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12 páginas.- 2 figuras.- 3 tablas.- 72 referencias.- Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s11104-021-04994-x, Aims Soil abiotic factors influence plant defensive traits by shaping the costs of defence production and these bottom-up effects on plants can in turn affect insect herbivory. However, few studies have disentangled direct and indirect effects of soil abiotic factors on plant defences and insect herbivory. Methods To address this gap, we tested the influence of soil abiotic factors on seed predation via changes in plant defences for sea fennel (Crithmum maritimum), a common coastal plant in southern Spain whose seeds are consumed by specialist caterpillars (Aethes species). To this end, we estimated seed predation on plants across several sea fennel populations, as well as measured different types of putative chemical seed defences (phenolics, terpenes) and soil abiotic factors (macro- and micro-elements, physicochemical variables). Results We found a positive association between seed chemical defences (terpenes such as alpha-thujene, alpha-pinene, beta-pinene, beta-myrcene, alpha-terpinene, y-terpinene, and thymol methylether) and seed predation. In addition, a few macro- and micro-elements such as Ca, S and Sr negatively correlated with seed defences; other macro- and micro-elements or physicochemical variables had no detectable association with defences. Despite observed effects of soil abiotic factors on defences and of the latter on seed predation, there was no detectable indirect effect of soil abiotic factors on seed attack. Conclusions Our findings suggest that variation in a few key soil macro- and micro-elements in coastal environments can exert an important influence on seed chemical defences in sea fennel, with potential consequences for interactions between sea fennel and seed predators., This research was financially supported by two grants from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099260-A-I00 to JC and RTI2018-099322-B-I00 to XM). XM and IMPR were financially supported by the Ramón y Cajal Research Programme (RYC-2013–13230 and RYC-2013–13937, respectively)., Peer reviewed

[Methods] In April 2021, we sowed 168 tubers from three different Solanum tuberosum varieties (cv. Baraka, cv. Desiree, and cv. Monalisa) in 4-L pots containing potting soil and peat (Gramoflor GmbH & Co. KG Produktion, Vechta, Germany). We grew plants in a glasshouse under controlled light (minimum 10 h per day, Photosynthetically Active Radiation = 725 ± 19 μmol m-2 s-1) and temperature (10°C night, 25°C day), and watered them twice a week up to field capacity. Five weeks after germination, we assigned half of the plants to one of two water availability treatments: high (i.e., well-watered) vs. low (i.e., reduced watering) water availability (Fig. 1). We watered plants in the high water availability treatment every three days to replenish the 100% of their water demand, whereas for plants in the low water availability treatment watering was reduced to meet the 25% of the total water demand. We estimated water demand gravimetrically.To corroborate that plants in the low water availability treatment were under higher physiological stress in comparison to well-watered plants, two weeks after the start of the treatments (right before applying the herbivory treatment, see below) we used a subset of 24 plants (half high and half low water availability; four of each potato variety) to measure stomatal conductance and photosynthesis. We measured stomatal conductance and net photosynthetic rate on a leaflet of a young, fully-expanded leaf from 11:30 to 12:30 am at an irradiance of 1500 μmol m-2 s-1 and CO2 concentration of 400 μmol mol-1 with a portable photosynthesis system Li-6400XT (Li-Cor Inc., Lincoln, NE, USA). Plants in the low water availability treatment exhibited significantly lower stomatal conductance (F1,22 = 22.1, P < 0.001) and photosynthetic rates (F1,22 = 31.5. P < 0.001) compared to well-watered plants. Specifically, reduced watering resulted in a 90 % and an 80% decrease in stomatal conductance (high water availability: 0.073 ± 0.01 mol H2O m-2 s-1; low water availability: 0.008 ± 0.01 mol H2O m-2 s-1) and photosynthesis rates (high water availability: 9.31 ± 0.94 µmol CO2 m-2 s-1; low water availability: 1.88 ± 0.94 µmol CO2 m-2 s-1), respectively (Fig. S1a, b).

