Abstract
The transparency of animals is an important biological feature. Ascidian eggs have various degrees of transparency, but this characteristic has not yet been measured quantitatively and comprehensively. In this study, we established a method for evaluating the transparency of eggs to first characterize the transparency of ascidian eggs across different species and to infer a phylogenetic relationship among multiple taxa in the class Ascidiacea. We measured the transmittance of 199 eggs from 21 individuals using a hyperspectral camera. The spectrum of the visual range of wavelengths (400–760 nm) varied among individuals and we calculated each average transmittance of the visual range as bio-transparency. When combined with phylogenetic analysis based on the nuclear 18S rRNA and the mitochondrial cytochrome c oxidase subunit I gene sequences, the bio-transparencies of 13 species were derived from four different families: Ascidiidae, Cionidae, Pyuridae, and Styelidae. The bio-transparency varied 10–90% and likely evolved independently in each family. Ascidiella aspersa showed extremely high (88.0 ± 1.6%) bio-transparency in eggs that was maintained in the “invisible” larva. In addition, it was indicated that species of the Ascidiidae family may have a phylogenetic constraint of egg transparency.
Highlights
The transparency of animals is an important biological feature
We present the first taxonomic exploration of bio-transparency in different ascidian eggs focused on the four different families in the orders Phlebobranchia and Stolidobranchia
A total of 99 individuals were randomly collected in four different locations: Honmoku, Misaki, Onagawa and Sado in Japan
Summary
The transparency of animals is an important biological feature. Ascidian eggs have various degrees of transparency, but this characteristic has not yet been measured quantitatively and comprehensively. It was indicated that species of the Ascidiidae family may have a phylogenetic constraint of egg transparency. Many marine organisms such as jellyfish, siphonophores, some crustaceans, pteropods, some squids, salps, and fish larvae are transparent[1,2,3,4,5,6]. The evaluation of transparency has been measured using a spectrophotometer and by specifying some wavelengths of the incident light[2] In this case, transmittance is expressed as a percentage relative to sea water. We precisely measured a wide range of the transmittance at 5-nm intervals via a hyperspectral camera and calculated the broad spectrum of visible transparency as “bio-transparency”.
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