Contributions to the cytotaxonomy of the Commelinaceae. Chromosome evolution in Tradescantia section Cymbispatha

The five species of Tradescantia section Cymbispatha studied, including one species T. poelliae D. R. Hunt, have chromosome numbers of In = 12, 14, 16, 22, 28, 30 and 36 and karyotypes of acrocentric, metacentric or telocentric chromosomes, or mixtures of both acrocentric and metacentric chromosomes. The numbers of major chromosome arms of these cytotypes give a nombre fondamentaP series of 14, 28, 42 and 56 which, in combination with meiotic analyses, indicates plants which, in genetical terms at least, are diploid, tetraploid, hexaploid and octoploid. This series has evolved from a 2 n = 14 acrocentric or telocentric karyotype by a combination of Robertsonian fusion and polyploidy. Pseudo-iso-chromosomes are sometimes formed in this evolutionary development and can persist as stable members of normal complements.     

Contributions to the Cytotaxonomy of the Commelinaceae. Gibasis linearis and its allies

Species of the Gibasis linearis alliance collected in Mexico in 1976 are shown to have a chromosome constitution of x = 6, but x = 5 has also been found in some populations of G. rhodantha and G. speciosa. These two basic numbers are associated with distinctive karyotypes, 2M + 4A and 3M + 2A respectively, which show a Robertsonian relationship with each other. The existence of 2n = 22 in G. speciosa , combining both basic numbers at the amphidiploid level provides evidence of pairing between metacentrics and acrocentrics in such a way as to substantiate the view that fusion or fission of chromosomes is responsible for the modification of basic number. This survey provides a basis for other studies which will determine the chromosome relationships of the species irrespective of chromosome number in this family.     

Karyotype evolution and cytotaxonomy in Brazilian species of Rhynchospora Vahl (Cyperaceae)

Karyotypes were analysed in 113 populations of 34 species of Rhynchospora (Cyperaceae). They showed typical holocentric chromosomes lacking primary constrictions. Nucleolar constrictions were observed in the terminal regions of a few chromosomes (except in R. nanuzae , in which they were interstitial). The chromosome numbers varied between 2 = 4 and 2n = 50. The primary base number seems to be x = 5; x = 6 and x = 9 are secondary. Dysploidy occurred at low frequency, whereas polyploidy seemed to be the predominant event in the karyotype evolution of the genus. Karyotypic differences were found in R. consanguinea var. speciosa and R. consanguinea var. rigida and the closely related R. emaciata, R. riparia and R. tenuis from section Tenues. On the other hand, karyotypic similarities occurred among sections Valderugosae, Marisculae, Stenophylku and Cemuae.     

Contributions to the Cytotaxonomy of the Commelinaceae. Gibasis linearis and its allies

Species of the Gibasis linearis alliance collected in Mexico in 1976 are shown to have a chromosome constitution of x = 6, but x = 5 has also been found in some populations of G. rhodantha and G. speciosa. These two basic numbers are associated with distinctive karyotypes, 2M + 4A and 3M + 2A respectively, which show a Robertsonian relationship with each other. The existence of 2n = 22 in G. speciosa , combining both basic numbers at the amphidiploid level provides evidence of pairing between metacentrics and acrocentrics in such a way as to substantiate the view that fusion or fission of chromosomes is responsible for the modification of basic number. This survey provides a basis for other studies which will determine the chromosome relationships of the species irrespective of chromosome number in this family.     

Chromosome evolution in the cercopithecidae and its relationship to human fragile sites and neoplasia

Seven species of the family Cercopithecidae have been studied using highresolution banding techniques. Comparative studies allowed us to identify the main chromosomal reorganizations in this group, as well as to establish the phylogenetic relationships between species. Some of the regions involved in evolutionary rearrangements correspond to human fragile sites and/or chromosomal rearrangements related to neoplasia.     

