Pollinator adaptation and the evolution of floral nectar sugar composition

A long-standing debate concerns whether nectar sugar composition evolves as an adaptation to pollinator dietary requirements or whether it is 'phylogenetically constrained'. Here, we use a modelling approach to evaluate the hypothesis that nectar sucrose proportion (NSP) is an adaptation to pollinators. We analyse ~ 2100 species of asterids, spanning several plant families and pollinator groups (PGs), and show that the hypothesis of adaptation cannot be rejected: NSP evolves towards two optimal values, high NSP for specialist-pollinated and low NSP for generalist-pollinated plants. However, the inferred adaptive process is weak, suggesting that adaptation to PG only provides a partial explanation for how nectar evolves. Additional factors are therefore needed to fully explain nectar evolution, and we suggest that future studies might incorporate floral shape and size and the abiotic environment into the analytical framework. Further, we show that NSP and PG evolution are correlated - in a manner dictated by pollinator behaviour. This contrasts with the view that a plant necessarily has to adapt its nectar composition to ensure pollination but rather suggests that pollinators adapt their foraging behaviour or dietary requirements to the nectar sugar composition presented by the plants. Finally, we document unexpectedly sucrose-poor nectar in some specialized nectarivorous bird-pollinated plants from the Old World, which might represent an overlooked form of pollinator deception. Thus, our broad study provides several new insights into how nectar evolves and we conclude by discussing why maintaining the conceptual dichotomy between adaptation and constraint might be unhelpful for advancing this field.

Terahertz meets sculptural and architectural art: Evaluation and conservation of stone objects with T-ray technology

Conservation of cultural heritage is an area where novel scientific techniques are having enormous impact. Given the value and uniqueness of art pieces, non-invasive diagnostic methods are highly appreciated by conservators. Terahertz radiation has shown enormous potential as non-contact probe that can be used for the three-dimensional reconstruction of internal structure of stone-made objects. In this article we report the evaluation of the internal damage state of two art pieces, a medallion from the Castle of Celle and a window sill from the St. Peter of Trier Cathedral. We also used terahertz radiation to follow and assess the restoration process of the window sill. We found that terahertz spectroscopy is an excellent non-destructive evaluation method for stone artwork that shows enormous potential as a tool for conservation.

Terahertz plastic compound lenses

We present terahertz (THz) lenses made of highly refracting polymeric compounds which provide a better focusing performance and an increased functionality in comparison to conventional THz lenses. Using mixtures consisting of polypropylene (PP) and alumina as well as PP and zinc sulfide allows a significant increase of the refractive index while simultaneously keeping a low extinction and dispersion. With these new material combinations, lenses with an increased focusing capability are realized. This is evaluated by focal plane measurements using a fiber coupled THz time-domain spectrometer.

Beating the wavelength limit: three-dimensional imaging of buried subwavelength fractures in sculpture and construction materials by terahertz time-domain reflection spectroscopy

We use reflection terahertz spectroscopy to locate and produce three-dimensional images of air gaps between stones that resemble fractures, even of subwavelength thicknesses. This technique is found to be promising tool for sculpture and building damage evaluation as well as structural quality control in other dielectric materials.

A Survey for 'Candidatus Liberibacter' Species in South Africa Confirms the Presence of Only 'Ca. L. africanus' in Commercial Citrus

Greening disease of citrus is a serious disease known in South Africa since the late 1920s. In South Africa, it is associated with infection by 'Candidatus Liberibacter africanus', a heat sensitive, phloem-limited, noncultured alpha-proteobacterium. Huanglongbing (HLB), a similar, but more devastating disease that was described initially from China but which now occurs in several citrus producing countries, is associated with a different Liberibacter species, 'Ca. L. asiaticus'. A 'Ca. L. africanus' subspecies, 'Ca. L. africanus subsp. capensis', has been found only in South Africa infecting an indigenous Rutaceous species, Calodendrum capense (Cape Chestnut), in the Western Cape in 1995. The discovery of a new Liberibacter species in Brazil, 'Ca. L. americanus', and the spread of 'Ca. L. asiaticus' to a number of additional countries over the last few years prompted us to assess whether only 'Ca. L. africanus' is present in commercial citrus orchards in South Africa. Samples displaying greening or similar symptoms were collected from 249 citrus trees from 57 orchards distributed throughout the greening affected citrus production areas of South Africa. Multiplex polymerase chain reaction (PCR) was performed on DNA extracts to detect the known citrus Liberibacters. Amplicons were obtained from 197 samples. None of the samples yielded a 1,027-bp amplicon indicative of 'Ca. L. americanus' infection. The amplicons of 84 samples were sequenced, and all were identical to the cognate 'Ca. L. africanus' Nelspruit sequence in GenBank. No instance of 'Ca. L. asiaticus' or 'Ca. L. africanus subsp. capensis' sequence was found. Geographically representative samples that tested negative for Liberibacter also tested negative for phytoplasmas based on real-time PCR results. Based on the results of this survey, it is concluded that to date only 'Ca. L. africanus' is associated with citrus greening in commercial citrus in South Africa.

A variant of a slam freezing device for electron microscopy

A home-made slam freezing device is presented that allows reproducible results in freezing various unfixed tissues. The heart of the device is an aluminum socket, which harbors a plunger that is set in motion by a spring. At the end of the plunger there is an electromagnet which holds the sample on a sheet metal planchette. During stop freezing the electrical contacts are interrupted and the plunger can be withdrawn leaving the specimen on the cooled copper block. This guarantees freezing of not only solid tissues, but also cell suspensions, such as blood or bone marrow.

Synthetic amino-acid diet prolongs survival in autoimmune murine disease

The effect of substituting a fully synthetic diet for standard laboratory pellet feed on the course of spontaneous autoimmune disease in New Zealand Black/White hybrid mice was examined. Delays in the development of anti-nuclear antibody, proteinuria and circulating immune complexes were seen; the survival was markedly prolonged. This type of dietary manipulation has a beneficial effect on the course of murine autoimmune disease.