Cellular immune response, stress resistance and competitiveness in nestling great tits in relation to maternally transmitted carotenoids

1. Egg yolks contain carotenoids that protect biological molecules against free-radical damage and promote maturation of the immune system. Availability of carotenoids to birds is often limited. Trade-offs can thus arise in the allocation of carotenoids to different physiological functions, and mothers may influence the immunocompetence of nestlings by modulating the transfer of carotenoid to the yolk.;2. In the great tit Parus major, we experimentally manipulated the dietary supply of carotenoid to mothers, and partially cross-fostered hatchlings to investigate the effect of an increased availability of carotenoids during egg laying on immunocompetence of nestlings.;3. In addition, we infested half of the nests with hen fleas Ceratophyllus gallinae to investigate the relationship between carotenoid availability, resistance to ectoparasites and immunocompetence.;4. We found that the procedure of cross-fostering can reduce the immune response of nestlings, but this effect can be compensated by the maternally transferred carotenoids. Cross-fostered nestlings of carotenoid-supplemented females show a similar immune response to non-cross-fostered nestlings, while cross-fostered nestlings of control females mounted a weaker cell-mediated immune response. This suggests that yolk carotenoids may help nestlings to cope with stress, for example the one generated by cross-fostering and/or they may enhance nestling competitiveness.;5. There was no statistically significant interaction between parasite and carotenoid treatments, as would be expected if carotenoids helped nestlings to fight parasites. Under parasite pressure, however, lighter nestlings raised a lower immune response, while the immune response was only weakly correlated with body mass in uninfested nests.

Insulin resistance, obesity and the metabolic syndrome. Is there a therapeutic role for endothelin-1 antagonists?

There is increasing evidence to suggest that chronic activation of the endothelin-1 system can lead to heterologous desensitization of the glucose-regulatory and mitogenic actions of insulin with subsequent development of glucose intolerance, hyperinsulinemia, impaired endothelial function and exacerbation of cardiovascular disease. Effects are mediated through a variety of mechanisms that include attenuation of key insulin signalling pathways and decreased tyrosine phosphorylation of insulin receptor substrates IRS-1, SHC and G alpha q/11. Other actions involve hemodynamic changes leading to reduced delivery of insulin and glucose to peripheral tissues as well as enhanced hepatic glycogenolysis, decreased glucose-transporter translocation and modulation of various adipokines that regulate insulin action. Overall the data suggest that ET-1 antagonists may provide an effective means of improving cardiac dysfunction and favourably influencing glucose tolerance in obese humans and patients with early insulin sensitivity where there is clear evidence for activation of the ET-1 system. Although most effects of ET-1 that modulate mechanisms leading to glucose intolerance appear to involve the ETA receptor subtype recent data indicates that combined ETA/ETB receptor antagonists may function as effectively as selective ETA blockers. Prospective trials are needed to assess whether ET-1 antagonists, either alone or in combination, are superior to other more conventional therapies such as insulin sensitizers and to evaluate effects of combined treatments on the development of insulin resistance and the progression of diabetes. Early screening of patients at risk for evidence of ET-1 activation would help to identify subjects who may benefit most from such treatment.

TRAIL-induced survival and proliferation of SCLC cells is mediated by ERK and dependent on TRAIL-R2/DR5 expression in the absence of caspase-8

