Chemical ecology: Difference between revisions

'''Chemical ecology''' is the study of chemically- mediated interactions between living organisms, and the effects of those interactions on the demography, behavior and ultimately evolution of the organisms involved. It is thus a vast and highly interdisciplinary field.<ref>{{Cite webjournal |last=Bunin |first=Barry A. |date=December 1996 |title=<i>Chemical Ecology: The Chemistry of Biotic Interaction.</i>Thomas Eisner , Jerrold Meinwald |url=httpshttp://wwwdx.ncbsdoi.resorg/10.in1086/ChemicalEcology/WhatIsChemicalEcology419565 |titlejournal=WhatThe isQuarterly ChemicalReview Ecology?of {{!}}Biology Chemical|volume=71 Ecology|issue=4 |publisherpages=NCBS562 |access-datedoi=2017-12-10.1086/419565 |issn=0033-5770}}</ref><ref name="Dyer et al">{{Cite journal|last1=Dyer|first1=Lee A.|last2=Philbin|first2=Casey S.|last3=Ochsenrider|first3=Kaitlin M.|last4=Richards|first4=Lora A.|last5=Massad|first5=Tara J.|last6=Smilanich|first6=Angela M.|last7=Forister|first7=Matthew L.|last8=Parchman|first8=Thomas L.|last9=Galland|first9=Lanie M.|date=2018-05-25|title=Modern approaches to study plant–insect interactions in chemical ecology|journal=Nature Reviews Chemistry|volume=2|issue=6|pages=50–64|doi=10.1038/s41570-018-0009-7|s2cid=49362070|issn=2397-3358}}</ref> Chemical ecologists seek to identify the specific molecules (i.e. [[semiochemical]]s) that function as signals mediating [[community (ecology)|community]] or [[ecosystem]] processes and to understand the evolution of these signals. The substances that serve in such roles are typically small, readily-diffusible [[organic compound|organic molecules]], but can also include larger molecules and small peptides.<ref>{{cite journal |journal=Journal of Chemical Education |volume=60 |issue=7 |year=1983 |title=Chemical Ecology: Chemical Communication in Nature |author1=Wood William F. |doi=10.1021/ed060p531|pages=531–539 }}</ref>

In practice, chemical ecology relies extensively on [[chromatography|chromatographic techniques]], such as [[thin-layer chromatography]], [[high performance liquid chromatography]], and [[gas chromatography]], to isolate and identify bioactive metabolites. To identify molecules with the sought-after activity, chemical ecologists often make use of [[bioassay]]-guided [[fractionation]]. Today, chemical ecologists also incorporate genetic and genomic techniques to understand the [[biosynthesis|biosynthetic]] and [[signal transduction]] pathways underlying chemically- mediated interactions.<ref name="Meinwald Eisner pp. 4539–4540">{{cite journal | last1=Meinwald | first1=J. | last2=Eisner | first2=T. | title=Chemical ecology in retrospect and prospect | journal=Proceedings of the National Academy of Sciences | volume=105 | issue=12 | date=19 March 2008 | issn=0027-8424 | doi=10.1073/pnas.0800649105 | pmid=18353981 | pages=4539–4540| pmc=2290750 | doi-access=free }}</ref>

Plant chemical ecology focuses on the role of chemical cues and signals in mediating interactions of plants with their biotic environment (e.g. microorganisms, phytophagous insects, and pollinators).<ref>{{Cite journal |last=Fraenkel |first=Gottfried S. |date=1959-05-29 |title=The Raison d'Être of Secondary Plant Substances: These odd chemicals arose as a means of protecting plants from insects and now guide insects to food |url=https://www.science.org/doi/10.1126/science.129.3361.1466 |journal=Science |language=en |volume=129 |issue=3361 |pages=1466–1470 |doi=10.1126/science.129.3361.1466 |issn=0036-8075}}</ref>

