Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

Dans le lagon de Moorea, en Polynésie Française, nous avons identifié un écosystème constitué de deux producteurs primaires (les cyanobactéries filamenteuses Lyngbya majuscula et Anabaena cf. torulosa), trois mollusques herbivores (Stylocheilus striatus, S. longicauda, et Bulla orientalis), un nudibranche carnivore (Gymnodoris ceylonica) et un crabe carnivore (Thalamita coerulipes). L. majuscula et A. cf torulosa prolifèrent sur de vastes zones jusqu’à épiphyter les coraux ; elles sont des producteurs importants de métabolites secondaires, principalement des lipopeptides cycliques, qui peuvent être toxiques ou répulsifs. Cependant, ces composés n’empêchent pas le lièvre de mer S. striatus de consommer les cyanobactéries. S. striatus, décrit comme un prédateur spécialiste de L. majuscula, est connu pour séquestrer et/ou biotransformer les métabolites secondaires de L. majuscula. Cependant nous avons également observé S. striatus, sur A. cf torulosa où il semble moins exposé à la prédation du nudibranch G. ceylonica que quand il est sur L. majuscula. Dans cet écosystème modèle, nous avons combiné le profilage des métabolomes des deux cyanobactéries et des expériences en écologie dans le but d’étudier le rôle des médiateurs chimiques dans la structuration de cet écosystème ; nous avons complété la caractérisation des profils métaboliques des deux cyanobactéries, étudié les transmissions verticale et horizontale des métabolites secondaires produits par les cyanobactéries le long de la chaine trophique, et étudié le rôle de ces composés dans les relations prédateurs-proies. De A. cf torulosa, nous avons isolé cinq analogues acyliques et deux analogues cyliques des laxaphycines que nous avons caractérisés par RMN (1D et 2D RMN : COSY, TOCSY, HSQC, HMBC, NOESY), spectrométrie de masse (spectrométrie de masse à haute résolution et fragmentation en MSn), ainsi que par dégradation chimique avec la méthode de Marfey. La présence de laxaphycines acycliques n’a jamais été décrite auparavant. Nous avons montré que les peptides de L. majuscula sont séquestrés sans biotransformation par les herbivores, alors que les herbivores présents sur A. cf torulosa biotransforment deux laxaphycines en quatre composés nouveaux que nous avons caractérisés. Il ne semble pas que la séquestration et la biotransformation soient opérées dans le but d’améliorer les défenses chimiques des herbivores mais plutôt comme un mécanisme de tolérance. Nous avons également montré que les mollusques herbivores utilisent les composés produits par les cyanobactéries comme signaux chimiques pour détecter à distance les cyanobactéries et pour le choix de leur nourriture. Ces expériences de choix semblent indiquer que S. striatus et B. orientalis sont des herbivores généralistes bien que l’influence des molécules des cyanobactéries suggère un comportement adaptatif permettant au mollusque de retrouver l’hôte sur lequel il a été prélevé. / In the lagoon of Moorea in French Polynesia, we have identified a relatively simple tropical marine ecosystem consisting of two primary producers (two filamentous cyanobacteria, Lyngbya majuscula and Anabaena cf. torulosa), three herbivorous molluscs (Stylocheilus striatus, S. longicauda and Bulla orientalis), a carnivorous nudibranch (Gymnodoris ceylonica) and a carnivorous crab (Thalamita coerulipes). L. majuscula and A. cf torulosa, that bloom ephemerally across wide sandy areas and even on corals, are prolific producers of secondary metabolites, mainly cyclic lipopeptides, which may either be toxic or act as feeding deterrents to potential consumers. However, these compounds do not prevent the sea hare S. striatus, feeding on cyanobacteria. S. striatus, considered as L. majuscula specialist, is known to sequester and transform some secondary metabolites produced by L. majuscula,. However we found also S. striatus feeding on