Seven weeks after germination (two weeks after establishing the water availability treatments), we paired 144 potato plants in 37.5 × 37.5 × 96.5 cm plastic cages to prevent VOCs cross-contamination between replicates. One plant of each pair (i.e., replicate) acted as the emitter (average height ± SE = 51.17 ± 0.64 cm) and the other served as the receiver (48.52 ± 0.70 cm). Within each cage, emitter and receiver plants were placed 20 cm apart so that they did not touch each other. Plants in each water stress treatment were randomly selected as either receiver or emitter plants resulting in a factorial design consisting on four combinations of water availability treatment in the emitter (two levels; high vs. low) and water availability treatment in the receiver (two levels; high vs. low) (Fig. 1). In addition, we randomly assigned emitter plants within each cage to one of the following herbivory treatments: (1) subjected to S. exigua feeding (“herbivore-induced plants” hereafter) or (2) control (intact; no herbivory) plants (Fig. 1). Overall, the experiment consisted in 72 replicate cages, namely 36 for the herbivore-induced treatment (nine per emitter vs. receiver water availability combination) vs. 36 for the control (nine per emitter vs. receiver water availability combination). Emitter and receiver plants were always of the same variety and varieties were similarly distributed across treatment combinations. For herbivore-induced emitters, we placed two third-instar larvae of S. exigua on each of three fully expanded leaves per plant using a fine paintbrush and covered these leaves with a nylon bag to prevent herbivore dispersal. For control plants, we covered three fully expanded leaves with a nylon bag but without adding the larvae to control for a possible bagging effect. After four days of herbivore feeding, we removed all emitter plants from cages and collected VOCs from each emitter (see below). After VOCs sampling, we collected leaves subjected to larvae feeding and photographed them with a Samsung Galaxy A30s (25 effective megapixels, 4× digital zoom). We estimated the percentage of leaf area consumed using the mobile application BioLeaf - Foliar Analysis™ (Brandoli Machado et al., 2016). Average percentage leaf area consumed by S. exigua for herbivore-induced emitters was 77.58% (± 3.72) and was homogeneously distributed among plants in the high (80.46% ± 3.50) vs. low (73.63% ± 4.25) water availability treatments (F1,33 = 0.7; P = 0.399).

We collected aboveground VOCs produced by emitter plants following Rasmann et al. (2011). Briefly, we bagged plants with a 2-L Nalophan bag and trapped VOCs on a charcoal filter (SKC sorbent tube filled with anascorb CSC coconut-shell charcoal) for two hours at a rate of 0.25 L min-1. We eluted traps with 150 μL dichloromethane (CAS#75-09-2, Merck, Dietikon, Switzerland) to which we had previously added one internal standard (tetralin [CAS#119-64-2], 200 ng in 10 μL dichloromethane). We then injected 1.5 μL of the extract for each sample into an Agilent 7890B gas chromatograph (GC) coupled with a 5977B mass selective detector (MSD) fitted with a 30 m × 0.25 mm × 0.25 μm film thickness HP-5MS fused silica column (Agilent, Santa Clara, CA, USA). We operated the GC in pulsed splitless mode (250 ºC, injection pressure 15 psi) with helium as the carrier gas (constant flow rate 0.9 mL min-1). The GC oven temperature programme was: 3.5 min hold at 40ºC, 5ºC min-1 ramp to 230ºC, then a 3 min hold at 250ºC post run. Transfer line was set at 280 ºC. In the MS detector (EI mode), a 33-350 (m/z) mass scan range was used with MS source and quadrupole set at 230ºC and 150ºC, respectively. We identified volatile terpenes using the NIST MS Search Program v.2.3 and by comparison with the terpenes reference database developed at the University of Neuchâtel and based on pure standards. We quantified total emission of individual VOCs using normalized peak areas and expressed it as nanograms per hour (ng h-1). We obtained the normalized peak area of each individual compound by dividing their integrated peak area by the integrated peak area of the internal standard (Abdala-Roberts et al., 2022). The total emission of VOCs was then calculated as the sum of individual VOCs.

The same day after collecting emitter VOCs, we set up an herbivore bioassay for receiver plants to test whether prior exposure to VOCs from herbivore-induced emitters increased herbivore resistance. For this, we placed one third-instar S. exigua larvae on each of two fully expanded leaves per plant following the same procedure described above for emitter induction. We kept larvae on receivers for three days and then estimated the percentage of leaf area consumed by S. exigua (‘leaf damage’ hereafter) using the same procedure described above for emitter plants., Airborne plant communication is a widespread phenomenon in which volatile organic compounds (VOCs) from damaged plants boost herbivore resistance in neighbouring, undamaged plants. Although this form of plant signalling has been reported in more than 30 plant species, there is still a considerable knowledge gap on how abiotic factors (e.g., water availability) alter its outcomes.

