Niche differentiation and maintenance of genetic identity in cohabiting Eucalyptus species

Differences in niche utilization between two cohabiting eucalypt species (Eucalyptus signata and E. umbra ssp. umbra) on North Stradbroke Island, Qld., are documented, including differences in morphology, growth patterns, seasonality, insect attack and a three month difference in peak seasonal uptake of most essential elements. The significance of these niche differences in aiding the coexistence of competing eucalypt species is supported by results using recent theoretical models from niche theory. It is noted that the presence of significant niche complementarity amongst cohabiting pairs of eucalypts will place hybrid offspring at a disadvantage relative to homozygous strains. This phenomenon helps explain the scarcity or absence of hybrids in a number of communities where potentially interbreeding species of Eucalyptus coexist. Co-occurrence of species pairs which are capable of interbreeding will not be favored by environmental selection both because of the reduced production of homozygous offspring, and because of the reduced niche separation exhibited by taxonomically closely-related species. Such differences help explain the scarcity of co-occurrence of interbreeding pairs of species of Eucalyptus in relatively unperturbed natural communities.     

Factors affecting the assessment of resistance of potatoes to gangrene (Phoma exigua var. foveata)

Three experiments designed to elucidate the effects and interactions of different inoculation methods, inoculation positions, strains of Phoma exigua var. foveata and clones of potato tubers inoculated were analysed using as data dimensions of the lesions and a more general surface score. The assessment of susceptibility was affected by all these factors. The ranking of varieties for resistance altered considerably depending upon whether the surface area or the depth of lesions was considered. Derivation of more complex scores combining these measurements reduced the relative genetic component and hence would be of no value to potato breeders.     

Two New Subspecies of Herpetomonas muscarum (Leidy, 1856) Kent, 1880

SYNOPSIS. Herpetomonas muscarum muscarum n. subsp. was isolated from Musca domestica L. In culture at 20 C it assumed the opisthomastigote (up to 15%), double-flagellate and flagellate promastigote forms. At 30 C or with 4% urea added to cultures at 20 C, the proportion of opisthomastigotes was greater (up to 40%). In experimentally infected flies only transient infections, which included both opisthomastigotes and promastigotes, occurred. The promastigotes were 15–30 μ long and the kinetoplast was small and subspherical or transversely elongate. H. muscarum ingenoplastis n. subsp. was isolated from Phormia regina (Meigen). In culture at 20 C almost all individuals were double-flagellate promastigotes 20–40 μ long and less than 1% were opisthomastigotes. At 30 C or with added urea there was no increase in the proportion of opisthomastigotes and the cultures were not vigorous. In experimentally infected flies opisthomastigotes were 5–39% of the population depending on the part of the gut sampled. In all stages the kinetoplast was large (1.5–2.5 μ long) and tear-drop-shaped with the point directed posteriorly.
In artificially mixed cultures of H. m. muscarum and H. m. ingenoplastis the former predominated after a short time and eventually survived alone. A mixed culture that was about 98% H. m. muscarum was fed to Phormia regina and produced heavy pure infections of H. m. ingenoplastis , which lasted for 22 days with no indication of decline. No evidence of cyst formation was found in either subspecies.     

A molecular phylogenetic appraisal of the systematics of the Aglaopheniidae (Cnidaria: Hydrozoa,Leptothecata) from the north‐east Atlantic and west Mediterranean

The hydrozoan family Aglaopheniidae (Cnidaria) is widespread worldwide and contains some of the most easily recognizable hydroids because of their large colony size and characteristic microscopic structure. The systematics of the group has, however, been controversial and dedicated molecular analyses are lacking. We therefore analysed existing and new 16S rRNA sequences of Aglaopheniidae, in a total of 98 16S sequences corresponding to 25 putative species (25 nominal and three undescribed) from seven genera. The monophyly of the subfamilies Gymnangiinae and Aglaopheniinae, and tribes Aglaopheniini and Cladocarpini were not verified with 16S sequence data. The genera Gymnangium and Aglaophenia can only be considered valid if both Gymnangium gracicaule and Aglaophenia latecarinata are removed from their respective genera. The phenotypically similar Cladocarpus and Streptocaulus are probably monophyletic and clearly distinct genetically. The genus Lytocarpia may be polyphyletic. The nominal species Aglaophenia pluma, Aglaophenia tubiformis, and Aglaophenia octodonta are probably conspecific, as are also the species Aglaophenia acacia and Aglaophenia elongata. The 16S data revealed the existence of two potentially unnamed species of Aglaophenia respectively from the Azores and Madeira. The phylogeographical structure of the taxa with the greatest representation of haplotypes from the north‐east Atlantic and Mediterranean, revealed the influence of Mediterranean waters in Madeira and the Azores, and gene flow between deep waters of the Mediterranean and Atlantic. The last glaciations in Europe may have caused genetic bottlenecks but also high intraspecific haplotype diversity. Finally, Macrorhynchia philippina was detected in samples from Madeira and possibly represents an invasive species. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 717–727.     

NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO2

The effect of elevated atmospheric CO₂ on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton (¹H) nuclear magnetic resonance (NMR) imaging. Exposure of 24-d-old plants to atmospheric CO₂-enriched air at 650 cm³ m^?3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short-term drying-stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO₂ (350 m³ m^?3), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO₂ does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO₂ environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate.     

Effects of nutrient loading and extreme rainfall events on coastal tallgrass prairies: invasion intensity, vegetation responses, and carbon and nitrogen distribution

Soil fertility and precipitation are major factors regulating transitions from grasslands to forests. Biotic regulation may influence the effects of these abiotic drivers. In this study, we examined the effects of extreme rainfall events, anthropogenic nutrient loading and insect herbivory on the ability of Chinese tallow tree ( Sapium sebiferum ) to invade coastal prairie to determine how these factors may influence woody invasion of a grassland. We manipulated soil fertility (NPK addition) and simulated variation in frequency of extreme rainfall events in a three growing season, full factorial field experiment. Adding water to or pumping water out of plots simulated increased and decreased rainfall frequencies. We added Sapium seeds and seedlings to each plot and manipulated insect herbivory on transplanted Sapium seedlings with insecticide. We measured soil moisture, Sapium performance, vegetation mass, and carbon and nitrogen in vegetation and soils (0–10 cm deep, 10–20 cm deep). Fertilization increased Sapium invasion intensity by increasing seedling survival, height growth and biomass. Insect damage was low and insect suppression had little effect in all conditions. Recruitment of Sapium from seed was very low and independent of treatments. Vegetation mass was increased by fertilization in both rainfall treatments but not in the ambient moisture treatment. The amount of carbon and nitrogen in plants was increased by fertilization, especially in modified moisture plots. Soil carbon and nitrogen were independent of all treatments. These results suggest that coastal tallgrass prairies are more likely to be impacted by nutrient loading, in terms of invasion severity and nutrient cycling, than by changes in the frequency of extreme rainfall events.