Temporal snychrony and patterns in an exotic host-parasitoid community

We studied an imported host-parasitoid community in Hawaii, asking to what extent the species covaried in a systematic fashion even though all species were exotic to Hawaii, and occurred in an artificial agroecosystem (a commercial guava, Psidium guajava L., orchard). Using knock-down pyrethrin sprays we were able to accurately quantify numbers of the host, [oriental fruit fly, Bactrocera dorsalis (Hendel)] and its four major parasitoid species [Biosteres arisanus (Sonan), Diachasmimorpha longicaudata (Ashmead), Psyttalia incisi (Silvestri), and Bi. vandenboschi (Fullaway)] at hourly intervals. We found that the parasitoids' activity and abundance was well correlated with the activity and abundance of their host, and that all four parasitoid species covaried in concert with one another. In fact, the magnitude of correlation between the different species in this system was greater than the correlation with temperature. This show clearly that an entirely exotic community, reassembled piecemeal as a result of biocontrol efforts, can end up with patterns of temporal covariation that are highly coincident. One other interesting result concerns the speed with which sprayed trees were recolonized by the fruit fly and its parasitoids. The time that it took each species to reach its mean density prior to removal by the first pyrethrin spray at 0600 hours varied. It took 2 h for female B. dorsalis to recolonize guava trees to pre-spray levels. It took 3 h for Bi. arisanus, 4 h for D. longicaudata, 7 h for Bi. vandenboschi and 14 h for P. incisi to reach pre-spray levels. The fact that Bi. arisanus recolonized vacant trees almost as rapidly as did the fruit fly pest suggest that there is little opportunity for the fruit fly to escape in space and time by staying one step ahead of its enemies.     

Characterization of a truncated form of arrestin isolated from bovine rod outer segments.

The inactivation of photolyzed rhodopsin requires phosphorylation of the receptor and binding of a 48-kDa regulatory protein, arrestin. By binding to phosphorylated photolyzed rhodopsin, arrestin inhibits G protein (Gt) activation and blocks premature dephosphorylation, thereby preventing the reentry of photolyzed rhodopsin into the phototransduction pathway. In this study, we isolated a 44-kDa form of arrestin, called p44, from fresh bovine rod outer segments and characterized its structure and function. A partial primary structure of p44 was established by a combination of mass spectrometry and automated Edman degradation of proteolytic peptides. The amino acid sequence was found to be identical with arrestin, except that the C-terminal 35 residues (positions 370-404) are replaced by a single alanine. p44 appeared to be generated by alternative mRNA splicing, because intron 15 interrupts within the nucleotide codon for 369Ser in the arrestin gene. Functionally, p44 binds avidly to photolyzed or phosphorylated and photolyzed rhodopsin. As a consequence of its relatively high affinity for bleached rhodopsin, p44 blocks Gt activation. The binding characteristics of p44 set it apart from tryptic forms of arrestin (truncated at the N- and C-termini), which require phosphorylation of rhodopsin for tight binding. We propose that p44 is a novel splice variant of arrestin that could be involved in the regulation of Gt activation.     

Histopathological studies ofSporothrix schenckii-inoculated mice

Defense mechanisms againstSporothrix schenckii were studied using mouse models. After an intracutaneous injection of the yeast form ofS. schenckii to the dorsal skin of the congenitally athymic nude and normal heterozygote littermate mice, nodules were formed. They regressed and disappeared in 10 weeks in the case of normal mice. On the other hand, nodules and then ulceration developed progressively in nude mice until all animals expired by dissemination of microorganisms at the 11th week of inoculation. Histopathologically the migrated cells were similar in both the normal and the nude mice, particularly during the early phase (within 24 h), with infiltration by PMNs being predominant. Fragmentation ofS. schenckii commenced early during the 12–24 h stage of inoculation in the normal mice, while such fragmentation was scarce in nude mice even though numerous PMNs accumulated. Microscopic observations in the early stages (within 24 h of inoculation) suggested that the lack of killing activity by PMNs in nude mice contributes more to the impaired defense than the lack of macrophage activation by T-cells.     