A. cf torulosa and in this case it was less susceptible to predation by the nudibranch G. ceylonicasa than when it fed on L. majuscula. In the study of this model ecosystem, we combine cyanobacterial metabolome profiling and ecological bioassays in order to study the cascading effects of chemical mediators in multi-trophic relationships; we completed the metabolic profile characterization of the two cyanobacteria, we studied vertical and horizontal transmissions of the cyanobacterial secondary metabolites along the trophic web, and studied the role of these compounds in predator-prey relationships. Focusing our attention on A. cf torulosa we isolated seven new lipopeptides, derived from the known laxaphycins, and characterized them using extensive NMR experiments (1D and 2D NMR: COSY, TOCSY, HSQC, HMBC, NOESY), mass spectrometry (HR-MS and fragmentation by MSn) and Marfey’s advanced method. It is the first time that acyclic analogs of laxaphycins have been described. Although the peptides from L. majuscula are found intact in herbivores, some lipopeptides from A. cf torulosa are biotransformed by sea hares into four new compounds we characterized. The sequestration and biotransformation by the herbivores may be considered as a tolerance mechanism rather than a defense mechanism. We demonstrate also that the herbivores use cyanobacterial compounds as chemical cues for cyanobacteria tracking and feeding choice. Our experiments suggest that S. striatus and B. orientalis are generalist consumers, although the influence of cyanobacterial chemical cues on their foraging preferences may suggest an adaptive behavior enabling the mollusc to track their host of origin.

Orientador: Anita Jocelyne Marsaioli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-19T18:09:49Z (GMT). No. of bitstreams: 1 Wouters_FelipeChristoff_M.pdf: 4919215 bytes, checksum: c2fb1e5605f041d7b55cee18189002ca (MD5) Previous issue date: 2011 / Resumo: Este trabalho consiste no estudo de secreções defensivas de 18 espécies de opiliões da família Gonyleptidae. A composição química das secreções dessas espécies foi investigada por cromatografia gasosa acoplada à espectrometria de massas (CG-EM). Os compostos encontrados nas espécies estudadas se dividem em três classes principais: cetonas, quinonas e fenóis. Análises de ressonância magnética nuclear (RMN) das secreções de três dessas espécies (Gonyleptes saprophilus, Magnispina neptunus e Progonyleptoidellus striatus) permitiram a caracterização de cinco compostos: 4-metilex-1-en-3-ona, 2-metil-1,4-benzoquinona, 2-etil-1,4-benzoquinona, 2,5-dimetilfenol e 2,3,6-trimetilfenol. Foram sintetizadas duas vinil cetonas encontradas nas secreções estudadas: 4-metilex-1-en-3-ona e 5-metilex-1-en-3-ona. Essas cetonas foram caracterizadas e confirmou-se sua presença nas secreções de seis das espécies estudadas. Os demais compostos tiveram suas estruturas sugeridas baseando-se nos dados de espectrometria de massas e/ou coinjeção em CG-EM com padrões. Além disso, foram realizados ensaios de atividade inibitória frente a diversos micro-organismos usando padrões sintéticos de compostos presentes nas secreções, representativos das três classes químicas encontradas / Abstract: This work consists on the study of defensive secretions from 18 harvestmen species belonging to the family Gonyleptidae. The chemical composition of these secretions was investigated by gas chromatography coupled to mass spectrometry (GC-MS). The identified compounds can be divided in three main classes: ketones, quinones and phenols. Nuclear Magnetic Resonance (NMR) analyses of secretions from three species (Gonyleptes saprophilus, Magnispina neptunus and Progonyleptoidellus striatus) allowed the characterization of five compounds: 4-methylhex-1-en-3-one, 2-methyl-1,4-benzoquinone, 2-ethyl-1,4-benzoquinone, 2,5-dimethylphenol, and 2,3,6-trimethylphenol. Two vinyl ketones found in the studied secretions were synthesized: 4-methylhex-1-en-3-one and 5-methylhex-1-en-3-one. These ketones were characterized and their presence in secretions of six species was confirmed. The other compounds had their structures suggested based on mass spectrometry data and/or GC-MS coinjection with standart samples. Moreover, inhibitory activity assays against microorganisms were performed with synthetic standarts of compounds found in the secretions, representatives of the three identified chemical classes / Mestrado / Quimica Organica / Mestre em Química

