Melanism and disease resistance in insects

There is growing evidence that insects in high-density populations invest relatively more in pathogen resistance than those in low-density populations (i.e. density-dependent prophylaxis). Such increases in resistance are often accompanied by cuticular melanism, which is characteristic of the high-density form of many phase polyphenic insects. Both melanism and pathogen resistance involve the prophenoloxidase enzyme system. In this paper the link between resistance, melanism and phenoloxidase activity is examined in Spodoptera lanae. In S. exempta, cuticular melanism was positively correlated with phenoloxidase activity in the cuticle, haemolymph and midgut. Melanic S. exempta larvae were found to melanize a greater proportion of eggs of the ectoparasitoid Euplectrus laphygmae than non-melanic larvae, and melanic S. littoralis were more resistant to the entomopathogenic fungus Beauveria bassiana (in S. exempta the association between melanism and fungal resistance was non-signficant). These results strengthen the link between melanism and disease resistance and implicate the involvement of phenoloxidase.

Can the protein costs of bacterial resistance be offset by altered feeding behaviour?

1. Mounting an immune response is likely to be costly in terms of energy and nutrients, and so it is predicted that dietary intake should change in response to infection to offset these costs. The present study focuses on the interactions between a specialist grass-feeding caterpillar species, the African armyworm Spodoptera exempta, and an opportunist bacterium, Bacillus subtilis.
2. The main aims of the study were (i) to establish the macronutrient costs to the insect host of surviving a systemic bacterial infection, (ii) to determine the relative importance of dietary protein and carbohydrate to immune system functions, and (iii) to determine whether there is an adaptive change in the host's normal feeding behaviour in response to bacterial challenge, such that the nutritional costs of resisting infection are offset.
3. We show that the survival of bacterially infected larvae increased with increasing dietary protein-to-carbohydrate (P:C) ratio, suggesting a protein cost associated with bacterial resistance. As dietary protein levels increased, there was an increase in antibacterial activity, phenoloxidase (PO) activity and protein levels in the haemolymph, providing a potential source for this protein cost. However, there was also evidence for a physiological trade-off between antibacterial activity and phenoloxidase activity, as larvae whose antibacterial activity levels were elevated in response to immune activation had reduced PO activity.
4. When given a choice between two diets varying in their P:C ratios, larvae injected with a sub-lethal dose of bacteria increased their protein intake relative to control larvae whilst maintaining similar carbohydrate intake levels. These results are consistent with the notion that S. exempta larvae alter their feeding behaviour in response to bacterial infection in a manner that is likely to enhance the levels of protein available for producing the immune system components and other factors required to resist bacterial infections (‘self-medication’).

Costs of resistance: genetic correlations and potential trade-offs in an insect immune system

Theory predicts that natural selection will erode additive genetic variation in fitness-related traits. However, numerous studies have found considerable heritable variation in traits related to immune function, which should be closely linked to fitness. This could be due to trade-offs maintaining variation in these traits. We used the Egyptian cotton leafworm, Spodoptera littoralis, as a model system to examine the quantitative genetics of insect immune function. We estimated the heritabilities of several different measures of innate immunity and the genetic correlations between these immune traits and a number of life history traits. Our results provide the first evidence for a potential genetic trade-off within the insect immune system, with antibacterial activity (lysozyme-like) exhibiting a significant negative genetic correlation with haemocyte density, which itself is positively genetically correlated with both haemolymph phenoloxidase activity and cuticular melanization. We speculate on a potential trade-off between defence against parasites and predators, mediated by larval colour, and its role in maintaining genetic variation in traits under natural selection.

Crinoids for lunch? An unexpected biotic interaction from the Upper Ordovician of Scotland

Specimens of the polyplacophoran mollusk 'Helminthochiton' thraivensis Reed from the Upper Ordovician of southwest Scotland provide rare examples of complete valve series preserved in near life position, albeit as external molds. Application of high-resolution X-ray microtomography to one such specimen has revealed the exceptional preservation of its last meal, which included elements of a crinoid column, in its intestine. The interaction was either predatory or scavenging; extant chitons are not known to be crinoidivorous. This is the earliest direct record of predation or scavenging on crinoids in the fossil record. It is also the first indication that the broad axial canal of primitive crinoids may have contained nutritious tissues. The predatory or scavenging habit of H. thraivensis is consistent with its inferred phylogenetic position as a stem-group aplacophoran and provides new data suggesting an origin of carnivory early in the evolution of this clade.

