Biological Diversity in Rare Aquatic Organisms
School of Marine Science and Technology, Tokai University
Biological diversity is the most practical and direct measure of the state of conservation of nature. Diversity can be defined at the gene, Species and ecosystem level. Diversity at the gene and species level can be measured by various genetic values, such as nucleon diversity and nucleotide diversity, calculated from the data obtained by DNA analysis. Data on genetic variability of the whole region of mitochondrial DNA (mtDNA) in a variety of aquatic organisms, such as marine crustaceans, fresh water and marine fish, and aquatic mammals, which were obtained by analysis of restriction length polymorphisms (RFLPs), are reported in the terms of the nucleon diversity and nucleotide diversity. Higher variability was observed in the D-loop region than the whole region of mtDNA. Of an amphidromous fish, the Ayu Plecoglossus altivelis, strategy for the maintenance of genetic variability,and lack of this strategy in the Ryukyu-ayu P. a. ryukyuensis, which resulted in population size, variability and distribution range are proposed. A remarkable loss of mtDNA variability was demonstrated in artificially breeding populations of the Ayu fish. The loss of genetic variability correlated with the number of female parents used for propagation in the respective strains, and proceeded more slowly at allozyme loci than mtDNA, as expected. The genetic variability observed was very same level throughout various aquatic invertebrates to vertebrates including mammals. However, monomorphisms were demonstrated in endangered fish species, such as the Cyprinid, Pseudprasbora pumila subsp. and the Formosan landlocked salmon Oncorynchus masou formusanus. A two step assessment is proposed, in which mtDNA variability using a very small amount of tissue obtained by such as fin clipping at the first step, followed by allozyme or nuclear DNA analysis at the 2nd step. A instance of low genetic variability caused by the founder effect in the Baikal seal Pusa sibilica, and low genetic variability probably attributed to a decrease in population size in the ringed seal P. hispida from the White sea are presented.