Small cell lung cancer (SCLC) is characterized by an aggressive phenotype and acquired resistance to a broad spectrum of anticancer agents. TNF-related apoptosis-inducing ligand (TRAIL) has been considered as a promising candidate for safe and selective induction of tumor cell apoptosis without toxicity to normal tissues. Here we report that TRAIL failed to induce apoptosis in SCLC cells and instead resulted in an up to 40% increase in proliferation. TRAIL-induced SCLC cell proliferation was mediated by extracellular signal-regulated kinase 1 and 2, and dependent on the expression of surface TRAIL-receptor 2 (TRAIL-R2) and lack of caspase-8, which is frequent in SCLC. Treatment of SCLC cells with interferon-gamma (IFN-gamma) restored caspase-8 expression and facilitated TRAIL-induced apoptosis. The overall loss of cell proliferation/viability upon treatment with the IFN-gamma-TRAIL combination was 70% compared to TRAIL-only treated cells and more than 30% compared to untreated cells. Similar results were obtained by transfection of cells with a caspase-8 gene construct. Altogether, our data suggest that TRAIL-R2 expression in the absence of caspase-8 is a negative determinant for the outcome of TRAIL-based cancer therapy, and provides the rationale for using IFN-gamma or other strategies able to restore caspase-8 expression to convert TRAIL from a pro-survival into a death ligand.

Different patterns of Siglec-9-mediated neutrophil death responses in septic shock

Sialic-acid-binding immunoglobulin-like lectin (Siglec) 9 mediates death signals in neutrophils. The objective of this study was to determine the heterogeneity of neutrophil death responses in septic shock patients and to analyze whether these ex vivo data are related to the severity and outcome of septic shock. In this prospective cohort study, blood samples of patients with septic shock (n = 26) in a medical-surgical intensive care unit (ICU) were taken within 24 h of starting the treatment of septic shock (phase A), after circulatory stabilization (phase B), and 10 days after admission or at ICU discharge if earlier (phase C). Neutrophil death was quantified in the presence and absence of an agonistic anti-Siglec-9 antibody after 24 h ex vivo. In phase A, two distinct patterns of Siglec-9-mediated neutrophil death were observed: resistance to neutrophil death (n = 14; Siglec-9 nonresponders) and increased neutrophil death (n = 12; Siglec-9 responders) after Siglec-9 ligation compared with neutrophils from normal donors. Experiments using a pharmacological pan-caspase-inhibitor provided evidence for caspase-independent neutrophil death in Siglec-9 responders upon Siglec-9 ligation. There were no differences between Siglec-9 responders and nonresponders in length of ICU or hospital stay of survivors or severity of organ dysfunction. Taken together, septic shock patients exhibit different ex vivo death responses of blood neutrophils after Siglec-9 ligation early in shock. Both the resistance and the increased susceptibility to Siglec-9-mediated neutrophil death tend to normalize within 72 h after shock. Further studies are required to understand the role of Siglec-9-mediated neutrophil death in septic shock.

Multiplex strategy for multilocus sequence typing, fla typing, and genetic determination of antimicrobial resistance of Campylobacter jejuni and Campylobacter coli isolates collected in Switzerland

We present an optimized multilocus sequence typing (MLST) scheme with universal primer sets for amplifying and sequencing the seven target genes of Campylobacter jejuni and Campylobacter coli. Typing was expanded by sequence determination of the genes flaA and flaB using optimized primer sets. This approach is compatible with the MLST and flaA schemes used in the PubMLST database and results in an additional typing method using the flaB gene sequence. An identification module based on the 16S rRNA and rpoB genes was included, as well as the genetic determination of macrolide and quinolone resistances based on mutations in the 23S rRNA and gyrA genes. Experimental procedures were simplified by multiplex PCR of the 13 target genes. This comprehensive approach was evaluated with C. jejuni and C. coli isolates collected in Switzerland. MLST of 329 strains resulted in 72 sequence types (STs) among the 186 C. jejuni strains and 39 STs for the 143 C. coli isolates. Fourteen (19%) of the C. jejuni and 20 (51%) of the C. coli STs had not been found previously. In total, 35% of the C. coli strains collected in Switzerland contained mutations conferring antibiotic resistance only to quinolone, 15% contained mutations conferring resistance only to macrolides, and 6% contained mutations conferring resistance to both classes of antibiotics. In C. jejuni, these values were 31% and 0% for quinolone and macrolide resistance, respectively. The rpoB sequence allowed phylogenetic differentiation between C. coli and C. jejuni, which was not possible by 16S rRNA gene analysis. An online Integrated Database Network System (SmartGene, Zug, Switzerland)-based platform for MLST data analysis specific to Campylobacter was implemented. This Web-based platform allowed automated allele and ST designation, as well as epidemiological analysis of data, thus streamlining and facilitating the analysis workflow. Data networking facilitates the exchange of information between collaborating centers. The described approach simplifies and improves the genotyping of Campylobacter, allowing cost- and time-efficient routine monitoring.

