, and understanding their relationship with the whale sharks has proven to be a challenge. The key question is: How do these microbes contribute to the health of these specific enormous hosts?
To tackle this puzzle, a team of scientists embarked on a journey to explore the microbial world of whale sharks. They studied 74 individual whale sharks from five different locations around the world, including La Paz, Cancun, Mafia Island, Ningaloo Reef, and Oslob. These whale shark populations were chosen for their global distribution, making them a perfect model to examine the relationships between the host and its microbial residents.
“Samples were collected using a two-way syringe device that circulates filtered seawater over the skin surface before being drawn into the backside of the syringe,” the authors explain in their paper. “This process enables the sampling of microbes from submerged whale sharks, whilst minimizing seawater microbiome contamination. From each shark we took four syringes, resulting in approximately 180 ml of sample water that was then passed through a filter, trapping all microbial life on the filter.” The research centered on epidermal microbiomes due to their non-intrusive nature, focusing on a particular shark region. This approach allowed the sharks to sustain their feeding and swimming activities with minimal disruption.
What the researchers discovered was remarkable. Despite the unique environments of each location, the microbial communities on the whale sharks’ skin showed striking similarities in their network architecture. Just like the intricate web of connections in a city, these microbial networks displayed modularity—distinct clusters of microorganisms working together within the larger community. Interestingly, the most important players in this microbial symphony were not the most abundant ones. The researchers found that microbial families with low abundance were actually the keystones holding the community structure together. These microbes, even though they were not numerically dominant, played a disproportionately significant role in shaping the network architecture.
The scientists also identified two core microbial groups, each associated with distinct ecological functions. One group specialized in breaking down essential nutrients found in the mucus secreted by the whale sharks’ skin, while the other group interacted with the environment and engaged in processes like the breakdown of aromatic compounds and lipid production. With these findings, scientists have revolutionized our understanding of the intricate relationship between whale sharks and their microbial hitchhikers. Instead of focusing solely on microbial diversity, it’s the complex architecture of these communities that holds the key to their health. By studying the patterns of microbial interactions on the skin of whale sharks, we gain insights into how these networks contribute to the well-being of these gentle giants.
As our knowledge of microbiomes grows, the implications extend beyond the world of whale sharks. Just as these microbes influence the health of these magnificent creatures, they also have a profound impact on the well-being of other organisms, including humans. By unraveling the mysteries of these hidden communities, scientists are opening doors to new possibilities for understanding and supporting the delicate balance of life on our planet.