Different colonization patterns of two closely related stream insects (Austrosimulium spp.) following disturbance

SUMMARY.

• 1 In many streams, blackfly larvae rapidly colonize scoured surfaces, then decline in numbers as other species are still increasing. Such a colonization pattern may be generated by species that seek disturbed substrata because they prefer scoured surfaces having low epilithon cover (i.e. they are opportunists) or because of lowered faunal densities (i.e. they are fugitives), but this has rarely been tested.
• 2 In the Acheron River, south-eastern Australia, the larvae of the blackfly Austrosimulium torrentium show the typical pattern of increase and decline whereas A. victoriae shows a different pattern of more gradual increase.
• 3 An experiment showed that A. torrentium, consistent with its colonization pattern, responded strongly to treatments that mimicked the effects of disturbance; it colonized bricks with few other animals present regardless of epilithon cover and therefore is potentially a fugitive species. A. victoriae did not respond convincingly to treatments, which is also consistent with its colonization pattern.
• 4 Blackfly larvae of both species preferentially colonized bricks that were in fast-moving water. Hence, A. torrentium only responded to the densities of other fauna when bricks occurred in currents greater than approximately 30 cm s^?1.
• 5 Whilst epilithon cover did not affect abundance of blackfly larvae, it did affect attachment positions. In one experimental treatment, epilithon was reduced on one half of the top surfaces of bricks. More than 50% of larvae on these bricks were attached to the epilithon-reduced halves.
• 6 Our results show that functional feeding or taxonomic groups do not necessarily contain ecologically equivalent taxa; colonization patterns may provide a more useful way of categorizing species for the purposes of modelling these assemblages.

     

Voltage transients elicited by sudden step-up of auxin

Abstract It is hypothesized (i) that the molecular mechanism for the reception of friction and flexure and the mechanism by which auxin enhances ethylene production have in common a release of free calcium into the cytosol, (ii) that elevated cytosolic calcium initiates vesicle exocytosis, and (iii) that the vesicles release a factor or set of factors which depolarizes the plasmalemma and promotes ethylene synthesis. One consequence of such exocytosis should be small, extracellularly observable voltage transients. Transients, ranging in size up to 600 μV and possessing risetimes (10–90%) of approximately 200 ms, are known to be elicited in etiolated stems of Pisum sativum L. by friction and are here shown to be elicited by sudden increase of auxin concentration and also by a Ca²⁺ ionophore.     

Further Studies on Substrates Inducing Metacyclogenesis in Trypanosoma cruzi

Epimastigotes of Trypanosoma cruzi, Peru strain, incubated in Contreras' artificial triatomine urine transformed into metacyclic trypomastigotes when 10 mM L-glutamine, L-asparagine or D-fructose was added to the medium. Metacyclogenesis with these substrates was comparable to the percent metacyclic morphotype formation induced by L-proline and significantly greater than that stimulated by 10 mM D-glucose. Sodium acetate (10 mM) increased transformation induced by L-proline, and L-hydroxyproline (10 mM) increased transformation induced by D-fructose. Phosphoenolpyruvate (10 mM) inhibited L-proline-induced metacyclic trypomastigote stage formation. Three antimetabolites, azetidine 2-carboxylate (5 mM), malonic acid (1 mM), and desthiobiotin (5 mM), completely inhibited D-fructose-induced but not L-proline-induced transformation. The Costa Rica, Y, and CL strains of T. cruzi showed different patterns of percent metacyclogenesis with substrates that induce transformation in the Peru strain.     

Stimulation of Ribulose Bisphosphate Carboxylase Activity by Inorganic Orthophosphate without an Increase in Bound Activating CO2: Co-operativity between the Subunits of the Enzyme

Parry, M. A. J., Schmidt, C. N. G., Cornelius, M. J., Keys,A. J., Millard, B. N. and Gutteridge, S. 1985. Stimulation ofribulose bisphosphate carboxylase activity by inorganic orthophosphatewithout an increase in bound activating CO²: co-operativitybetween the subunits of the enzyme.—J. exp. Bot. 36: 1396–1404 Ribulose bisphosphate carboxylase/oxygenase (E.C. 4.1.1.39 [EC] )from wheat (Triticum aestivum L.), already activated by reactionwith CO² and Mg²⁺, was increased in activity on addition ofinorganic orthophosphate. This further activation took placewithout a significant increase in the amount of bound activatingCO² and the effect was relatively greater with smaller amountsof bound CO². With less than 2·0 mol of CO² bound permol holoenzyme, phosphate increased activity about five-foldwhilst with 7·0 mol of bound activating CO² per mol holoenzyme,phosphate increased activity by a factor of only 1 ·8.This decrease in the effect of orthophosphate with increasein bound activating CO² suggests negative co-operativity betweenactivated sites. The stimulation of activity by inorganic orthophosphatemust be a process distinct from activation by CO²; it was observedwith both the slow and the rapidly activating forms of ribulosebisphosphate carboxylase/oxygenase from wheat. Key words: Ribulose bisphosphate carboxylase, activation, inorganic orthophosphate CO², co-operativity     

