Karyotypic diversification and its contribution to the taxonomy of Eleocharis (Cyperaceae) from Brazil

Abstract

A karyotype analysis of 147 populations of 25 Brazilian species of Eleocharis (Cyperaceae) was carried out, including representatives of the three subgenera that occur in the country: Limnochloa, Scirpidium and Eleocharis. The analyses showed chromosomes without centromeres, but with terminal nucleolar constrictions (satellites) in some chromosomes. The chromosome numbers varied from 2n = 6 in E. subarticulata and E. maculosa to 2n = 60 in E. laeviglumis, but the chromosome basic number x = 5 was confirmed. Species of the subgenera Eleocharis and Scirpidium possess fewer and larger chromosomes, while those in the subgenus Limnochloa have small and more numerous chromosomes. These features indicate that the karyotypes of the subgenera Eleocharis and Scirpidium are more closely related, in agreement with morphological and phylogenetical data. The representatives of the section Eleocharis exhibited the largest differences in chromosome number and size, probably due to chromosome fission and fusion. Polyploidy was the most common event in this group. Nevertheless, most of the studied species exhibited regular meiosis with only bivalent formation, even the polyploids, such as in E. geniculata and E. sellowiana. The cytogenetic information obtained showed quite variable karyotypes with chromosomes gradually decreasing in size, and predominance of polyploidy. These results are useful in the differentiation of the subgenera.

Correlated evolution of LTR retrotransposons and genome size in the genus eleocharis

“…As indicated by the positive correlation between genome size and chromosome number, our results confirm previous assumptions [35] that polyploidy occurs in the genus Eleocharis . However, the small genome sizes and high chromosome counts observed in our study indicate that agmatoploidy is the most important process determining chromosome number in the subgenera Limnochloa and Zinserlingia .…”

“…1) Chromosome numbers were taken from previous studies ([68]: E. palustris, E. waltersii ; [49]: E. sterneri because of sample identity; [69]: E. quinqueflora because of population identity; [35]: E. interstincta ). For the remaining samples, chromosome numbers were counted by O. Rotreklová and P. Bureš (unpublished data).…”

“…It is likely that a similar deviation also exists in species of the subgenus Limnochloa , which are predicted to have small genomes based on the DNA content estimated for E. cellulosa (2C = 0.84 pg) and which have chromosome numbers ranging from 40 to 200 [ 34,35 ] . Nevertheless, the high chromosome numbers observed in the basal clades Zinserlingia and Limnochloa resulted rather from agmatoploidy (chromosomal fission) than polyploidy [35], similar to Carex (see discussion above). Thus, higher polyploids appear to belong to the evolutionary youngest subgenus of Eleocharis .…”

“…Subsequently, a new peak is reached by natural selection, favoring beneficial non-transposon mutations [47,48]. Because species from the subseries Eleocharis are polyploid [[35,49-51], this study], they carry duplicate or multiple copies of all genes, and thus, the negative consequences of TE activity can be balanced [52,53]. A greater number of TEs within a genome increases the potential to produce fecund lineages with strong abilities to evolve and adapt to various conditions [47,48].…”

Holocentric Karyotype Evolution in Rhynchospora Is Marked by Intense Numerical, Structural, and Genome Size Changes

“…The increase in chromosome number by polyploidy has also been proposed in genera such as Eleocharis R.Br. (Da Silva et al, 2010;Zedek et al, 2010) and Rhynchospora Vahl . High chromosome numbers were also found in Cyperus cyperoides Kuntze (n = 112; Tejavathi, 1988), C. esculentus L. (n = 104; Sharma, 1970), Carex hirta L. (n = 56-57; Luceño, 1994), and Rhynchospora faurieri Franch.…”