Article

Shrinking genomes? Evidence from genome size variation in Crepis (Compositae)

Botanic Garden and Botanical Museum Berlin-Dahlem, Freie Universität Berlin, Berlin, Germany.
Plant Biology (Impact Factor: 2.41). 01/2011; 13(1):185-93. DOI: 10.1111/j.1438-8677.2010.00341.x
Source: PubMed

ABSTRACT Large-scale surveys of genome size evolution in angiosperms show that the ancestral genome was most likely small, with a tendency towards an increase in DNA content during evolution. Due to polyploidisation and self-replicating DNA elements, angiosperm genomes were considered to have a 'one-way ticket to obesity' (Bennetzen & Kellogg 1997). New findings on how organisms can lose DNA challenged the hypotheses of unidirectional evolution of genome size. The present study is based on the classical work of Babcock (1947a) on karyotype evolution within Crepis and analyses karyotypic diversification within the genus in a phylogenetic context. Genome size of 21 Crepis species was estimated using flow cytometry. Additional data of 17 further species were taken from the literature. Within 30 diploid Crepis species there is a striking trend towards genome contraction. The direction of genome size evolution was analysed by reconstructing ancestral character states on a molecular phylogeny based on ITS sequence data. DNA content is correlated to distributional aspects as well as life form. Genome size is significantly higher in perennials than in annuals. Within sampled species, very small genomes are only present in Mediterranean or European species, whereas their Central and East Asian relatives have larger 1C values.

0 Followers
 · 
159 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We discuss and experimentally demonstrate several approaches for output power enhancement of metal-semiconductor-metal (MSM) structures of photomixers fabricated using molecular-beam epitaxial (MBE) GaAs grown at low substrate temperature. We focus on the parameters, following from the theory describing output power from a photomixer device. While low carrier lifetime and high photoconductivity was achieved by optimised LT GaAs growth conditions, substantial breakdown voltage increase was attained by improving MSM geometry, by metallic contacts recessing, as well as transferring the thin LT GaAs layer on top of high bandgap and high thermal conductivity substrates. Our results indicate a responsivity enhancement of up, to 40% as compared to the photodetectors with standard surface contacts
    Electron Devices for Microwave and Optoelectronic Applications, 2001 International Symposium on; 02/2001
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Studies in experimental grasslands have shown variation in plant individual performance in response to neighbourhood diversity. To which extent these responses are due to phenotypic plasticity or genetic variation is largely unknown. We collected seed families of five herbaceous species (Cirsium oleraceum, Crepis biennis, Plantago lanceolata, Plantago media and Rumex acetosa) in monocultures and 60-species mixtures five years after establishment and replanted or transplanted the offspring into the same monocultures and 60-species mixtures. In all five species the actual environment significantly affected plant survival, growth and performance in terms of shoot biomass and investment into reproduction, indicating stronger competition for light and different levels of herbivory in mixtures as compared with monocultures. Effects of the original environment were smaller and less consistent, but indicated differential selection in monocultures vs. mixtures. The interaction between actual and original environment, corresponding to the “home” vs. “away” comparison, was rarely significant, yet this was providing a first sign of local adaptation. We conclude that, for the investigated plant species, more than five growing seasons in monocultures or mixtures would be needed to better demonstrate the selection of genotypes specifically adapted to monocultures or mixtures. A faster local adaptation may have been prevented by the ability of these species to respond to variation in neighbourhood diversity to a large degree via phenotypic plasticity and other factors.
    Basic and Applied Ecology 06/2011; 12(4):360-371. DOI:10.1016/j.baae.2011.03.005 · 2.39 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The systematics of the Hypochaeridinae subtribe was re-evaluated based on a combination of published and new molecular data. Newly emerging clades were additionally characterized using published and new phytochemical data. In addition to flavonoids and sesquiterpene lactones, which recently had been reviewed as chemosystematic markers in the Cichorieae, we analysed the reported occurrences of caffeic acid derivatives and their potential as chemosystematic markers. The molecular results required changes in the systematics of the subtribe: the genus Hedypnois proved to be very closely related to a few Mediterranean members of Leontodon section Leontodon. This clade comprises all members of the genus Hedypnois, Leontodon siculus (Guss.) Nyman, L. boryi DC., L. rosani (Ten.) DC., and L. villarsii (Willd.) Loisel. and is more closely related to Leontodon section Asterothrix than to all members of Leontodon section Leontodon. Instead of splitting Leontodon into even a higher number of segregate genera we propose to include Hedypnois into Leontodon s.str., thus comprising members of sections Asterothrix, Leontodon, and Thrincia sensu Widder (1975) plus the taxa currently assigned to the genus Hedypnois. Leontodon sections Leontodon and Astrerothrix are merged into a single section Leontodon. The newly defined genus Leontodon is supported by high bootstrap values and characterized by the unique occurrence of hydroxyhypocretenolides. The monophyly of the genus Hypochaeris is not supported. There are two separate molecular clades within Hypochaeris. The clade Hypochaeris I comprises the majority of the European and Mediterranean as well as all South American taxa of Hypochaeris s.l. while the clade Hypochaeris II only encompasses H. achyrophorus L., H. glabra L., H. laevigata Benth. & Hook.f., and H. radicata L.
    Organisms Diversity & Evolution 03/2012; 12(1):1-16. DOI:10.1007/s13127-011-0064-0 · 3.37 Impact Factor