Variation in Chromosome Number and its role in Speciation in Dracaena Metallica Hort.
TL;DR: It is clear that the chromosome numbers have got some common characteristics in all the offshoots, but differences in the tendencies of variation were noticed, particularly in the occurrence of the most frequent chromosome numbers.
Abstract: From the study of somatic chromosomes of Dracaena metallica Hort., which shows a high degree of variation in chromosome number, and which is propagated exclusively by vegetative means, it is clear that the chromosome numbers have got some common characteristics in all the offshoots. Counting of a large number of plates in the root tips of different offshoots shows the repetition of almost similar types of chromosome numbers which tend to remain as multiples of 7. In spite of this homogeneity in the offshoots, differences in the tendencies of variation were noticed, particularly in the occurrence of the most frequent chromosome numbers. In the long run, such differences may lead to the production of new species having distinct chromosome complements.
TL;DR: It is concluded that the evolutionary and geographic success of Acer lie in the versatility of sexual systems, diverse modes of maturation of reproductive organs, reproductive success, and the ability to colonise wider areas.
Abstract: This study focuses on variation in reproductive systems in Acer (maple) species, and how Acer might be a useful genus for understanding floral morphology and the evolution of these highly variable systems. The goals were (1) to conduct a survey of reproductive characters in the genus Acer with an emphasis on floral morphometrics of A. ginnala Maxim., A. tataricum L., and the hybrid A. ginnala × tataricum and (2) present a compilation of the reproductive biology of Acer based on the literature and online information. Morphometric analyses showed that the hybrid A. ginnala × tataricum exhibits intermediacy in vegetative morphology and some floral traits compared to the parents. Literature and an online survey revealed some information on the reproductive biology of 40 Acer species, plus the hybrid, representing only 32.3% of the taxonomic diversity. The reproductive modes of Acer include monoecy, dioecy, trioecy, andromonoecy, androdioecy, and andropolygamy, with a trend towards unisexuality. Temporal patterns of maturation of reproductive parts revealed duodichogamy, heterodichogamy, simultaneous, and dichogamy. The pollination syndrome is entomophilous, anemophilous, and ambophilous. We conclude that the evolutionary and geographic success of Acer lie in the versatility of sexual systems, diverse modes of maturation of reproductive organs, reproductive success, and the ability to colonise wider areas.
Cites methods from "Variation in Chromosome Number and ..."
...This idea is based on Harrington et al.’s (2005) cladogram with primarily insect-pollinated out-groups Peganum harmala L....
TL;DR: L'importanza delle modificazioni cromosomiche del soma nel problema della speciazione delle piante che si riproducono vegetativamente si delinea.
Abstract: RIASSUNTOL'A delinea l'importanza delle modificazioni cromosomiche del soma nel problema della speciazione delle piante che si riproducono vegetativamente
TL;DR: In this paper, the authors propose a method to solve the problem of the problem: this paper...,.. ].. ).. ]... )...
TL;DR: RIASSUNTOVengono riportati i cartogrammi di ventotto specie, appartenenti a quindici generi di Araceae spontanee e coltivate, la cui propagazione avviene generalmente per via vegetativa e viene tracciata la loro probabile derivazione filogenetica da un numero base x=7.
Abstract: (1955). Cytology of Different Species of Aroids with a View to Trace the Basis of their Evolution. Caryologia: Vol. 7, No. 2, pp. 221-291.
TL;DR: The somatic number has been found to differ from cell to cell within the root tips of Paphiopedilum Wardii Summerhayes, one of the mottledleaved Burmese lady slipper orchids, and the word "aneusomaty" is adopted as a name for the phenomenon.
