Scientists have long been puzzled by the apparent contradiction of nutrient-poor tropical oceans supporting thriving reef ecosystems. Known as the Darwin Paradox, this phenomenon has intrigued researchers since Charles Darwin first described it in 1842. However, a recent international study led by researchers at KAUST has shed light on this paradox by uncovering how a sea anemone called Aiptasia efficiently recycles nitrogen waste in nutrient-poor environments.
Previous studies had focused on identifying the source of limited nutrients, particularly nitrogen, in the ocean environment. Some studies proposed that coral-algae symbiosis played a role in creating these nutrient-rich hotspots, but the molecular mechanism behind cnidarians’ ability to build such diverse ecosystems remained elusive.
The KAUST researchers, supervised by Manuel Aranda, examined the symbiotic relationship at the tissue level, focusing on the two major cell layers of cnidarians: the gastrodermis and the epidermis. Using a laser microdissection technique, they separated these tissue layers in Aiptasia and studied the gene expression associated with symbiosis at a cellular scale. This study marked the first time such techniques were used to investigate symbiosis in sea anemones.
The researchers identified the key transporters responsible for nitrogen assimilation and tracked their localization within the anemone using antibody staining. They discovered that the anemone alters the expression and localization of nutrient transporters to distribute the glucose received from its symbionts throughout its tissues. By doing so, the anemone utilizes most of its body mass to recycle nitrogen waste and process available ammonium in the environment.
This study challenges the prevailing belief that algae are solely responsible for nitrogen assimilation. Instead, the researchers found that the anemone plays a significant role in recycling this scarce nutrient, effectively transforming the entire organism into a nitrogen assimilator. The anemone and its symbionts form a inseparable meta-organism, working together in a mutually beneficial relationship.
The implications of this research are promising. The findings could contribute to the development of improved selective breeding methods and help protect reef ecosystems. The team plans to expand their research to explore symbiotic relationships across different cnidarian taxa and ecological contexts, further enhancing our understanding of these fascinating organisms and their ecosystems.