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Taehwan Lee - One of the best experts on this subject based on the ideXlab platform.

  • pronounced karyological divergence of the north american congeners Sphaerium rhomboideum and s occidentale bivalvia veneroida sphaeriidae
    Journal of Molluscan Studies, 2007
    Co-Authors: Romualda Petkeviciūtė, Taehwan Lee, Virmantas Stunžėnas, Gražina Staneviciūtė, Diarmaid Ó Foighil
    Abstract:

    Chromosome sets of two North American sphaeriid species, Sphaerium rhomboideum Say, 1822 and S. occidentale Lewis, 1856, were studied using conventional Giemsa staining and karyometric analysis. Pronounced karyological divergence of congeners was revealed. The diploid number of 2n ¼ 44 was reported for S. rhomboideum and this is the first record of a diploid species in the highly polychromosomic Nearctic sphaeriid fauna. The karyotype was characterized by medium-sized and small chromosomes, which decreased in size gradually from 5.77 to 1.9 mm. Biarmed chromosomes with medially and submedially located centromeres predominated, but six pairs of subtelo-telocentric elements were also observed in the karyotype. The estimated mitotic chromosome number for S. occidentale ranges from 189 to 213, but most of the cells examined contained about 204– 209 chromosomes. A first attempt to karyotype a polyploid sphaeriid was made. It was revealed that the comparatively large and middle-sized chromosomes could be grouped in four, so the karyotype presumably evolved through tetraploidization. The small chromosomes formed the large fraction, about 137. Due to their similar and indistinct morphologies, it was impossible to arrange them into subgroups with confidence. Revealed karyological characteristics are discussed with reference to the existing phylogenetic interpretations of the evolutionary history of the Sphaeriinae.

  • Phylogenetic structure of the Sphaeriinae, a global clade of freshwater bivalve molluscs, inferred from nuclear (ITS-1) and mitochondrial (16S) ribosomal gene sequences
    Zoological Journal of the Linnean Society, 2003
    Co-Authors: Taehwan Lee, Diarmaid Ó Foighil
    Abstract:

    The Sphaeriidae represent one of the primary molluscan radiations into freshwater environments. We have reconstructed phylogenetic relationships of the Sphaeriinae, a cosmopolitan sphaeriid subfamily, using variation in nuclear ribosomal first internal transcribed spacer (ITS-1) and mitochondrial large ribosomal subunit (16S) gene fragments. A total of 38 New World, Eurasian and Antipodean taxa were characterized, including all primary taxonomic groupings except for Neopisidium, and members of the sister clade Euperinae were employed as outgroups. Phylogenetic analyses of individual and combined (16S + ITS1) datasets all recovered a paraphyletic Pisidium and a derived clade of asynchronous brooding Sphaerium/Musculium taxa. Maximum parsimony as well as maximum likelihood analyses of combined data yielded largely congruent and well-resolved topologies, and robustly supported clades were utilized to revise current sphaeriine taxonomy. Instead of the traditionally accepted three cosmopolitan genera, Pisidium s.l., Musculium, and Sphaerium, five major monophyletic lineages, Afropisidium, Odhneripisidium, Pisidium, Cyclocalyx and Sphaerium, were recognized at the generic level. In addition, a number of subgeneric level groups were recovered in Sphaerium: Herringtonium, Sphaerium s.s., Sphaerinova, Amesoda, and Musculium, together with one unassigned species, S. transversum.

  • 6 phosphogluconate dehydrogenase pgd allele phylogeny is incongruent with a recent origin of polyploidization in some north american sphaeriidae mollusca bivalvia
    Molecular Phylogenetics and Evolution, 2002
    Co-Authors: Taehwan Lee, Diarmaid Ó Foighil
    Abstract:

    Although polyploidization is rare among bivalve mollusks, recent cytogenetic studies have revealed a remarkable degree of genome amplification (up to 13n) in the freshwater bivalve family Sphaeriidae. We generated single-copy nuclear gene trees in order to test hypotheses addressing the evolutionary origins of sphaeriid genome duplication. Polyploid North American members of three cosmopolitan sphaeriid genera (Sphaerium, Musculium, and Pisidium) were characterized for their expressed allelic repertoire of a 526 nt c-DNA fragment of 6-phosphogluconate dehydrogenase (PGD). Pronounced levels of intra-individual genetic variation were uncovered in most of the polyploid taxa and a minority of alleles showed strong evidence of recombination. Phylogenetic analyses resolved polyploid sphaeriid PGD alleles into two clades (A, B), each of which contained a subsample of intra-individual allelic diversity of the genus Sphaerium. These two clades were also recovered in Musculium, however one (B) is represented here by a single recombinant allele. With the exception of a divergent segment in one putatively recombinant allele, the expressed PGD repertoire of the three Pisidium species investigated was restricted to one of the two clades (A). Major within-clade PGD gene tree branching patterns were congruent with mitochondrial gene tree topologies for these taxa. These results are inconsistent with a pattern of recent independent attainment of a polyploid status by our Sphaerium/Musculium study taxa and indicate that they may share a common genome duplication event predating the Miocene appearance of these two genera in the fossil record.

  • polyploidy and meiosis in the freshwater clam Sphaerium striatinum lamarck and chromosome numbers in the sphaeriidae bivalvia veneroida
    Cytologia, 1999
    Co-Authors: Taehwan Lee
    Abstract:

    Spermatogenetic meiosis as well as a very large number of chromosomes (n=76, 2n=ca. 152) were observed in a North American freshwater clam, Sphaerium striatinum. Sphaeriid species studied to date, except for one species, are all polyploids having high mitotic chromosome numbers, which range from ca. 150 to ca. 247. These results indicate that pronounced polyploidization may have played a major role in the evolution of the Sphaeriidae.This study also suggests that the basic chromosome number of the sphaeriid polyploids may be 19 and that a very significant variation in ploidy levels (2n to 13n) occur in the Sphaeriidae. Even though meiosis has been observed in a polyploid species, S. striatinum, and in the diploid S. corneum (n=18, 2n=36), it is not clear whether or not polyploidy in any of the other sphaeriid species is associated with asexuality.