Abstract: THE CHROMOSOME number has been found to differ from cell to cell within the root tips of Paphiopedilum Wardii Summerhayes, one of the mottledleaved Burmese lady slipper orchids. Lack of constancy as regards somatic chromosome number within an individual is not unknown in plants. An occasional cell, for example, or a number of scattered cells, or a group of associated cells within a root may be tetraploid or octaploid. Langlet's (1927) term "polysomaty" is commonly applied in these cases. There are, however, species or varieties in which the somatic complement of chromosomes fluctuates in the vicinity of the diploid number with no evidence of duplication of the entire set. Apparently these variations have diverse histories and are to be explained differently. The chromosome or chromosomes contributing to variability may be supernumerary to the normal complement and much smaller than its members. The B chromosomes of maize are an example (Kuwada, 1919; Fisk, 1927; Longley, 1927) as are the-centric fragments surviving from the last previous meioses referred to by Darlington (1937). The variability, on the other hand, may involve replication of members of the complement. There has been little observation on mitoses leading to varying numbers other than through polysomaty. Since the mechanism by which the change in number is brought about can be followed with considerable ease in P. Wardii, a -brief investigation was made. The process involves only certain members of the chromosome set and leads to cells polysomic, in Blakeslee's terminology, for those members of the complement. The causal mechanism bears close resemblance to that of polysomaty. These facts lead to the adoption of the word "aneusomaty"2 as a name for the phenomenon. Root tips were fixed in Randolph's modification of Navashin's fluid, imbedded in paraffin, sectioned, and stained with crystal violet-iodine. Counts of chromosomes were made in serial sections from the root tip through the embryonic region. Although the plants supplying the root tips came from two different sources, they may be members of a single clone since the species is rare in cultivation and is propagated vegetatively. The idiogram (fig. 6) shows the complement to contain seven pairs of atelomitic chromosomes of graduated lengths, two shorter pairs having about the same length. Each member of one pair of chromosomes has a secondary constriction which delimits a region similar in size to the smallest chromosomal type of the complement. The remainder of the chromosomes are rod-shaped; they vary 1 Received for publication March 19, 1945. 2 The author wishes to express his appreciation for Prof. C. E. Allen's advice in selecting an appropriate name. from 27 to 31 in number according to the present observations. Their lengths are graduated so that the longer and shorter rod-shaped chromosomes can be distinguished easily. Some of the types of intermediate length have morphological peculiarities which are sufficient to distinguish them but this group is generally difficult to assort. The rod-shaped chromosomes are not all strictly telomitic; the locations of their centric regions vary from apparently terminal to sufficiently subterminal so that an extremely short second arm is visible. The somatic number as determined in equatorial plates ranges from 41 to 45 (fig. 3 and 2, respectively). The shortest type of chromosome (no. 20) is almost spherical; it possesses two horn-like proj ections, one to a chromatid, at the end anterior in polar congression. Because of its shape and the fact that it is from one-half to two-thirds the length of the next shortest chromosome, it is recognized easily. Two to six (fig. I and 5) chromosomes of this type are present in various plates; they may occur in several kinds of associations lying on the periphery of the spindle or they may be scattered throughout the plate. The latter condition is more frequent. The total number of chromosomes, omitting those of type 20, varies from 38 to 40 (fig. 4 and 1). Two additional types of chromosomes have different frequencies of occurrence in equatorial plates. One of these (no. 19) likewise belongs to the class of smaller chromosomes. It has a swollen midregion and tapers toward each end, the end anterior in polar migration sometimes being stretched. It is almost as easily distinguishable as the shortest chromosomal type. Two, three, or four (fig. 4, 2, and 1) may be present in somatic plates. The other variant (no. 10) is one of the medium-sized chromosomal types, being roughly three times as long as type 20. Like chromosomes of type 20 and 19, it has a single projection or two small projections, depending upon the view and state of division, at its forward end. Two or three of these (fig. 5 and 3) may be present in an equatorial plate. Table 1 presents an analysis of the equatorial plates shown in figures 1-5. The variable number of occurrences of three chromosomal types allows similar total number of chromosomes to be reached by different means. The data in table 1 dealing with figures 2 and 5 demonstrate this point. Chromosomes of type 20 are the most variable in numbers. So frequent are misdivisions of chromosomes of this type that some stages in their progress have been observed. The apparent explanation is that the two daughter chromatids of a type 20 chromosome may dissociate at the end opposite the centric region before or during the early stages