Chromosome numbers were determined for 97 samples of 95 sedge taxa (Carex) from the following countries: Austria (6 records), Bulgaria (1), the Canary Islands (Spain, 1), Cape Verde (1), the Czech Republic (51), Hungary (1), Italy (2), Norway (8), Russia (15), Slovakia (1), Sweden (1) and 9 North American plants cultivated in Czech botanical gardens. Chromosome numbers for Carex argunensis, C. callitrichos, C. campylorhina, C. flavocuspis subsp. krascheninnikovii, C. paniculata subsp. hansenii, C. pallida, C. quadriflora and C. xiphium are reported here for the first time. The first reports are presented for the European portion of the distribution area of Carex obtusata and for the Central European portion of the distributional areas of C. chordorrhiza, C. otrubae, C. rhizina and C. strigosa. New counts for the Czech Republic fill the gaps in the karyological data for this genus in relation to the Flora project in the Czech Republic.
Pollen viability was analysed causally between and within Central European Cirsium species and their hybrids to determine (i) how frequently hybrids are fertile and produce viable pollen; (ii) how the pollen viability of hybrids and their parents are related and how this is affected by the genetic distance between parents; (iii) how species promiscuity relates to species pollen viability; (iv) to what extent the pollen viability of a hybrid may predetermine its frequency in nature; (v) how the pollen viability of a hybrid and sympatricity of its parental species are related; and (vii) how the frequency of females in populations of gynodioecious species may affect the observed pollen viability. Altogether, the viability of 656,363 pollen grains was analysed using Alexander’s staining (1185 flowers from 301 plants from 67 field populations of 13 pure species and 1693 flowers from 345 plants from 96 field populations of 16 natural hybrids). The particular characters potentially related with pollen viability were estimated using following methods: natural hybrid frequency and species interfertility (by herbarium data), genetic distance (by AFLP), sympatricity (in local scale based on herbaria and literature data; on a global scale using the similarity between digitized maps of natural ranges). The strengths of pre- or postzygotic isolation were estimated for hybridizing species pairs using geographical data and pollen viability analyses. All hermaphrodite plants of the Cirsium hybrids had viable pollen, generally at lower levels than those found in pure species. The pollen viability of a hybrid generally decreased with increasing genetic distance between the parents and when the parental species had lower pollen viability. The pollen viability was decreased in frequently hybridizing species where occasionally individuals of pure species morphology may show decreased pollen viability. In some instances these might represent some unrecognized hybrid backcrosses. In populations of gynodioecious species where females co-occurred, pollen viability (in hermaphrodites)was also lower, indicating some degree of inbreeding depression. Hybrids between sympatric species exhibited higher post-pollination isolation (decrease of pollen viability), which suggests that the reproductive isolation had been increased by natural selection (effect similar to the Wallace effect). The strength of the postzygotic barrier (based on pollen viability) was generally stronger than that of the prezygotic barrier (based on distribution overlap) in studied hybridizing species pairs.
Intraspecific variation in genome size makes it possible to study ongoing processes of genome size evolution. Although there are over 200 papers on intraspecific variation in genome size, there is still limited understanding of this phenomenon, especially as many of these papers are based on weak methodology and therefore report biased or false evidence of the extent of intraspecific variation. In this paper the recent progress in understanding the spatio-temporal dynamics of intraspecific variation in genome size caused by the gradual accumulation of mutations is reviewed. The results of the case studies on Microseris douglasii, Zea mays, Silene latifolia, Hordeum spontaneum and Lolium hybrids, and in particular that on Festuca pallens, are discussed. The variation in genome size that occurs within species is caused mainly by differences in the content of repetitive DNA, in particular it is a consequence of the dynamics of transposable elements. Variation may be induced and maintained polytopically.We assume that it is probably more frequent in groups of young radiating species. Even in the initial stages, the variation in genome size generated within a population seems to be restricted by selection, which is also important in stabilizing genome size within species. The long-term persistence of the variation within a population and its further accumulation may be enhanced by gametes with different genome sizes, produced by the segregation of unequally sized homeologous chromosomes. Over large geographical scales and across contrasting environmental gradients, the distribution of genome sizes within species may be influenced by the nucleotype effect, with smaller genomes being more successful at higher latitudes and altitudes and under stressful conditions. However, the small differences in genome size within species seem generally to be of minor importance relative to other components of plant fitness that may be selectively favourable under particular environmental or habitat conditions. The processes generating variation in genome size may be associated with phenotypic variation. While the shift in the genome size of a population through selection enables adaptive evolution of genome size in a newly arising species, the spatio-temporal variation in genome size within an ancestral species allows for a rapid multiple genome size divergence of related species through random drift in genome size (founder effect, bottleneck effect) during range fragmentation, hybridization and/or polyploidization.