Researchers demonstrated how giant clams use iridescent structures to operate "living greenhouses" that grow algae as symbiotic food sources.
The findings could help lead to the development of improved solar panels or reactors for growing biofuels, the University of Pennsylvania reported.
"Many mollusks, like squid, octopuses, snails and cuttlefish have iridescent structures, but almost all use them for camouflage or for signaling to mates," said Alison Sweeney, assistant professor in the department of physics and astronomy in Penn's School of Arts and Sciences. "We knew giant clams weren't doing either of those things, so we wanted to know what they were using them for."
Giant clams host symbiotic algae that grow within their flesh. These algae convert sunlight into energy, but are not especially efficient at thriving in the intense rays present in the giant clams' reef habitat. Researchers hypothesized clams' iridescent structures, dubbed iridocytes, were being used to maximize the usefulness of the light, but this idea was contradicted by the fact that pillars of algae on the clams' flesh were oriented in the opposite way needed to utilize the energy source.
"When we saw the complete picture, we understood that the pillars are oriented exactly the wrong way if you want to catch sunlight," Sweeney said. "That's where the iridocytes come into play."
The analysis suggested iridocytes scatter light wavelengths in "cone like" distributions pointing inwards towards the clam.
To back up their theory, the researchers constructed fiber optic probes with spherical tips the size of individual algae. These probes allowed them to detect light scattered by the iridocytes, while flat-tipped probes that could only pick up downward-tilting light detected nothing.
"We see that, at any vertical position within the clam tissue, the light comes in at just about the highest rate at which these algae can make use of photons most efficiently," Sweeney said. "The entire system is scaled so the algae absorb light exactly at the rate where they are happiest."
These findings could lead to new approaches in boosting the efficiency of photovoltaic cells.
"The clam has to make every square inch count when it comes to efficiency," Sweeney said. "Likewise, all of our alternatives are very expensive when it comes to surface area, so it makes sense to try to solve that problem the way evolution has."
The findings were published in a recent edition of the Journal of the Royal Society Interface.
