Etho-Metabolomics und Artvergleichsstudie zum Einfluss arbuskulärer Mykorrhizierung auf Entwicklung und Verhalten Spross-herbivorer Insekten und zugrunde liegende Mechanismen der Interaktionen
Zusammenfassung der Projektergebnisse
In their natural habitats, plants face diverse abiotic and biotic environmental factors, which influence their fitness in different ways. One of these biotic factors is the interaction with arbuscular mycorrhizal fungi (AMF), which occur almost everywhere. Root colonising AMF are integral parts of the plant physiology, because they influence plant phytohormone signaling, deliver water and nutrients (mainly phosphate) to the plant and receive plant-derived photoassimilates in return. Due to this close interaction with the plant, AMF may also affect the physiology and metabolism of systemic aboveground plant tissues. However, little was known on influences of arbuscular mycorrhiza (AM) on the foliar metabolism. Moreover, although the fungus is morphologically restricted to the roots, the changes in the metabolic composition of aboveground plant tissues may also affect the interaction of the plant with aboveground-feeding herbivores. Whereas several studies have explored plantmediated AM effects on herbivore performance, almost nothing was known in how far AM also influences the behavioural phenotype of insects. Furthermore, knowledge was lacking about the effects of age of the AM and age of the insect on the outcome of these tripartite interactions. Therefore, this project aimed to characterise general versus species-specific plant responses to AM and to investigate the consequences of such changes on herbivore performance as well as on the behaviour of insect herbivores with different feeding styles, using an etho-metabolomics approach. Plants of dicot species of different relatedness and the monocot Poa annua were either treated with an inoculum of the AMF Rhizophagus irregularis (AM plants) or with an autoclaved inoculum (nonmycorrhized, NM plants). After about two months of infestation, plants were harvested for chemical analyses using various metabolomics platforms. Other sets of similarly treated plants were offered to generalist herbivores with chewing feeding style (Mamestra brassicae and Heliothis virescens, Lepidoptera) or to the phloem-sucking aphid Myzus persicae (Heteroptera). Their survival and development on AM and NM plants was compared. Furthermore, different tests were developed to characterise the behavioural phenotypes of the larval or nymphal stages in a comprehensive way and to test whether diet experience and age of the insect juveniles influence their behaviour. Most metabolic changes induced by the AM were highly distinct, even though plant species shared up to 25 % of their polar leaf metabolomes and showed comparable AMF root colonisation intensities. The high species-specificity in response to an identical AMF species may be due to the long coevolution between the single plant species and their fungal partner, shaping the metabolic outcome of the interaction in distinct directions for each plant species. Thus, between-species knowledge transfers are limited and should be done with care. In consequence of the plant speciesspecific responses to AM and the distinct metabolomes of the plant species in general, the performance of herbivores differed profoundly between plant species. Moreover, AM had an effect on herbivore survival, development and body mass, but these effects depended on the plant and insect species under investigation. While larvae of H. virescens developed equally well on AM and NM plants, larvae of M. brassicae showed an improved performance when feeding on AM plants. Furthermore, AM-mediated metabolic shifts changed along with the development of the mutualism, but were only partly caused by the improved PO43—uptake. Moreoever, Plantago plants with a well established AM showed enhanced CO2 assimilation and transpiration rates, indicating that, for example, increased water uptake, phytohormone changes and the strong fungal C sink play a pivotal role in AM-mediated effects on foliar physiology. The changes in the plant quality over time, i.e., with the establishment of the AM and the development of the plant, were taken into account when testing effects on aphid performance. On older P. lanceolata plants with a well established AM, aphids showed a poorer performance than on young plants with a minor AM establishment. These results may be due to decreased nutritional quality and a decreased access to the nutrients caused by higher leaf toughness in older plants. While studies carried out by different researchers in different systems already indicated that AM effects may differ with AM establishment, this is, to my knowledge, the first study that systematically tested these effects within one system. Finally, differences in herbivore performance, caused by distinct food qualities, were expected to influence the behavioural phenotypes of the herbivores. However, towards AM-mediated changes in plant quality, the insect behaviour of the tested Lepidoptera and aphid species was rather robust and stable and only changed with age of the juveniles. In summary, our results highlight that AM-induced modifications of host plant quality affect larval development of generalist herbivores, whereas the behavioural phenotype seems to be more fixed at least under the test conditions used in our study systems. Future studies should consider the stage of the AM establishment and test also the effects of other AMF species on herbivore performance and behavioural phenotypes.
Projektbezogene Publikationen (Auswahl)
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(2015) Leaf metabolome in arbuscular mycorrhizal symbiosis. Current Opinion in Plant Biology 26: 120-126
Schweiger R, Müller C
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(2016) Effects of arbuscular mycorrhiza on plant chemistry and the development and behavior of a generalist herbivore. Journal of Chemical Ecology 42: 1247-1258
Tomczak VV, Schweiger R, Müller C
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(2017) Influence of arbuscular mycorrhizal stage and plant age on the performance of a generalist aphid. Journal of Insect Physiology 98: 258-266
Tomczak VV, Müller C
