Distribution Of Polyploidy Research Articles

Ecological range shift in the polyploid members of the South American genus Fosterella (Bromeliaceae).

The distribution of polyploidy along a relatively steep Andean elevation and climatic gradient is studied using the genus Fosterella L.B. Sm. (Bromeliaceae) as a model system. Ecological differentiation of cytotypes and the link of polyploidy with historical biogeographic processes such as dispersal events and range shift are assessed. 4',6-Diamidino-2-phenylindole (DAPI) staining of nuclei and flow cytometry were used to estimate the ploidy levels of 159 plants from 22 species sampled throughout the distribution range of the genus. Ecological differentiation among ploidy levels was tested by comparing the sets of climatic variables. Ancestral chromosome number reconstruction was carried out on the basis of a previously generated phylogeographic framework. This study represents the first assessment of intrageneric, intraspecific and partially intrapopulational cytotype diversity in a genus of the Bromeliaceae family. In Fosterella , the occurrence of polyploidy was limited to the phylogenetically isolated penduliflora and rusbyi groups. Cytotypes were found to be ecologically differentiated, showing that polyploids preferentially occupy colder habitats with high annual temperature variability (seasonality). The combined effects of biogeographic history and adaptive processes are presumed to have shaped the current cytotype distribution in the genus. The results provide indirect evidence for both adaptive ecological and non-adaptive historical processes that jointly influenced the cytotype distribution in the predominantly Andean genus Fosterella (Bromeliaceae). The results also exemplify the role of polyploidy as an important driver of speciation in a topographically highly structured and thus climatically diverse landscape.

Cytotype distribution at a diploid–tetraploid contact zone inChamerion(Epilobium)angustifolium(Onagraceae)

In North America, the geographic distributions of diploid and tetraploid Chamerion (formerly Epilobium) angustifolium overlap in a narrow zone along the southern border of the boreal forest and along the Rocky Mountains. We examined the frequency and distribution of diploid and tetraploid cytotypes in a narrow (5 km) zone of sympatry across an elevational gradient and in putatively uniform diploid and tetraploid reference populations on the Beartooth Pass, in the Rocky Mountains of southern Montana-northern Wyoming. All five reference populations sampled were dominated by a single cytotype, but only one was completely uniform. In the zone of sympatry, 27 transects were sampled every 2 m for a total of 238 plants. Reproductive status (vegetative, flower buds, open flowers) was recorded, and the ploidy of each plant was determined by flow cytometry. Diploid and tetraploid plants predominated (36 and 55%, respectively) but were heterogeneously distributed among the transects. Six of the 27 transects were fixed for a single cytotype (four transects, diploid; two transects, tetraploid), and in seven others either diploids or tetraploids predominated (frequency >75%). Triploids represented 9% of the total sample and occurred most frequently in transects containing both diploids and tetraploids (G = 3.4, df = 2, P = 0.07). Diploids were more often reproductive (in bud, flower, or fruit) than either triploids or tetraploids (G = 12.0, df = 2, P < 0.001) and were the only cytotype to have produced open flowers. These results suggest that the zone of sympatry is best characterized as a mosaic rather than a cline, with diploid and tetraploids in close proximity and that the distribution of polyploidy is regulated by ecological sorting in a heterogeneous physical environment.

Polyploidy and the evolution of domesticated plants

Polyploidy and domestication are common features of plant evolution. A number of selective advantages conferred by polyploidy appear relevant to domestication. Surprisingly, the correlation between the two has not previously been examined. Anderson (Plants, man and life. University of California Press, Berkeley, CA, 1969) asserted that we do not yet know exactly what percentage of cultivated plants and weeds are polyploid, but it must be high. Heiser (Seeds to civilization, the story of food, 2d ed., W. H. Freeman, San Francisco, CA, 1981) stated that a large number of the major food crops are polyploids, giving wheat, sugar cane, potatoes, sweet potatoes, and bananas as examples. In this study, the distribution of polyploidy in 244 crop species was compared to the estimates of polyploidy in their respective higher categories. The proportion of polyploidy in crop plants was considered in relation to taxonomic origin, habitat, and reproductive strategies of the crops. The study showed that the crop species were a random selection as far as ploidy level is concerned and that domestication did not appear to have favored polyploid over diploid genomes or vice versa. Vegetative, seed, and tree crops were statistically homogenous in their polyploid composition. The distribution of polyploidy in annual and perennial crops did not differ statistically. The data imply that polyploid genomic constitution neither facilitated nor hindered the ability of wild species for domestication.

Distribution of Polyploidy in Elongating and Non-Elongating Shoot Axis of Pisum sativum

In the shoot of the dwarf pea Pisum sativum «Kleine Rheinländerin» the ploidy level of the cortex cells in the first 5 internodes was determined after treatment with GA 3 and FdUrd. GA 3 has a similar effect as darkness in enhancing the ploidy level in these cells. The hormone will provide this effect at concentrations up to 2.5 × 10 -6 M. DNA content per cell of non growing internodes is not altered by this treatment. However in growing internodes an increase in DNA-content can be recorded immediately after the treatment. The growth and fresh weight do not increase proportionally to the DNA-content. Employing FdUrd as an inhibitor of DNA-synthesis will however terminate growth entirely. The results demonstrated that shoot growth of peas - as in many other plants - is always followed by a higher DNA content of the individual cells.