Fertilizing Pollen Tubes Parasitise Ovary Wall in Grevillea

Tissue-invasive pollen tube branching occurs in an Australianshrub, Grevillea banksii R.Br. (Proteaceae). Parenchyma andphloem of the ovary wall are soon infiltrated after fertilization,by intercellular branches and the lumina of xylem elements areentered. Ovular tissues are not affected. Grevillea banksii, pollen, haustoria, ovary wall     

Monitoring the persistence of Laccaria bicolor as an ectomycorrhizal symbiont of nursery-grown Douglas fir by PCR of the rDNA intergenic spacer

The large-scale inoculation of selected beneficial ectomycorrhizal fungi in forest nurseries has generated renewed interest in the ecology of these symbiotic fungi. However, information on the dissemination and persistence of introduced symbionts is scarce due to the limitation of the current identification methods. To identify ectomycorrhizal fungi on single root tips, we investigated the polymorphism of the PCR-amplified ribosomal DNA intergenic spacer (IGS) from a wide range of ectomycorrhizal fungi. To investigate the reliability of this molecular approach in large-scale surveys, the dissemination and persistence on Douglas fir seedlings of the introduced Laccaria bicolor S238N were assessed in a forest nursery in the Massif Central (France). Several hundred ectomycorrhizas and fruiting bodies were sampled from plots where control and L. bicolor inoculated-Douglas fir seedlings were grown for 1.5 years. PCR typing of mycorrhizas indicated that trees inoculated with L. bicolor S238N remained exclusively colonized by that isolate (or sexually derived isolates) for the entire test period. In contrast, control seedlings were infected by indigenous isolates of Laccaria laccata and Thelephora terrestris. The molecular evidence for the persistence of the introduced mycobiont despite the competition from indigenous isolates of the same species provides further illustration of the potential of exotic species for large-scale microbial application.     

The speckled wood butterflies Pararge xiphia and P. aegeria (Satyridae) on Madeira: distribution, territorial behaviour and possible competition

Madeira is home to two species of speckled wood butterfly. Pararge xiphia is endemic and is common at mid to high altitudes, within and around the edges of the indigenous laurel forest. In 1976 P. aegeria colonized the island and anecdotal reports suggest that it may have been responsible for the loss of P. xiphia from some of its former haunts. The aims of this paper were (1) to provide comprehensive data on the distribution, habitat preferences and recent changes of range of the two species and (2) to examine territorial behaviour to see if inter-specific competition is taking place. Census results show that there are basic differences between the species in altitudinal range and habitat, but they are found together at high densities at habitat boundaries. Repetition of some of the census routes after a 4-year gap suggests that P. aegeria is expanding its range into the areas dominated by P. xiphia. Behavioural data demonstrate that the males may be competing by causing each other to expend more energy in defence of territories. Although competition may be present, it is not yet possible to establish which species is more affected and how competition may have contributed to the recent changes in the species' ranges.     

Site-specific isotope fractionation of hydrogen in the biosynthesis of plant fatty acids

The overall deuterium content of plant lipids has been investigated by isotope ratio mass spectrometry (IRMS), and the site-specific natural isotope fractionation of hydrogen has been studied by ²H-NMR at natural abundance (SNIF-NMR). An analytical strategy has been developed in order to exploit the isotopomeric composition determined in clusters associated with different chemical sites of one or several fatty acid components. The method, which combines spectrometric and chromatographic data, enables isotopic criteria to be directly derived from raw vegetable oils containing in general two saturated and two unsaturated fatty acids. These results provide new information on isotopic fractionation caused by biochemical, physiological and natural environmental effects. Some alternation in the molecular deuterium distribution has been detected which may be related to the mechanism of fatty acid elongation. The successive methylene groups introduced through malonyl CoA are the subjects of different kinetic isotope effects since one of them is exclusively derived from NADH whereas the other has a contribution from pyruvate. A discriminant analysis of the cluster isotopic parameters enables several kinds of botanical precursors to be distinguished. The authenticating performances can be improved by taking into account the influence of climatic effects related to the region in which the plant grew.     

Interspecific host discrimination and competition in Apoanagyrus (Epidinocarsis) lopezi and A.(E.)diversicornis, parasitoids of the cassava mealybug Phenacoccus manihoti

Abstract.

• 1 Choice experiments on interspecific host discrimination in A.lopezi and A. diversicornis were carried out on discs of cassava leaf containing four hosts (P.manihoti) that had been parasitized by the other species and four unparasitized hosts.
• 2 A.lopezi accepted both host types equally for oviposition, whereas A.diversicornis accepted fewer hosts that had been parasitized by A.lopezi than unparasitized ones. A.diversicornis is therefore capable of interspecific host discrimination, but such a capability was not demonstrated for A.lopezi.
• 3 Survival probability in singly parasitized hosts was 0.85 for both parasitoid species. When the time interval between ovipositions was 2 h or less, survival in multiparasitized hosts was 0.68 for A.lopezi and 0.17 for A.diversicornis, irrespective of priority. Increasing A.lopezi priority to 24±2h did not increase A.lopezi survival. A.diversicornis survival, however, increased to 0.43 when A.diversicornis was given 24 ± 2 h priority. A.diversicornis eggs took 19 h longer than A.lopezi eggs to hatch. This could explain the difference in competitive abilities in multiparasitized hosts.
• 4 The observed difference in host selection behaviour between A.lopezi and A.diversicornis is in accordance with the different benefits of multiparasitism: A.lopezi gains more than A.diversicornis because of its superior within-host competitive abilities.
• 5 Neither species avoided multiparasitism completely. The low survival probability of A.diversicornis in multiparasitized hosts may partly explain its failure to establish when introduced into Africa as part of a biological control programme of P.manihoti.