We performed a greenhouse experiment to test for communication between potato plants (Solanum tuberosum) in response to herbivory by the generalist insect Spodoptera exigua and whether communication was affected by water availability. We paired emitter and receiver potato plants, with half of the emitters damaged by S. exigua larvae and half serving as undamaged controls. Both emitter and receiver plants were subjected to one of two water availability treatments: high (i.e., well-watered) vs. low (i.e., reduced watering) availability, thus effectively teasing apart water availability effects on the emission and reception components of signalling. After four days of herbivore feeding, we collected emitter VOCs and receivers were subjected to feeding by S. exigua to test for effects of signalling on induced resistance.

Herbivory by S. exigua led to increased VOCs emissions as well as changes in VOCs composition in emitter plants. Furthermore, emitters subjected to low water availability exhibited a weaker induction of VOCs in response to herbivory relative to well-watered emitters. Results from the feeding bioassay indicated that receivers exposed to VOCs from herbivore-induced emitters showed lower S. exigua damage (i.e. higher induced resistance) compared to receivers exposed to undamaged emitters. However, we did not observe a significant effect of water availability in either emitters or receivers on plant communication.

Overall, our study contributes to the understanding of how the abiotic context affects plant communication by providing evidence of water availability effects on the induction of VOCs that may act as airborne signals between plants. The observed changes in induced VOCs had no visible consequences for plant communication. These findings thus suggest that the induction of key compounds mediating communication was not compromised by our experimental conditions., Ministerio de Ciencia, Innovación y Universidades, Award: RTI2018-099322-B-I00. Consejo Superior de Investigaciones Científicas, Award: 2021AEP082. Xunta de Galicia, Award: IN607A 2021/03. Xunta de Galicia, Award: IN606B 2021/004., Peer reviewed

Airborne plant communication is a widespread phenomenon in which volatile organic compounds (VOCs) from damaged plants boost herbivore resistance in neighbouring, undamaged plants. Although this form of plant signalling has been reported in more than 30 plant species, there is still a considerable knowledge gap on how abiotic factors (e.g. water availability) alter its outcomes.
We performed a greenhouse experiment to test for communication between potato plants Solanum tuberosum in response to herbivory by the generalist insect Spodoptera exigua and whether communication was affected by water availability. We paired emitter and receiver potato plants, with half of the emitters damaged by S. exigua larvae and half serving as undamaged controls. Both emitter and receiver plants were factorially subjected to one of two watering treatments: high (i.e. well-watered) vs. low (i.e. reduced watering) availability, thus effectively teasing apart water availability effects on the emission and reception components of signalling. After 4 days of herbivore feeding, we collected emitter VOCs and receivers were subjected to feeding by S. exigua to test for effects of signalling on induced resistance.
Herbivory by S. exigua led to increased VOCs emissions as well as changes in VOCs composition in emitter plants. Furthermore, emitters subjected to low water availability exhibited a weaker induction of VOCs in response to herbivory relative to well-watered emitters. Results from the feeding bioassay indicated that receivers exposed to VOCs from herbivore-induced emitters showed lower S. exigua damage (i.e. induced resistance) compared to receivers exposed to undamaged emitters. However, we did not observe a significant effect of water availability in either emitters or receivers on plant signalling effects on receiver resistance.
Overall, our study contributes to understanding how the abiotic context affects plant communication by providing evidence of water availability effects on the induction of VOCs that act as airborne signals between plants. The observed changes in induced VOCs due to the water treatment had no detectable consequences for plant communication. Accordingly, the induction of key compounds mediating communication was apparently not compromised by our experimental conditions., This study was supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B-I00) to X.M., a grant from the Spanish National Research Council (2021AEP082) to X.M. and a grant from the Regional Government of Galicia (IN607A2021/03) to X.M. and C.V.-G. C.V.-G was supported by a postdoctoral fellowship from the Xunta de Galicia-GAIN/Fulbright (IN606B2021/004)., Peer reviewed

