Host plant species affects the quality of the generalist Trichoplusia ni as a host for the polyembryonic parasitoid Copidosoma floridanum

Diet of herbivorous insects can influence both the herbivores and their natural enemies. We examined the direct and indirect effects of diet on the interactions between the polyphagous herbivore Trichoplusia ni Hübner (Lepidoptera: Noctuidae) and its polyembryonic parasitoid Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae). To determine how host plant species and host plant iridoid glycoside content affect host caterpillars and their parasitoids, parasitized and unparasitized T. ni were given leaves of either Plantago lanceolata L., which contains the iridoid glycosides aucubin and catalpol, Plantago major L. (Plantaginaceae), which contains only aucubin, or Taraxacum officinale F.H. Wigg (Asteraceae), which contains neither. Survival of unparasitized T. ni was much lower when fed P. major compared with the other two host plants, whereas pupae were smallest when fed T. officinale and developed most slowly when fed P. lanceolata as larvae. Neither aucubin nor catalpol were detected in intact Plantago‐fed T. ni larvae or their hemolymph, and only trace amounts of aucubin were detected in frass, suggesting that these compounds are mostly metabolized in the midgut and are not encountered by the parasitoid. Copidosoma floridanum clutch size was almost doubled when reared from P. lanceolata‐fed T. ni compared with T. officinale‐fed larvae and tripled compared with P. major‐fed larvae, although the percent of parasitoids surviving to adulthood was uniformly high regardless of host diet. The observed variation in C. floridanum fitness among host diets is likely mediated by the effect of the diets on host quality, which in turn may be influenced more by other factors in the host plants than their iridoid glycoside profiles. Interactions between plant metabolites, generalist herbivores like T. ni, and their parasitoids may be predominantly indirect.     

The septation apparatus,an autonomous system in budding yeast

Actomyosin ring contraction and chitin primary septum deposition are interdependent processes in cell division of budding yeast. By fusing Myo1p, as representative of the contractile ring, and Chs2p for the primary septum, to different fluorescent proteins we show herein that the two processes proceed essentially at the same location and simultaneously. Chs2p differs from Myo1p in that it reflects the changes in shape of the plasma membrane to which it is attached and in that it is packed after its action into visible endocytic vesicles for its disposal. To ascertain whether this highly coordinated system could function independently of other cell cycle events, we reexamined the septum-like structures made by the septin mutant cdc3 at various sites on the cell cortex at the nonpermissive temperature. With the fluorescent fusion proteins mentioned above, we observed that in cdc3 at 37 degrees C both Myo1p and Chs2p colocalize at different spots of the cell cortex. A contraction of the Myo1p patch could also be detected, as well as that of a Chs2p patch, with subsequent appearance of vesicles. Furthermore, the septin Cdc12p, fused with yellow or cyan fluorescent protein, also colocalized with Myo1p and Chs2p at the aberrant locations. The formation of delocalized septa did not require nuclear division. We conclude that the septation apparatus, composed of septins, contractile ring, and the chitin synthase II system, can function at ectopic locations autonomously and independently of cell division, and that it can recruit the other elements necessary for the formation of secondary septa.     

Electrical and adaptive properties of rod photoreceptors in bufo marinus. II. Effects of cyclic nucleotides and protaglandins

Substances known to alter cyclic nucleotide levels in cells were applied to the isolated toad retina and effects on rod electrical and adaptive behavior were studied. The retina was continually superfused in control ringer’s or ringer’s containing one or a combination of drugs, and rod activity was recorded intracellularly. Superfusion with cGMP, Bu(2)GMP, isobutylmethylxanthine (IBMX; a phosphodiesterase inhibitor), or PGF(2α) (a prostaglandin) caused effects in rods that closely match those observed when extracellular Ca(2+) levels were lowered. For example, short exposures (up to 6 min) of the retina to these substances caused depolarization of the membrane potential, increase in response amplitudes, and some changes in waveform; but under dark-adapted or partially light-adapted conditions receptor sensitivity was virtually unaffected. That is, the position of the V-log I curve on the intensity axis was determined by the prevailing light level, not by drug level. These drugs, like lowered extracellular Ca(2+), also decreased the period of receptor saturation after a bright-adapting flash, resulting in an acceleration of the onset of membrane and sensitivity recovery during dark adaptation.

Long-term (6-15 min) exposure of a dark-adapted retina to 5 mM IBMX or a combination of IBMX and cGMP caused a loss of response amplitude and a desensitization of the rods that was similar to that observed in rods after a long-term low Ca(2+) (10(-9)M) treatment. Application of high (3.2 mM) Ca(2+) to the retina blocked the effects of applied Bu(2)cGMP. PGE(1) superfusion mimicked the effects of increasing extracellular Ca(2+). The results show that increased cGMP and lowered Ca(2+) produce similar alterations in the electrical activity of rods. These findings suggest that Ca(2+) and cGMP are interrelated messengers. We speculate that low Ca(2+) may lead to increased intracellular cGMP, and/or that applied cGMP, and/or that applied cGMP may lower cytosol Ca(2+), perhaps by stimulating Ca(2+)- ATPase pumps in the outer segment.

     

Predation hazard and seed removal by small mammals: microhabitat versus patch scale effects

Predator avoidance may involve response strategies of prey species that are time and space specific. Many studies have shown that foraging individuals avoid predators by altering microhabitat usage; alternatively, sites may be selected according to larger-scale features of the habitat mosaic. We measured seed removal by two small mammal species (Peromyscus leucopus, and Microtus pennsylvanicus) at 474 stations over an experimentally created landscape of 12 patches, and under conditions of relatively high (full moon) and low (new moon) predatory hazard. Our objective was to determine whether predator avoidance involved the selection of small-, medium-, or large-scale features of the landscape (i.e., at the scale of microhabitats, habitats, or habitat patches). We found rates of seed removal to vary more with features of whole patches than according to variation in structural microhabitats within patches. Specific responses included: under-utilization of patch edge habitats during full moon periods, and microhabitat effects that were only significant when considered in conjunction with larger-scale features of the landscape. Individuals residing on large patches altered use of microhabitats/habitats to a greater extent than those on smaller patches. Studies just focusing on patterns of microhabitat use will miss responses at the larger scales, and may underestimate the importance of predation to animal foraging behavior.     

A Simple Method Using Alizarin Red S For the Detection of Calcium in Epoxy Resin Embedded Tissue

This report presents a simple procedure for staining 1-2 μm epoxy plastic sections of cells and mineralizing matrix present in fetal bovine bone tissue cultures. A 0.3% aqueous toluidine blue 0 solution was used as a cellular stain and was followed with 2% alizarin red S for the detection of calcium at sites of mineralition. Effects of concentration and pH of alizarin red S on the penetration of epon embedded thick sections were investigated Optimal staining was achieved with a 2% aqueous alizarin red S solution adjusted to a pH of 5.5-6.5. This staining procedure provides unusually clear contrast between mineral and bone cells in plastic sections for light microscopy.     

Synthesis and biological activities of pseudopeptide analogues of LH-RH: agonists and antagonists

Using solid phase methods, seven agonist and antagonist analogues of LH-RH have been prepared containing enzyme-resistant CH₂S linkages as selected amide bond replacements. Agonists modified at the 5–6, 6–7 and 9–10 position had 2, < 0.1, and 10% of the $\text{in}\text{vitro}$ activity of LH-RH, respectively. Among potential antagonists, 6–7 position analogues showed only minimal inhibitory activity but N- and C-terminal modified analogues retained substantial LH-RH-LH and FSH inhibitory activity. In addition, a 1–2 position methylene thioether analogue of the parent [Ac-Pro¹, D-Phe², D-Trp^3,6]LH-RH antagonist was completely inhibitory at 30 ng $\text{in}\text{vitro}$ and represents the first such structure-modification that may be at least as active as its corresponding amide linked congener. However, neither 1–2 nor 9–10 methylene thioether position antagonists showed $\text{in}\text{vivo}$ antiovulatory activity at the 250 μg level.     

The function of chitin synthases 2 and 3 in the Saccharomyces cerevisiae cell cycle

The morphology of three Saccharomyces cerevisiae strains, all lacking chitin synthase 1 (Chs1) and two of them deficient in either Chs3 (calR1 mutation) or Chs2 was observed by light and electron microscopy. Cells deficient in Chs2 showed clumpy growth and aberrant shape and size. Their septa were very thick; the primary septum was absent. Staining with WGA-gold complexes revealed a diffuse distribution of chitin in the septum, whereas chitin was normally located at the neck between mother cell and bud and in the wall of mother cells. Strains deficient in Chs3 exhibited minor abnormalities in budding pattern and shape. Their septa were thin and trilaminar. Staining for chitin revealed a thin line of the polysaccharide along the primary septum; no chitin was present elsewhere in the wall. Therefore, Chs2 is specific for primary septum formation, whereas Chs3 is responsible for chitin in the ring at bud emergence and in the cell wall. Chs3 is also required for chitin synthesized in the presence of alpha-pheromone or deposited in the cell wall of cdc mutants at nonpermissive temperature, and for chitosan in spore walls. Genetic evidence indicated that a mutant lacking all three chitin synthases was inviable; this was confirmed by constructing a triple mutant rescued by a plasmid carrying a CHS2 gene under control of a GAL1 promoter. Transfer of the mutant from galactose to glucose resulted in cell division arrest followed by cell death. We conclude that some chitin synthesis is essential for viability of yeast cells.     

Truncating ribosomal protein S19 mutations and variable clinical expression in Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a rare constitutional erythroblastopenia characterized by a specific defect in erythroid differentiation. Recently, mutations in the gene encoding ribosomal protein (RP) S19 were found in a subset of patients with the disease. To characterize further RPS19 mutations and to investigate genotype-phenotype relationships, we screened this gene for mutations in patients with DBA by direct sequencing and Southern-blot analysis. Four novel mutations were identified. A G120A nonsense mutation resulting in a stop at codon 33, a C302T nonsense mutation introducing a premature stop at codon 84, and a 327delG which results in a frame shift at codon 103. A fourth and more complex mutation (TT157-158AA, 160insCT) resulting in a Leu45Gln and a frame shift from codon 47 was found in three affected family members with variable phenotypes. The different clinical expression for identical mutations suggest the presence of other modulating factors for the disease. The mutations presented here further support the role of RPS19 in erythropoietic differentiation and proliferation.     

Use of an exotic host plant reduces viral burden in a native insect herbivore

Incorporation of exotic plants into the diets of native herbivores is a common phenomenon, influencing interactions with natural enemies and providing insight into the tritrophic costs and benefits of dietary expansion. We evaluated how use of an exotic plant, Plantago lanceolata, impacted immune performance, development and susceptibility to pathogen infection in the neotropical herbivore Anartia jatrophae (Lepidoptera: Nymphalidae). Caterpillars were reared on P. lanceolata or a native plant, Bacopa monnieri, and experimentally infected with a pathogenic virus, Junonia coenia densovirus. We found that virus-challenged herbivores exhibited higher survival rates and lower viral burdens when reared on P. lanceolata compared to B. monnieri, though immune performance and development time were largely similar on the two plants. These findings reveal that use of an exotic plant can impact the vulnerability of a native herbivore to pathogen infection, suggesting diet-mediated protection against disease as a potential mechanism facilitating the incorporation of novel resources.