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.     

Ultrastructural changes associated with June Yellows in strawberry and with leaf yellowing symptoms of viral and genetic origin in Fragaria, Rubus and Ribes

Light and electron microscopy was used to study the ultrastructural effects of June Yellows (JY) in leaves of strawberry. Four cultivars of strawberry, affected to different extents by JY, were compared with healthy (JY-free) cv. Cambridge Favourite and with strawberry infected with strawberry crinkle rhabdovirus, Fragaria vesca infected with strawberry mottle virus (SMotV), raspberry and black currant showing virus-induced yellowing and with strawberry and raspberry showing chaemeric yellow sectors in the leaves. Except for isometric virus-like particles detected in SMotV-infected F. vesca, no virus-like particles or structures of other pathogenic agents were found in any of the tissues examined. Leaf cells of JY-affected strawberry showed severe disruption of chloroplasts and plasmalemma, whorls of membranous vesicles and decreased vacuole size. The extent and severity of these abnormalities increased with increased severity of JY symptoms but, even in leaves with mild JY symptoms, chloroplast abnormalities were obvious. In the most severely affected leaves, the cells lacked discrete vacuoles and extensive hypertrophy was seen in other organelles such as nuclei and mitochondria. Few, if any, ultrastructural abnormalities were observed in virus-infected strawberry or F. vesca, or in chaemeric leaves of strawberry and raspberry. By contrast, in raspberry and black currant with yellowed leaves caused by virus infection, the cells showed enlarged chloroplasts, decreased vacuole size and vesicle formation. However, chloroplast enlargement and disruption in this material seemed due to increased size of starch grains which were largely absent from swollen chloroplasts of JY-affected strawberry. The ultrastructural abnormalities observed in JY-affected strawberry are, therefore, not inconsistent with the possibility that a pathogenic agent may be involved in the condition.     

Infectibility of some new raspberry cultivars with arabismosaic and raspberry ringspot viruses and further evidence for variation in British isolates of these two nepoviruses

In field trials at sites of an outbreak of arabis mosaic nepovirus (AMV) in England and of raspberry ringspot nepovirus (RRV) in Scotland, the results of exposure of some new raspberry cultivars to natural infection with these viruses showed discrepancies from those obtained in graft inoculation tests using AMV-Lib and RRV-S, the Scottish type isolates. In particular, cv. Glen Prosen, which is immune to AMV-Lib and RRV-S, was infected with AMV and RRV in the field trials. Studies on these and other field isolates of AMV and RRV showed that they differed from the type isolates in Rubus host range and in symptomatology in herbaceous hosts. However, whereas four isolates of RRV found infecting Rubus were distinguishable by spur formation in gel double-diffusion serological tests, six AMV isolates were indistinguishable by this method. Immunoelectrophoresis of virus particles did not distinguish the six AMV isolates, but isolates RRV-MX and RRV-T were distinguishable from RRV-S and the English type isolate, RRV-E. Like the two RRV type isolates, RRV-MX contained a single electrophoretic component, but it migrated must faster whereas RRV-T contained two components, one with a migration rate similar to that of RRV-MX and the other similar to that of the type isolates. Polyacrylamide gel electrophoresis of protein preparations from highly purified virus particles of RRV isolates E, S and MX detected a single polypeptide of estimated mol. wt 54 × 10³, 54 × 10³ and 50 × 10³ respectively but that of isolate T contained two polypeptides of estimated mol. wt 54 × 10³ and 50 × 10³. These data suggest that RRV-T is a mixture of two isolates. In laboratory tests the nematode Xiphinema diversicaudatum transmitted four isolates of AMV efficiently whereas two populations of the nematode Longidorus elongatus were less efficient vectors of four RRV isolates. Neither vector species transmitted virus to any of nine raspberry cultivars. The results are discussed in relation to the control of nepoviruses in raspberry and to the biology of these viruses.     

Development of the magnetic capture system for recovery of Xiphinema americanum

Xiphinema americanum is listed as a quarantine nematode by The European Plant Protection Organisation because of its ability to transmit quarantine viruses. Detection of this nematode in soil samples, or in mixed nematode samples extracted from soil, is therefore of paramount importance. We recently described the use of magnetic beads (Dynabeads) in combination with probes such as lectins or antibodies for recovery of small endoparasitic nematodes including Meloidogyne spp. and Globodera rostochiensis from mixed nematode samples. Here we show that magnetic capture can be used with much larger nematodes such as X. americanum. We describe lectins and antisera that bind to the surface of this nematode and show that the antisera can be used in the Dynabeads system to recover and enrich X. americanum from mixed nematode samples.     

GROWTH OF HETEROSIGMA CARTERAE (RAPHIDOPHYCEAE) ON NITRATE AND AMMONIUM AT THREE PHOTON FLUX DENSITIES: EVIDENCE FOR N STRESS IN NITRATE-GROWING CELLS

The marine alga Heterosigma carterae Hulburt (Raphidophyta) was grown in N-limiting batch cultures using either nitrate or ammonium as the N source, at photon flux densities (PFDs) of 50, 200, and 350 μmol·m^-2·s^-1 in a 12:12 h LD cycle. Carbon content could be estimated from biovolume (μg C = 0.278 × nL; R = 0.98) but not reliably from pigment content. During exponential growth, ammonium-grown cells (in comparison with nitrate-grown cells at the same PFD) attained higher growth rates by at least 20%, contained more N, and had a lower C:N ratio, higher concentrations of intracellular free amino acids, and higher ratios of glutamine: glutamate (Gln: Glu) and asparagine: aspartate (Asn:Asp). Growth was nearly light-saturated on ammonium at 200 μmol·m^-2·s^-1 (cell-specific growth rate of 1.2 d^-1) but probably not saturated in nitrate-grown cells at 350 μmol·m^-2·s^-1. PFD did not affect Gln: Glu or Asn: Asp for a given N source. These results indicate that the nitrate-growing cells were more N-stressed than those using ammonium (which in contrast were relatively C-stressed) and that this organism would show an enhanced competitive advantage against other species when supplied with a transient supply of ammonium rather than nitrate .     

A predicted consensus structure for the protein kinase C2 homology (C2H) domain,the repeating unit of synaptotagmin

A secondary structure has been predicted for the protein kinase C2 regulatory domain found in homologous form in synaptotagmin, some phospholipases, and some GTP activated proteins. The proposed structure is built from seven consecutive beta strands followed by a terminal alpha helix. Considerations of overall surface exposure of individual secondary structural elements suggest that these are packed into a 2-sheet beta sandwich structure, with one of only three of the many possible folds being preferred. © 1995 Wiley-Liss, Inc.