64 research outputs found
Floquet theory of radical pairs in radiofrequency magnetic fields.
This is the final version of the article. Available from AIP Publishing via the DOI in this record.We present a new method for calculating the product yield of a radical pair recombination reaction in the presence of a weak time-dependent magnetic field. This method successfully circumvents the computational difficulties presented by a direct solution of the Liouville-von Neumann equation for a long-lived radical pair containing many hyperfine-coupled nuclear spins. Using a modified formulation of Floquet theory, treating the time-dependent magnetic field as a perturbation, and exploiting the slow radical pair recombination, we show that one can obtain a good approximation to the product yield by considering only nearly degenerate sub-spaces of the Floquet space. Within a significant parameter range, the resulting method is found to give product yields in good agreement with exact quantum mechanical results for a variety of simple model radical pairs. Moreover it is considerably more efficient than the exact calculation, and it can be applied to radical pairs containing significantly more nuclear spins. This promises to open the door to realistic theoretical investigations of the effect of radiofrequency electromagnetic radiation on the photochemically induced radical pair recombination reactions in the avian retina which are believed to be responsible for the magnetic compass sense of migratory birds.We gratefully acknowledge funding from the European
Research Council under the European Unionâs 7th Framework
Programme, FP7/2007-2013/ERC Grant Agreement
No. 340451, and from the US Air Force (USAF) Office of
Scientific Research under the Air Force Materiel Command,
USAF Award No. FA9550-14-1-0095
Breeding systems in Tolpis (Asteraceae) in the Macaronesian islands: the Azores, Madeira and the Canaries
Plants on oceanic islands often originate from
self-compatible (SC) colonizers capable of seed set by self fertilization. This fact is supported by empirical studies,
and is rooted in the hypothesis that one (or few) individuals
could find a sexual population, whereas two or more would
be required if the colonizers were self-incompatible (SI).
However, a SC colonizer would have lower heterozygosity
than SI colonizers, which could limit radiation and diver sification of lineages following establishment. Limited
evidence suggests that several species-rich island lineages
in the family Asteraceae originated from SI colonizers with
some ââleakinessââ (pseudo-self-compatibility, PSC) such
that some self-seed could be produced. This study of Tolpis
(Asteraceae) in Macaronesia provides first reports of the
breeding system in species from the Azores and Madeira,
and additional insights into variation in Canary Islands.
Tolpis from the Azores and Madeira are predominately SI
but with PSC. This study suggests that the breeding sys tems of the ancestors were either PSC, possibly from a
single colonizer, or from SI colonizers by multiple dis seminules either from a single or multiple dispersals. Long distance colonists capable of PSC combine the advantages
of reproductive assurance (via selfing) in the establishment
of sexual populations from even a single colonizer with the
higher heterozygosity resulting from its origin from an
outcrossed source population. Evolution of Tolpis on the
Canaries and Madeira has generated diversity in breeding
systems, including the origin of SC. Macaronesian Tolpis is
an excellent system for studying breeding system evolution
in a small, diverse lineage.info:eu-repo/semantics/publishedVersio
Linking Self-Incompatibility, Dichogamy, and Flowering Synchrony in Two Euphorbia Species: Alternative Mechanisms for Avoiding Self-Fertilization?
Background: Plant species have several mechanisms to avoid selfing such as dichogamy or a self-incompatibility response.
Dichogamy in a single flower may reduce autogamy but, to avoid geitonogamy, plants must show flowering
synchronization among all their flowers (i.e. synchronous dichogamy). It is hypothesized that one species would not
simultaneously show synchronous dichogamy and self-incompatibility because they are redundant mechanisms to reduce
selfing; however, this has not been accurately assessed.
Methodology/Principal Findings: This expectation was tested over two years in two natural populations of the closely
related Mediterranean spurges Euphorbia boetica and E. nicaeensis, which completely avoid autogamy by protogyny at the
cyathia level. Both spurges showed a high population synchrony (Z,79), and their inflorescences flower synchronously. In E.
nicaeensis, there was no overlap among the cyathia in anthesis of successive inflorescence levels and the overlap between
sexual phases of cyathia of the same inflorescence level was uncommon (4â16%). In contrast, E. boetica showed a high
overlap among consecutive inflorescence levels (74â93%) and between sexual phases of cyathia of the same inflorescence
level (48â80%). The flowering pattern of both spurges was consistent in the two populations and over the two successive
years. A hand-pollination experiment demonstrated that E. nicaeensis was strictly self-compatible whereas E. boetica was
partially self-incompatible.
Conclusions/Significance: We propose that the complex pattern of synchronized protogyny in E. nicaeensis prevents
geitonogamous crosses and, consequently, avoids selfing and inbreeding depression. In E. boetica, a high probability of
geitonogamous crosses may occur but, alternatively, this plant escapes selfing through a self-incompatibility response. We
posit that synchronous dichogamy and physiological self-incompatibility do not co-occur in the same species because each
process is sufficiently effective in avoiding self-fertilization.España Ministerio de Ciencia y TecnologĂa PLO CGL2005-03731; CGL2008-02533-EEspaña Ministerio de Ciencia y TecnologĂa MA CGL2009-0825
Unilateral incompatibility within the Brassicaceae: further evidence for the involvement of the self-incompatibility (S)-locus
Unilateral incompatibility within the brassicaceae: further evidence for the involvement of the self-incompatibility (S)-locus.
Unilateral pollen-pistil incompatibility within the Brassicaceae has been re-examined in a series of interspecific and intergeneric crosses using 13 self-compatible (SC, Sc) species and 12 self-incompatible (SI) species from ten tribes. SC x SC crosses were usually compatible, SI x SC crosses showed unilateral incompatibility, while SI x SI crosses were often incompatible or unilaterally incompatible. Unilateral incompatibility (UI) is shown to be overcome by bud pollination or treating stigmas with cycloheximide - features in common with self-incompatibility. Treating stigmas with pronase prevents pollen tubes from penetrating the stigma in normally compatible intra-and interspecific pollinations. The results presented show that the presence of an incompatibility system is important in predicting the outcome of interspecific and intergeneric crosses and, combined with the physiological similarities between UI and SI, would suggest an involvement of the S-locus in UI
Synthesis and phosphorylation of pollen proteins during the pollen-stigma interaction in self-compatible <i>Brassica napus</i> L. and self-incompatible <i>Brassica oleracea</i> L
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