Gražina Staneviciūtė - One of the best experts on this subject based on the ideXlab platform.

Diarmaid Ó Foighil - One of the best experts on this subject based on the ideXlab platform.

  • pronounced karyological divergence of the north american congeners Sphaerium rhomboideum and s occidentale bivalvia veneroida sphaeriidae
    Journal of Molluscan Studies, 2007
    Co-Authors: Romualda Petkeviciūtė, Taehwan Lee, Virmantas Stunžėnas, Gražina Staneviciūtė, Diarmaid Ó Foighil
    Abstract:

    Chromosome sets of two North American sphaeriid species, Sphaerium rhomboideum Say, 1822 and S. occidentale Lewis, 1856, were studied using conventional Giemsa staining and karyometric analysis. Pronounced karyological divergence of congeners was revealed. The diploid number of 2n ¼ 44 was reported for S. rhomboideum and this is the first record of a diploid species in the highly polychromosomic Nearctic sphaeriid fauna. The karyotype was characterized by medium-sized and small chromosomes, which decreased in size gradually from 5.77 to 1.9 mm. Biarmed chromosomes with medially and submedially located centromeres predominated, but six pairs of subtelo-telocentric elements were also observed in the karyotype. The estimated mitotic chromosome number for S. occidentale ranges from 189 to 213, but most of the cells examined contained about 204– 209 chromosomes. A first attempt to karyotype a polyploid sphaeriid was made. It was revealed that the comparatively large and middle-sized chromosomes could be grouped in four, so the karyotype presumably evolved through tetraploidization. The small chromosomes formed the large fraction, about 137. Due to their similar and indistinct morphologies, it was impossible to arrange them into subgroups with confidence. Revealed karyological characteristics are discussed with reference to the existing phylogenetic interpretations of the evolutionary history of the Sphaeriinae.

  • Phylogenetic structure of the Sphaeriinae, a global clade of freshwater bivalve molluscs, inferred from nuclear (ITS-1) and mitochondrial (16S) ribosomal gene sequences
    Zoological Journal of the Linnean Society, 2003
    Co-Authors: Taehwan Lee, Diarmaid Ó Foighil
    Abstract:

    The Sphaeriidae represent one of the primary molluscan radiations into freshwater environments. We have reconstructed phylogenetic relationships of the Sphaeriinae, a cosmopolitan sphaeriid subfamily, using variation in nuclear ribosomal first internal transcribed spacer (ITS-1) and mitochondrial large ribosomal subunit (16S) gene fragments. A total of 38 New World, Eurasian and Antipodean taxa were characterized, including all primary taxonomic groupings except for Neopisidium, and members of the sister clade Euperinae were employed as outgroups. Phylogenetic analyses of individual and combined (16S + ITS1) datasets all recovered a paraphyletic Pisidium and a derived clade of asynchronous brooding Sphaerium/Musculium taxa. Maximum parsimony as well as maximum likelihood analyses of combined data yielded largely congruent and well-resolved topologies, and robustly supported clades were utilized to revise current sphaeriine taxonomy. Instead of the traditionally accepted three cosmopolitan genera, Pisidium s.l., Musculium, and Sphaerium, five major monophyletic lineages, Afropisidium, Odhneripisidium, Pisidium, Cyclocalyx and Sphaerium, were recognized at the generic level. In addition, a number of subgeneric level groups were recovered in Sphaerium: Herringtonium, Sphaerium s.s., Sphaerinova, Amesoda, and Musculium, together with one unassigned species, S. transversum.

  • 6 phosphogluconate dehydrogenase pgd allele phylogeny is incongruent with a recent origin of polyploidization in some north american sphaeriidae mollusca bivalvia
    Molecular Phylogenetics and Evolution, 2002
    Co-Authors: Taehwan Lee, Diarmaid Ó Foighil
    Abstract:

    Although polyploidization is rare among bivalve mollusks, recent cytogenetic studies have revealed a remarkable degree of genome amplification (up to 13n) in the freshwater bivalve family Sphaeriidae. We generated single-copy nuclear gene trees in order to test hypotheses addressing the evolutionary origins of sphaeriid genome duplication. Polyploid North American members of three cosmopolitan sphaeriid genera (Sphaerium, Musculium, and Pisidium) were characterized for their expressed allelic repertoire of a 526 nt c-DNA fragment of 6-phosphogluconate dehydrogenase (PGD). Pronounced levels of intra-individual genetic variation were uncovered in most of the polyploid taxa and a minority of alleles showed strong evidence of recombination. Phylogenetic analyses resolved polyploid sphaeriid PGD alleles into two clades (A, B), each of which contained a subsample of intra-individual allelic diversity of the genus Sphaerium. These two clades were also recovered in Musculium, however one (B) is represented here by a single recombinant allele. With the exception of a divergent segment in one putatively recombinant allele, the expressed PGD repertoire of the three Pisidium species investigated was restricted to one of the two clades (A). Major within-clade PGD gene tree branching patterns were congruent with mitochondrial gene tree topologies for these taxa. These results are inconsistent with a pattern of recent independent attainment of a polyploid status by our Sphaerium/Musculium study taxa and indicate that they may share a common genome duplication event predating the Miocene appearance of these two genera in the fossil record.

Romualda Petkeviciūtė - One of the best experts on this subject based on the ideXlab platform.

Virmantas Stunžėnas - One of the best experts on this subject based on the ideXlab platform.