Invasive species are alien to the ecosystem under consideration and cause economic or environmental damage or harm to human health. Two alien insects that fit this description are the brown marmorated stink bug, Halyomorpha halys and the spotted lanternfly, Lycorma delicatula. Both invaders are polyphagous pests that feed on a myriad of plant species and inflict severe crop losses. As sustainable control methods depend on the accurate monitoring of species’ invasion and involve the use of natural enemies, we addressed these two facets by exploring novel monitoring techniques and deciphering host-parasitoid interactions for improved integrated pest management. Thus, we adopted ‘BugMap’, a citizen science initiative that enables students, farmers and everyday citizens to report sightings of H. halys from Italy, with emphasis on Trentino-Alto Adige. Aside from fostering citizen participation in scientific endeavors and the enhanced literacy that ensues, BugMap helped uncover the invasion dynamics of H. halys and forecast its potential distribution in Trentino, all while coordinating technical monitoring and informing management strategies. The most promising agent currently under study for the classical biological control of H. halys is the Asian egg parasitoid Trissolcus japonicus. To assess the wasp’s potential non-target impacts, we investigated its foraging behavior in response to chemical traces ‘footprints’ deposited by its main host H. halys and by a suboptimal predatory species, the spined soldier bug, Podisus maculiventris. Wasps exhibited a ‘motivated searching’ when in contact with footprints originating from both species. However, T. japonicus arrestment was significantly stronger in response to H. halys footprints, compared with P. maculiventris, implying the presence of underlying chemical cues that shape its natural preferences. A series of GC-MS chemical analyses revealed that n-tridecane and (E)-2-decenal were more abundant in H. halys footprints and are probably the key components utilized by the wasp for short range host location. The function of the aforementioned compounds was studied, n-tridecane acted as an arrestant, prolonging T. japonicus residence time, whereas (E)-2-decenal fulfilled its presumed defensive role and repelled the wasp. These results shed new light on the chemical ecology of T. japonicus and help expand the understanding of parasitoid foraging and its implications for classical biological control. Moving to the other invader L. delicatula, an egg parasitoid Anastatus orientalis was reported attacking it at high rates in its native range in Eastern Asia and may play a key role in reducing its populations there. A series of bioassays revealed that wasps responded to footprints deposited by L. delicatula gravid females by initiating a strong searching behavior. Moreover, A. orientalis preferred to oviposit in egg masses with intact oothecae, suggesting that the host’s egg covering functions as a trigger for A. orientalis probing and oviposition. Thus, A. orientalis not only overcomes, but also reverses an important line of host structural defense for its own fitness gains. This dissertation discusses the benefits of combining citizen science with traditional monitoring, and the usefulness of decoding host-parasitoid interactions to design more efficacious management strategies of invasive insect pests.