Coffee consumption attenuates short-term fructose-induced liver insulin resistance in healthy men.

BACKGROUND Epidemiologic and experimental data have suggested that chlorogenic acid, which is a polyphenol contained in green coffee beans, prevents diet-induced hepatic steatosis and insulin resistance. OBJECTIVE We assessed whether the consumption of chlorogenic acid-rich coffee attenuates the effects of short-term fructose overfeeding, dietary conditions known to increase intrahepatocellular lipids (IHCLs), and blood triglyceride concentrations and to decrease hepatic insulin sensitivity in healthy humans. DESIGN Effects of 3 different coffees were assessed in 10 healthy volunteers in a randomized, controlled, crossover trial. IHCLs, hepatic glucose production (HGP) (by 6,6-d2 glucose dilution), and fasting lipid oxidation were measured after 14 d of consumption of caffeinated coffee high in chlorogenic acid (C-HCA), decaffeinated coffee high in chlorogenic acid, or decaffeinated coffee with regular amounts of chlorogenic acid (D-RCA); during the last 6 d of the study, the weight-maintenance diet of subjects was supplemented with 4 g fructose · kg(-1) · d(-1) (total energy intake ± SD: 143 ± 1% of weight-maintenance requirements). All participants were also studied without coffee supplementation, either with 4 g fructose · kg(-1) · d(-1) (high fructose only) or without high fructose (control). RESULTS Compared with the control diet, the high-fructose diet significantly increased IHCLs by 102 ± 36% and HGP by 16 ± 3% and decreased fasting lipid oxidation by 100 ± 29% (all P < 0.05). All 3 coffees significantly decreased HGP. Fasting lipid oxidation increased with C-HCA and D-RCA (P < 0.05). None of the 3 coffees significantly altered IHCLs. CONCLUSIONS Coffee consumption attenuates hepatic insulin resistance but not the increase of IHCLs induced by fructose overfeeding. This effect does not appear to be mediated by differences in the caffeine or chlorogenic acid content. This trial was registered at clinicaltrials.gov as NCT00827450.

Non-phenotypic tests to detect and characterize antibiotic resistance mechanisms in Enterobacteriaceae

In the past 2 decades, we have observed a rapid increase of infections due to multidrug-resistant Enterobacteriaceae. Regrettably, these isolates possess genes encoding for extended-spectrum β-lactamases (e.g., blaCTX-M, blaTEM, blaSHV) or plasmid-mediated AmpCs (e.g., blaCMY) that confer resistance to last-generation cephalosporins. Furthermore, other resistance traits against quinolones (e.g., mutations in gyrA and parC, qnr elements) and aminoglycosides (e.g., aminoglycosides modifying enzymes and 16S rRNA methylases) are also frequently co-associated. Even more concerning is the rapid increase of Enterobacteriaceae carrying genes conferring resistance to carbapenems (e.g., blaKPC, blaNDM). Therefore, the spread of these pathogens puts in peril our antibiotic options. Unfortunately, standard microbiological procedures require several days to isolate the responsible pathogen and to provide correct antimicrobial susceptibility test results. This delay impacts the rapid implementation of adequate antimicrobial treatment and infection control countermeasures. Thus, there is emerging interest in the early and more sensitive detection of resistance mechanisms. Modern non-phenotypic tests are promising in this respect, and hence, can influence both clinical outcome and healthcare costs. In this review, we present a summary of the most advanced methods (e.g., next-generation DNA sequencing, multiplex PCRs, real-time PCRs, microarrays, MALDI-TOF MS, and PCR/ESI MS) presently available for the rapid detection of antibiotic resistance genes in Enterobacteriaceae. Taking into account speed, manageability, accuracy, versatility, and costs, the possible settings of application (research, clinic, and epidemiology) of these methods and their superiority against standard phenotypic methods are discussed.