State of the art: Theory predicts that herbivore pressure should be weaker on islands than on the mainland, owing to lower herbivore abundance and diversity because of dispersal constraints and environmental filtering. As a result, plants on islands should invest less in defences against herbivory. Although early empirical studies supported these predictions, recent systematic island–mainland comparisons have questioned this paradigm, with some studies reporting either no difference between islands and mainland or higher herbivory and plant defences on islands. Current data therefore appear to be unsupportive of predictions on insularity effects on plant–herbivore interactions, calling for more research to reassess predictions and to test underlying mechanisms for observed patterns. Research opportunities: To meet this challenge, a renewed research programme based on the accrual of studies with specific features is needed. These should include more robust experimental designs with replication within and across systems, integrative and more nuanced assessments of plant defensive phenotypes and herbivory, a food web approach that considers the multi-trophic context in which plant–herbivore interactions are embedded, and a consideration of historical factors (e.g., island origin and biogeographical factors, defensive anachronisms). Outlook: This new research programme will require integration of evolutionary ecology research on plant–herbivore interactions with island biogeography, palaeoecology and community ecology to understand the influence of factors acting at different scales, from local factors driving herbivory and plant defences to historical processes and regional drivers of species composition determining species traits and their interactions., This research was supported financially by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B-I00), a grant from the Regional Government of Galicia (IN607D 2016/001) and the Ramón y Cajal Research Programme (RYC-2013-13230) to X.M.

Plant communication via airborne volatile organic compounds is a widespread phenomenon by which volatile organic compounds from damaged plants boost herbivore resistance in receiver plants. This phenomenon has been studied only in a handful of crop species. We tested for communication between potato (Solanum tuberosum) plants in response to herbivory by the Colorado potato beetle, Leptinotarsa decemlineata. For this, we performed a greenhouse experiment with 15 potato varieties for which we caged pairs of plants (i.e., emitters and receivers) of the same variety. Half of the emitter plants were subjected to leaf damage by beetle larvae and the other half remained intact. We collected volatile organic compounds from emitter plants and estimated L. decemlineata damage on receivers. We found no evidence of quantitative (total production) or qualitative (compound composition) changes in volatile organic compound emissions due to beetle herbivory. In addition, the leaf damage treatment on emitters had no significant effect on receiver herbivore resistance, suggesting no communication between infested and non-infested potato plants in response to Colorado potato beetle damage. Overall, this study provides baseline information on airborne signalling (or the lack of thereof) in potato plants which can inform subsequent work that identifies airborne volatiles with potentially strong effects on priming or defence induction., This research was financially supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B-I00) and the Ramon y Cajal Research Programme (RYC-2013-13230) to Xoaquín Moreira., Peer reviewed

Aim: It is predicted that insular plant taxa have evolved reduced defences in response to lower herbivore pressure on islands. However, the few studies testing this hypothesis have addressed variation in individual defensive traits, without paying attention to patterns of correlated trait expression (i.e. defence syndromes). Location: Balearic and Canary Islands. Taxon: Ninety-one woody plant species. Methods: We tested whether plant species with contrasting histories of insularity (namely, endemics, non-endemic natives and exotics) differed in their defensive syndromes using a suite of morphological, physical, and chemical traits putatively associated with herbivory. For this, we measured eight leaf traits of 42 endemic, 29 native non-endemic and 20 introduced species for which specimens were sourced from botanical gardens found in two archipelagos: the Balearic and Canary Islands. Results: We conducted phylogenetic-controlled analyses which showed that, contrary to predictions, insular taxa (endemics and non-endemic natives) across both archipelagos were more defended (thicker, smaller leaves with less nutrients) than exotic species. There were no differences in chemical defence (phenolic compounds) between endemics, non-endemic natives and exotics. Finally, we also found different defence syndromes between archipelagos: whereas species from the Balearic Islands were more physically defended, on average, those from the Canary Islands had higher chemical defences. Main conclusions: Overall, these results point to a defence syndrome based on low-nutrient and physically defended leaves characteristic of insular plant taxa that is indistinct for endemic and non-endemic taxa, relative to introduced species, as well as quantitative and qualitative differences in defences between archipelagos owing to changes in species composition and likely also to different histories of biotic or abiotic pressure., This research was financially supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B- I00) and the Ramón y Cajal Research Programme (RYC-2013- 13230) to XM. CG-V was supported by a Vicenç Mut Grant (Govern de les Illes Balears, Conselleria d'Innovació, Recerca i Turisme and the European Social Fund). No permits were required for this research.