The different banding patterns produced by restriction endonuclease digestion in mitotic chromosomes of the American and European eel

The detection of three classes of C-heterochromatin by in situ restriction endonuclease digestion allowed a karyotype differentiation between the American and the European eel.     

Karyological evolution in Rhaponticum Vaill. (Asteraceae, Cardueae) and related genera

Chromosome counts are reported in 29 populations representing 20 species and one subspecies of the genera Callicephalus (one sp.), Klasea (seven spp.), Myopordon (two spp.), Oligochaeta (one sp.), and Rhaponticum (nine spp., one ssp.). Eleven reports are new, the others supplement limited previous data. New and published cytological data are summarized and evaluated critically in light of current taxonomic treatments and evolutionary hypotheses. Basic chromosome numbers are a valuable source of taxonomic information and relate well to the phylogeny. They are quite conserved in Klasea (only x  = 15), the sister group of the remaining genera, and in the early branching genera of the Rhaponticum group ( x  = 14 for Centaurothamnus and Callicephalus ). However, a more complex pattern of genome evolution is present among the more derived clades, Oligochaeta plus Myopordon ( x  = 12, 14) and the genus Rhaponticum ( x  = 12, 13). The occurrence of x  = 12 in Oligochaeta divaricata and Rhaponticum carthamoides seems to be the result of a recent event of chromosome fusion, as suggested by the fragility of particularly long pairs of chromosomes. The use of chromomycin staining, including an enzymatic digestion step that facilitates spreading and permits a reduction of potential fragmentation, only partially resolves this problem.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 193–201.     

Karyotype evolution and phylogenetic analyses in the genus Cardiospermum L. (Paullinieae,Sapindaceae)

Cardiospermum L. belongs to the Paullinieae tribe (Sapindaceae) and comprises 16 species. Of these, 12 species are present in South America and all occur in Brazil. Cardiospermum shows the most variable chromosome number of the tribe. Phylogenetic relationships within the genus Cardiospermum, especially with other species of the tribe, are poorly understood. This research focuses on characterisation of the karyotypic features of Cardiospermum using conventional cytogenetic methods, CMA/DAPI chromosome banding and fluorescence in situ hybridisation (FISH). To elucidate the phylogeny of the genus, the nuclear markers ITS1 and ITS2 were sequenced and analysed using maximum parsimony and Bayesian inference. Cardiospermum shows important diversity in basic numbers, with x = 7, 9, 10, 11 and 12. All species studied have metacentric and submetacentric chromosomes, some species have subtelocentric chromosomes, while telocentric chromosomes are absent. The interphase nuclei differentiate the Cardiospermum species into two groups. The CMA₃/DAPI chromosome banding revealed the presence of an AT‐rich terminal region in C. corindum, C. grandiflorum and C. urvilleoides, whereas GC‐rich regions were found in C. grandiflorum, C. halicacabum var. halicacabum, C. halicacabum var. microcarpum, C. heringeri and C. integerrimum. FISH revealed syntenic and non‐syntenic distribution of the 18‐5.8‐26S and 5S rDNA. The syntenic distribution always occurred in the short arms of the same chromosome in all of the species. The phylogenetic relationships reveal, in part, the taxonomic arrangement of the genus Cardiospermum.     

