Intraspecific structure within three caviar-producing sturgeons (Acipenser gueldenstaedtii, A. stellatus, and Huso huso) based on mitochondrial DNA analysis

A survey of three mitochondrial DNA regions (control region, NADH5, cytochrome b) and comprehensive sequencing of the control region (631–646 bps) was conducted to examine whether subspecies and geographic populations within three species of Eurasian sturgeons, Acipenser gueldenstaedtii, A. stellatus, and Huso huso, are genetically distinct. Neither subspecies nor populations exhibited diagnostic distinction or reciprocal monophyly in any gene region examined. For the control region, molecular variance analyses (amova ) indicate that most of the variance is because of differences among haplotypes within subspecies (H. huso: 99.6%; A. stellatus: 95.0%; A. gueldenstaedtii: 81.0%) and populations (A. gueldenstaedtii: 76.1%). Significant pairwise F‐values were found for all pairwise comparisons except for Sea of Azov and Caspian Sea A. gueldenstaedtii and Caspian Sea and Black Sea A. stellatus and H. huso. Only weak genetic differentiation is apparent between select subspecies and populations, reflective of biogeographic and management history. High genetic diversity within A. gueldenstaedtii suggests the possibility of additional population structure. Future research and management projects should consider these results.     

Molecular phylogeny of Acipenserinae and black caviar species identification.

The first phylogenetic tree for the Acipenserinae based on the combined sequence data for fragments of three mitochondrial genes, the cytochrome b (650 bp) gene, 12S (150 bp) and 16S (350 bp) rRNA genes is described. Three general conclusions are inferred from the tree: 1) Scaphirhynchus albus is the sister-species of all Acipenser and Huso species; 2) The two species of Huso are embedded within the genus Acipenser. Therefore, the genus Huso is not a separate taxonomic unit; and 3) There are three main clades within Acipenser: (a) A. sturio-A. oxyrinchus, (b) A. schrenckii-A. transmontanus, and (c) all Ponto-Caspian species plus A. dabryanus and A. brevirostrum. A method based on the identification of diagnostic nucleotide positions in the cytochrome b gene was developed and used to survey the United States and European caviar markets. The survey of 95 lots of caviar obtained at the American market suggests that in December 1995 and April 1996 17% of the designations made by caviar suppliers were mislabeled with respect to species identification. In December of 1996, this figure jumped to 32%. The main commercially harvested species (Huso huso, A. stellatus, A. gueldenstaedtii, A. schrenckii, and H. dauricus), as well as A. nudiventris, A. persicus, and A. baerii are threatened due to the increased demand of the international caviar market.     

On the karyotypes of the Neorhabdocoela species and karyological evolution of Turbellaria

The karyotypes of 10 species belonging to the Neorhabdocoela order (Turbellaria) are described: Proxenetes flabelliger, 2n=6 (Trigonostomidae), Promesostoma rostratum, 2n=12 (Promesostomatidae), Castrada sp., 2n=6, Rhynchomesostoma rostratum, 2n=6, Bothromesostoma esseni, 2n=10, Mesostoma lingua, 2n=8 (Typhloplanidae), Provortex karlingi, 2n=8 (Provorticidae), Halamovortex macropharynx, 2n=16 (Dalyellidae), Macrorhynchus crocea, 2n=16, and Gyratrix hermaphroditus, 2n=4 (Polycystidae). It is proposed that the karyotypes of the ancestral marine neorhabdocoel forms, as well as those of the other groups of turbellarians, must have consisted of 16–20 biarmed chromosomes. The processes of adaptation and speciation in each group seem to be accompanied by a gradual decrease in chromosome number to 2n=8–4, this being due to Robertsonian fusions and translocations. In some freshwater turbellarians the diploid number increased by polyploidisation. The same processes evidently took place in different groups of parasitic worms.     

On the karyology of trematodes of the genus Microphallus and their intermediate gastropod host,Littorina saxatilis II. Karyological study of Littorina saxatilis (Gastropoda: Prosobranchia)

The karyotypes of Littorina saxatilis Olivi specimens from exposed areas of the Yarnyshnaya inlet littoral (the Kola Peninsular, USSR) consist of 34 chromosomes, i.e. 10 pairs of meta- and submetacentrics and 7 pairs of subtelo- and telocentrics. Two pairs of bi-armed homologues are much bigger than the others. On the whole these karyotypes are similar to those of the individuals from the Swedish and English populations.     