The chemical ecology of plant-insect interaction is a significant subfield of chemical ecology.<ref name="Dyer et al" /><ref name="Mithfer">{{Citation|last1=Mithfer|first1=Axel|chapter=Chemical Ecology of Plant–Insect Interactions|pages=261–291|publisher=Wiley-Blackwell|language=en|doi=10.1002/9781444301441.ch9|isbn=978-1-4443-0144-1|last2=Boland|first2=Wilhelm|last3=Maffei|first3=Massimo E.|title=Molecular Aspects of Plant Disease Resistance|year=2008}}</ref><ref name="Dyer 50–64">{{Cite journal|last1=Dyer|first1=Lee A.|last2=Philbin|first2=Casey S.|last3=Ochsenrider|first3=Kaitlin M.|last4=Richards|first4=Lora A.|last5=Massad|first5=Tara J.|last6=Smilanich|first6=Angela M.|last7=Forister|first7=Matthew L.|last8=Parchman|first8=Thomas L.|last9=Galland|first9=Lanie M.|date=2018-05-25|title=Modern approaches to study plant–insect interactions in chemical ecology|journal=Nature Reviews Chemistry|language=En|volume=2|issue=6|pages=50–64|doi=10.1038/s41570-018-0009-7|s2cid=49362070|issn=2397-3358}}</ref> In particular, plants and insects are often involved in a chemical [[evolutionary arms race]]. As plants develop chemical defencesdefenses to herbivory, insects which feed on them evolve immunity to these poisons, and in some cases, repurpose these poisons for their own [[Chemicalchemical defense|chemical defence]] against predators. OneFor ofexample, the more well-known examplescaterpillars of this is the [[monarch butterfly]], thesequester caterpillars[[cardenolide]] oftoxins whichfrom feed on thetheir [[Asclepias|milkweed]] planthost-plants and are able to use them as an anti-predator defense.<ref>{{Cite Milkweedsjournal contain|last1=Brower [[cardenolide]]|first1=L toxins,P but|last2=van monarchBrower butterfly|first2=J caterpillars|last3=Corvino have|first3=J [[EvolutionaryM arms|date=April 1967 race|evolved]]title=Plant topoisons remainin unaffecteda byterrestrial food chain. |journal=Proceedings of the toxinNational Academy of Sciences |language=en |volume=57 |issue=4 |pages=893–898 |doi=10.1073/pnas.57.4.893 Instead,|doi-access=free they|issn=0027-8424 sequester|pmc=224631 the|pmid=5231352}}</ref> toxinsWhereas duringmost theirinsects larvalare stagekilled andby thecardenolides, poisonwhich remainsare inpotent inhibitors of the adult[[Na+/K+-ATPase]], makingmonarchs ithave unpalatableevolved resistance to predators.the Manytoxin otherover suchtheir long evolutionary history with milkweeds. Other examples of this exist,sequestration includinginclude the tobacco hornworm ''[[Manduca sexta]]'', caterpillars which actively sequesteruse [[nicotine]] foundsequestered in thefrom [[Nicotiana|tobacco plant]]s in predator defense;<ref name="Mithfer" /> and the [[Utetheisa ornatrix|bella moth]], which secretes a [[quinone]]-containing froth fromto itsdeter head when disturbed by a potential predatorpredators obtained from feeding on ''[[Crotalaria]]'' speciesplants as a caterpillar.

Plant interactions with [[microorganism]]s are also mediated by chemistry. PlantsBoth mobilizeconstitutive chemicaland defensesinduced tosecondary resistmetabolites invasion(specialized bymetabolites in modern terminology) are involved in plant defense against pathogens. Chemicaland chemical signals are also important in the establishment and maintenance of resource [[Mutualism (biology)|mutualisms]]. For example, both [[rhizobia]] and [[mycorrhiza]]e responddepend toon chemical signals, such as [[strigolactone]]s and [[flavanoid]]s exuded from plant roots, in order to find a suitable host.

Mycorrhizae and other fungal endophytes may also benefit their host plants by producing [[antibiotic]]s or other [[secondary metabolite]]s/ specialized metabolites that ward off harmful fungi, bacteria and herbivores in the soil.<ref>{{Cite journal |doi = 10.1039/C4NP00166D|pmid = 26038303|title = Chemical ecology of fungi|journal = Natural Product Reports|volume = 32|issue = 7|pages = 971–993|year = 2015|last1 = Spiteller|first1 = Peter}}</ref> Some [[entomopathogenic fungus|entomopathogenic fungi]] can also form endophytic relationships with plants and may even transfer nitrogen directly to plants from insects they consume in the surrounding soil.<ref>Behie, S. W., P. M. Zelisko, and M. J. Bidochka. 2012. Endophytic Insect-Parasitic Fungi Translocate Nitrogen Directly from Insects to Plants. Science 336:1576–1577.</ref>

Many plants produce secondary/ specialized metabolites (known as [[allelochemical]]s) that can inhibit the growth of neighboring plants. Many examples of allelopathyallelopathic [[Competition (biology)|competition]] have been controversial due to the difficulty of positively demonstrating a causal link between allelopathic substances and plant performance under natural conditions,<ref>Duke, S. O. 2010. Allelopathy: Current status of research and future of the discipline: A commentary.</ref> but it is widely accepted that phytochemicals are involved in competitive interactions between plants. One of the clearest examples of allelopathy is the production of [[juglone]] by [[Juglans|walnut trees]], whose strong competitive effects on neighboring plants were recognized in the ancient world as early as 36 BC.<ref>Willis, R. J. 2000. Juglans spp., juglone and allelopathy. Allelopathy Journal 7:1–55.</ref>

=== DefenceDefense ===

[[File:Vi - Zoanthus sociatus - 2.jpg|thumb|leftright|''Zoanthus sociatus'' produces palytoxin]]

TheMany usemarine oforganisms chemicalsuse arechemical oftendefenses usedto adeter meanspredators. ofFor survivalexample, for marine organisms. Somesome [[crustacean]]s and [[mesograzer]]s, such as the ''[[Pseudamphithoides incurvaria]]'', use particulartoxic [[algae]] and seaweeds as a meansshield ofagainst deterrencepredation by covering their bodies in these plants. These plants produce [[alcoholPhycotoxin|phycotoxins]], [[diterpene]]s such as pachydictyol-A and dictyol-E, which preventhave thebeen [[predation]] of the crustacean. When this seaweed is absent or another seaweed without these alcohols are worn, the rate at which these crustaceans are eaten is much higher. Other crustaceans use their natural defences in conjuncture with produced chemicalsshown to defend themselves. Chemicals within their urine help coordinate them into groups. This combined with their spikes make them a much harder target fordeter predators.<ref name="Mark E. Hay">{{Citecitation journal|last=Hay|first=Mark E.needed|date=2009|title=MarineOctober Chemical Ecology: Chemical Signals and Cues Structure Marine Populations, Communities, and Ecosystems|journal=Annual Review of Marine Science|volume=1|pages=193–212|issn=1941-1405|pmc=3380104|pmid=21141035|doi=10.1146/annurev.marine.010908.163708|bibcode=2009ARMS....1..193H2022}}</ref> OthersOther secretemarine [[mucus]]organisms orproduce [[toxin]]schemicals thatendogenously maketo itdefend difficultthemselves. forFor predators to eat themexample, such as the finless sole, (''[[Pardachirus marmoratus]]'',) which usesproduces a toxin capable ofthat paralyzingparalyzes the jaws of a would-be predatorpredators. Many [[Zoantharia|zoanthids]] produce potent toxins, such as [[palytoxin]], which is one of the most poisonous known substances. Some species of these zooanthids are very brightly colored, which may be indicative of [[aposematism|aposematic]] defense.<ref>{{Cite journal|last1=Bakus|first1=Gerald J.|last2=Targett|first2=Nancy M.|last3=Schulte|first3=Bruce|title=Chemical ecology of marine organisms: An overview|journal=Journal of Chemical Ecology|language=en|volume=12|issue=5|pages=951–987|doi=10.1007/bf01638991|pmid=24307042|issn=0098-0331|year=1986|s2cid=34594704}}</ref>

ChemicalMany communicationmarine isorganisms veryuse important[[Pheromone|pheromones]] toas thechemical reproductioncues ofalerting marinepossible organisms.mates Somethat processesthey are relativelyready simple,to suchreproduce.<ref>{{Cite asweb attracting|title=CH105: oneChapter individual6 to- anotherA Brief History of Natural Products and Organic Chemistry |url=https://wou.edu/chemistry/courses/online-chemistry-textbooks/ch105-consumer-chemistry/ch105-chapter-6-hydrocarbons/ Male|access-date=2024-09-15 |website=Chemistry |language=en-US}}</ref> For example, male [[sea lamprey]]s attract ovulating females by emitting a bile that can be detected many metresmeters downstream.<ref>{{Cite journal| doi = 10.1126/science.1067797| issn = 0036-8075 | volume = 296| issue = 5565| pages = 138–141| last1 = Li| first1 = Weiming| last2 = Scott| first2 = Alexander P.| last3 = Siefkes| first3 = Michael J.| last4 = Yan| first4 = Honggao| last5 = Liu| first5 = Qin| last6 = Yun| first6 = Sang-Seon| last7 = Gage| first7 = Douglas A.| title = Bile Acid Secreted by Male Sea Lamprey That Acts as a Sex Pheromone| journal = Science| access-date = 2020-10-19| date = 2002-04-05| url = https://sciencewww.sciencemagscience.org/contentdoi/29610.1126/5565/138science.1067797| pmid = 11935026| bibcode = 2002Sci...296..138L| s2cid = 1688247}}</ref> Other processes can be more complex, such as the mating habits of crabs. Due to the fact that matingfemale crabs can only bemate doneduring shortlya aftershort theperiod femaleafter [[Moulting|moults]] from her shell, female crabs produces pheromones before she begins to moult in order to attract a mate. Male crabs will detect these pheromones and defend their potential mate until she has finished molted. However, due to the cannibalistic tendencies of crabs, the female produces an additional pheromone to suppresses cannibalistic instincts in her male guardian. These pheromones are very potent—so much so that they can induce male crabs to try to copulate with rocks or sponges that have been coated in pheromone by researchers.<ref name="Mark E. Hay">{{Cite journal|last=Hay|first=Mark E.|date=2009|title=Marine Chemical Ecology: Chemical Signals and Cues Structure Marine Populations, Communities, and Ecosystems|journal=Annual Review of Marine Science|volume=1|pages=193–212|issn=1941-1405|pmc=3380104|pmid=21141035|doi=10.1146/annurev.marine.010908.163708|bibcode=2009ARMS....1..193H}}</ref>

Determining [[Dominance (ethology)|dominanceDominance]] among crustaceans areis veryalso closelymediated tied tothrough chemical cues. When crustaceans fight to determine dominance they releaseurinate urine, which helps to determineinto the victorwater. AfterLater, aif fightthey ismeet concludedagain, both individuals willcan recognize each other inby thepheromones futurecontained throughin their urine, rememberingallowing whothem isto theavoid dominanta offight, theif twodominance andhas therebyalready avoidingbeen established. When a fight.lobster Thisencounters canthe alsourine haveof ananother impactindividual, onit futurewill fights.act Whendifferently anaccording individualto isthe perceived status of the urinator (e.g. more submissively when exposed to the urine of a more dominant crustaceancrab, it will actor more submissive, and oppositelyboldly when exposed to the urine of a subdominant individual). When individuals are unable to communicate through urine, fights canmay be longer and more unpredictable.<ref name="Mark E. Hay" />

=== Pest Controlcontrol ===

Chemical ecology has been utilized in the development of sustainable [[pest control]] strategies. Semiochemicals (especially insect [[sex pheromones]]) are widely used in [[integrated pest management]] for surveillance, [[pheromone trap|trapping]] and [[mating disruption]] of pest insects.<ref name=Witzgall2010>Witzgall, P., P. Kirsch, and A. Cork. 2010. Sex Pheromones and Their Impact on Pest Management. J Chem Ecol 36:80–100.</ref> Unlike conventional insecticides, pheromone-based methods of pest control are generally species-specific, non-toxic and extremely potent. In forestry, mass trapping has been used successfully to reduce tree mortality from [[bark beetle]] infestations in spruce and pine forests and from [[Rhynchophorus|palm weevils]] in palm plantations.<ref name=Witzgall2010/> In an aquatic system, a sex pheromone from the invasive [[sea lamprey]] has been registered by the United States Environmental Protection Agency for deployment in traps.<ref>KleinJan. 20, K., 2016, and 1:30 Pm. 2016. So long suckers! Sex pheromone may combat destructive lampreys.</ref> A strategy has been developed in Kenya to protect cattle from [[sleeping sickness|trypanosomiasis]] spread by [[Tsetse flies|Tsetse fly]] by applying a mixture of repellent odors derived from a non-host animal, the [[waterbuck]].<ref>Saini, R. K., B. O. Orindi, N. Mbahin, J. A. Andoke, P. N. Muasa, D. M. Mbuvi, C. M. Muya, J. A. Pickett, and C. W. Borgemeister. 2017. Protecting cows in small holder farms in East Africa from tsetse flies by mimicking the odor profile of a non-host bovid. PLOS Neglected Tropical Diseases 11:e0005977. Public Library of Science.</ref>

In 1959, [[Adolf Butenandt]] identified the first intraspecific chemical signal ([[bombykol]]) from the silk moth, ''[[Bombyx mori]]'', with material obtained by grinding up 500,000 moths.<ref>Wyatt, T. D. 2009. Fifty years of pheromones. Nature 457:262–263. Nature Publishing Group.</ref> The same year, Karlson and Lüscher proposed the term 'pheromone' to describe this type of signal.<ref name=Bergstrom2007>Bergström, G. 2007. Chemical ecology = chemistry + ecology! Pure and Applied Chemistry 79:2305–2323.</ref> Also in 1959, Gottfried S. Fraenkel also published his landmark paper, "The Raison d'être of Secondary Plant Substances", arguing that plant secondary/ specialized metabolites are not metabolic waste products, but actually evolved to protect plants from consumers.<ref>Fraenkel, G. S. 1959. The Raison d’Être of Secondary Plant Substances: These odd chemicals arose as a means of protecting plants from insects and now guide insects to food. Science 129:1466–1470. American Association for the Advancement of Science.</ref> Together, these papers marked the beginning of modern chemical ecology. In 1964, [[Paul R. Ehrlich]] and [[Peter H. Raven]] coauthored a paper proposing their influential theory of [[escape and radiate coevolution]], which suggested that an evolutionary '"arms-race'" between plants and insects can explain the extreme diversification of plants and insects.<ref>Ehrlich, P. R., and P. H. Raven. 1964. Butterflies and Plants: A Study in Coevolution. Evolution 18:586–608.</ref> The idea that plant metabolites could not only contribute to the survival of individual plants, but could also influence broad [[macroevolution]]ary patterns, would turn out to be highly influential. However, [[:hu:Jermy_Tibor|Tibor Jermy]] questioned the view of an evolutionary arms race between plants and their insect herbivores and proposed that the evolution of phytophagous insects followed and follows that of plants without major evolutionary feedback, i.e. without affecting plant evolution.<ref>{{Cite journal |last=Jermy |first=Tibor |date=1984 |title=Evolution of insect/host plant relationships |url=https://www.journals.uchicago.edu/doi/abs/10.1086/284302 |journal=The American Naturalist |volume=124 |issue=5 |pages=609–630|doi=10.1086/284302 }}</ref> He coined the term sequential evolution to describe plant-insect macroevolutionary patterns, which emphasizes that selection pressure exerted by insect attack on plants is weak or lacking.<ref>{{Cite journal |last=Jermy |first=Tibor |date=1993 |title=Evolution of insect-plant relationships - a devil's advocate approach |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1570-7458.1993.tb00686.x |journal=Entomologia Experimentalis et Applicata |volume=66 |issue=1 |pages=3–12|doi=10.1111/j.1570-7458.1993.tb00686.x }}</ref>