6 páginas, 2 figuras, 1 tabla, VOC emissions increased with herbivore load, but this did not result in concomitant increases in resistance in neighbouring plants, suggesting that communication occurred independently of herbivore load in emitter plants. Herbivore-damaged plants emit volatile organic compounds (VOCs) that can alert neighbours and boost their resistance. While VOC-mediated plant communication has been shown to be herbivore-specific, we know little about its contingency on variation in herbivore load. To address this knowledge gap, we tested herbivore load effects on VOC-mediated communication between potato plants (Solanum tuberosum) using the generalist herbivore Spodoptera exigua. First, we tested whether herbivore load (three levels: undamaged control, low, and high load) affected total VOC emissions and composition. Second, we matched emitter and receiver plants and subjected emitters to the same herbivore load treatments. Finally, we performed a bioassay with S. exigua on receivers to test for induced resistance due to VOC-mediated communication. We found that herbivory significantly increased total VOC emissions relative to control plants, and that such increase was greater under high herbivore load. In contrast, we found no detectable effect of herbivory, regardless of the load, on VOC composition. The communication experiment showed that VOCs released by herbivore-induced emitters boosted resistance in receivers (i.e., lower leaf damage than receivers exposed to VOCs released by control emitters), but the magnitude of such effect was similar for both levels of emitter herbivore load. These findings suggest that changes in VOCs due to variation in herbivore load do not modify the outcomes of plant communication., This research was supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B-I00) to XM, a grant from the Spanish National Research Council (2021AEP082) to XM, and a grant from the Regional Government of Galicia (IN607A 2021/03) to XM and CVG. CVG was supported by a postdoctoral fellowship from the Xunta de Galicia-GAIN/Fulbright (IN606B 2021/004). LMC was supported by a predoctoral fellowship from the Spanish Ministry of Science, Innovation and Universities (PRE2019-091096), Peer reviewed

12 páginas 5 figuras, Insect herbivory is a dominant interaction across virtually all ecosystems globally and has dramatic effects on plant function such as reduced photosynthesis activity and increased levels of defenses. However, most previous work assessing the link between insect herbivory, photosynthesis and plant defenses has been performed on cultivated model plant species, neglecting a full understanding of patterns in natural systems. In this study, we performed a field experiment to investigate the effects of herbivory by a generalist foliar feeding insect (Lymantria dispar) and leaf mechanical damage on multiple leaf traits associated with defense against herbivory and photosynthesis activity on two sympatric oak species with contrasting leaf habit (the evergreen Quercus coccifera L. and the deciduous Quercus pubescens Willd). Our results showed that, although herbivory treatments and oak species did not strongly affect photosynthesis and dark respiration, these two factors exerted interactive effects. Insect herbivory and mechanical damage (vs control) decreased photosynthesis activity for Q. coccifera but not for Q. pubescens. Insect herbivory and mechanical damage tended to increase chemical (increased flavonoid and lignin concentration) defenses, but these effects were stronger for Q. pubescens. Overall, this study shows that two congeneric oak species with contrasting leaf habit differ in their photosynthetic and defensive responses to insect herbivory. While the evergreen oak species followed a more conservative strategy (reduced photosynthesis and higher physical defenses), the deciduous oak species followed a more acquisitive strategy (maintained photosynthesis and higher chemical defenses)., X.M. was financially supported by a grant from the Spanish Ministry of Science, Innovation and Universities (grant number RTI2018-099322-B-I00).

9 páginas, 2 figuras, 1 tabla, Plants are often attacked sequentially by multiple enemies. Pathogen sequential co-infections can lead to indirect interactions mediated by plant induced responses whose outcome is contingent on differences in the magnitude and type of plant induced defences elicited by different species or guilds. To date, however, most studies have tested unidirectional effects of one pathogen on another, not discerning between conspecific vs. heterospecific infections, and often not measuring plant induced responses underlying such outcomes. To address this, we conducted a greenhouse experiment testing for the impact of initial infection by two leaf pathogens (Alternaria solani and Phytophthora infestans) on subsequent infection by each of these pathogens on potato (Solanum tuberosum) plants, and also measured induced plant defences (phenolic compounds) to inform on interaction outcomes. We found contrasting results depending on the identity of the initially infecting pathogen. Specifically, initial infection by A. solani drove induced resistance (lower necrosis) by subsequently infecting A. solani (conspecific induced resistance) but had no effect on subsequent infection by P. infestans. In contrast, initial infection by P. infestans drove induced resistance to subsequent infection by both conspecifics and A. solani. Patterns of plant induced defences correlated with (and potentially explained) induced resistance to conspecific but not heterospecific (e.g., in the case of P. infestans) subsequent infection. Overall, these results further our understanding of plant-mediated pathogen interactions by showing that plant-mediated interactions between pathogen species can be asymmetrical and in some cases not reciprocal, that pathogen species can vary in the importance of conspecific vs. heterospecific effects, and shed mechanistic insight into the role of plant induced responses driving such interactions., This research was financially supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B-I00), a grant from the Spanish National Research Council (2021AEP082), and a Regional Government of Galicia Grant (IN607A 2021/03) to XM., Peer reviewed