Chromosome numbers in plant taxa endemic to the Balearic Islands

Mitotic chromosome numbers are reported from 20 vascular plant taxa that are endemic to the Balearic Islands and poorly known cytogenetically. The chromosome numbers of Arenaria grandiflora L. ssp. glabrescens (Willk.) G. López & Nieto Feliner (2 n  = 44), Dianthus rupicola Viv. ssp. bocchoriana L. Llorens & Gradaille (2 n  = 30), Solenopsis minuta (L.) C. Presl. ssp. balearica (E. Wimm.) Meikle (2 n  = 28), Romulea asumptionis Font Quer & Garcías Font (2 n  = 56), Scutellaria balearica Barceló (2 n  = 22) and Galium balearicum Briq. (2 n  = 22) have been determined for the first time. A new chromosome number was found in two populations of Helictotrichon crassifolium (Font Quer) Holub (2 n  =  c. 98) suggesting that this species is a high polyploid (14 x ), in contrast to an earlier report of a lower chromosome count (2 n  = 12 x  = 84). Cytogenetic observations suggest that Naufraga balearica Constance & Cannon has a diploid chromosome complement of 2 n  = 20, with 0–2 accessory chromosomes. The banded karyotype (chromomycin A₃) of Crepis triasii (Cambess.) Fries was determined for individuals belonging to eight populations from three islands. Two chromomycin A₃-positive regions were recorded in the diploid complement. These are present on the telomeric regions of the shortest subtelocentric chromosomes. This species is karyologically stable in chromosome number, karyotype and fluorochrome-banding pattern among populations from separate islands.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 219–228.     

Fraying around the edges: negative effects of the invasive Tradescantia zebrina Hort. ex Bosse (Commelinaceae) on tree regeneration in the Atlantic Forest under different competitive and environmental conditions

Aims Invasive plants modify the structure and functioning of natural environments and threat native plant communities. Invasive species are often favored by human interference such as the creation of artificial forest edges. Field removal experiments may clarify if invasive plants are detrimental to native plant regeneration and how this is related to other local factors. We assessed the joint effect of environment and competition with the invasiveTradescantia zebrinaon tree species recruitment in an Atlantic Forest fragment.     

A karyosystematic study of the genus Bellevalia Lapeyr. (Hyacinthaceae) in Greece

The genus Bellevalia is represented in Greece by eight taxa, three of which are endemic. Bellevalia brevipedicellata (2n = 8) and B. sitiaca (2n = 16) are restricted to the island of Kriti, while B. hyacinthoides (2n = 8, 12) is distributed in the Kiklades Islands, the central and southern mainland and the Ionian Islands. Four taxa, i.e. B. dubia subsp. boissieri (2n = 8), B. trifoliata (2n = 8), B. romana (2n = 8) and B. ciliata (2n = 8, 16) are Mediterranean elements. The presence of B. edirnensis (2n = 24) is reported as new for the Greek flora. New ploidy levels of three Bellevalia species (triplo‐, tetra‐ and hexaploids) are reported for the first time. The main morphological features, the chromosome numbers, the karyotype morphology, as well as the geographical distribution and further issues of taxonomy and conservation of all Bellevalia taxa in Greece are presented and discussed. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 723–739.     

The evolutionary origin of a novel karyotype in Timarcha (Coleoptera, Chrysomelidae) and general trends of chromosome evolution in the genus

In this work, we have analysed the karyotypes of six species of Timarcha for the first time and updated the cytological information for two additional taxa, for one of them confirming previous results ( Timarcha erosa vermiculata ), but not for the other ( T. scabripennis ). We describe the remarkable karyotype of T. aurichalcea , the lowest chromosome number in the genus (2 n  = 18), distinctive as well for the presence of an unusual chiasmatic sexual bivalent hitherto unreported for Timarcha . This study increases the number of species studied cytologically in this genus to forty. Additional cytogenetic analyses are performed on several species, including Ag-NOR staining and fluorescent in situ hybridization (FISH) studies with ribosomal DNA probes. Karyotype evolution is analysed by tracing different karyotype coding strategies on a published independent phylogenetic hypothesis for Timarcha based on the study of three genetic markers. The implementation of a likelihood model of character change optimized onto the phylogeny is tentatively used to detect possible drifts in chromosome changes. These analyses show that karyotype is conservative in the evolution of the genus and that there is an apparent trend to reducing chromosome number. Cytological and phylogenetic data are used to explain the evolutionary origin of the karyotype of T. aurichalcea by two centric fusions involving one pair of acrocentric autosomes and the sexual chromosomes.     