In the 1960s and 1970s, a number of plant biologists, ecologists, and entomologists expanded this line of research on the ecological roles of plant secondary/ specialized metabolites. During this period, [[Thomas Eisner]] and his close collaborator [[Jerrold Meinwald]] published a series seminal papers on chemical defenses in plants and insects.<ref name="Eisner pp. 1318–1320">{{cite journal | last=Eisner | first=T. | title=Catnip: Its Raison d'Etre | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=146 | issue=3649 | date=4 December 1964 | issn=0036-8075 | doi=10.1126/science.146.3649.1318 | pages=1318–1320| pmid=14207462 | bibcode=1964Sci...146.1318E | s2cid=11282193 }}</ref><ref>{{Cite journal| issn = 0036-8075| volume = 153| issue = 3742| pages = 1341–1350| last1 = Eisner| first1 = Thomas| last2 = Meinwald| first2 = Jerrold| title = Defensive Secretions of Arthropods| journal = Science| access-date = 2020-10-25| date = 1966| doi = 10.1126/science.153.3742.1341| url = https://www.jstor.org/stable/1719969| jstor = 1719969| pmid = 17814381| bibcode = 1966Sci...153.1341E}}</ref> A number of other scientists at Cornell were also working on topics related to chemical ecology during this period, including Paul Feeny, [[Wendell L. Roelofs]], [[Robert Whittaker (ecologist)|Robert Whittaker]] and [[Richard B. Root]]. In 1968, the first course in chemical ecology was initiated at Cornell.<ref>{{Cite web|url=http://www.chemicalecology.cornell.edu/historyandintro.html|title = History and Introduction}}</ref> In 1970, Eisner, Whittaker and the ant biologist William L. Brown, Jr. coined the terms [[allomone]] (to describe semiochemicals that benefit the emitter, but not the receiver) and [[kairomone]] (to describe semiochemicals that benefit the receiver only).<ref>Brown, W. L., T. Eisner, and R. H. Whittaker. 1970. Allomones and Kairomones: Transspecific Chemical Messengers. BioScience 20:21–21. Oxford Academic.</ref> Whittaker and Feeny published an influential review paper in ''Science'' the following year, summarizing the recent research on the ecological roles of chemical defenses in a wide variety of plants and animals and likely introducing Whittaker's new taxonomy of semiochemicals to a broader scientific audience.<ref>Whittaker, R. H., and P. P. Feeny. 1971. Allelochemics: Chemical Interactions between Species. Science 171:757–770. American Association for the Advancement of Science.</ref> Around this time, [[Lincoln Brower]] also published a series of important ecological studies on monarch sequestration of cardenolides. Brower has been credited with popularizing the term "ecological chemistry" which appeared in the title of a paper he published in ''Science'' in 1968<ref>Brower, L. P., W. N. Ryerson, L. L. Coppinger, and S. C. Glazier. 1968. Ecological Chemistry and the Palatability Spectrum. Science 161:1349–1350. American Association for the Advancement of Science.</ref> and again the following year in an article he wrote for ''[[Scientific American]]'', where the term also appeared on the front cover under an image of a giant bluejay towering over two monarch butterflies.<ref name=Bergstrom2007/><ref>{{Cite web|url=https://monarchwatch.org/blog/2018/08/02/dr-lincoln-brower/|title = Dr. Lincoln Brower|date = 3 August 2018}}</ref>

The specialized ''[[Journal of Chemical Ecology]]'' was established in 1975, and the journal,Journal ''Chemoecology'', was founded in 1990. In 1984, the International Society of Chemical Ecology was established and in 1996, the [[Max Planck Institute of Chemical Ecology]] was founded in Jena, Germany.<ref name=Bergstrom2007/>

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