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  • 1
    Electronic Resource
    Electronic Resource
    Genetic population structure of a species' complex of blue mussels (Mytilus spp.) (1993)
    Springer
    Marine biology 117 (1993), S. 105-112 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Blue mussels representing two nominal species (Mytilus trossulus Gould, 1850 and Mytilus galloprovincialis Lamarck, 1819 were collected from 28 intertidal locations along the Pacific coast of the USA in 1990–1991 (total N=1255) and examined for variation at 15 allozyme loci. Twelve samples, mostly from a region of suspected hybridization, were analyzed for variation in seven shell characters. Principal-components analysis of allozyme data revealed three groups based on first principal-component scores, which were identified as M. trossulus, M. galloprovincialis, and hybrids. Canonical discriminant analysis of shell characters was less successful in separating mussels into discrete groups. Each location was characterized for four environmental variables: (1) temperature, (2) salinity, (3) tidal height and (4) degree of exposure to wave action, which were then used as independent variables in a series of multiple-regression analyses, with the proportions of the two species as dependent variables. Temperature and salinity had significant (P〈0.05) effects on the macrogeographic distribution of the two species, whereas the effects of height in the tidal zone and degree of wave exposure were not statistically significant. Salinity was found to have a greater influence than temperature on the microgeographic distribution of the two species. M. trossulus was more abundant at locations with lower temperatures and greater salinity variation than M. galloprovincialis. The two species appear to be ecologically distinct, and their genetic integrity is at least partly the result of environmental heterogeneity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346431
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  • 2
    Electronic Resource
    Electronic Resource
    Genetic population structure of the southern oyster drillStramonita (=Thais)haemostoma (1991)
    Springer
    Marine biology 111 (1991), S. 71-79 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nine collections in the southeastern USA of the thaidid molluscStramonita haemastoma, comprising 963 individuals, were made between June 1988 and November 1989, and examined for allozyme variation at 18 electrophoretically-detected loci. Two genetically-differentiated groups were identified and are referred to ascanaliculata-like andfloridana-like snails, based on previously-described subspecies ofS. haemastoma. The two groups were differentiated genetically at a level that is characteristic of congeneric species in other molluscan taxa. The two groups maintained their genetic differences in areas of sympatry, although rare hybrid individuals occurred (about 1.2% of the total set). Shell and radular characters showed little variation within or between the two groups. Within each group, allozyme allele frequencies showed little geographic variation across distances as great as 1 500 km. This result is consistent with the suggestion that species with planktonic larvae (such asS. haemastoma) should have higher rates of gene flow than related brooding species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01986348
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  • 3
    Electronic Resource
    Electronic Resource
    Are meiofaunal species cosmopolitan? Morphological and molecular analysis of Xenotrichula intermedia (Gastrotricha: Chaetonotida) (1996)
    Springer
    Marine biology 125 (1996), S. 735-742 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many meiofaunal species are reported to be cosmopolitan, but due to uncertainties of identification, the affiliation of specimens from geographically distant areas to the same species-taxon is problematic. In this study, we examined morphological and molecular variation in samples of Xenotrichula intermedia Remane (Gastrotricha: Chaetonotida) from the Mediterranean Sea, the northwestern Atlantic and the northern Gulf of Mexico. Univariate analysis of 16 morphological traits was unable to detect differences among populations, except for the length of the pharynx, which was significantly shorter in the Gulf of Mexico specimens. Canonical discriminant analysis separated the Gulf of Mexico specimens from the other two populations, with pharynx length contributing about half of the total discrimination. Molecular analysis based on restriction-fragment length polymorphisms (RFLPs) in a 710-base pair polymerase chain-reaction (PCR) produet representing roughly half of the mitochondrial cytochrome oxidase I (COI) gene detected four haplotypes: one each from the Mediterranean and the Gulf of Mexico populations and two coexisting within the Atlantic population. The estimated nucleotide-sequence divergence calculated for each pairwise combination of haplotypes (based on the proportion of shared fragments) ranged from 5.3 to 11.5%. The high genetic divergence and the inability to clearly separate populations based on morphology suggest that individuals characterized by different haplotypes are genetically isolated sibling species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349256