Ripe fleshy fruits contain an enormous diversity of metabolites that influence ecological interactions with mutualistic and antagonistic species. This dissertation investigates the impact of fruit secondary metabolites on the foraging behavior and digestive physiology of bats (Chapters 2-4) while applying insights from basic chemical ecology to inform forest regeneration strategies (Chapter 5). The studies were conducted in northeastern Costa Rica at La Selva Biological Station. Chapter Two examines the variability and associations between nutrients and secondary metabolites within ripe Piper sancti-felicis fruits, showing that intraindividual variation of chemical traits can surpass interindividual variation and associations between chemical traits are scale-dependent, varying in strength and direction. Chapter Three explores how bats balance nutrient acquisition with defensive metabolite avoidance and the impact of metabolite consumption on bat nutrient absorption. It reveals that nutrient composition is the primary driver of bat foraging behavior and that defensive metabolites can interfere with protein absorption. Chapter Four further uses untargeted metabolomics to explore the influence of secondary metabolites on nutrient absorption, demonstrating that four commercial secondary metabolites induce dose-dependent changes in bat fecal metabolome, altering essential nutrient absorption. Chapter Five translates principles of chemical ecology into practical use by demonstrating the effectiveness of synthetic volatiles in attracting fruit bats and increasing seed rain. Taken together, this dissertation shows the impact of defensive metabolites on a key seed disperser while demonstrating the potential application of chemical ecology to address forest regeneration challenges. / Doctor of Philosophy / Fleshy fruits exhibit a remarkable chemical complexity. Fruit pulp is not only rich in essential nutrients (sugars, proteins, and lipids) but also contains a diverse array of other chemicals collectively known as secondary metabolites. These metabolites shape ecological interactions between fruits and frugivores. This dissertation focuses on understanding the ecological and physiological effects of fruit chemistry on frugivores. The studies were conducted at La Selva Biological Station in northeastern Costa Rica, focusing on fruit bats and pepper plants. Chapter two examines the relationships and variation between nutrients and toxins within ripe fruits of pepper plants (Piper sancti-felicis), finding that the chemical variation within a single plant can exceed the differences between separate plants. Also, depending on the scale studied, toxins and nutrients can be positively or negatively associated. Chapters Three and Four describe the preferences of a fruit bat (Carollia perspicillata) for nutrients and toxins, showing that nutrients are the primary driving force behind food choices and demonstrating that certain fruit toxins alter the ability of bats to absorb nutrients, including different sugars, proteins, and lipids. Chapter Five demonstrates the potential of synthetic chemical lures to attract fruit bats and enhance seed dispersal, offering a promising strategy to promote forest regeneration in degraded areas. Overall, this research demonstrates how fruit chemicals can significantly impact fruit bats, which play a crucial role in dispersing seeds and maintaining forest diversity.

Millipedes (class Diplopoda) are ubiquitous in forests worldwide, with about 12,000 described species and an estimated 30,000 undescribed species. The most species-rich order is the Polydesmida, the flat-backed millipedes, which encompasses about 3,500 species. Appalachia has an abundance of Polydesmida, and is a biodiversity hotspot for millipedes in the family Xystodesmidae. These diplopods are chemically defended with hydrogen cyanide and benzaldehyde, and sometimes form mimicry rings based on shared color. The evolutionary dynamics of model and mimic are incompletely known in these rings, so I investigated a mimicry ring in the central Appalachian Mountains to determine if the species Apheloria polychroma functions as a model for the genus Brachoria. I measured the size of the chemical gland to assess toxicity in 15 species, and reconstructed the ancestral dimensions of the gland to determine the direction of volume change over evolutionary time. Using a molecular phylogeny, I traced the miniaturization of chemical glands in the mimic genus Brachoria and found that in areas without Apheloria, Brachoria and related xystodesmids have larger chemical glands. Non-aposematic millipedes of the genus Nannaria have significantly smaller glands, and ostensibly rely on camouflage to avoid predation. This genus is known as the twisted claw millipedes and occur throughout eastern North America, but have their center of diversity in the Appalachian Mountains. About 22 species are described, but many undescribed species are known. To determine the diversity of this group, field collection and examination of museum specimens took place from 2015-2020. Examination of morphology, combined with molecular phylogenetics, revealed two distinct clades in the genus. One is distributed throughout the eastern United States, while the other is found only in the Appalachian Mountains. This Appalachian clade contains six described species, and I describe an additional 18 species, quadrupling the diversity of the group. Additionally, the phylogenetics of the polydesmid genus Pseudopolydesmus is investigated in an integrative taxonomic framework using five genes. I find that the genus is monophyletic, contains 8 species, and are related to one another in a hierarchical way according to a molecular phylogeny. I provide complete distributional records and live photographs of each species. / Doctor of Philosophy / Millipedes are common animals in forests. There are about 12,000 known species in the world, with an estimated 30,000 undescribed species still awaiting discovery and description. The largest group of millipedes are the flat-backed millipedes, with about 3,500 known species. They are some of the most common millipedes in North America, and many of these species defend themselves with poisons that are harmful to predators, but smell sweet like cherries to humans. Some of these millipedes have bright red or yellow spots against dark colors to warn predators of their toxins, and look similar to other species that live near them. I wanted to know if some of these species are more or less poisonous than others, and measured how large their poison reserves were. I found that one species, called Apheloria polychroma, is more poisonous than similar-looking species called Brachoria, which are less poisonous. If Brachoria doesn't live near Apheloria though, Brachoria is more poisonous. Not all of these millipedes are brightly colored, and a group called Nannaria, or the twisted claw millipedes, are camouflaged with brown colors on the forest floor. These millipedes only live in the eastern United States, especially the Appalachians, and aren't found anywhere else in the world. We know about 20 species of them, but based on specimens stored in scientific collections in museums and through discovery from fieldwork, we knew that more species existed. Each species of twisted-claw millipede only lives in a small area, sometimes only a few miles wide, and could be threatened by habitat loss and other dangers. So, to learn more about them, we need to find them in the forest and describe what they look like and most importantly, giving them a name. I did this by collecting them, illustrating their anatomy, and sequencing their DNA. I found two groups within Nannaria, and focused on the group that only lives in Appalachia. Scientists know 6 of these species, but I found 18 more species and describe them. A related group called Pseudopolydesmus lives throughout North America, and I studied their anatomy and DNA as well, finding 8 species.

Interactions are important drivers of selection and community structure, which makes the study of multi-species interactions critical for understanding the ecology and evolution of organisms. This dissertation includes four data chapters that examine the biotic and abiotic mechanisms that shape multi-species interactions in both tropical and temperate ecosystems. The first three data chapters (Chapters 2–4) were completed within a Neotropical rainforest in Costa Rica and focus on one plant genus, Piper (Piperaceae). The final data chapter (Chapter 5) was conducted within a working landscape of soybean (Glycine max) fields in eastern Maryland, USA. In Chapter 2, I explore intra- and inter-specific dietary niche partitioning of Piper fruits among three frugivorous bats, illustrating the importance of fine-scale mechanisms that facilitate species coexistence and influence plant–animal interactions. In Chapter 3, I demonstrate how the chemical ecology of a Neotropical shrub, Piper sancti-felicis, shapes fruit interactions with antagonists (fruit fungi) and mutualists (frugivorous bats and birds), developing a foundation for understanding evolutionary ecology of plant chemical traits based on phytochemical investment patterns. In Chapter 4, I describe the direct and indirect impacts of elevated temperature and CO2 concentration on the plant traits and interactions in Piper generalense, improving our understanding of the effects of climate change on a Neotropical plant–herbivore system. In Chapter 5, I explore the biotic (herbivore-induced plant volatiles) and abiotic (fine-scale weather conditions) drivers affecting insectivorous bat foraging in soybean fields in eastern Maryland, providing a pathway to further investigate new strategies for integrated pest management. As a collective work, this dissertation disentangles the nuances of multi-species interactions, exploring foundational mechanisms underlying biodiversity maintenance as well as answering applied questions to address a changing climate and aid sustainable agriculture. / Doctor of Philosophy / Everything in nature is connected, so studying ecological interactions requires us to view them from many different angles. As with most relationships, ecological interactions are multi-faceted and context-dependent. In this dissertation, I describe both tropical and temperate systems, collecting a variety of measurements from plants, microbes, and animals to explore the complicated relationships that exist between them. In Chapter 2, I explore how three species of fruit-eating bats may divide the use of a shared food resource (tropical pepper fruits in the genus Piper) to maintain separate populations and how those foraging differences may affect Piper plant populations. In Chapter 3, I characterize a chemical compound found in the fruits of a Piper plant species and test the effect of that compound on fruit fungi and fruit-eating bats and birds, leading to a better understanding of the selective pressures affecting fruit chemistry. In Chapter 4, I describe the direct and indirect effects of climate change on a Piper plant in the first study to measure the responses of tropical understory plants to treatments that mimic climate change using active warming and CO2 supplementation. In Chapter 5, I explore the fine-scale drivers of bat activity in soybean fields, including how weather conditions and the specific compounds emitted by insect-damaged plants may affect bat activity. As a collective work, this dissertation describes the complex relationships among plants and their many interactors, exploring questions from biodiversity maintenance to integrated pest management strategies.

The stink bugs, (Pentatomidae) harlequin bug (Murgantia histrionica), brown marmorated stink bug (Halyomorpha halys), and southern green stink bug (Nezara viridula) are significant agricultural pests both in the United States and globally. The aggregation or sex pheromones produced by these insects are known to be bisabolene-type sesquiterpenoids; however, the biosynthetic pathways in the formation of these pheromones are unknown. Here we provide evidence that Pentatomidae produce sesquiterpene aggregation pheromones de novo and discuss the evolution of terpene biosynthesis in stink bugs. According to transcriptome analyses, the investigated stink bug species express at least two isoprenyl diphosphate synthases (IDSs), one of which makes (E,E)-farnesyl diphosphate (FPP) as the general precursor in sesquiterpene synthesis, whereas other IDS-type proteins function as terpene synthases (TPSs) generating intermediates in sesquiterpene pheromone formation. The TPS genes are expressed in a sex- and tissue-specific manner. Based on phylogenetic analysis, these IDS-type TPSs arose from trans-IDS progenitors in divergence from bona fide IDS proteins. Compared to microbes and plants, the evolution of TPS function from IDS progenitors in insects appears to have occurred more recently. The discovery of TPS genes in stink bugs provides valuable insight into pentatomid and insect terpene biosynthesis. Moreover, the identified genes may be used in developing alternative management strategies for stink bug pests. / PHD / The stink bugs harlequin bug, brown marmorated stink bug, and southern green stink bug are significant agricultural pests both in the United States and globally. These stink bugs, as many others, release terpene type pheromones for aggregation and mating. In contrast to the general notion that insects depend on their host plants or microbes as sources of terpene pheromones, we provide evidence that stink bugs produce these pheromones de novo. We found that stink bug pheromone formation depends on proteins with terpene synthase activity, which are derived from enzymes producing linear intermediates in the core terpene metabolic pathway (isoprenyl diphosphate synthases). Expression of the terpene synthase genes is confined to specific tissues of males according to the male-specific release of the pheromones. Compared to microbes and plants, the evolution of terpene synthase function from isoprenyl diphosphate synthase progenitors in insects appears to have occurred more recently. The discovery of terpene synthase genes in stink bugs provides valuable insight into pentatomid and insect terpene biosynthesis. Moreover, the identified genes may be used in developing alternative management strategies for stink bug pests.

Herbivores and pathogens pose a consistent threat to plant productivity. In response, plants invest in structural and/or chemical defenses that minimize damage caused by these biotic stressors. In salt marshes along the Atlantic coast of the United States, a facultative mutualism between snails (Littoraria irrorata) and multiple species of fungi exert intense top-down control of the foundation grass species Spartina alterniflora. Since exposure to herbivores and pathogens are tightly coupled in this system, I investigated whether S. alterniflora utilizes chemical and/or structural defenses to deter both snails and fungi, and examined how plant defenses varied among S. alterniflora individuals and populations. I also assessed how other marsh plants prevent snails from establishing farms, and considered whether interspecific variation in plant chemical defenses influences marsh community structure. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that plant secondary chemistry was the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that differences in plant chemistry were the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability against S. alterniflora. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future.

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