Genomic changes following the reversal of a Y chromosome to an autosome in Drosophila pseudoobscura

Robertsonian translocations resulting in fusions between sex chromosomes and autosomes shape karyotype evolution by creating new sex chromosomes from autosomes. These translocations can also reverse sex chromosomes back into autosomes, which is especially intriguing given the dramatic differences between autosomes and sex chromosomes. To study the genomic events following a Y chromosome reversal, we investigated an autosome‐Y translocation in Drosophila pseudoobscura. The ancestral Y chromosome fused to a small autosome (the dot chromosome) approximately 10–15 Mya. We used single molecule real‐time sequencing reads to assemble the D. pseudoobscura dot chromosome, including this Y‐to‐dot translocation. We find that the intervening sequence between the ancestral Y and the rest of the dot chromosome is only ～78 Kb and is not repeat‐dense, suggesting that the centromere now falls outside, rather than between, the fused chromosomes. The Y‐to‐dot region is 100 times smaller than the D. melanogaster Y chromosome, owing to changes in repeat landscape. However, we do not find a consistent reduction in intron sizes across the Y‐to‐dot region. Instead, deletions in intergenic regions and possibly a small ancestral Y chromosome size may explain the compact size of the Y‐to‐dot translocation.     

Chromosomal evolution of the house mouse, Mus musculus domesticus, in the Aeolian Archipelago (Sicily, Italy)

We describe the chromosomal evolution of the metacentric populations of the house mouse, Mus musculus domesticus , which constitute the Robertsonian System of Aeolian Islands (Sicily, Italy). Eighty-nine specimens from all the seven islands that form the Archipelago were cytogenetically examined. The analysis shows the presence of 4 Rb races with a large number of shared metacentric chromosomes: 2 n  = 36 on Panarea, 2 n  = 34 on Alicudi, 2 n  = 26 on Lipari and Stromboli, and a different 2 n  = 26 race on Vulcano. On Salina and Filicudi, the standard karyotype was found. Polymorphism was only found in a population on Panarea Island and this population shares no metacentrics with the other races. The distribution of metacentrics among the races and the comparison between the Aeolian metacentrics and those found in the 97 previously documented metacentric populations allows us to formulate a hypothesis of chromosomal evolution for the Aeolian Robertsonian system. Six of the twelve metacentric chromosomes found in the Aeolian Islands come from localities outside the archipelago. The evolutionary model highlights how the chromosomal races originated inside the Archipelago and involve several factors, such as formation in situ of metacentrics, zonal raciation and, whole arm reciprocal translocation. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 194–202.     

New perspectives on the mechanisms of chromosome evolution in parasitic flowering plants

In an attempt to find any association between chromosomal characters and parasitism, a cytological study of parasitic flowering plants in Israel has been carried out. While no such association was found, evidence for three levels of chromosome evolution could be discerned: intra-chromosomal modifications, polyploidy per se , and genome restructuring in polyploids. Our conclusions may serve as a paradigm of the multiple pathways of chromosomal evolution in plants in general. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 138 , 117–122.     

Chromosome investigations in annual Medicago species (Fabaceae) with emphasis on the origin of the polyploid Medicago rugosa and M. scutellata

Chromosome number variations play an important role in the genus Medicago. In addition to polyploidy there are cases of dysploidy as evidenced by two basic numbers, x = 8 and x = 7, the latter limited to five annual species having 2n = 14. Annuals are diploid with the exception of Medicago scutellata and Medicago rugosa which have 2n = 30 and are considered the result of crosses between the 2n = 16 and 2n = 14 species. However, this hypothesis has never been tested. This study was carried out to investigate the 2n = 14 and 2n = 30 karyotypes and verify the allopolyploid origin of M. scutellata and M. rugosa. Fluorescence in situ hybridization (FISH) of rDNA probes and genomic in situ hybridization (GISH) were performed. FISH showed that all five diploids with 2n = 14 have one pair of 45S and one pair of 5S rDNA sites. M. scutellata displayed four sites of 45S and four sites of 5S rDNA, while in M. rugosa only one pair of each of these sites was found. GISH did not produce signals useful to identify the presumed progenitors with 14 chromosomes. This result suggests alternative evolutionary pathways, such as the formation of tetraploids (2n = 32) and subsequent dysploidy events leading to the chromosome number reduction.     

