156 research outputs found
T-minima on convex sets and Mosco-convergence
No full textHalf century ago, Umberto Mosco was the ``relatore di tesi (tesi about the Mosco- convergence) di laurea'' of the first author; a quart of century ago, the first author was the ``relatore di tesi di laurea'' of the second author. The roots of this paper are the Mosco-convergence of convex sets and the minimization of integral functionals of the Calculus of Variations. We consider integral functionals of the type J(v)=∫Ω j(x,Dv)-∫Ω f(x)v(x). We study the existence of T-minima (infinite energy minima) on convex sets of the Sobolev space W01,p(Ω) and the stability of the T-minima under the Mosco-convergence of the convex sets
Il dossier egiziano nel Prato spirituale di Giovanni Mosco
No full textThis paper investigates the 7th century description of Egypt drawn from Il Prato Spirituale by Giovanni Mosco. Every element of the text asserts the triumph of the only true practicable road, i.e. Chalcedon orthodoxy. The 451 Council had led to a schism of the Christian church between those who accepted and those who repudiated it and were from then on called «monophysites». The reasons behind the adjustments of the objective datum are the defence of Chalcedon and the attacks on monachism considered heterodox. The retrieval is attempted by way of a critical reading of the text and a confrontation with the available documentary source material, which is less mediated and closer to reality
Genetic heterogeneity, reproductive isolation and host preferences in mealy aphids of the Hyalopterus pruni complex (Homoptera, Aphidoidea).
No full textThree taxa were detected by allozyme markers within the mealy aphids of the Hyalopterus pruni complex, having different cultivated Prunus species as main primary hosts. The genetically closer H. pruni and H. amygdali A (DNei= 0.10) never share primary hosts, whereas H. amygdali A and B (DNei= 0.32) may occasionally share them, producing few F1 hybrids. The three species proved reproductively isolated in the field, with no gene exchange. Their speciation seem to have occurred long before the agricultural revolution, crop colonization representing a host range expansion rather than a host shift, as in sympatric speciatio
Evidence of hybrid speciation in the North American primroses Primula suffrutescens, P. parryi, P. rusbyi and P. angustifolia (Primulaceae)
No full textThe genetic structure of tetraploid (4x = 44) North American species of Primula subgenus Auriculastrum: P. suffrutescens,P. parryi, P. rusbyi, and P. angustifolia was analyzed at seven enzyme loci and compared with that of the related diploidP. cuneifolia and P. nipponica. The studied tetraploid species showed fixed or almost fixed heterozygosity at various loci,indicating a hybrid origin. About half of their alleles were shared with Cuneifolia taxa sampled, suggesting that they arose from crosses involving a maternal Cuneifolia-like ancestor. A preliminary survey of their possible paternal species, as inferred from their genotypes, was carried out among different Primula groups. Several paternal alleles expected were observed in subgenus Aleuritia, particularly among taxa of sect. Crystallophlomis (e.g., P. chionantha, P. minor, and P. nivalis xanthobasis). However, none of these taxa proved to be a suitable paternal species. Hybridization events that originated P. suffrutescens, P. parryi, P. rusbyi, and P. angustifolia presumably occurred during Pleistocene secondary contacts in Beringia and involved a maternalCuneifolia-like ancestor and at least two paternal species, for sect. Suffrutescens and Parryi, respectively. Further studies,involving a genetic survey of Aleuritia taxa from Siberia will be needed to detect such paternal species, if not extinct
Interspecific hybridization as a source of new species in orchids of the genus Dactylorhiza
No full textThe Palaearctic genus Dactylorhiza includes 8 diploid,10 autotetraploid,and about 40 allopolyploid species. Most of the latter derived by multiple crosses in space and time between the diploid (2n=40) D.saccifera s.l. and either D.incarnata s.l. or D.euxina; they have 4x=80 and reproduce sexually (Allotetraploid Marsh Orchids,AMOs). AMO species are differentiated morphologically, ecologically and genetically, have distinct ranges and show different combinations of alleles from local races of their parental species. Hybridization between D.saccifera s.l. and D.incarnata s.l. also gave origin to a few allotriploid taxa, as yet undescribed, with apomictic reproduction and clonal structure. Other Dactylorhiza hybrid species originated from crosses between the diploid (2n=40) D.romana and D.sambucina. They include: 1) the apomictic allotriploid D.insularis (3x=60), which combines two genomes of D.romana and one of D.sambucina, and had a single origin in an Iberian hybrid zone; 2) the sexual allotetraploid D.cantabrica, which combines two genomes of each parental species, and had a single quite recent origin, as indicated by its very restricted range, much smaller than that of D.insularis. The ecological and evolutionary success of Dactylorhiza hybrid species is considered, with particular regard to their mode of reproduction, environmental adaptations, and competitive success
Speciation by hybridization in European orchids: evidence by nuclear and chloroplastic markers
No full textA number of hybrid species has been recently detected in orchids of the genus Dacylorhiza, by the use of codominant single copy nuclear markers (e.g. enzyme loci). They differ in ploidy level, mode of reproduction, genetic variation and single versus multiple origin. The Allotetraploid Marsh Orchids (D. elata s.l.) show sexual reproduction and have 4x=80; their parental species are D. saccifera s.l. (2n=40) and D. incarnata s.l. (2n=40), as suggested on chromosome basis by Heslop-Harrison (1953, 1954, 1957) and assessed on allozyme basis (Hedrén, 1996a, b; Bullini et al., 2002). Genetic comparison of various AMO taxa from Europe and Caucasus showed their multiple origin, both in time and space; the maternal species was generally D. saccifera s.l., as shown by cpDNA. Other hybrid Dactylorhiza species are allotriploid and reproduce by apomixis. Among marsh orchids, four triploid apomictic taxa, as yet undescribed, have been evidenced: three of them show 2 genomes from D. incarnata and 1 from D. saccifera, the fourth has 2 saccifera and 1 incarnata genomes. Their origin from occasionally fertile backcrosses of AMOs with either parental species has been suggested; according to the taxon, cpDNA was contributed from either D. saccifera or D. incarnata (Bullini et al., in press). The Western Mediterranean orchid D. insularis (3x=60) shows sporophytic polyembriony; this species derived from hybridization between D. romana (2n=40) and D. sambucina (2n=40), which contributed two and one genomes, respectively, as assessed by allozyme markers; the maternal species was D. romana. D. insularis had a single, recent origin and shows limited clonal variation (Bullini et al., 2001). Genetic relationships between Dactylorhiza hybrid taxa and their parental species, as inferred from cpDNA, are generally similar to those reported for nuclear ribosomal intergenic spacer (ITS; Bateman et al., 1997; Bateman, 2001). These findings suggest that concerted evolution, i.e. homogenization towards one parental species, has occurred in hybrid Dactylorhiza taxa at ITS level, highly biased towards the maternal parent
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