Browsing by Subject "CHEMICAL DEFENSE"

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  • Rosa, Elena; Woestmann, Luisa; Biere, Arjen; Saastamoinen, Marjo (2018)
    Host plant chemical composition critically shapes the performance of insect herbivores feeding on them. Some insects have become specialized on plant secondary metabolites, and even use them to their own advantage such as defense against predators. However, infection by plant pathogens can seriously alter the interaction between herbivores and their host plants. We tested whether the effects of the plant secondary metabolites, iridoid glycosides (IGs), on the performance and immune response of an insect herbivore are modulated by a plant pathogen. We used the IG-specialized Glanville fritillary butterfly Melitaea cinxia, its host plant Plantago lanceolata, and the naturally occurring plant pathogen, powdery mildew Podosphaera plantaginis, as model system. Pre-diapause larvae were fed on P. lanceolata host plants selected to contain either high or low IGs, in the presence or absence of powdery mildew. Larval performance was measured by growth rate, survival until diapause, and by investment in immunity. We assessed immunity after a bacterial challenge in terms of phenoloxidase (PO) activity and the expression of seven pre-selected insect immune genes (qPCR). We found that the beneficial effects of constitutive leaf IGs, that improved larval growth, were significantly reduced by mildew infection. Moreover, mildew presence downregulated one component of larval immune response (PO activity), suggesting a physiological cost of investment in immunity under suboptimal conditions. Yet, feeding on mildew-infected leaves caused an upregulation of two immune genes, lysozyme and prophenoloxidase. Our findings indicate that a plant pathogen can significantly modulate the effects of secondary metabolites on the growth of an insect herbivore. Furthermore, we show that a plant pathogen can induce contrasting effects on insect immune function. We suspect that the activation of the immune system toward a plant pathogen infection may be maladaptive, but the actual infectivity on the larvae should be tested.
  • Kamyab, Elham; Goebeler, Norman; Kellermann, Matthias Y.; Rohde, Sven; Reverter, Miriam; Striebel, Maren; Schupp, Peter J. (2020)
    Sea cucumbers are bottom dwelling invertebrates, which are mostly found on subtropical and tropical sea grass beds, sandy reef flats, or reef slopes. Although constantly exposed to fouling communities in these habitats, many species are surprisingly free of invertebrate epibionts and microfouling algae such as diatoms. In our study, we investigated the anti-fouling (AF) activities of different crude extracts of tropical Indo-Pacific sea cucumber species against the fouling diatom Cylindrotheca closterium. Nine sea cucumber species from three genera (i.e., Holothuria, Bohadschia, Actinopyga) were selected and extracted to assess their AF activities. To verify whether the sea cucumber characteristic triterpene glycosides were responsible for the observed potent AF activities, we tested purified fractions enriched in saponins isolated from Bohadschia argus, representing one of the most active anti-fouling extracts. Saponins were quantified by vanillin-sulfuric acid colorimetric assays and identified by LC-MS and LC-MS/MS analyses. We were able to demonstrate that AF activities in sea cucumber extracts were species-specific, and growth inhibition as well as attachment of the diatom to surfaces is dependent on the saponin concentration (i.e., Actinopyga contained the highest quantities), as well as on the molecular composition and structure of the present saponins (i.e., Bivittoside D derivative was the most bioactive compound). In conclusion, the here performed AF assay represents a promising and fast method for selecting the most promising bioactive organism as well as for identifying novel compounds with potent AF activities for the discovery of potentially novel pharmacologically active natural products.
  • Kikuchi, David W.; Waldron, Samuel J.; Valkonen, Janne K.; Dobler, Susanne; Mappes, Johanna (2020)
    Mullerian mimicry is a classic example of adaptation, yet Muller's original theory does not account for the diversity often observed in mimicry rings. Here, we aimed to assess how well classical Mullerian mimicry can account for the colour polymorphism found in chemically defended Oreina leaf beetles by using field data and laboratory assays of predator behaviour. We also evaluated the hypothesis that thermoregulation can explain diversity between Oreina mimicry rings. We found that frequencies of each colour morph were positively correlated among species, a critical prediction of Mullerian mimicry. Predators learned to associate colour with chemical defences. Learned avoidance of the green morph of one species protected green morphs of another species. Avoidance of blue morphs was completely generalized to green morphs, but surprisingly, avoidance of green morphs was less generalized to blue morphs. This asymmetrical generalization should favour green morphs: indeed, green morphs persist in blue communities, whereas blue morphs are entirely excluded from green communities. We did not find a correlation between elevation and coloration, rejecting thermoregulation as an explanation for diversity between mimicry rings. Biased predation could explain within-community diversity in warning coloration, providing a solution to a long-standing puzzle. We propose testable hypotheses for why asymmetric generalization occurs, and how predators maintain the predominance of blue morphs in a community, despite asymmetric generalization.
