Chromosome numbers and evolution inOphrys (Orchidaceae)

The diploid basic chromosome number forOphrys is 2n = 36. Tetraploidy has been found inO. fusca agg. only. Aneuploidy and aneusomaty are wide-spread; supernumerary chromosomes behave B-like, but do not differ by shape or structure from A-chromosomes. A new staining method reveals clearly differentiated bipartite meiotic kinetochores. Evolutionary aspects of homogamic hybridization, chromosome instability, and of the basic chromosome number x = 18 are discussed.     

Chromosome evolution in pseudoxyrhophiine snakes from Madagascar: a wide range of karyotypic variability

In this first cytogenetic survey on the lamprophiid snake subfamily Pseudoxyrhophiinae, we studied the karyology of ten snake species belonging to seven genera from Madagascar (Compsophis, Leioheterodon, Liophidium, Lycodryas, Madagascarophis, Phisalixella and Thamnosophis) using standard and banding methods. Our results show a wide range of different karyotypes ranging from 2n = 34 to 2n = 46 elements (FN from 40 to 48), with nucleolus organizer regions (NORs) on one (plesiomorphic) or two (derived/apomorphic) microchromosome pairs, and W chromosome at early or advanced states of diversification from the Z chromosome. The observed W chromosome variations further support the most accepted hypothesis that W differentiation from the Z chromosome occurred by progressive steps. We also propose an evolutionary scenario for the observed high karyotype diversity in this group of snakes, suggesting that it is derived from a putative primitive pseudoxyrhophiine karyotype with 2n = 46, similar to that of Leioheterodon geayi, via a series of centric fusions and inversions among macrochromosomes and translocations of micro‐ either to micro‐ or to macrochromosomes. This primitive Pseudoxyrhophiinae karyotype might have derived from a putative Lamprophiidae ancestor with 2n = 48, by means of a translocation of a micro‐ to a macrochromosome. In turn, the karyotype of this lamprophiid common ancestor may have derived from the assumed primitive snake karyotype (2n = 36 chromosomes, with 16 biarmed macro‐ and 20 microchromosomes) by a series of centric fissions and one inversion. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 450–460.     

Chromosome identification and comparative karyotypic analyses of four Pinus species

Chromosomal landmarks in four Pinus species: P. densiflora, P. thunbergii, P. sylvestris, and P. nigra were identified by fluorescence in situ hybridization (FISH) using hapten- or fluorochrome-labeled probes for the plant telomere repeat, centromeric repeat (PCSR), and rDNA. FISH landmarks were located at the interstitial and proximal regions of chromosomes and allowed us to identify nearly all of the homologous chromosomes in each species. A comparative analysis of the FISH karyotypes among the four species showed that the interstitial FISH signals obtained by hybridization with the telomere and rDNA sequences were stable and could be used to identify homologous chromosomes among species. The identification of homologous chromosomes among species facilitated a detailed comparative karyotype analysis. The results suggest that the degree of chromosomal differentiation among the four Pinus species is very low and that the proximal regions vary in their DNA sequences. The similarities and differences among FISH karyotypes are discussed in relation to phylogeny.     

Chromosome numbers and karyotype evolution in holoparasitic Orobanche (Orobanchaceae) and related genera

Chromosome numbers and karyotypes of species of Orobanche, Cistanche, and Diphelypaea (Orobanchaceae) were investigated, and 108 chromosome counts of 53 taxa, 19 counted for the first time, are presented with a thorough compilation of previously published data. Additionally, karyotypes of representatives of these genera, including Orobanche sects. Orobanche and Trionychon, are reported. Cistanche (x = 20) has large meta- to submetacentric chromosomes, while those of Diphelypaea (x = 19) are medium-sized submeta- to acrocentrics. Within three analyzed sections of Orobanche, sects. Myzorrhiza (x = 24) and Trionychon (x = 12) possess medium-sized submeta- to acrocentrics, while sect. Orobanche (x = 19) has small, mostly meta- to submetacentric, chromosomes. Polyploidy is unevenly distributed in Orobanche and restricted to a few lineages, e.g., O. sect. Myzorrhiza or Orobanche gracilis and its relatives (sect. Orobanche). The distribution of basic chromosome numbers supports the groups found by molecular phylogenetic analyses: Cistanche has x = 20, the Orobanche-group (Orobanche sect. Orobanche, Diphelypaea) has x = 19, and the Phelipanche-group (Orobanche sects. Gymnocaulis, Myzorrhiza, Trionychon) has x = 12, 24. A model of chromosome number evolution in Orobanche and related genera is presented: from two ancestral base numbers, x(h) = 5 and x(h) = 6, independent polyploidizations led to x = 20 (Cistanche) and (after dysploidization) x = 19 (Orobanche-group) and to x = 12 and x = 24 (Phelipanche-group), respectively.     

Chromosome numbers of Thai Rubiaceae

Chromosome numbers for 14 taxa of indigenous Thai Rubiaceae are presented. They include first counts for 3 genera: Aphaenandra (A. uniflora), Prismatomeris (P. tetrandra subsp. malayana) and Tarennoidea (T. wallichii) ; all show diploidy on x=11. The remaining counts are first counts for species: Argostemma diversifolium, A. neurocalyx and A. pictum, Coptosapelta flavenscens, Gardenia saxtilis, Ixora sp., Morinda sp., Mussaenda sanderiana, Oxyceros horridus, Rothmannia wittii (first count for an Asiatic species of the genus) (all diploid on x=11), and Canthium sp. (tetraploid on x=11). The poor state of karyological knowledge of indigenous Thai Rubiaceae is discussed, and a table including all relevant known chromosome counts is presented. Chromosome data are only known for 38 genera (ca. 41% of all Rubiaceae genera occurring in Thailand); chromosome numbers are often only available for one or few taxa of each genus [in sum, for only about 50 (or for roughly 10% of all) taxa]. Of only 14 genera (ca. 15%), chromosomes were counted from Thai material (for the others, counts originate from elsewhere, i.e. refer to more widely distributed taxa also extending into Thailand).     