P2X7 receptors mediate resistance to toxin-induced cell lysis

In the majority of cells, the integrity of the plasmalemma is recurrently compromised by mechanical or chemical stress. Serum complement or bacterial pore-forming toxins can perforate the plasma membrane provoking uncontrolled Ca(2+) influx, loss of cytoplasmic constituents and cell lysis. Plasmalemmal blebbing has previously been shown to protect cells against bacterial pore-forming toxins. The activation of the P2X7 receptor (P2X7R), an ATP-gated trimeric membrane cation channel, triggers Ca(2+) influx and induces blebbing. We have investigated the role of the P2X7R as a regulator of plasmalemmal protection after toxin-induced membrane perforation caused by bacterial streptolysin O (SLO). Our results show that the expression and activation of the P2X7R furnishes cells with an increased chance of surviving attacks by SLO. This protective effect can be demonstrated not only in human embryonic kidney 293 (HEK) cells transfected with the P2X7R, but also in human mast cells (HMC-1), which express the receptor endogenously. In addition, this effect is abolished by treatment with blebbistatin or A-438079, a selective P2X7R antagonist. Thus blebbing, which is elicited by the ATP-mediated, paracrine activation of the P2X7R, is part of a cellular non-immune defense mechanism. It pre-empts plasmalemmal damage and promotes cellular survival. This mechanism is of considerable importance for cells of the immune system which carry the P2X7R and which are specifically exposed to toxin attacks.

THE ROLE AND MECHANISM OF THE HOMEOBOX GENE DLX4 IN TRANSFORMING GROWTH FACTOR-B RESISTANCE IN CANCER

Transforming growth factor-b (TGF-b) is a cytokine that plays essential roles in regulating embryonic development and tissue homeostasis. In normal cells, TGF-b exerts an anti-proliferative effect. TGF-b inhibits cell growth by controlling a cytostatic program that includes activation of the cyclin-dependent kinase inhibitors p15Ink4B and p21WAF1/Cip1 and repression of c-myc. In contrast to normal cells, many tumors are resistant to the anti-proliferative effect of TGF-b. In several types of tumors, particularly those of gastrointestinal origin, resistance to the anti-proliferative effect of TGF-b has been attributed to TGF-b receptor or Smad mutations. However, these mutations are absent from many other types of tumors that are resistant to TGF-b-mediated growth inhibition. The transcription factor encoded by the homeobox patterning gene DLX4 is overexpressed in a wide range of malignancies. In this study, I demonstrated that DLX4 blocks the anti-proliferative effect of TGF-b by disabling key transcriptional control mechanisms of the TGF-b cytostatic program. Specifically, DLX4 blocked the ability of TGF-b to induce expression of p15Ink4B and p21WAF1/Cip1 by directly binding to Smad4 and to Sp1. Binding of DLX4 to Smad4 prevented Smad4 from forming transcriptional complexes with Smad2 and Smad3, whereas binding of DLX4 to Sp1 inhibited DNA-binding activity of Sp1. In addition, DLX4 induced expression of c-myc, a repressor of p15Ink4B and p21WAF1/Cip1 transcription, independently of TGF-b signaling. The ability of DLX4 to counteract key transcriptional control mechanisms of the TGF-b cytostatic program could explain in part the resistance of tumors to the anti-proliferative effect of TGF-b. This study provides a molecular explanation as to why tumors are resistant to the anti-proliferative effect of TGF-b in the absence of mutations in the TGF-b signaling pathway. Furthermore, this study also provides insights into how aberrant activation of a developmental patterning gene promotes tumor pathogenesis.

Mechanisms of Adenovirus-Mediated Autophagy

A patient diagnosed with a glioma, generally, has an average of 14 months year to live after implementation of conventional therapies such as surgery, chemotherapy, and radiation. Glioblastomas are highly lethal because of their aggressive nature and resistance to conventional therapies and apoptosis. Thus other avenues of cell death urgently need to be explored. Autophagy, which is also known as programmed cell death type II, has recently been identified as an alternative mechanism to kill apoptosis- resistant cancer cells. Traditionally, researchers have studied how cells undergo autophagy during viral infection as an immune response mechanism, but recently researchers have discovered how viruses have evolved to manipulate autophagy for their benefit. Extensive studies of viral-induced autophagy provide a rationale to investigate other viruses, such as the adenovirus, which may be developed as part of a therapy against cancers resistant to apoptosis. Despite the present and relatively poor understanding of the mechanisms behind adenoviral-induced autophagy, adenovirus is a promising candidate, because of its ability to efficiently eradicate tumors. A better understanding of how the adenovirus induces autophagy will allow for the development of viruses with increased oncolytic potency. We hypothesized that adenovirus induces autophagy in order to aid in lysis. We found that replication, not infection, was required for adenovirus-mediated autophagy. Loss of function analysis of early genes revealed that, of the early genes tested, no single gene was sufficient to induce autophagy alone. Examination of cellular pathways for their role in autophagy during adenovirus infection revealed a function for the eIF2α pathway and more specifically the GCN2 kinase. Cells lacking GCN2 are more resistant to adenovirus-mediated autophagy in vitro; in vivo we also found these cells fail to undergo autophagy, but display more cell death. We believe that autophagy is a protective mechanism the cell employs during adenoviral infection, and in the in vivo environment, cells cannot recover from virus infection and are more susceptible to death. Congruently, infected cells deficient for autophagy through deletion of ATG5 are not able undergo productive cell lysis, providing evidence that the destruction of the cytoplasm and cell membrane through autophagy is crucial to the viral life cycle. This project is the first to describe a gene, other than a named autophagy gene, to be required for adenovirus- mediated autophagy. It is also the first to examine autophagic cell death as a means to aid in viral-induced cell lysis.

Mechanisms of Adenovirus-Mediated Autophagy

A patient diagnosed with a glioma, generally, has an average of 14 months year to live after implementation of conventional therapies such as surgery, chemotherapy, and radiation. Glioblastomas are highly lethal because of their aggressive nature and resistance to conventional therapies and apoptosis. Thus other avenues of cell death urgently need to be explored. Autophagy, which is also known as programmed cell death type II, has recently been identified as an alternative mechanism to kill apoptosis- resistant cancer cells. Traditionally, researchers have studied how cells undergo autophagy during viral infection as an immune response mechanism, but recently researchers have discovered how viruses have evolved to manipulate autophagy for their benefit. Extensive studies of viral-induced autophagy provide a rationale to investigate other viruses, such as the adenovirus, which may be developed as part of a therapy against cancers resistant to apoptosis. Despite the present and relatively poor understanding of the mechanisms behind adenoviral-induced autophagy, adenovirus is a promising candidate, because of its ability to efficiently eradicate tumors. A better understanding of how the adenovirus induces autophagy will allow for the development of viruses with increased oncolytic potency. We hypothesized that adenovirus induces autophagy in order to aid in lysis. We found that replication, not infection, was required for adenovirus-mediated autophagy. Loss of function analysis of early genes revealed that, of the early genes tested, no single gene was sufficient to induce autophagy alone. Examination of cellular pathways for their role in autophagy during adenovirus infection revealed a function for the eIF2α pathway and more specifically the GCN2 kinase. Cells lacking GCN2 are more resistant to adenovirus-mediated autophagy in vitro; in vivo we also found these cells fail to undergo autophagy, but display more cell death. We believe that autophagy is a protective mechanism the cell employs during adenoviral infection, and in the in vivo environment, cells cannot recover from virus infection and are more susceptible to death. Congruently, infected cells deficient for autophagy through deletion of ATG5 are not able undergo productive cell lysis, providing evidence that the destruction of the cytoplasm and cell membrane through autophagy is crucial to the viral life cycle. This project is the first to describe a gene, other than a named autophagy gene, to be required for adenovirus- mediated autophagy. It is also the first to examine autophagic cell death as a means to aid in viral-induced cell lysis.

