No abstract

Knowledge of the chromosome variation in wild populations is essential to understand the pathways and restrictions of karyotype evolution in plants. The aim of this study is to conduct an intraspecific analysis of the karyotypes by fluorochrome banding and ribosomal DNA (rDNA) loci detection by fluorescent in situ hybridization (FISH) and of the meiotic behaviour in natural populations of Lathyrus nervosus, sect. Notolathyrus. Chromosome banding showed that, despite the high constancy in the karyotype formula and in the rDNA loci among populations, there is intraspecific variation in the amount and distribution pattern of 4',6-diamidino-2-phenylindole (DAPI ? ) heterochromatin. However, those changes were not related to the total chromosome length of the haploid complements. This fact demonstrates that structural chromosome changes may be one of the most important mechanisms for karyotype variation among natural populations of L. nervosus. The chromosome number surveyed at the population level revealed the first case of polyploidy in South American species and the first case of uneven polyploidy of the genus. All the chromosome markers analysed indicated that the polyploids found originated by autopolyploidy. The meiotic analysis showed different chromosome abnormalities that may be generating numerical and structural changes in the sporads. The finding of unreduced gametes that are alive at anthesis suggests sexual polyploidization as the most probable mechanism involved in the origin of these 3x and 4x autopolyploid cytotypes in L. nervosus.

The genome size was surveyed in 13 Notolathyrus species endemic to South America by flow cytometry and analyzed in an evolutionary and biogeographic context. A DNA content variation of 1.7-fold was registered, and four groups of species with different DNA content were determined. Although, the 2C values were correlated with the total chromosome length and intrachromosomal asymmetry index (A1), the karyotype formula remained almost constant. The conservation of the karyotype formula is in agreement with proportional changes of DNA in the chromosome arms. Species with annual life cycle and shorter generation time had the lowest DNA content and the data suggest that changes in DNA content involved reductions of genome size in the perennial to annual transitions. The variation of 2C values was correlated with precipitation of the coldest quarter and, to some extent, with altitude. Additional correlations with other variables were observed when the species were analyzed separately according to the biogeographic regions. In general, the species with higher DNA content were found in more stable environments. The bulk of evidence suggests that changes on genome size would have been one of the most important mechanisms that drove or accompanied the diversification of Notolathyrus species.

Commelina benghalensis es una hierba pequeña, nativa de Africa y Asia tropical, aunque en la actualidad crece en casi todo el mundo. En América se la reporta creciendo en campo abierto, borde de bosques y áreas cultivadas (sur de USA,