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Author

S. Wada

Bio: S. Wada is an academic researcher. The author has contributed to research in topics: Balaenoptera. The author has an hindex of 1, co-authored 1 publications receiving 52 citations.
Topics: Balaenoptera

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Journal ArticleDOI
TL;DR: It is demonstrated that population bottlenecks cause a characteristic mode-shift distortion in the distribution of allele frequencies at selectively neutral loci, and a qualitative graphical method is illustrated and evaluated for detecting a bottleneck-induced distortion of allele frequency distributions.
Abstract: We use population genetics theory and computer simulations to demonstrate that population bottlenecks cause a characteristic mode-shift distortion in the distribution of allele frequencies at selectively neutral loci. Bottlenecks cause alleles at low frequency ( .80) to detect an allele frequency distortion after a bottleneck of < or = 20 breeding individuals when 8 to 10 polymorphic microsatellite loci are analyzed.

1,451 citations

Journal ArticleDOI
TL;DR: A statistical test (a sign test for heterozygosity excess) for detecting recent historical bottlenecks using allele frequency data (Cornuet & Luikart 1996) is developed and evaluated by analyzing 56 allozyme and 37 microsatellite data sets from bottlenecked and nonbottlenecked natural populations.
Abstract: Identifying recently bottlenecked populations (populations severely reduced in size) is important because bottlenecks can increase demographic stochasticity, rate of inbreeding, loss of genetic variation, and fixation of deleterious alleles and, thereby, reduce adaptive potential and increase the probability of population extinction (Frankel & Soulé 1981; Lande 1988, 1994; Leberg 1990; Hedrick & Miller 1992; Mills & Smouse 1994; Frankham 1995 a , 1995 b ; but see Bryant et al. 1986; Goodnight 1987). Unfortunately, it is usually difficult to determine if a population has recently experienced a bottleneck because historical population sizes and levels of genetic variation are seldom known. We developed a statistical test (a sign test for heterozygosity excess) for detecting recent historical bottlenecks using allele frequency data (Cornuet & Luikart 1996). The test requires no data on historical population sizes or levels of genetic variation; it requires only measurements of allele frequencies from 5 to 20 polymorphic loci in a sample of approximately 20-30 individuals. The test has reasonable statistical power when applied to allele frequency data sets generated by computer simulations (Cornuet & Luikart 1996). The performance of the test, however, must be evaluated by means of empirical data from natural populations before it can be used with confidence. Our objectives were to (1) explain to conservation biologists the principle of the sign test for detecting heterozygosity excess and (2) evaluate the reliability of the test by analyzing 56 allozyme and 37 microsatellite data sets from bottlenecked and nonbottlenecked natural populations.

1,093 citations

Journal ArticleDOI
TL;DR: This study examines the evolutionary pattern of the different functional mtDNA regions as accurately as possible on the grounds of available data, revealing some important ``genomic laws.
Abstract: We present here for the first time a comprehensive study based on the analysis of closely related organisms to provide an accurate determination of the nucleotide substitution rate in mammalian mitochondrial genomes. This study examines the evolutionary pattern of the different functional mtDNA regions as accurately as possible on the grounds of available data, revealing some important ``genomic laws.'' The main conclusions can be summarized as follows. (1) High intragenomic variability in the evolutionary dynamic of mtDNA was found. The substitution rate is strongly dependent on the region considered, and slow- and fast-evolving regions can be identified. Nonsynonymous sites, the D-loop central domain, and tRNA and rRNA genes evolve much more slowly than synonymous sites and the two peripheral D-loop region domains. The synonymous rate is fairly uniform over the genome, whereas the rate of nonsynonymous sites depends on functional constraints and therefore differs considerably between genes. (2) The commonly accepted statement that mtDNA evolves more rapidly than nuclear DNA is valid only for some regions, thus it should be referred to specific mitochondrial components. In particular, nonsynonymous sites show comparable rates in mitochondrial and nuclear genes; synonymous sites and small rRNA evolve about 20 times more rapidly and tRNAs about 100 times more rapidly in mitochondria than in their nuclear counterpart. (3) A species-specific evolution is particularly evident in the D-loop region. As the divergence times of the organism pairs under consideration are known with sufficient accuracy, absolute nucleotide substitution rates are also provided.

450 citations

Journal ArticleDOI
TL;DR: Current data suggest that, of the various threats potentially affecting baleen whales, only entanglement in fishing gear and ship strikes may be significant at the population level, and then only in those populations which are already at critically low abundance.
Abstract: Most species of baleen whales were subject to intensive overexploitation by commercial whaling in this and previous centuries, and many populations were reduced to small fractions of their original sizes. Here, we review the status of baleen whale stocks, with an emphasis on those that are known or thought to be critically endangered. Current data suggest that, of the various threats potentially affecting baleen whales, only entanglement in fishing gear and ship strikes may be significant at the population level, and then only in those populations which are already at critically low abundance. The impact of some problems (vessel harassment, and commercial or aboriginal whaling) is at present probably minor. For others (contaminants, habitat degradation, disease), existing data either indicate no immediate cause for concern, or are insufficient to permit an assessment. While the prospect for many baleen whales appears good, there are notable exceptions; populations that are of greatest concern are those suffering from low abundance and associated problems, including (in some cases) anthropogenic mortality. These include: all Northern Right Whales Eubalaena glacialis, Bowhead Whales Balaena mysticetus of the Okhotsk Sea and various eastern Arctic populations, western Gray Whales Eschrichtius robustus, and probably many Blue Whale Balaenoptera musculus populations. We review the status of these populations and, where known, the issues potentially affecting their recovery. Although Humpback Whales Megaptera novaeangliae and Southern Right Whales Eubalaena australis were also heavily exploited by whaling, existing data indicate strong recovery in most studied populations of these species.

381 citations

Journal ArticleDOI
TL;DR: Genetic studies have revealed that species defined by morphological characters are complexes of cryptic or sibling species, which is consistent with the diversity and distribution of marine and terrestrial taxa having been strongly influenced by geological and climatic cooling events over the last 70 years.
Abstract: The Antarctic biota is highly endemic, and the diversity and abundance of taxonomic groups differ from elsewhere in the world. Such characteristics have resulted from evolution in isolation in an increasingly extreme environment over the last 100 Myr. Studies on Antarctic species represent some of the best examples of natural selection at the molecular, structural and physiological levels. Analyses of molecular genetics data are consistent with the diversity and distribution of marine and terrestrial taxa having been strongly influenced by geological and climatic cooling events over the last 70 Myr. Such events have resulted in vicariance driven by continental drift and thermal isolation of the Antarctic, and in pulses of species range contraction into refugia and subsequent expansion and secondary contact of genetically distinct populations or sister species during cycles of glaciation. Limited habitat availability has played a major role in structuring populations of species both in the past and in the present day. For these reasons, despite the apparent simplicity or homogeneity of Antarctic terrestrial and marine environments, populations of species are often geographically structured into genetically distinct lineages. In some cases, genetic studies have revealed that species defined by morphological characters are complexes of cryptic or sibling species. Climate change will cause changes in the distribution of many Antarctic and sub-Antarctic species through affecting population-level processes such as life history and dispersal.

199 citations