11 páginas, 4 figuras, 1 tabla, Plant-plant signalling via volatile organic compounds (VOCs) has been studied intensively, but its contingency on abiotic conditions (e.g., soil nutrients, drought, warming) is poorly understood. To address this gap, we carried out a greenhouse experiment testing whether soil nutrients influenced signalling between potato (Solanum tuberosum) plants in response to insect leaf herbivory by the generalist caterpillar Spodoptera exigua. We placed pairs of plants in plastic cages, where one plant acted as a VOC emitter and the other as a receiver. We factorially manipulated soil nutrients for both emitter and receiver plants, namely: unfertilized (baseline soil nutrients) vs. fertilized (augmented nutrients). Then, to test for signalling effects, half of the emitters within each fertilization level were damaged by S. exigua larvae and the other half remained undamaged. Three days after placing larvae, we collected VOCs from emitter plants to test for herbivory and fertilization effects on VOC emissions and placed S. exigua larvae on receivers to test for signalling effects on leaf consumption and larval mass gain as proxies of induced resistance. We found that herbivory increased total VOC emissions and altered VOC composition by emitter plants, but these effects were not contingent on fertilization. In addition, bioassay results showed that receivers exposed to VOCs from herbivore-damaged emitters had lower levels of herbivory compared to receivers exposed to undamaged emitters. However, and consistent with VOC results, fertilization did not influence herbivore-induced signalling effects on receiver resistance to herbivory. In sum, we found evidence of S. exigua-induced signalling effects on resistance to herbivory in potato plants but such effects were not affected by increased soil nutrients. These results call for further work testing signalling effects under broader range of nutrient concentration levels (including nutrient limitation), teasing apart the effects of specific nutrients, and incorporating other abiotic factors likely to interact or covary with soil nutrients., This research was financially supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B-I00) to XM, a grant from the Spanish National Research Council 2021AEP082) to XM, and a grant from the Regional Government of Galicia (IN607A 2021/03) to XM and CVG. CVG was supported by a postdoctoral fellowship from the Xunta de Galicia-GAIN/Fulbright (IN606B 2021/004). LMC was supported by a predoctoral fellowship from the Spanish Ministry of Science, Innovation and Universities (PRE2019-091096)., Peer reviewed

14 páginas, 4 tablas, 5 figuras, Plant enemies can indirectly affect pollinators by modifying plant traits, but simultaneous tests of herbivore and pathogen effects are lacking, and the role of floral volatiles has seldom been assessed. In this study, we tested for indirect effects of insect herbivores and pathogens on pollinator attraction via altered floral volatile emissions, and its consequences for plant fitness in Brassica rapa. Plants in the field were exposed to either no damage or damage by caterpillars (Mamestra brassicae), aphids (Brevicoryne brassicae), a leaf fungus (Sclerotinia sclerotiorum), or a bacterium (Xanthomonas campestris pv. campestris). We then recorded pollinator visits and measured floral traits (flower number, volatiles) and plant fitness-correlates. We additionally performed a greenhouse experiment with artificial floral emitters to test for effects of target volatiles on pollinator attraction. In the field experiments, relative to controls, plants subjected to herbivory by the aphid B. brassicae (but not those exposed to the other enemies) exhibited a marked reduction in the emission of two volatile organic compounds (nonanal and 2-butyl-1-octanol), experienced lower pollinator visits and produced seeds of lower quality in terms of seed biomass and germination rate, while flower output itself was not affected. Consistently, artificial emitters with reduced amounts of these volatile organic compounds were less attractive to pollinators under greenhouse conditions. Synthesis. These results provide strong evidence for volatile-mediated indirect interactions between plant enemies and pollinators ultimately impacting plant fitness, and further point at enemy and compound specificity in such effects., This research was financially supported by two grants from the Spanish Ministry of Science, Innovation and Universities (RTI2018-096591-BI00 to EC and RTI2018-099322-B-I00 to XM) and a grant from the Regional Government of Galicia (IN607A 2021/03) to XM, PS, CVG and EC. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)., Peer reviewed

