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  • 1
    ISSN: 1432-2242
    Keywords: Genetic diversity ; Population genetics ; Bertholletia excelsa ; Brazil nut ; Isozyme analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We provide an estimate of genetic variation within and between two populations of Bertholletia excelsa (Brazil nut), a large canopy tree found in the rain forests of South America. Average heterozygosity is 0.190, and 54.3% of the sampled loci are polymorphic. The population structure deviates significantly from Hardy-Weinberg expectations for Fest2 and Pgm2 (F =0.405 and 0.443, respectively) in one population, and highly significantly (F=-0.341) for Gdh in the other population. Although allele frequencies of the two populations differ significantly for Aat2, Est5, Mdh1, and Mdh2B, Nei's coefficient of gene differentiation (Gst) indicates that the between-population component (Dst) of genic diversity represents only 3.75% of the size of the within-population component (Hs). The implications of these findings in terms of conservation genetics are that much of the genetic diversity of this species may be preserved within one or a few populations. However, such populations must be very large because it appears that the large amount of genetic variation in Brazil nut populations is maintained by extensive gene flow and bonds of mating over a large area. The genetic architecture of Bertholletia excelsa is similar to that expected for an extensively diploidized paleopolyploid species.
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  • 2
    ISSN: 1432-2242
    Keywords: Outcrossing rate ; Bertholletia excelsa ; Brazil nut ; Isozyme analysis ; Tropical rain forest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Here we report the results of a mating system analysis of an Amazonian population of Bertholletia excelsa, a tropical rain forest canopy tree species. Using progeny data from 29 seed parents, two highly polymorphic isozymes were analyzed to derive single locus and multilocus estimates of outcrossing, based on a mixed mating model. The two single locus estimates were very similar, and both were somewhat smaller than the multilocus estimate, indicating the possibility that the populations are genetically structured. The multilocus outcrossing estimate (tm=0.85±0.03) reveals that outcrossing is prevalent, but that a significantly low level of inbreeding may be occurring. The high outcrossing rate indicates that even though dispersion of individuals is very low within populations of this tropical rain forest tree, pollen dispersal mechanisms appear to be adequate to enable crosses with a relatively large number of potential mates.
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  • 3
    ISSN: 1432-2242
    Keywords: Key words Poplars (Populus) ; Simple sequencerepeats ; Microsatellite loci ; Polymorphism ; Clone identification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We have identified, isolated, and characterized microsatellite/simple sequence repeat (SSR) loci in trembling aspen (Populus tremuloides) by screening partial genomic libraries. We have also examined the compatibility and use of the P. tremuloides SSR primers to resolve microsatellites in other Populus species. Fourteen microsatellites were identified from 1600 clones screened. The TC/AG microsatellites were the most abundant. A total of 29 alleles were detected in 36 P. tremuloides individuals at the four SSR loci (two each of di- and tri-nucleotide repeats) characterized. The number of alleles at the SSR loci ranged from 5 to 11, with an average of 7.25 alleles per locus, and the observed heterozygosity ranged from 0.19 to 0.82, with a mean of 0.46 per locus. Although the highest polymorphism was observed for a dinucleotide SSR locus, the trinucleotide SSR loci showed substantial polymorphism. There were 34 unique multilocus genotypes among the 36 P. tremuloides individuals examined, and 89% of the individuals had unique multilocus genotypes. Two pairs of SSR primers were successful in PCR, amplifying genomic DNA and resolving microsatellites of comparable size from Populus deltoides, P. nigra, P.×canadensis, and P. maximowiczii. The microsatellite DNA markers developed could be used for clonal fingerprinting, certification of controlled crosses, genome mapping, marker-assisted early selection, genetic diversity assessments, and conservation and sustainable management of poplar genetic resources.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 342 (1989), S. 625-625 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR—In asking "why do plants produce so many more ovules than seeds", Charles-worth1 and Wiens et al.2 have addressed an important issue. Wiens et al. attribute the high level of ovule abortion observed in many plants to genetic load, a factor also emphasized by Charlesworth in her ...
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  • 5
    ISSN: 1615-6110
    Keywords: Angiosperms ; Leguminosae ; Caesalpinioideae ; Bauhinia ungulata. — Fruit production ; seed production ; position effects ; herbivory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Patterns of seed and fruit production ofBauhinia ungulata, a small tree legume indigenous in tropical America, were studied in Costa Rica. Only about 8% of flowers produced fruits. The average pod had 19 ovules and about two thirds of these began seed development, with mature pods containing an average of 9.7 mature undamaged seeds. About half of the mature pods were damaged by herbivores and within these, 27% of ovules or seeds had been eaten. Among trees there was no significant variation in pod production, but the number of ovules per pod and seed production per pod varied significantly. Within infructescences most pods were retained at middle positions. Within pods, the probability of an ovule developing into a seed increased toward the distal end. The pattern of seed and fruit production in this species agrees well in general with that reported for other neotropical legumes. The abortion of seeds and fruits can be regarded as a way of controlling maternal investment, and as a response to herbivory.
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  • 6
    ISSN: 1615-6110
    Keywords: Angiosperms ; Fabaceae ; pigeonpea ; Cajanus cajan ; Sex allocation ; mating systems ; fruit and seed set
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sex allocation theory predicts that: (1) resources allocated to androecium should decrease with an increase in selfing, (2) a decrease in androecium biomass should be accompanied by an increase in the biomass of pistils, and (3) a decrease in androecium biomass should be coupled with a decrease in flower size, specifically corolla biomass. Another predicted change in reproductive traits associated with variation in selfing concerns seed to ovule ratios, but does not directly stem from sex allocation theory. It has been postulated that seed to ovule ratios should be positively correlated with the amount of selfing. These predictions were tested for six accessions of pigeonpea,Cajanus cajan L., that differed in selfing rates. The results were remarkably in accordance with the predictions. We conclude that sex allocation theory provides a powerful tool to understand the evolution of many reproductive traits in plants.
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 352 (1991), S. 204-205 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] DESPITE worldwide concern, the rate of tropical deforestation is accelerating and in 1989 was almost twice that in 1979. (Norman Myers, Deforestation Rates in Tropical Forests and their Climatic Im-plications, Friends of the Earth, Lon-don). The pace of change is alarming, and only a small fraction ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 383 (1996), S. 398-399 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR á€" Canopy trees, the main structural elements of tropical rain forests, typically occur at the density of one adult or less per hectare1'3. Because these trees are strongly outcrossed4"6, their populations are expected to cover large areas of hundreds of square kilometres. ...
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 25 (1968), S. 90-95 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract B-chromosomes are reported for the first time for woody angiosperms. Out of six species from the eastern Himalayas in which B-chromosomes were observed, two are polyploid. The number of B-chromosomes varied from 0–5 in the different species. In Sambucus canadensis, Glerodendrum colebrookianum and Neolitsea zeylanica B's were found to pair with each other at Metaphase-I.
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  • 10
    Publication Date: 2011-12-28
    Type: paper
    Format: application/pdf
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