ANALYSIS OF THE CORYNEBACTERIUM PARVUM-INDUCED DECLINE OF MURINE NATURAL KILLER CELL-MEDIATED CYTOTOXICITY

Treatment of mice with the immunomodulating agent, Corynebacterium parvum (C. parvum), was shown to result in a severe and long-lasting depression of splenic natural killer (NK) cell-mediated cytotoxicity 5-21 days post-inoculation. Because NK cells have been implicated in immunosurveillance against malignancy (due to their spontaneous occurrence and rapid reactivity to a variety of histological types of tumors), as well as in resistance to established tumors, this decreased activity was of particular concern, since this effect is contrary to that which would be considered therapeutically desirable in cancer treatment (i.e. a potentiation of antitumor effector functions, including NK cell activity, would be expected to lead to a more effective destruction of malignant cells). Therefore, an analysis of the mechanism of this decline of splenic NK cell activity in C.parvum treated mice was undertaken.^ From in vitro co-culturing experiments, it was found that low NK-responsive C. parvum splenocytes were capable of reducing the normally high-reactivity of cells from untreated syngeneic mice to YAC-1 lymphoma, suggesting the presence of NK-directed suppressor cells in C. parvum treated animals. This was further supported by the demonstration of normal levels of cytotoxicity in C. parvum splenocyte preparations following Ficoll-Hypaque separation, which coincided with removal of the NK-suppressive capabilities of these cells. The T cell nature of these regulatory cells was indicated by (1) the failure of C. parvum to cause a reduction of NK cell activity, or the generation of NK-directed suppressor cells in T cell-deficient athymic mice, (2) the removal of C. parvum-induced suppression by T cell-depleting fractionation procedures or treatments, and (3) demonstration of suppression of NK cell activity by T cell-enriched C. parvum splenocytes. These studies suggest, therefore, that the eventual reduction of suppression by T cell elimination and/or inhibition, may result in a promotion of the antitumor effectiveness of C. parvum due to the contribution of "freed" NK effector cell activity.^ However, the temporary suppression of NK cell activity induced by C. parvum (reactivity of treated mice returns to normal levels within 28 days after C. parvum injection), may in fact be favorable in some situations, e.g. in bone marrow transplantation cases, since NK cells have been suggested to play a role also in the process of bone marrow graft rejection.^ Therefore, the discriminate use of agents such as C. parvum may allow for the controlled regulation of NK cell activity suggested to be necessary for the optimalization of therapeutic regimens. ^

Sequence of arrival determines plant-mediated interactions between herbivores

Induced changes in plant quality can mediate indirect interactions between herbivores. Although the sequence of attack by different herbivores has been shown to influence plant responses, little is known about how this affects the herbivores themselves. We therefore investigated how induction by the leaf herbivore Spodoptera frugiperda influences resistance of teosinte (Zea mays mexicana) and cultivated maize (Zea mays mays) against root-feeding larvae of Diabrotica virgifera virgifera. The importance of the sequence of arrival was tested in the field and laboratory. Spodoptera frugiperda infestation had a significant negative effect on colonization by D. virgifera larvae in the field and weight gain in the laboratory, but only when S. frugiperda arrived on the plant before the root herbivore. When S. frugiperda arrived after the root herbivore had established, no negative effects on larval performance were detected. Yet, adult emergence of D. virgifera was reduced even when the root feeder had established first, indicating that the negative effects were not entirely absent in this treatment. The defoliation of the plants was not a decisive factor for the negative effects on root herbivore development, as both minor and major leaf damage resulted in an increase in root resistance and the extent of biomass removal was not correlated with root-herbivore growth. We propose that leaf-herbivore-induced increases in feeding-deterrent and/or toxic secondary metabolites may account for the sequence-specific reduction in root-herbivore performance. Synthesis. Our results demonstrate that the sequence of arrival can be an important determinant of plant-mediated interactions between insect herbivores in both wild and cultivated plants. Arriving early on a plant may be an important strategy of insects to avoid competition with other herbivores. To fully understand plant-mediated interactions between insect herbivores, the sequence of arrival should be taken into account. © 2011 The Authors. Journal of Ecology © 2011 British Ecological Society.