  • Winters, Anne E.; Lommi, Jenna; Kirvesoja, Jimi; Nokelainen, Ossi; Mappes, Johanna (2021)
    Aposematic organisms warn predators of their unprofitability using a combination of defenses, including visual warning signals, startling sounds, noxious odors, or aversive tastes. Using multiple lines of defense can help prey avoid predators by stimulating multiple senses and/or by acting at different stages of predation. We tested the efficacy of three lines of defense (color, smell, taste) during the predation sequence of aposematic wood tiger moths (Arctia plantaginis) using blue tit (Cyanistes caeruleus) predators. Moths with two hindwing phenotypes (genotypes: WW/Wy = white, yy = yellow) were manipulated to have defense fluid with aversive smell (methoxypyrazines), body tissues with aversive taste (pyrrolizidine alkaloids) or both. In early predation stages, moth color and smell had additive effects on bird approach latency and dropping the prey, with the strongest effect for moths of the white morph with defense fluids. Pyrrolizidine alkaloid sequestration was detrimental in early attack stages, suggesting a trade-off between pyrrolizidine alkaloid sequestration and investment in other defenses. In addition, pyrrolizidine alkaloid taste alone did not deter bird predators. Birds could only effectively discriminate toxic moths from non-toxic moths when neck fluids containing methoxypyrazines were present, at which point they abandoned attack at the consumption stage. As a result, moths of the white morph with an aversive methoxypyrazine smell and moths in the treatment with both chemical defenses had the greatest chance of survival. We suggest that methoxypyrazines act as context setting signals for warning colors and as attention alerting or "go-slow" signals for distasteful toxins, thereby mediating the relationship between warning signal and toxicity. Furthermore, we found that moths that were heterozygous for hindwing coloration had more effective defense fluids compared to other genotypes in terms of delaying approach and reducing the latency to drop the moth, suggesting a genetic link between coloration and defense that could help to explain the color polymorphism. Conclusively, these results indicate that color, smell, and taste constitute a multimodal warning signal that impedes predator attack and improves prey survival. This work highlights the importance of understanding the separate roles of color, smell and taste through the predation sequence and also within-species variation in chemical defenses.
  • Rojas, Bibiana; Burdfield-Steel, Emily; De Pasqual, Chiara; Gordon, Swanne; Hernandez, Linda; Mappes, Johanna; Nokelainen, Ossi; Ronka, Katja; Lindstedt, Carita (2018)
    Chemically defended animals often display conspicuous color patterns that predators learn to associate with their unprofitability and subsequently avoid. Such animals (i.e., aposematic), deter predators by stimulating their visual and chemical sensory channels. Hence, aposematism is considered to be "multimodal." The evolution of warning signals (and to a lesser degree their accompanying chemical defenses) is fundamentally linked to natural selection by predators. Lately, however, increasing evidence also points to a role of sexual selection shaping warning signal evolution. One of the species in which this has been shown is the wood tiger moth, Arctia plantaginis, which we here put forward as a promising model to investigate multimodality in aposematic and sexual signaling. A. plantaginis is an aposematic diurnal moth which exhibits sexually dimorphic coloration as well as sex-limited polymorphism in part of its range. The anti-predator function of its coloration and, more recently, its chemical defenses (even when experimentally decoupled from the visual signals), has been well-demonstrated. Interestingly, recent studies have revealed differences between the two male morphs in mating success, suggesting a role of coloration in mate choice or attraction, and providing a possible explanation for its sexual dimorphism in coloration. Here, we: (1) review the lines of evidence showing the role of predation pressure and sexual selection in the evolution of multimodal aposematic signals in general, and in the wood tiger moth in particular; (2) establish gaps in current research linking sexual selection and predation as selective pressures on aposematic signals by reviewing a sample of the literature published in the last 30 years; (3) highlight the need of identifying suitable systems to address simultaneously the effect of natural and sexual selection on multimodal aposematic signals; and (4) propose directions for future research to test how aposematic signals can evolve under natural and sexual selection.