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  • 4
    Electronic Resource
    Electronic Resource
    Mitochondrial DNA polymorphisms reveal additional genetic heterogeneity within the Leptasterias hexactis (Echinodermata: Asteroidea) species complex (1996)
    Springer
    Marine biology 125 (1996), S. 569-578 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sea stars of the Leptasterias hexactis complex are important members of the rocky intertidal community of the temperate and subarctic North American Pacific coasts. Recent attempts to determine the genetic structure and taxonomic relationships of these sea stars have not been completely successful, due to the combination of extreme morphological variability and relative scarcity of taxonomically-informative genetic (allozyme) polymorphisms. The present study used mitochondrial DNA restriction-site polymorphisms for PCR (polymerase chain-reaction)-amplified products to provide additional information about this complex. Five restriction-site haplotypes were identified in southern Alaska and in the Puget Sound region that were allozymically distinct. Because the allozymic differences (Nei's unbiased genetic differences 〉0.08) are maintained in sympatry, the haplotypes behave evolutionarily as conventional species. Although most haplotypes show deficiencies of heterozygotes for polymorphic allozyme loci, there is no evidence for the existence of cryptic species within any of the haplotypes. Rather than consisting of a few polytypic and cosmopolitan species, the L. hexactis complex is apparently composed of numerous species with more restricted ranges. Determining the exact ranges and taxonomic relationships of the various species will require additional study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00353269
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  • 5
    Electronic Resource
    Electronic Resource
    Population genetics and systematics of theLeptasterias hexactis (Echinodermata: Asteroidea) species complex (1990)
    Springer
    Marine biology 105 (1990), S. 477-489 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Morphological characters and 14 enzyme loci were examined for 1 040 sea stars, currently recognized as forms ofLeptasterias hexactis, from Lynn Canal, Alaska, and Puget Sound, Washington, USA, between March 1988 and April 1989. Three morphologically and two genetically distinctLeptasterias forms were identified. The most common form found at both localities wasL. epichlora (Brandt)sensu Verrill.L. hexactis (Stimpson)sensu Verrill co-occurred withL. epichlora at all study sites and apparently hybridizes extensively withL. epichlora in the Puget Sound region, but rarely, if at all, in Alaska. The presumptive product of this hybridization morphologically resembledL. aequalis (Stimpson)sensu Fisher, and was conspicuously absent from Alaskan samples. Considerable genetic distance existed betweenL. epichlora andL. hexactis (Nei'sD=0.19±0.01) and moderate genetic differentiation occurred between populations of each species from Alaska and Washington (Weir and Cockerham'sF RT =0.29±0.04 forL. epichlora and 0.21±0.15 forL. hexactis). A significant (p〈0.05) deficiency in the proportion of heterozygous individuals was found compared to Hardy-Weinberg expectations (Wright's fixation index,F ID=0.12±0.04 and 0.31±0.08 forL. epichlora andL. hexactis, respectively). However, mean observed heterozygosity for each species (0.09±0.03, 0.14±0.04 and 0.14±0.04 forL. epichlora, L. hexactis andL. aequalis, respectively) fell within the range of reported values for other asteroid species (ca. 0.04 to 0.37). The results of this study indicate that considerable genetic integrity is maintained betweenL. epichlora andL. hexactis, which warrants their recognition as distinct species despite their apparent hybridization in the Puget Sound region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01316319
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  • 6
    Electronic Resource
    Electronic Resource
    Genetics and taxonomy of ribbed mussels (Geukensia spp.) (1992)
    Springer