N-terminally modified glucagon-like peptide-1(7-36) amide exhibits resistance to enzymatic degradation while maintaining its antihyperglycaemic activity in vivo

Glucagon-like peptide-1 (7-36)amide (tGLP-1) is inactivated by dipeptidyl peptidase (DPP) IV by removal of the NH2-terminal dipeptide His(7)-Ala(8). We examined the degradation of NH2-terminally modified His(7)-glucitol tGLP-1 and its insulin-releasing and antihyperglycaemic activity in vivo, tGLP-1 was degraded by purified DPP IV after 4 h (43% intact) and after 12 hi 89% was converted to GLP-1(9-36)amide. In contrast > 99% of His(7)-glucitol tGLP-1 remained intact at 12 h. His(7)-glucitol tGLP-1 was similarly resistant to plasma degradation in vitro. His7-glucitol tGLP-1 showed greater resistance to degradation in vivo (92% intact) compared to tGLP-1 (27% intact) 10 min after i.p. administration to Wistar rats. Glucose homeostasis was examined following i.p. injection of both peptides (12 nmol/kg) together with glucose (18 mmol/kg). Plasma glucose concentrations were significantly reduced and insulin concentrations elevated following peptides administration compared with glucose alone. The area under the curve (AUC) for glucose for controls (AUC 691 +/- 35 mM/min) was significantly lower after administration of tGLP-1 and His7-glucitol tGLP-1 (36 and 49% less; AUC; 440 +/- 40 and 353 +/- 31 mM/min, respectively; P

Autobiography and Invention: Towards a Critical Understanding of Identity, Dialogue and Resistance in Improvised Musics

In this article I will argue that acts of improvisation are not productively understood in opposition to other practices which form our wider musical culture. Improvisation might be better understood as both rooted in, but not limited by, personal and cultural memory. Improvisational activities are legible to the performer and audience through a shared understanding of social norms, but only become a singular instance of improvisation through unique performative actions. This tension between experience and invention is played out in a dialogue between performer and listener, demanding a response that crucially takes the form of self-articulation, or autobiography. Finally, I contend that it is from this position that improvisation offers the possibility to transgress established personal and cultural identities.

Micro-Raman and Spreading Resistance Analysis on Beveled Implanted Germanium for Layer Transfer Applications

Raman and spreading resistance profiling have been used to analyze defects in germanium caused by hydrogen and helium implants, of typical fluences used in layer transfer applications. Beveling has been used to facilitate probing beyond the laser penetration depth. Results of Raman mapping along the projection area reveal that after post-implant annealing at 400°C, some crystal damage remains, while at 600°C, the crystal damage has been repaired. Helium implants create acceptor states beyond the projected range, and for both hydrogen and helium, 1×1016 acceptors/cm2 remain after 600°C. These are thought to be vacancy-related point defect clusters.

Low cytosine triphosphate synthase 2 expression renders resistance to 5-fluorouracil in colorectal cancer

Understanding the determinants of resistance of 5-fluorouracil (5FU) is of significant value to optimizing administration of the drug, and introducing novel agents and treatment strategies. Here, the expression of 92 genes involved in 5FU transport, metabolism, co-factor (folate) metabolism and downstream effects was measured by real-time PCR low density arrays in 14 patient-derived colorectal cancer xenografts characterized for 5FU resistance. Candidate gene function was tested by siRNA and uridine modulation, and immunoblotting, apoptosis and cell cycle analysis. Predictive significance was tested by immunohistochemistry of tumors from 125 stage III colorectal cancer patients treated with and without 5FU. Of 8 genes significantly differentially expressed between 5FU sensitive and resistant xenograft tumors, CTPS2 was the gene with the highest probability of differential expression (p = 0.008). Reduction of CTPS2 expression by siRNA increased the resistance of colorectal cancer cell lines DLD1 and LS174T to 5FU and its analog, FUDR. CTPS2 siRNA significantly reduced cell S-phase accumulation and apoptosis following 5FU treatment. Exposure of cells to uridine, a precursor to the CTPS2 substrate uridine triphosphate, also increased 5FU resistance. Patients with low CTPS2 did not gain a survival benefit from 5FU treatment (p = 0.072), while those with high expression did (p = 0.003). Low CTPS2 expression may be a rationally-based determinant of 5FU resistance.

Structure-Based Mutational Analysis of eIF4E in Relation to sbm1 Resistance to Pea Seed-Borne Mosaic Virus in Pea

Background: Pea encodes eukaryotic translation initiation factor eIF4E (eIF4E(S)), which supports the multiplication of Pea seed-borne mosaic virus (PSbMV). In common with hosts for other potyviruses, some pea lines contain a recessive allele (sbm1) encoding a mutant eIF4E (eIF4E(R)) that fails to interact functionally with the PSbMV avirulence protein, VPg, giving genetic resistance to infection.

Molecular characterization and phylogenetic analysis of quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC and parE gene loci in viridans group streptococci isolated from adult patients with cystic fibrosis

This study demonstrated key resistance genes to fluroquinilones in Streptococcci isolated from sputum of people with CF. This suggests that other bacteria which are sometimes considered commensal may be a resovoir for resistance. Jse designed the study with Moore.