Basic scientific research can sometimes inform creative applications that are beneficial to a great number of people. A recent example comes from two researchers who are using newly understood biological traits of giant clams to develop a novel way to manage solar power. This animal uses the sun to grow symbiotic algae, providing a reliable source of food for itself. Investigation into the structures used to scatter and direct the sunlight may result in more efficient means of collecting solar energy, as well as more efficient solar production of algal biofuels.
Giant clams are recognizable for the fleshy, brilliantly colored “lips” that protrude from the opening of their shell. These lips are part of the clam’s mantle, the portion of its body that also extends to cover the viscera within the shell. The apparent iridescent blue color of the mantle does not result from pigmented cells, as reds and yellows do. Blue, instead, is what’s called a structural color; the cells themselves are actually shiny and reflective. When light strikes these reflective cells, called iridocytes, it reflects back to our eyes the color blue. But as it turns out, that isn’t all iridocytes in giant clams can do.
A research team from the University of California, Santa Barbara and the University of Pennsylvania recently found a previously unknown function for iridocytes, and it involves another organism present within the clam’s mantle. Giant clams participate in a process called symbiosis, a mutually beneficial relationship between two organisms. The symbiotic partner in this instance is algae, which lives in the mantle. Giant clams provide algae with a habitat and allow access to sunlight, and in return, the algae produces nutrients that allows the clam to grow to its large size. The novel part of this interaction is how the giant clams use their iridocytes to direct sunlight into internal algae greenhouses.
Typically, the amount of sunlight at the equator (where the clams live) is too intense for algae to use; if the sun is too strong it can actually disrupt photosynthesis, thereby reducing the ability of the algae to generate energy. Penn State researcher Alison Sweeney, along with her collaborators, had a hypothesis about the function of the iridocytes in the clam’s mantles. They suspected that these cells were being used to maximize the effectiveness of the sunlight by somehow directing it towards the algae. They found that this hypothesis was correct, but that the system was much more sophisticated than they had suspected.
First off, the algal cells were not arranged in a surface layer. Instead, they were stacked in pillars, and only the iridocyte cells were located at the surface of the mantle. This allowed the iridocytes to scatter sunlight into the clam’s mantle, at such an angle that the stacks of algal cells received the maximum amount of light they could process, while reducing the intensity so as not to damage the algae.
Though this system may seem an unusual one for study, the most compelling ideas sometimes come from unexpected sources. In this case, the iridocyte-algae setup has inspired researchers to try to build more efficient photovoltaic cells. Alison Sweeney and a colleague, Shu Yang, recently received a National Science Foundation grant that will award them $3 million over the next five years to pursue this line of questioning. What they hope to do is develop new synthetic materials based on the structures inside giant clams, providing more efficient, more damage-resistant photovoltaic materials. Not only that, but learning more about the organization of the iridocytes and algal cells may allow these scientists to improve production of algae biofuels. So in this example, what seems an unlikely source has provided the potential to solve some large-scale problems in alternative energy production. May we never stop looking to nature for inspiration.