| Budget Amount *help |
¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 1991: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1990: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
1. Four different types of the sea-urchin, Echinometra mathaei which are distinguishable by several characters such as color pattern of spines are observed abundantly on Okinawa, southern Japan. Their taxonomic and evolutionary relationships were examined by enzyme electrophoresis. The allozyme studies demonstrated that the four types of sea-urchins designated as Types A, B, C and D do not share gene pools with each other in spite of their sympatric distribution. They were fixed for different alleles at 7 genetic loci in a total of 28 genetic loci scored. This clearly shows no gene flow between the four types, and is a strong evidence for that they are reproductively isolated and genetically distinct species. The Nei's genetic distances between the four types were significantly higher than those between conspecific local populations, and comparable to those between closely related species in many other animal groups. We therefore proposed that these four types of sea-urchins should be
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classified as distinct and separate species of the genus Echinometra. The molecular phylogenetic tree constructed from the Nei's genetic distances revealed the close affinities between Types A and C and between Types B and D. Further, the molecular dendrogram suggested that the four types speciated in relatively recent geological age of the middle Pleistocene.
2. As a preliminary study to elucidate the evolutionary origin of the sea-urchins of the order Echinoida, enzyme polymorphism and genetic relationship were investigated in two sea-urchin species, Glyptocidaris crenularis and Stomopneustes variolaris belonging to the order Arbacioida by enzyme electrophoresis. The degree of genetic variation was comparable to that observed in many other echinoderms from shallow water, but was considerable lower than that from deep-sea water. The Nei's genetic distance between the two species of the different families was 1.417, and comparable to the D values between closely related families of the order Echinoida. This suggested that the two species have the more recent evolutionary origin.
3. The phylogenetic relationships among four classes of echinoderms(Asteroidea, Echinoidea, Ophiuroidea and Holothuroidea)have been much disputed among many zoologists and remain unclear. In order to elucidate the phylogenetic relationships, the kinetic properties of glucose-6-phosphate dehydrogenases(G6PDs)purified from four echinoderm groups were compared with each other and the kinetic similarities between the enzymes were estimated. The biochemical dendrogram for four echinoderm groups constructed from the kinetic similarities demonstrated the followings : Asteroid and holothurian are the most closely related to each other and more recent groups. Opiuroid is more closely related to the cluster consisted of asteroid and holothurian than echinoid. Echinoid is the most distant group of the four echinoderms and ancestral form. The biochemical results were consistent with embryological and other biochemical evidence. The evolutionary process of echinoderms was speculated from the biochemical dendrogram and non"molecular data. Less
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