Antibody raised against extracellular proteinases ofSporothrix schenckii inS. schenkii inoculated hairless mice

Sporothrix schenckii produces two extracellular proteinases, namely proteinase I and II. Proteinase I is a serine proteinase, inhibited by chymostatin, while proteinase II is an aspartic proteinase, inhibited by pepstatin. Studies on substrate specificity and the effect of proteinase inhibitors on cell growth suggest an important role for these proteinases in terms of fungal invasion and growth. There has, however, been no evidence presented demonstrating thatS. schenckii produces 2 extracellular proteinases in vivo. In order to substantiate the in vivo production of proteinases and to attempt a preliminary serodiagnosis of sporotrichosis, serum antibodies against 2 proteinases were assayed usingS. schenckii inoculated hairless mice. Subsequent to an intracutaneous injection ofS. schenckii to the mouse skin, nodules spontaneously formed and disappeared for a period of 4 weeks. Histopathological examination results were in accordance with the microscopic observations. Micro-organisms disappeared during the fourth week. Serum antibody titers against purified proteinases I and II were measured weekly, using enzyme-linked immunosorbent assay (EIA). As a result, the time course of the antibody titers to both proteinases I and II were parallel to that of macroscopic and microscopic observations in an experimental mouse sporotrichosis model. These results suggest thatS. schenckii produces both proteinases I and II in vivo. Moreover, the detection of antibodies against these proteinases can contribute to a serodiagnosis of sporotrichosis.     

Gastric colonization withCandida albicans

This is the first report on the isolation ofCryptococcus neoformans from pigeon droppings in China and their serotypes.C. neoformans colonies which produced brown colonies on caffeic acid-cornmeal agar were found in Twenty-five out of thirty-six samples of pigeon droppings. Fifty-one colonies randomly picked from the positive samples were identified asC. neoformans by a commercially available kit for carbon source assimilation test and Christensen's urea agar. Forty (78%) out of the 51 strains were serotyped as A and 11 (22%) as AD. At the same time, seventeen out of nineteen clinical isolates were serotyped as A and 2 as B. There are three findings in our results. One is that onlyC. neoformans var.neoformans strains could be isolated from pigeon droppings, although the varietygattii strains were found in the clinical isolates obtained in the same geographic site in China. The second is that serotype A strains were most frequently seen in natural and clinical materials in the southeast part of China, and serotype AD strains were isolated in pigeon droppings but not in clinical materials. The third is that the coexistence of serotype A and AD cells ofC. neoformans strains in same samples of pigeon droppings were observed.     

Two bacteria causing farmer's lung: Fine structure ofThermoactinomyces vulgaris andSaccharopolyspora rectivirgula

Larval cuticle ofHelicoverpa (Heliothis)zea and yeast extract added to a minimal medium (MM) induced germination of conidia ofNomuraea rileyi whereas sterile distilled water or MM alone did not. Yeast extract increased mycelial yield, but when cuticle was added, mycelial yield significantly decreased. Proteases and chitinases ofN. rileyi were only expressed when cuticle was added to the MM.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by US Department of Agriculture.     

Mechancial properties of bat wing membrane skin

The skin of the bat wing in functionally unique among mammals: it serves as a major locomotor organ in addition to its protective and regulatory functions. We used tensile testing to investigate the mechanical capabilities of wing membrane skin, and compared stiffness, strength, load at failure, and energy absorption among specific wing regions and among a variety of bat taxa. We related these characteristics to the highly architectural fibrous supporting network of the wing membrane. We found that all material properties showed a strong anisotropy. In particular, wing membrane skin shows maximum stiffness and stregth parallel to the wing skeleton, and greatest extensibility parallel to the wing's trailing edge. We also found significant variation among wing regions. The uropatagium (tail membrane) supported the greatest load at failure, and the plagiopatagium (proximal wing membrane between laterl body wall and hand skeleton) is the weakest and most extensible part of the wing. We believe that the increased load bearing ability of the uropatagium relats to its key role in capture of insect prey, and that the great extensibility of the plagiopatagium promotes development of camber near the wing's centre of lift. In interspecific comparisons, energy absorpion and load to failure were greatest in Artibeus jamaicensis , the largest bat in our sample and the species with the highest wing loading, suggesting that wing loading may play a role in dictating the fuctional design of wing membranes.     

Habitat-specific predation susceptibilities of a littoral rotifer to two invertebrate predators

The rotifer Euchlanis dilatata lives associated with submerged vegetation in the littoral zone of freshwater lakes and ponds. I assessed habitat-specific predation susceptibilities for this rotifer in the presence of three aquatic macrophytes (Myriophyllum exalbescens, Elodea canadensis, and Ceratophyllum demersum) and two predators (damselfly nymphs — Enallagma carunculata; and cnidarians — Hydra). Rotifer survival was greatest on Myriophyllum in the presence of both predators. Conversely, the presence of the other macrophyte species actually increase rotifer suspectibility to predation by damselfly nymphs. I also manipulated plant structural complexity. As predicted, decreasing the relative complexity of each plant resulted in lower rotifer survival.