Piriformospora indica and Sebacina vermifera increase growth performance at the expense of herbivore resistance in Nicotiana attenuata

A Sebacinales species was recovered from a clone library made from a pooled rhizosphere sample of Nicotiana attenuata plants from 14 native populations. Axenic cultures of the related species, Piriformospora indica and Sebacina vermifera, were used to examine their effects on plant performance. Inoculation of N. attenuata seeds with either fungus species stimulated seed germination and increased growth and stalk elongation. S. vermifera inoculated plants flowered earlier, produced more flowers and matured more seed capsules than did non-inoculated plants. Jasmonate treatment during rosette-stage growth, which slows growth and elicits herbivore resistance traits, erased differences in vegetative, but not reproductive performance resulting from S. vermifera inoculation. Total nitrogen and phosphorous contents did not differ between inoculated and control plants, suggesting that the performance benefits of fungal inoculation did not result from improvements in nutritional status. Since the expression of trypsin proteinase inhibitors (TPI), defensive proteins which confer resistance to attack from Manduca sexta larvae, incur significant growth and fitness costs for the plant, we examined the effect of S. vermifera inoculation on herbivore resistance and TPI activity. After 10 days of feeding on S. vermifera-inoculated plants, larval mass was 46% higher and TPI activity was 48% lower than that on non-inoculated plants. These results suggest that Sebacina spp. may interfere with defense signaling and allow plants to increase growth rates at the expense of herbivore resistance mediated by TPIs.

Seedling resistance, tolerance and escape from herbivores: insights from co-dominant canopy tree species in a resource-poor African rain forest

* Although plants can reduce the impacts of herbivory in multiple ways, these defensive traits are often studied in isolation and an understanding of the resulting strategies is incomplete. * In the study reported here, empirical evidence was simultaneously evaluated for the three main sets of traits available to plants: (i) resistance through constitutive leaf traits, (ii) tolerance to defoliation and (iii) escape in space, for three caesalpiniaceous tree species Microberlinia bisulcata, Tetraberlinia bifoliolata and T. korupensis, which co-dominate groves within the lowland primary rain forest of Korup National Park (Cameroon). * Mesh cages were placed around individual wild seedlings to exclude insect herbivores at 41 paired canopy gap and understorey locations. After following seedling growth and survival for c. 2 years, caged and control treatments were removed, leaves harvested to determine nutrient and phenolic concentrations, leaf mass per area estimated, and seedling performance in gaps followed for a further c. 2 years to quantify tolerance to the leaf harvesting. * The more nutrient-rich leaves of the weakly shade-tolerant M. bisulcata were damaged much more in gaps than the two strongly shade-tolerant Tetraberlinia species, which had higher leaf mass per area and concentrations of total phenols. Conversely, the faster-growing M. bisulcata was better able to tolerate defoliation in terms of height growth (reflushing capacity), but not at maintaining overall leaf numbers, than the other two species. * Across gaps, insect-mediated Janzen–Connell effects were most pronounced for M. bisulcata, less so for T. korupensis, and not detectable for T. bifoliolata. The three species differed distinctly in their secondary metabolic profiles. * Taken together, the results suggested a conceptual framework linking the three sets of traits, one in which the three co-dominant species adopt different strategies towards herbivore pressure depending on their different responses to light availability. This study is one of the first in a natural forest ecosystem to examine resistance to, tolerance of, and escape from herbivory among a group of co-occurring tropical tree species.