Iridocytes in giant clams
- Susann
- 12. Aug. 2020
- 3 Min. Lesezeit
Bio-inspired materials have recently taken a vital role for the latest technological trends - as nature itself provides a vast repertoire of examples for unique structures and materials, developed for often highly specialized applications or adaptations. Interdisciplinary research is hereby often bridging the communication gap between science and engineering, as shown by a recent project of Susann’s Ph.D. thesis research at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.
Research campus of KAUST
This research started as Prof. Carlos M. Duarte challenged Susann to find out why Tridacna maxima has such a broad range of colors, and what is their ecological significance. These charismatic clams are prominent members of tropical coral reefs, in the Red Sea and throughout the Indo-Pacific, but they also play an important ecological role for a healthy reef. As one of very few groups of bivalves, they are known to live in a symbiotic relationship with unicellular algae (Symbiodinaceae) – which is thought to be the reason why Tridacninae exhibit their impressive sizes and, thus got their common name, ‘giant clams’.
A Tridacna maxima giant clam, embedded into a Porites massive coral
As a joint project, Susann from the research team of Prof. Carlos M. Duarte, focusing on Red Sea ecology, and Ram Chandra Subedi, Ph.D. candidate in the group of Prof. Boon S. Ooi, leading the photonic team at KAUST, explored the photonic properties of Red Sea giant clams (Tridacna maxima).
These clams, which are important components of Red Sea coral reefs, are also remarkably colorful and beautiful. Likewise to corals, which harbor the same algal symbionts, the coloration of giant clams was credited to their photosynthetic algae. However, the irradiant coloration of giant clams conceals one additional secret: their iridocyte cells. These are tiny nano-reflectors, that are used to manage rapid color transitions across a large number of animals, ranging from chameleons to octopi. But giant clams (Tridacninae) use them for a new purpose.
Left: Outer mantle of a T. maxima giant clam. Right: Transmission Electron Microscopy Image of an Iridocyte cell
As Prof. Boon Ooi’s group is working on photonic devices for optical communications, and they are always searching for new materials that can solve current bottlenecks in high-performance photonic technology, the project initially started with the exploration the optical properties of these iridocytes, focusing on making novel light-emitting devices and photodetectors.
However, while their research was initially targeted to explore the response of the iridocyte cells to specific wavelengths of light (hopefully serving as an inspiration for photonic applications ), the scientists quickly realized that their results were in fact also helpful in explaining processes relevant to the ecology of giant clams: Iridocyte cells (located in the colorful, outer mantle of some Tridacninae species), absorb potentially damaging UV radiation and, through successive emission, emit light at longer wavelengths (i.e. blue or green). By doing so, the bivalve host and its algal symbionts are sheltered from (potentially) damaging UVR, while at the same time, the flux of wavelengths that are ‘useful’ for the algal symbiont increases, allowing them to enhance their high photosynthetic rates.
The high diversity of mantle color variants in these clams would be therefore caused by individually different relative densities of these iridocytes cells, (with their blue-greenish coloration) and the brownish algal symbionts, within the giant clams mantle tissues.
Different color variants of the T. maxima mantle
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