Chromosome numbers of dominican compositae

Chromosome numbers of 34 species of Dominican Compositae in 26 genera and nine tribes are reported. First counts are given forCoreopsis buchii (2n = 64),Lagascea mollis (2n = 34),Spilanthes urens (n = 16),Liabum subacaule (n = 18),Eupatorium sciatraphes (2n = 40),Hieracium gronovii (2n = 18),Vernonia buxifolia (2n = 34),V. sprengeliana (2n = 34),V. racemosa (2n = 28), andChaptalia leiocarpa (2n = 48,ca. 58). Our report forNarvalina domingensis (2n = 120) is the first for any species of this genus.     

Chromosome evolution

The idea of evolution as a principle for the origin of biodiversity fits all phenomena of life, including the carriers of nuclear inheritance, the chromosomes. Insights into the evolutionary mechanisms that contribute to the shape, size, composition, number and redundancy of chromosomes elucidate the high plasticity of nuclear genomes at the chromosomal level, and the potential for genome modification in the course of breeding processes. Aspects of chromosome fusion, as exemplified by karyotype evolution of relatives of Arabidopsis, have recently received special attention.     

Chromosome numbers and morphology in Cathaya

The authors have for the time observed that somatic cell of Cathaya argyrophylla contains 24 chromosomes (2n=24) (plate I, 3). One pair of them are subtelocentric chromosomes and the rest are metacentric or submetacentric (Fig. 1). This shows that Cathaya is similar to most of genera in Pinaceae in chromosome numbers, but different from Pseutotsuga (2n-26). It seems that Cathaya is not closely related to Pseudot-suga, although its wood anatomy is very similar to that of Pseudotsuga.     

Cervid satellite DNA and karyotypic evolution of Indian muntjac

Five satellite DNA families (designated as satellite I?CV) have been identified in the Cervidae so far. Among those, satellite I, II and IV are centromere specific. Satellite I and II are shared by large number of deer species, where satellite IV is highly conserved among several deer species examined. Satellite III was initially thought to be roe deer specific but later identified in Chinese water deer as well. SatelliteV is Y-chromosome specific for several Asian deer species examined but also found in the pericentric region of Indian muntjac chromosome 3 and in X chromosome of Chinese water deer. The observation of interstitial hybridization sites on Indian muntjac chromosomes with satellite DNA I probe generated from Chinese muntjac provides the first molecular evidence supporting the tandem fusion theory that 2n=6??/7??of Indian muntjac karyotype could derive from an ancestral Chinese muntjac-like species with 2n=46. Interspecies chromosome painting study and the maximum number of interstitial hybridization detected with satellite I and satellite II DNA probes lend support to the hypothesis that the Indian muntjac karyotype could evolve directly from an ancestral Chinese water deer-like species with 2n=70. Such hypothesis is further substantiated by the finding of satellite V signals presented in specific chromosome regions between the Chinese water deer and the Indian muntjac chromosomes.     

A study on sex-determination and karyotypic evolution inTetranychidae

The chromosome complements of 45 species of spider mites (Tetranychidae) were studied, making the total number of species now examined in this family 57, approximately 10% of all species known. The chromosome numbers range fromn=2 ton=7. The modal number of the family is 3 (found in 44% of the species). It is argued that the ancestral number isn=2 (21% of the species).In the more primitive subfamily of theBryobiinae both thelytokous and arrhenotokous species occur, whereas the subfamily of theTetranychinae exclusively exhibits arrhenotoky. The karyotype evolution is discussed in connection with arrhenotoky. It is stated that karyotype information is a useful tool for the spider mite taxonomist.This study was financially supported by the Netherlands Foundation for the Advancement of Tropical Research (W.O.T.R.O.) and the Uyttenboogaart-Eliasen Foundation.     

Chromosome numbers in Nigerian Compositae

Chromosome counts are presented for 54 collections of Nigerian Compositae. The collections comprise 37 taxa belonging to 21 genera and 34 specieS. Most of the taxa studied are colonisers of disturbed habitats.     

Chromosome numbers and differentiation of centrospermous families

The patterns of variation of chromosome numbers in theCentrospermae suggest a common ancestry of centrospermous anthocyanin and betalain families. Phylogenetic divergence in the order may have originated with progenitors similar to extantMolluginaceae, Aizoaceae orPhytolaccaceae taxa with x = 9. Evolutionary radiation and advancement in several lines then seems to have been paralleled by trends for increasing chromosome base numbers through dysploidy and polyploidy, e.g. towardsCaryophyllaceae, Portulacaceae-Basellaceae, Hectorellaceae, Cactaceae, Didieraceae, Nyctaginaceae andChenopodiaceae-Amaranthaceae. Presented in the Symposium Evolution of Centrospermous Families, during the XIIth International Botanical Congress, Leningrad, July 8, 1975.     

Chromosome numbers in Malawian Commelinaceae

In this account chromosome numbers of 22 species and varieties from five genera of Commelinaceae occurring in Malawi are given. For 14 of them this is the first time their chromosome numbers have been reported. A wide range of chromosome numbers of 2n = 26 , 28, 30. 44. 52 and 60 is noted in Commelina.