8 páginas, 3 tablas, 4 figuras,
Supplementary data to this article can be found online at https://doi.org/10.1016/j.phytochem.2022.113561, It has been proposed that plant-plant signalling via herbivore-induced volatile organic compounds (VOCs) should be stronger between closely related than unrelated plants. However, empirical tests remain limited and few studies have provided detailed assessments of induced changes in VOCs emissions across plant genotypes to explain genetic relatedness effects. In this study, we tested whether airborne signalling in response to herbivory between Solanum tuberosum (potato) plants was contingent on plant genetic relatedness, and further investigated genotypic variation in VOCs potentially underlying signalling and its contingency on relatedness. We carried out a greenhouse experiment using 15 S. tuberosum varieties placing pairs of plants in plastic cages, i.e. an emitter and a receiver, where both plants were of the same genotype or different genotype thereby testing for self-recognition, an elemental form genetic relatedness effects. Then, for half of the cages within each level of relatedness the emitter plant was damaged by Spodoptera exigua larvae whereas for the other half the emitter was not damaged. Three days later, we placed S. exigua larvae on receivers to test for emitter VOC effects on leaf consumption and larval weight gain (i.e. induced resistance). In addition, we used a second group of plants subjected to the same induction treatment with the same S. tuberosum varieties to test for herbivore-induced changes in VOC emissions and variation in VOC emissions among these plant genotypes. We found that herbivory drove changes in VOC composition but not total emissions, and also observed quantitative and qualitative variation in constitutive and induced VOC emissions among varieties. Results from the bioassay showed that the amount of leaf area consumed and larval weight gain on receiver plants exposed to damaged emitters were significantly lower compared to mean values on receivers exposed to control emitters. However, and despite genotypic variation in induced VOCs, this signalling effect was not contingent on plant genetic relatedness. These findings provide evidence of VOCs-mediated signalling between S. tuberosum plants in response to S. exigua damage, but no evidence of self-recognition effects in signalling contingent on variation in VOC emissions among S. tuberosum varieties., This research was financially supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI 2018-099322-B-I00) to XM, a grant from the Spanish National Research Council (2021AEP082) to XM, and a grant from the Regional Government of Galicia (IN607A 2021/03) to XM and CVG. CVG was supported by a postdoctoral fellowship from the Xunta de Galicia-GAIN/Fulbright (IN606B 2021/004). LMC was supported by a predoctoral fellowship from the Spanish Ministry of Science, Innovation and Universities (PRE2019-091096).

Phenotypic plasticity (i.e. the ability to express different phenotypes under changing environmental conditions) is thought to play a key role in habitat adaptation, but little is known about how trait plasticity evolves following dispersal into novel island habitats. We hypothesize that shifts from seasonal Mediterranean climates to more stable (subtropical) island conditions would promote a net reduction in trait plasticity over time. To test this hypothesis, we set two common gardens with contrasting environmental (low resource vs. mesic) conditions, where we grew seedlings of wild olive (Olea europaea var. sylvestris) populations that represented two Canary Island lineages with different colonization times (old vs. young) and their Mediterranean ancestral lineage (N = 275 individuals). Plasticity was assessed for 12 morphological, photosynthetic and chemical traits by (i) subjecting half of the seedlings to simulated herbivore browsing (50% of aerial biomass removal) and (ii) comparing phenotypic values between both common garden settings. Simulated herbivore browsing induced few plastic responses, mostly restricted to photosynthetic traits, but these were similarly displayed by all lineages. Comparisons between common gardens revealed a contrasting response between the Mediterranean and both subtropical island lineages in leaf phenotypes. Furthermore, the older island lineage showed an overall lack of plasticity (i.e. environmental canalization) in morphological and chemical traits. These results suggest that, unlike photosynthetic traits that are fundamental for fast acclimation to environmental shifts, some developmental traits may lose plasticity over time as a result of phenotypic adjustment to subtropical insular conditions., This research was financially supported by a Vincenç Mut fellowship (Conselleria d′Innovació, Recerca i Turisme, Govern de les Illes Balears and the European Social Fund) to CGV, a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018–099322-B-I00) to XM and the Ramón y Cajal Research Programme (RYC-2013–13230) to XM. Funding for the open access charge was kindly provided by the Universidad de Granada / CBUA.