2020/12/01
Keio University
Takumi Shito, a first-year master's student, Professor Kotaro Oka, and Associate Professor Koji Hotta from the Faculty of Science and Technology at Keio University have discovered surprisingly transparent ascidian larvae, through which approximately 90% of visible light can pass.
In this study, we quantitatively analyzed the transparency of eggs from various ascidian species using a hyperspectral camera and discussed the evolution of transparency in ascidian eggs. Although biological transparency is an ecologically important factor that appears in diverse groups of organisms, its evolutionary aspects have not received much attention. Ascidian eggs also exhibit a rich variety of colors and transparency among species, but this characteristic has not been quantitatively and comprehensively measured until now. In this study, we established a method for evaluating the transparency of ascidian eggs, compared the transparency of eggs from different ascidian species along the coast of Japan, and elucidated the phylogenetic relationships among these species. The transparency ranged widely from 10% to 90%, suggesting that it may have evolved independently in each family. The eggs of *Ascidiella aspersa* showed exceptionally high transparency among those measured, proving to be as transparent as glass beads. The tadpole larvae that hatched from these eggs also possessed similar properties, exhibiting such transparency that only their eyes were visible. Furthermore, the eggs of other ascidians in the same family as *A. aspersa*, Ascidiidae, were also highly transparent, suggesting the possibility of a phylogenetic constraint that maintains high egg transparency.
The rich variety of transparency in ascidian eggs shown in this study is thought to have arisen from the diversification of transparency as a result of various developmental and ecological factors in the environment surrounding the eggs and larvae. While there are still few studies on biological transparency, it is a very attractive "blue ocean" research area that could have a significant impact on technologies such as fisheries, medicine, and biomimetics.
The research results were published online in the British scientific journal "Scientific Reports" on November 30, 2020 (at 10:00 a.m. UK time).
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