Endogenous Gibberellins and Growth of Tobacco Callus Cultures

Tobacco callus grown under a range of conditions for different lengths of time contained various levels of gibberellin-like substances. Culture conditions, viz: light versus darkness and the quantity of cytokinin in the medium, affected the amount of gibberellins found in the tissue. These culture conditions were also important in controlling growth rate of the callus and modified the ability of the tissue to respond to exogenous gibberellins. Furthermore, substances which are known to inhibit gibberellin biosynthesis and also thought to block gibberellin action in some cases, were found to reduce the rate of growth. These data support the idea that endogenous gibberellins may be important in the control of the normal growth of tobacco cells in culture.     

'Floral' scent production by Puccinia rust fungi that mimic flowers

Crucifers (Brassicaceae) in 11 genera are often infected by rust fungi in the Puccinia monoica complex. Infection causes a 'pseudoflower' to form that is important for attracting insect visitors that sexually outcross the fungus. 'Pollinator' attraction is accomplished through visual floral mimicry, the presence of a nectar reward and floral fragrances. Here we used gas chromatography and mass spectrometry to identify and quantify fragrance production by these rust fungi on several Arabis hosts, and by co-occurring true flowers that share insect visitors. Fungal pseudoflowers produced distinctive floral fragrances composed primarily of aromatic alcohols, aldehydes and esters. Pseudoflower fragrances were chemically similar to noctuid-moth-pollinated flowers, such as Cestrum nocturnum and Abelia grandiflora , but were very different from host flowers, host vegetation and the flowers of coblooming, nonhost angiosperms. There was variation in the quantity and composition of fragrance profiles from different fungal species as well as within and among hosts. The evolution of scent chemistry is relatively conservative in these fungi and can be most parsimoniously explained in three steps by combining chemical data with a previously determined rDNA ITS sequence-based phylogeny. Pseudoflower scent does not appear to represent a simple modification of host floral or vegetative emissions, nor does it mimic the scent of coblooming flowers. Instead, we suspect that the unique fragrances, beyond their function as pollinator attractants, may be important in reducing gamete loss by reinforcing constancy among foraging insects.     

Cytoskeleton of Toxoplasma gondii1

The cytoskeleton of Toxoplasma gondii was studied by electron microscopy using 1) whole mounts of detergent-extracted parasites and 2) thin sections of routine preparations, tannic acid-stained organisms, and detergent-extracted parasites. In whole mounts, the spiral arrangement of the 22 pellicular microtubules closely corresponded to the pattern of surface ridges seen previously by scanning electron microscopy and reflected the torsion of the parasite body during locomotion. The microtubules had free posterior ends and were anchored anteriorly in the polar ring, presumed to be a microtubule organizing center (MTOC). The insertions of the microtubules were supported by blunt projections of the polar ring, forming a cogwheel pattern in transverse view. The internal microtubules had 13 protofilaments and were twice the length of the conoid. They extended through the conoid and ended at the anterior preconoidal ring, presumably a second MTOC. The subunits of the conoid were arranged in a counterclockwise spiral when traced from base to tip, as were the pellicular microtubules. We postulate that as the conoid moves, the polar ring complex moves along the spiral pathway of the conoid subunits. Retraction of the conoid would then rotate the polar ring, producing the torsion of the body we observed by SEM.     

The influence of pH and temperature on initiation of growth of Salmonella spp.

The ability of 13 strains of Salmonella , representing 12 serotypes, to grow in a tryptone-yeast extract-glucose medium, acidified with HC1 to pH values between 3.80 and 5.60 at intervals of 0.20 units, has been investigated. During incubation at 30°C, growth occurred at minimum pH values of 3.8–4.0 in 1–3 d. At 20°C, growth occurred at minimum pH values of 3.8–4.2 in 3–5 d. In tests incubated at 10°C, growth occurred at minimum pH values of 4.4–4.8 in between 10 and 19 d.