Caterpillars use different strategies to protect themselves from their enemies; many are camouflaged, while others use their bright colors as warning signals, have stinging hairs or secrete toxic substances, some even take threatening postures.
Interaction between the caterpillar Manduca sexta and the spider Camptocosa parallela. The caterpillars nicotin breath frigthens the spider.
Danny Kessler; Grafics: Pavan Kumar and Sagar Pandit, MPI chem Ökol.
Spider Camptocosa parallela attacks a caterpillar.
Pavan Kumar, MPI chem. Ökol.
Scientists at the Max Planck Institute for Chemical Ecology have now discovered a previously unknown protective mechanism: Tobacco hornworm larvae can exhale a small fraction of nicotine they ingest as they feed on tobacco leaves.
To do so, they transfer some of the nicotine they ingest into their hemolymph (insect blood) from which a “defensive halitosis” is created that repels a major predator.
These insights were made possible by combining molecular techniques with a natural history approach in field experiments in the native habitat of the study organisms. (Proceedings of the National Academy of Sciences of the United States of America, December 30; 2013, DOI 10.1073/pnas.1314848111)
The importance of the ecosystem for studying gene functions
Understanding the function of genes is a central objective of biological research. Ultimately, genes function at the level of the organism, where their influence on an organism’s Darwinian fitness determines whether a gene is retained, modified or lost from genomes over evolutionary time. Gene silencing is a successful research method used to identify the function of individual genes and their relevance for the survival and fitness of an organism.
In addition to a gene’s biochemical and physiological roles that can be studied in the laboratory, the ecological role of a gene needs to be studied, and for this, there can be no better laboratory than the organism’s natural habitat. Scientists from the Department of Molecular Ecology headed by Ian Baldwin pioneer this approach and call it an unbiased, “ask the ecosystem” approach.
“Nature is our most important teacher,” Ian Baldwin emphasizes. “Nature is the arbitrator of who survives. Elucidation of gene functions is only possible if you study organisms in their native environment − including all the unknowns of the wild.”
For their field experiments, researchers planted tobacco plants that were deficient in producing nicotine. In addition, they used a plant-mediated RNAi technique to silence a cytochrome P450 enzyme in the midgut of tobacco hornworm larvae (see press release “Yellow Biotechnology: Using plants to silence insect genes in a high-throughput manner”, February 2, 2012) which is usually activated by nicotine ingested when the larvae feed on tobacco leaves. The scientists then observed what happened to caterpillars feeding on nicotine-deficient plants in order to compare their fate with those caterpillars that had ingested nicotine but lacked the active catalyzer for the toxin in their midgut.
Predatory spider assists the process of elucidating a defense mechanism
The function of the cytochrome P450 proved hard to reveal by laboratory-based experiments, but then the researchers received unexpected support from a wolf spider Camptocosa parallela. Surprisingly, the nocturnal predator preferably preyed not only on larvae that fed on nicotine-free leaves, but also preyed on their cytochrome P450-silenced conspecifics that were deficient in their response to nicotine in the food. The gene must therefore have played an important role in a spider defense mechanism that usually excludes the spider from the list of Manduca sexta’s enemies.
Further analysis revealed that the enzyme plays a role in transporting the ingested nicotine from midgut to the hemolymph which allows the nicotine to be exhaled out the spiracles, the nose-equivalents of the caterpillars. Caterpillars exhale a small fraction of this nicotine. And this functions as an anti-spider signal. Other predators of Manduca sexta, such as bugs or antlions, seem to be completely insensitive to this defensive halitosis.
Nicotine, the defensive substance in their host plant, is too toxic for the larvae to sequester. Most of it is excreted. That the larvae repurposes only a tiny amount of the toxin for their own defense in order to ward off spiders with a kind of toxic halitosis came as a surprise for the scientists. “This case of toxic breath as a defense is unique,” says Ian Baldwin. The example of the wolf spider illustrates the importance of combining molecular biology and natural history to understand the function of genes at the level of the organism. [AO]Original Publication:
Download of movies and high resolution pictures on www.ice.mpg.de/ext/735.html
Angela Overmeyer | Max-Planck-Institut
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences