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1. Complex multitrophic species interactions and fitness costs: Intricate consequences of jasmonate and salicylate induced plant defences

   https://doi.org/10.1111/1365-2656.70243  

   Kersch‐Becker, Mônica F; Pinheiro, Guilherme P; Schweller, Thaís S; Pareja, Martin; Pocius, Victoria M; Trigo, José R; Romero, Gustavo Q (April 2026, Journal of Animal Ecology)

   Abstract - Induced plant defences regulated by jasmonic acid (JA) and salicylic acid (SA) initiate a cascade of effects, from defence expression to changes in arthropod community structure and species interactions that can ultimately influence plant fitness. Yet the long‐term consequences of these processes remain poorly understood, particularly in perennial tropical systems. We investigated how activation of JA and SA signalling pathways shapes arthropod community composition and plant reproductive success in Trichogoniopsis adenantha (Asteraceae), a glandular trichome‐bearing shrub native to the Brazilian Atlantic rainforest. Using chemical elicitors, we induced JA and SA defences for up to 16 months and monitored herbivore and predator assemblages, herbivory patterns, trichome expression, pyrrolizidine alkaloid concentrations and plant short‐term fecundity. JA‐elicited plants exhibited higher pyrrolizidine alkaloid levels in flowers, reduced leaf herbivory and lower seed damage by pre‐dispersal seed predators. However, these plants experienced increased colonization by sap‐feeding insects. In contrast, SA‐elicited plants were more vulnerable to chewing herbivores but more resistant to sap‐feeders. Despite similar reductions in seed predation across both treatments, JA and SA induction significantly reduced ovary fertilization, likely due to changes in floral traits and decreased pollinator visitation, ultimately imposing substantial fitness costs. Additionally, seasonal turnover in arthropod communities was accompanied by temporal variation in how defences structured species composition and abundance. Our findings demonstrate that phytohormone‐mediated defences can simultaneously induce resistance and susceptibility across herbivore guilds, with divergent impacts on predator associations. Although defence induction reduced herbivore damage, it compromised short‐term fecundity, revealing trade‐offs between defence and reproduction. By linking induced defences to multitrophic interactions over time, this study highlights the ecological complexity of plant defence strategies in biodiverse tropical ecosystems. 

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2. Evolutionary trajectories of multiple defense traits across phylogenetic and geographic scales in Vitis

   https://doi.org/10.1002/ecog.07722  

   Graham, Carolyn_D K; Weber, Marjorie G (May 2025, Ecography)

   The processes driving defense trait correlations may vary within and between species based on ecological or environmental contexts. However, most studies of plant defense theory fail to address this potential for shifts in trait correlations across scales. In this work, we tested for correlations between multiple defensive traits (secondary chemistry, carbon to nitrogen ratio, domatia, leaf toughness, trichomes, and pearl bodies) across a common garden of 21Vitisspecies and eighteen genotypes of the speciesVitis ripariato identify when and where patterns of defense trait evolution persist or break down across biological scales. Additionally, we asked whetherVitisdefense trait investment correlates with environmental variables as predicted by plant defense theory, using environmental metrics for eachVitisspecies andV. ripariagenotype from the GBIF and WorldClim databases. We tested for correlations between defense trait investment, herbivore palatability, and environmental variables using phylogenetically informed models. Beyond a few likely physiological exceptions, we observed a lack of significant correlations between defense traits at both intra‐ and interspecific scales, indicating that these traits evolve independently of each other inVitisrather than forming predictable defense syndromes. We did find that investment in carbon:nitrogen (at both scales) and pearl bodies increases with proximity to the equator, demonstrating support for plant defense theory's prediction of higher investment in defenses at more equatorial environments for some, but not all, defense traits. Overall, our results challenge commonly held hypotheses about plant defense evolution, namely the concept of syndromes, by demonstrating that strong correlations between defense traits are not the prevailing pattern both across and withinVitisspecies. Our work also provides the first comprehensive evaluation of the evolutionary divergence in approaches thatVitis, a genus with significant agricultural value, have evolved to defend themselves against herbivores. 

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3. Evolutionary signatures of a trade-off in direct and indirect defenses across the wild grape genus, Vitis

   https://doi.org/10.1093/evolut/qpad140  

   Graham, Carolyn D; Forrestel, Elisabeth J; Schilmiller, Anthony L; Zemenick, Ash T; Weber, Marjorie G (August 2023, Evolution)

   Kronforst, Marcus; Connallon, Tim (Ed.)

   Abstract Evolutionary correlations between chemical defense and protection by mutualist bodyguards have been long predicted, but tests of these patterns remain rare. We use a phylogenetic framework to test for evolutionary correlations indicative of trade-offs or synergisms between direct defense in the form of plant secondary metabolism and indirect defense in the form of leaf domatia, across 33 species in the wild grape genus, Vitis. We also performed a bioassay with a generalist herbivore to associate our chemical phenotypes with herbivore palatability. Finally, we tested whether defensive traits correlated with the average abiotic characteristics of each species’ contemporary range and whether these correlations were consistent with plant defense theory. We found a negative evolutionary correlation between domatia size and the diversity of secondary metabolites in Vitis leaf tissue across the genus, and also that leaves with a higher diversity and richness of secondary metabolites were less palatable to a generalist herbivore, consistent with a trade-off in chemical and mutualistic defense investment. Predictions from plant defense theory were not supported by associations between investment in defense phenotypes and abiotic variables. Our work demonstrates an evolutionary pattern indicative of a trade-off between indirect and direct defense strategies across the Vitis genus. 

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4. Functional trait and diversity measurements to understand the effects of climate and herbivory in California oak woodland understory communities, 2017-2019

   https://doi.org/10.5063/f1sq8xwp  

   Klope, Maggie; Harris-Gavin, Ruby; Copeland, Stephanie; Orr, Devyn; Young, Hillary (January 2025, KNB Data Repository)

   This study examines how global changes in large herbivore populations (declining wild herbivores and increasing domestic herbivores) interacts with climate to influence plant communities by utilizing a large herbivore exclosure experiment in an oak savanna ecosystem in California with three herbivore assemblages (all herbivores, cattle-only excluded, all large herbivores excluded) across a topo-climatic gradient. Samples of plants were collected and processed to measure specific leaf area (SLA), leaf area (LA), and leaf dry matter content (LDMC). Additional traits (leaf nitrogen content and seed mass) were determined via web database searches. The finding of this study highlight complex interactions between herbivore assemblages and climate. 

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5. Top-down effects from parasitoids may mediate plant defence and plant fitness

   https://doi.org/DOI: 10.1111/1365-2435.13617  

   Tan, C.-W.; Peiffer, Michelle; Ali, Jared G.; Luthe, D.S.; Felton, Gary w. (October 2020, Functional ecology)

   null (Ed.)

   1. Plants face many environmental stresses that can impact their survival, development and fitness. Insects are the most diverse, abundant and threatening herbivores in nature. As a consequence, plants produce direct chemical and physical defences to reduce herbivory. They also release volatiles to recruit natural enemies that indirectly protect them from herbivory. The recruitment of parasitic wasps can benefit plant fitness because they ultimately kill their insect hosts. 2. Recently, studies showed that parasitoids can indirectly mediate plant defences by modulating herbivore oral secretions. In addition to the direct benefits of parasitoids in terms of reducing herbivore survival, we tested if the reduction in induced defences by parasitized caterpillars compared to non-parasitized caterpillars may reduce the costs associated with defence expression. 3. We provide evidence that tomato plants treated with saliva from parasitized caterpillars have significantly higher fitness parameters including increased flower numbers (16.3%) and heavier fruit weight (13.5%), compared to plants treated with saliva from non-parasitized caterpillars. Since plants were grown without actual herbivores, the higher values for these fitness parameters were due to lower costs of induced defences and not due to reduced herbivory by parasitized caterpillars. Furthermore, the resulting seed germination time was shorter and the germination rate was higher when the maternal plants were previously exposed to parasitized herbivore treatment compared to control (non-treated) plants. 4. Overall, application of saliva did not result in transgenerational priming of offspring defence responses. However, offspring of parents exposed to caterpillar saliva had lower constitutive levels and higher induced levels of trypsin inhibitor than offspring from unexposed parents. 5. This study shows that the saliva of parasitized caterpillars can modulate plant defences and further demonstrates that the lower induction of plant defences is associated with elevated plant fitness in the absence of herbivore feeding, suggesting that induced plant defences are costly. 

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