    Marine biology 113 (1992), S. 385-390 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ribbed mussels (232 in all) representing the nominal species Geukensia demissa (Dillwyn, 1817) were collected at nine coastal North American locations (two Pacific, four Atlantic and three Gulf Coast locations) between January 1990 and September 1991, and examined for nine shell characters and for variation at 18 allozyme loci. Two genetically-differentiated groups were identified and called demissa-type and granosissima-type mussles, based on similarity of geographic range to previously recognized subspecies of G. demissa. There was very little genetic differentiation of populations over moderate to large (3000 km) distances along the Atlantic coast (for demissa-type mussels), along the Gulf Coast (for granosissima-type mussels), or between Pacific and Atlantic populations of demissa-type mussles. The two types of mussels were differentiated genetically (Nei's unbiased genetic distance =0.55±0.20) at a level characteristic of separate species in other molluscan taxa, and to a lesser extent were differentiated morphologically. We recommend that the two types of mussels be treated as separate species within the genus Geukensia: G. demissa (Dillwyn, 1817) and G. granosissima (Sowerby, 1914).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349163
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  • 7
    Electronic Resource
    Electronic Resource
    Apparent overdominance of enzyme specific activity in two marine bivalves (1992)
    Springer
    Genetica 85 (1992), S. 231-239 
    Details
    ISSN: 1573-6857
    Keywords: Allozymes ; bivalves ; enzyme activity ; overdominance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Electrophoretic examination of a natural population sample of 332 mussels (Mytilus trossulus) revealed ten active allozyme alleles for the octopine dehydrogenase (Odh) locus and a statistically significant (P〈0.005) departure from expected genotypic proportions caused by a deficiency of heterozygous genotypes. In vitro specific activity for octopine dehydrogenase (E.C. 1.5.1.11) was determined for 207 mussels representing 17 different Odh genotypes. Odh heterozygotes had an average specific activity that was 19% greater than that of apparently homozygous genotypes, a significant (P〈0.05) difference. Electrophoretic examination of a natural population sample of 209 oysters (Crassostrea virginica) revealed 23 active allozyme alleles for the leucine aminopeptidase-2 (Lap-2) locus and a non-significant (P〉0.05) deficiency of heterozygous genotypes. In vitro specific activity for leucine aminopeptidase (E.C. 3.4.-.-) was determined for 89 oysters representing 19 different Lap-2 genotypes. Lap-2 heterozygotes had an average specific activity that was 56% greater than that of homozygous genotypes, a significant (P〈0.0001) difference. Possible explanations for the apparent overdominance in enzyme specific activity and the deficiency of heterozygotes include null alleles, molecular imprinting and aneuploidy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00132275
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  • 8
    Electronic Resource
    Electronic Resource
    Minimal selection requirements for the correlation between heterozygosity and growth, and for the deficiency of heterozygotes, in oyster populationBased on a lecture delivered in September 1983, at the International Conference in Biochemical and Developmental Genetics, Kos, Greece. (1983)
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 4 (1983), S. 393-405 
    Details
    ISSN: 0192-253X
    Keywords: marine molluscs ; heterozygosity ; growth ; selection models ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We examine several models that may account for the observation that in populations of marine molluscs in general, and of the American oyster (Crassostrea virginica) in particular, the growth of an individual is related to its degree of heterozygosity and, also, that the number of heterozygous individuals in the population is less than expected on the assumption of random mating and no selection. We classify these models into nonselective, selective, and mixed models. We conclude that mixed models are the most likely to apply to real populations, but cannot exclude selective models. Nonselective models appear least likely. Current evidence favors a model that assumes that heterozygotes enjoy a fitness advantage as adults, primarily because of their faster growth, and that the lower numbers of heterozygotes in the population result from some form of nonrandom fertilization. One possible source of nonrandom fertilization is variation in the time of spawning of individuals due to differences in body size.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/dvg.1020040413
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  • 9
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    Apparent overdominance of enzyme specific activity in two marine bivalves (1992)
    Springer
    Details
    Publication Date: 1992-01-01
    Print ISSN: 0016-6707
    Electronic ISSN: 1573-6857
    Topics: Biology
    Published by Springer
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  • 10
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    Genetics and taxonomy of ribbed mussels (Geukensia spp.) (1992)
    Springer
    Details
    Publication Date: 1992-07-01
    Print ISSN: 0025-3162
    Electronic ISSN: 1432-1793
    Topics: Biology
    Published by Springer
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