Patterns of cytotype distribution and genome size variation in the genus Sesleria Scop. (Poaceae)

Polyploidization has played an important role in the diversification of the genus Sesleria (Poaceae), which comprises c. 48 species and subspecies mostly distributed in Europe. The genus' centre of diversity clearly is the Balkan Peninsula, harbouring about 80% of the species, half of which are endemic to this area. We employed chromosome counts, measurements of absolute genome size and determination of relative DNA‐content for 460 populations belonging to 43 species of Sesleria. Our main aim was to provide essential baseline data for future molecular genetic reconstructions of the genus' evolutionary history. Relative genome size allowed for a mostly clear separation of four ploidy levels. The most frequent and widespread cytotypes are tetraploids followed by octoploids, while di‐ and dodecaploids were only found in a few species. We present first chromosome numbers for the tetraploid species S. doerfleri, S. phleoides, S. skipetarum and S. tuzsonii as well as for diploid S. ovata. Based on relative and partly also on absolute genome size measurements, ploidy level was determined in tetraploid S. rhodopaea and S. voronovii for the first time, and new cytotypes were identified in S. interrupta, S. kalnikensis and S. wettsteinii (tetraploids), S. caerulea, S. klasterskyi, S. latifolia, S. tenerrima, S. ujhelyii and S. vaginalis (octoploids), and S. albanica and S. vaginalis (dodecaploids). While most Sesleria species are ploidy‐uniform, several comprise two or even, in the case of S. vaginalis, three ploidy levels. Genome downsizing after polyploidization was confirmed by significant negative correlation between ploidy level and monoploid genome size. Finally, we found a significant increase in monoploid relative genome size towards the margin of the genus' distribution area, which may be triggered by increased activity of transposable element in populations exposed to environmental or genomic stress. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 126–143.     

Variation and Evolution in the Karyotype of Lycoris (Amaryllidaceae) V. Chromosomal Variation in L. sanguinea Maxim.

Abstract In 554 bulbs from 38 populations of Lycoris sanguinea , several chromosomal variations have been discovered. Most of the bulbs have a common karyotype consisting of 22 acrocentric ( A ) chromosomes. Though their frequencies are low, some rearranged chromosomes which are aberrant have been found. The aberrants are as follows: 1. Subtelocentrics ( ST ); 2. Telocentrics ( T' ); 3. Metacentrics ( M' ); 4. Very small acrocentrics (a); 5. Very small metacentrics (m); 6. Acentric fragments ( Ac ); and 7. Dicentrics ( Di ) chromosome. All can be easily suspected to be derived from A s. Some aberrations of the satellite chromosomes have been observed also. In addition, a new karyotype composed of 2n=32=31 A + 1 M' chromosomes has been found.     

Contributions to the karyological study of the genus Ranunculus L. subgenus Batrachium (DC.) A Gray from the Iberian Peninsula

DIOSDADO. J. C, PASTOR, J. E. & VALDÉS, B. 1993. Contributions to the karyological study of the genus Ranunculus L. subgenus Batrachium (DC.) A. Gray from the Iberian Peninsula. The somatic and gametic chromosome numbers and detailed chromosome morphology are presented for eight taxa of aquatic ranunculi from the Iberian Peninsula. Within the subgenus Batrachium diploid and tetraploid levels have been observed (2 n = 16, 32) the commoner of which is the diploid. From the karyological data relationships have been established between the subgenus Batrachium and subgenus Ranunculus.