Polyphyly of mtDNA lineages in the Russian sturgeon, Acipenser gueldenstaedtii: forensic and evolutionary implications

Molecular species identification methods are an important component of CITES monitoring programs for trade in sturgeon and caviar. To date, obtaining molecular evidence for distinguishing caviar from four closely related Eurasian sturgeon species Acipenser baerii (Siberian sturgeon), A. gueldenstaedtii (osetra), A. persicus (Persian sturgeon), A. naccarii (Italian sturgeon) remains problematic. Using approximately 2.3 kb of mtDNA sequence data (cytochrome b, NADH5, control region), we find this to be attributable to the polyphyletic nature of these mitochondrial DNA markers in the Russian sturgeon, A. gueldenstaedtii. Two mitochondrial lineages are present within this species: one is phylogenetically affiliated with A. persicus and A. naccarii, while the other clusters with A. baerii. These findings have a direct impact on molecular testing of commercial caviar and demonstrate the necessity of using large sample sizes when constructing forensic databases. Furthermore, the results affect current taxonomic designations for these species as well as hypotheses concerning their evolutionary origins.     

Tetraploid-octoploid relationships and karyological evolution in the order Acipenseriformes (Pisces) karyotypes,nucleoli, and nucleolus-organizer regions in four acipenserid species

The karyotypes of four Acipenseriformes species, Acipenser gueldenstaedti, 2n=250±8, A. ruthenus, A. stellatus and Huso huso, 2n=118±2, are described. In all four karyotypes the majority of chromosomes are meta- and submetacentric macrochromosomes, and microchromosomes of different morphology make up about one third of the set. In A. ruthenus the NORs are located in the telomeric region of a pair of microchromosomes and at least in one pair of middle-size acrocentrics, and in A. stellatus and Huso huso also in the telomeric regions of at least one pair of microchromosomes. The modal number of active nucleoli in A. gueldenstaedti nuclei amounts to 6–8 (range 2–12), in A. ruthenus, A. stellatus and H. huso nuclei to 2–3 (range 1–6). The data obtained point to the tetraploid origin of Acipenseriformes species with 120 chromosomes and to the octoploid origin of species with 240–260 chromosomes.     

5S rRNA sequences of 12 species of flatworms: implications for the phylogeny of the Platyhelminthes

5S rRNAs from 12 species of free living and parasitic platyhelminthes were sequenced. In the phylogenetic analysis, attention was focused on the statistical estimates of the trees corresponding to existing phylogenetic hypotheses. The available 5S rRNA data agree well with widely accepted views on the relationships between the Acoela, Polycladida, Tricladida, and Neorhabdocoela; our analysis of the published 18S rRNA sequences also demonstrated good correspondence between these views and molecular data. With available 5S rRNA data the hypothesis that the dalyellioid turbellarians is the sister group of the Neodermata is less convincing than the hypotheses proposing the Neodermata as the sister group of the Neorhabdocoela, or of the Seriata, or of the branch uniting them. A relatively low rate of base replacement in parasitic flatworms, probably, accounts for the uncertain position of the Neodermata, while a relatively high rate in planarians may explain a relatively too early divergence of the Tricladida in several published phylogenetic trees constructed from various rRNA data.     

Identifying families with likely genetic protective factors against Alzheimer disease

Elderly individuals who lived beyond the age of 90 years without dementia were hypothesized to have increased concentrations of genetic protective factors against Alzheimer disease (AD), conferring a reduced liability for this disease relative to less-aged nondemented elderly. However, testing this hypothesis is complicated by having to distinguish such a group from those who may lack genetic risk factors for AD, have had protective environmental exposures, or have escaped dementia for other reasons. Probands carrying genetic protective factors, however, should have relatives with lower illness rates not only for earlier-onset disease, when genetic risk factors are a strong contributing factor to the incidence of AD, but also for later-onset disease, when the role of these factors appears to be markedly diminished. AD dementia was assessed through family informants in 6,660 first-degree relatives of 1,049 nondemented probands aged 60-102 years. The probands were grouped by age (60-74, 75-89, and 90-102 years), and the cumulative survival from AD and 10-year-age-interval hazard rates of AD were calculated in their first-degree relatives. Cumulative survival from AD was significantly greater in the relatives of the oldest proband group (aged 90-102 years) than it was in the two younger groups. In addition, the reduction in the rate of illness for this group was relatively constant across the entire late life span. The results suggest that genetic factors conferring a lifelong reduced liability of AD may be more highly concentrated among nondemented probands aged >/=90 years and their relatives. Efforts to identify protective allele-bearing genes that are associated with very late-onset AD should target the families of nonagenarians and centenarians.